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  • 1. Acke, B.
    et al.
    Min, M.
    Dominik, C.
    Vandenbussche, B.
    Sibthorpe, B.
    Waelkens, C.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Degroote, P.
    Smolders, K.
    Pantin, E.
    Barlow, M. J.
    Blommaert, J. A. D. L.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    De Meester, W.
    Dent, W. R. F.
    Exter, K.
    Di Francesco, J.
    Fridlund, M.
    Gear, W. K.
    Glauser, A. M.
    Greaves, J. S.
    Harvey, P. M.
    Henning, Th
    Hogerheijde, M. R.
    Holland, W. S.
    Huygen, R.
    Ivison, R. J.
    Jean, C.
    Liseau, R.
    Naylor, D. A.
    Pilbratt, G. L.
    Polehampton, E. T.
    Regibo, S.
    Royer, P.
    Sicilia-Aguilar, A.
    Swinyard, B. M.
    Herschel images of Fomalhaut An extrasolar Kuiper belt at the height of its dynamical activity2012In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 540, p. A125-Article in journal (Refereed)
    Abstract [en]

    Context. Fomalhaut is a young (2 +/- 1 x 10(8) years), nearby (7.7 pc), 2 M-circle dot star that is suspected to harbor an infant planetary system, interspersed with one or more belts of dusty debris. Aims. We present far-infrared images obtained with the Herschel Space Observatory with an angular resolution between 5.7 '' and 36.7 '' at wavelengths between 70 mu m and 500 mu m. The images show the main debris belt in great detail. Even at high spatial resolution, the belt appears smooth. The region in between the belt and the central star is not devoid of material; thermal emission is observed here as well. Also at the location of the star, excess emission is detected. We aim to construct a consistent image of the Fomalhaut system. Methods. We use a dynamical model together with radiative-transfer tools to derive the parameters of the debris disk. We include detailed models of the interaction of the dust grains with radiation, for both the radiation pressure and the temperature determination. Comparing these models to the spatially resolved temperature information contained in the images allows us to place strong constraints on the presence of grains that will be blown out of the system by radiation pressure. We use this to derive the dynamical parameters of the system. Results. The appearance of the belt points toward a remarkably active system in which dust grains are produced at a very high rate by a collisional cascade in a narrow region filled with dynamically excited planetesimals. Dust particles with sizes below the blow-out size are abundantly present. The equivalent of 2000 one-km-sized comets are destroyed every day, out of a cometary reservoir amounting to 110 Earth masses. From comparison of their scattering and thermal properties, we find evidence that the dust grains are fluffy aggregates, which indicates a cometary origin. The excess emission at the location of the star may be produced by hot dust with a range of temperatures, but may also be due to gaseous free-free emission from a stellar wind.

  • 2. Amiaux, J
    et al.
    Andra, 40
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Development approach and first infrared test results of JWST/Mid Infra Red Imager Optical Bench2008In: Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter, 2008Conference paper (Other academic)
  • 3. Barlow, M. J.
    et al.
    Krause, O.
    Swinyard, B. M.
    Sibthorpe, B.
    Besel, M. -A
    Wesson, R.
    Ivison, R. J.
    Dunne, L.
    Gear, W. K.
    Gomez, H. L.
    Hargrave, P. C.
    Henning, Th.
    Leeks, S. J.
    Lim, T. L.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Polehampton, E. T.
    A Herschel PACS and SPIRE study of the dust content of the Cassiopeia A supernova remnant2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, p. L138-Article in journal (Refereed)
    Abstract [en]

    Using the 3.5-m Herschel Space Observatory, imaging photometry of Cas A has been obtained in six bands between 70 and 500 mu m with the PACS and SPIRE instruments, with angular resolutions ranging from 6 to 37 ''. In the outer regions of the remnant the 70-mu m PACS image resembles the 24-mu m image Spitzer image, with the emission attributed to the same warm dust component, located in the reverse shock region. At longer wavelengths, the three SPIRE bands are increasingly dominated by emission from cold interstellar dust knots and filaments, particularly across the central, western and southern parts of the remnant. Nonthermal emission from the northern part of the remnant becomes prominent at 500 mu m. We have estimated and subtracted the contributions from the nonthermal, warm dust and cold interstellar dust components. We confirm and resolve for the first time a cool (similar to 35 K) dust component, emitting at 70-160 mu m, that is located interior to the reverse shock region, with an estimated mass of 0.075 M-circle dot.

  • 4. Barlow, M. J.
    et al.
    Swinyard, B. M.
    Owen, P. J.
    Cernicharo, J.
    Gomez, H. L.
    Ivison, R. J.
    Krause, O.
    Lim, T. L.
    Matsuura, M.
    Miller, S.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Polehampton, E. T.
    Detection of a Noble Gas Molecular Ion, (ArH+)-Ar-36, in the Crab Nebula2013In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 342, no 6164, p. 1343-1345Article in journal (Refereed)
    Abstract [en]

    Noble gas molecules have not hitherto been detected in space. From spectra obtained with the Herschel Space Observatory, we report the detection of emission in the 617.5- and 1234.6-gigahertz J = 1-0 and 2-1 rotational lines of (ArH+)-Ar-36 at several positions in the Crab Nebula, a supernova remnant known to contain both molecular hydrogen and regions of enhanced ionized argon emission. Argon-36 is believed to have originated from explosive nucleosynthesis in massive stars during core-collapse supernova events. Its detection in the Crab Nebula, the product of such a supernova event, confirms this expectation. The likely excitation mechanism for the observed (ArH+)-Ar-36 emission lines is electron collisions in partially ionized regions with electron densities of a few hundred per centimeter cubed.

  • 5. Bjerkeli, P.
    et al.
    Liseau, R.
    Brinch, C.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Santangelo, G.
    Cabrit, S.
    Benedettini, M.
    Black, J. H.
    Herczeg, G.
    Justtanont, K.
    Kristensen, L. E.
    Larsson, Bengt
    Stockholm University, Faculty of Science, Department of Astronomy.
    Nisini, B.
    Tafalla, M.
    Resolving the shocked gas in HH54 with Herschel CO line mapping at high spatial and spectral resolution2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 571, article id A90Article in journal (Refereed)
    Abstract [en]

    Context. The HH 54 shock is a Herbig-Haro object, located in the nearby Chamaeleon II cloud. Observed CO line profiles are due to a complex distribution in density, temperature, velocity, and geometry. Aims. Resolving the HH 54 shock wave in the far-infrared (FIR) cooling lines of CO constrain the kinematics, morphology, and physical conditions of the shocked region. Methods. We used the PACS and SPIRE instruments on board the Herschel space observatory to map the full FIR spectrum in a region covering the HH 54 shock wave. Complementary Herschel-HIFI, APEX, and Spitzer data are used in the analysis as well. The observed features in the line profiles are reproduced using a 3D radiative transfer model of a bow-shock, constructed with the Line Modeling Engine code (LIME). Results. The FIR emission is confined to the HH 54 region and a coherent displacement of the location of the emission maximum of CO with increasing J is observed. The peak positions of the high-J CO lines are shifted upstream from the lower J CO lines and coincide with the position of the spectral feature identified previously in CO(10-9) profiles with HIFI. This indicates a hotter molecular component in the upstream gas with distinct dynamics. The coherent displacement with increasing J for CO is consistent with a scenario where IRAS12500 - 7658 is the exciting source of the flow, and the 180 K bow-shock is accompanied by a hot (800 K) molecular component located upstream from the apex of the shock and blueshifted by -7 km s(-1). The spatial proximity of this knot to the peaks of the atomic fine-structure emission lines observed with Spitzer and PACS ([O I]63, 145 mu m) suggests that it may be associated with the dissociative shock as the jet impacts slower moving gas in the HH 54 bow-shock.

  • 6.
    Brandeker, Alexis
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Cataldi, Gianni
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Vandenbussche, B.
    Acke, B.
    Barlow, M. J.
    Blommaert, J. A. D. L.
    Cohen, M.
    Dent, W. R. F.
    Dominik, C.
    Di Francesco, J.
    Fridlund, M.
    Gear, W. K.
    Glauser, A. M.
    Greaves, J. S.
    Harvey, P. M.
    Heras, A. M.
    Hogerheijde, M. R.
    Holland, W. S.
    Huygen, R.
    Ivison, R. J.
    Leeks, S. J.
    Lim, T. L.
    Liseau, R.
    Matthews, B. C.
    Pantin, E.
    Pilbratt, G. L.
    Royer, P.
    Sibthorpe, B.
    Waelkens, C.
    Walker, H. J.
    Herschel detects oxygen in the beta Pictoris debris disk2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 591, article id A27Article in journal (Refereed)
    Abstract [en]

    The young star beta Pictoris is well known for its dusty debris disk produced through collisional grinding of planetesimals, kilometre-sized bodies in orbit around the star. In addition to dust, small amounts of gas are also known to orbit the star; this gas is likely the result of vaporisation of violently colliding dust grains. The disk is seen edge on and from previous absorption spectroscopy we know that the gas is very rich in carbon relative to other elements. The oxygen content has been more difficult to assess, however, with early estimates finding very little oxygen in the gas at a C/O ratio that is 20x higher than the cosmic value. A C/O ratio that high is difficult to explain and would have far-reaching consequences for planet formation. Here we report on observations by the far-infrared space telescope Herschel, using PACS, of emission lines from ionised carbon and neutral oxygen. The detected emission from C+ is consistent with that previously reported observed by the HIFI instrument on Herschel, while the emission from O is hard to explain without assuming a higher density region in the disk, perhaps in the shape of a clump or a dense torus required to sufficiently excite the O atoms. A possible scenario is that the C/O gas is produced by the same process responsible for the CO clump recently observed by the Atacama Large Millimeter/submillimeter Array in the disk and that the redistribution of the gas takes longer than previously assumed. A more detailed estimate of the C/O ratio and the mass of O will have to await better constraints on the C/O gas spatial distribution.

  • 7.
    Brandeker, Alexis
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Cataldi, Gianni
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Vandenbussche, Bart
    Acke, Bram
    Barlow, Michael J.
    Blommaert, Joris A. D. L.
    Cohen, Martin
    Dent, William R. F.
    Dominik, Carsten
    Di Francesco, James
    Fridlund, Malcolm
    Gear, Walter K.
    Glauser, Adrian Michael
    Greaves, Jane S.
    Harvey, Paul M.
    Heras, Ana M.
    Hogerheijde, Michiel R.
    Holland, Wayne S.
    Huygen, Rik
    Ivison, Rob J.
    Leeks, Sarah J.
    Lim, Tanya L.
    Liseau, René
    Matthews, Brenda C.
    Pantin, Eric
    Pilbratt, Göran L.
    Royer, Pierre
    Sibthorpe, Bruce
    Waelkens, Christoffel
    Walker, Helen J.
    Herschel detects oxygen in the β Pictoris debris diskIn: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed)
  • 8.
    Cataldi, Gianni
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Chen, C. H.
    Dent, W. R. F.
    Kamp, I.
    Roberge, A.
    Vandenbussche, B.
    Constraints on the gas content of the Fomalhaut debris belt Can gas-dust interactions explain the belt's morphology?2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 574, article id L1Article in journal (Refereed)
    Abstract [en]

    Context. The 440 Myr old main-sequence A-star Fomalhaut is surrounded by an eccentric debris belt with sharp edges. This sort of a morphology is usually attributed to planetary perturbations, but the orbit of the only planetary candidate detected so far, Fomalhaut b, is too eccentric to efficiently shape the belt. Alternative models that could account for the morphology without invoking a planet are stellar encounters and gas-dust interactions. Aims. We aim to test the possibility of gas-dust interactions as the origin of the observed morphology by putting upper limits on the total gas content of the Fomalhaut belt. Methods. We derive upper limits on the CII 158 mu m and 01 63 pint emission by using non detections from the Photocletector Array Camera and Spectrometer (PACS) onboard the Herschel Space Observatory. Line fluxes are converted into total gas mass using the non-local thermodynamic equilibrium (non-LTE) code RADEX. We consider two different cases for the elemental abundances of the gas: solar abundances and abundances similar to those observed for the gas in the beta Pictoris debris disc. Results. The gas mass is shown to be below the millimetre dust mass by a factor of at least similar to 3 (for solar abundances) respectively similar to 300 (for beta Pic-like abundances). Conclusions. The lack of gas co-spatial with the dust implies that gas-dust interactions cannot efficiently shape the Fomalhaut debris belt. The morphology is therefore more likely due to a yet unseen planet (Fomalhaut c) or stellar encounters.

  • 9.
    Cataldi, Gianni
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Larsson, Bengt
    Stockholm University, Faculty of Science, Department of Astronomy.
    Liseau, R.
    Blommaert, J.
    Fridlund, M.
    Ivison, R.
    Pantin, E.
    Sibthorpe, B.
    Vandenbussche, B.
    Wu, Y.
    Herschel/HIFI observations of ionised carbon in the beta Pictoris debris disk2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 563, article id A66Article in journal (Refereed)
    Abstract [en]

    Context. The dusty debris disk around the similar to 20 Myr old main-sequence A-star beta Pictoris is known to contain gas. Evidence points towards a secondary origin of the gas as opposed to being a direct remnant from the initial protoplanetary disk, although the dominant gas production mechanism is so far not identified. The origin of the observed overabundance of C and O compared with solar abundances of metallic elements such as Na and Fe is also unclear. Aims. Our goal is to constrain the spatial distribution of C in the disk, and thereby the gas origin and its abundance pattern. Methods. We used the HIFI instrument on board the Herschel Space Observatory to observe and spectrally resolve C II emission at 158 mu m from the beta Pic debris disk. Assuming a disk in Keplerian rotation and a model for the line emission from the disk, we used the spectrally resolved line profile to constrain the spatial distribution of the gas. Results. We detect the C II 158 mu m emission. Modelling the shape of the emission line shows that most of the gas is located at about similar to 100 AU or beyond. We estimate a total C gas mass of 1.3(-0.5)(+1.3) x 10(2) M-circle plus (central 90% confidence interval). The data suggest that more gas is located on the south-west side of the disk than on the north-east side. The shape of the emission line is consistent with the hypothesis of a well mixed gas (constant C/Fe ratio throughout the disk). Assuming instead a spatial profile expected from a simplified accretion disk model, we found it to give a significantly poorer fit to the observations. Conclusions. Since the bulk of the gas is found outside 30 AU, we argue that the cometary objects known as falling evaporating bodies are probably not the dominant source of gas; production from grain-grain collisions or photodesorption seems more likely. The incompatibility of the observations with a simplified accretion disk model might favour a preferential depletion explanation for the overabundance of C and O, although it is unclear how much this conclusion is affected by the simplifications made. More stringent constraints on the spatial distribution will be available from ALMA observations of C I emission at 609 mu m.

  • 10.
    Cataldi, Gianni
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Thébault, Philippe
    Ahmed, Engy
    de Vries, Bernard L.
    Neubeck, Anna
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Singer, Kelsi
    Searching for biosignatures in exoplanetary impact ejectaIn: Astrobiology, ISSN 1531-1074, E-ISSN 1557-8070Article in journal (Refereed)
  • 11.
    Cataldi, Gianni
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Thébault, Philippe
    Singer, Kelsi
    Ahmed, Engy
    Stockholm University, Faculty of Science, Department of Geological Sciences. Royal Institute of Technology (KTH), Sweden.
    de Vries, Bernard L.
    Stockholm University, Faculty of Science, Department of Astronomy. European Space Research and Technology Centre (ESA/ESTEC), The Netherlands.
    Neubeck, Anna
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Searching for Biosignatures in Exoplanetary Impact Ejecta2017In: Astrobiology, ISSN 1531-1074, E-ISSN 1557-8070, Vol. 17, no 8, p. 721-746Article in journal (Refereed)
    Abstract [en]

    With the number of confirmed rocky exoplanets increasing steadily, their characterization and the search for exoplanetary biospheres are becoming increasingly urgent issues in astrobiology. To date, most efforts have concentrated on the study of exoplanetary atmospheres. Instead, we aim to investigate the possibility of characterizing an exoplanet (in terms of habitability, geology, presence of life, etc.) by studying material ejected from the surface during an impact event. For a number of impact scenarios, we estimate the escaping mass and assess its subsequent collisional evolution in a circumstellar orbit, assuming a Sun-like host star. We calculate the fractional luminosity of the dust as a function of time after the impact event and study its detectability with current and future instrumentation. We consider the possibility to constrain the dust composition, giving information on the geology or the presence of a biosphere. As examples, we investigate whether calcite, silica, or ejected microorganisms could be detected. For a 20km diameter impactor, we find that the dust mass escaping the exoplanet is roughly comparable to the zodiacal dust, depending on the exoplanet's size. The collisional evolution is best modeled by considering two independent dust populations, a spalled population consisting of nonmelted ejecta evolving on timescales of millions of years, and dust recondensed from melt or vapor evolving on much shorter timescales. While the presence of dust can potentially be inferred with current telescopes, studying its composition requires advanced instrumentation not yet available. The direct detection of biological matter turns out to be extremely challenging. Despite considerable difficulties (small dust masses, noise such as exozodiacal dust, etc.), studying dusty material ejected from an exoplanetary surface might become an interesting complement to atmospheric studies in the future.

  • 12.
    Cataldi, Gianni
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. National Astronomical Observatory of Japan, USA; Hungarian Academy of Sciences, Hungary.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Wu, Yanqin
    Chen, Christine
    Dents, William
    de Vries, Bernard L.
    Stockholm University, Faculty of Science, Department of Astronomy. European Space Research and Technology Centre (ESA/ESTEC), The Netherlands.
    Kamp, Inga
    Liseau, René
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pantin, Eric
    Roberge, Aki
    ALMA Resolves CI Emission from the beta Pictoris Debris Disk2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 861, no 1, article id 72Article in journal (Refereed)
    Abstract [en]

    The debris disk around beta Pictoris is known to contain gas. Previous ALMA observations revealed a CO belt at similar to 85 au with a distinct clump, interpreted as a location of enhanced gas production. Photodissociation converts CO into C and O within similar to 50 a. We resolve C I emission at 492 GHz using ALMA and study its spatial distribution. C I shows the same clump as seen for CO. This is surprising, as C is expected to quickly spread in azimuth. We derive a low C mass (between 5 x 10(-4) and 3.1 x 10(-3) MA(circle plus)), indicating that gas production started only recently (within similar to 5000 a). No evidence is seen for an atomic accretion disk inward of the CO belt, perhaps because the gas did not yet have time to spread radially. The fact that C and CO share the same asymmetry argues against a previously proposed scenario where the clump is due to an outward-migrating planet trapping planetesimals in a resonance, nor can the observations be explained by an eccentric planetesimal belt secularly forced by a planet. Instead, we suggest that the dust and gas disks should be eccentric. Such a configuration, we further speculate, might be produced by a recent tidal disruption event. Assuming that the disrupted body has had a CO mass fraction of 10%, its total mass would be greater than or similar to 3M(Moon).

  • 13. Cernicharo, J.
    et al.
    Decin, L.
    Barlow, M. J.
    Agundez, M.
    Royer, P.
    Vandenbussche, B.
    Wesson, R.
    Polehampton, E. T.
    De Beck, E.
    Blommaert, J. A. D. L.
    Daniel, F.
    De Meester, W.
    Exter, K. M.
    Feuchtgruber, H.
    Gear, W. K.
    Goicoechea, J. R.
    Gomez, H. L.
    Groenewegen, M. A. T.
    Hargrave, P. C.
    Huygen, R.
    Imhof, P.
    Ivison, R. J.
    Jean, C.
    Kerschbaum, F.
    Leeks, S. J.
    Lim, T. L.
    Matsuura, M.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Posch, T.
    Regibo, S.
    Savini, G.
    Sibthorpe, B.
    Swinyard, B. M.
    Waelkens, C.
    Detection of anhydrous hydrochloric acid, HCl, in IRC+10216 with the Herschel SPIRE and PACS spectrometers Detection of HCI in IRC+102162010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, p. L136-Article in journal (Refereed)
    Abstract [en]

    We report on the detection of anhydrous hydrochloric acid (hydrogen chlorine, HCl) in the carbon-rich star IRC+10216 using the spectroscopic facilities onboard the Herschel satellite. Lines from J = 1-0 up to J = 7-6 have been detected. From the observed intensities, we conclude that HCl is produced in the innermost layers of the circumstellar envelope with an abundance relative to H-2 of 5 x 10(-8) and extends until the molecules reach its photodissociation zone. Upper limits to the column densities of AlH, MgH, CaH, CuH, KH, NaH, FeH, and other diatomic hydrides have also been obtained.

  • 14. Chauvin, M.
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Jackson, M.
    Kamae, T.
    Kawano, T.
    Kiss, M.
    Kole, M.
    Mikhalev, V.
    Moretti, E.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Rydström, S.
    Takahashi, H.
    Iyudin, A.
    Arimoto, M.
    Fukazawa, Y.
    Kataoka, J.
    Kawai, N.
    Mizuno, T.
    Ryde, F.
    Tajima, H.
    Takahashi, T.
    Pearce, M.
    Observation of polarized hard X-ray emission from the Crab by the PoGOLite Pathfinder2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 456, no 1, p. l84-L88Article in journal (Refereed)
    Abstract [en]

    We have measured the linear polarization of hard X-ray emission from the Crab in a previously unexplored energy interval, 20-120 keV. The introduction of two new observational parameters, the polarization fraction and angle stands to disentangle geometrical and physical effects, thereby providing information on the pulsar wind geometry and magnetic field environment. Measurements are conducted using the PoGOLite Pathfinder - a balloon-borne polarimeter. Polarization is determined by measuring the azimuthal Compton scattering angle of incident X-rays in an array of plastic scintillators housed in an anticoincidence well. The polarimetric response has been characterized prior to flight using both polarized and unpolarized calibration sources. We address possible systematic effects through observations of a background field. The measured polarization fraction for the integrated Crab light curve is 18.4(-10.6)(+9.8) per cent, corresponding to an upper limit (99 per cent credibility) of 42.4 per cent, for a polarization angle of (149.2 +/- 16.0)degrees.

  • 15. Chauvin, M.
    et al.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Jackson, M.
    Kamae, T.
    Kawano, T.
    Kiss, M.
    Kole, M.
    Mikhalev, V.
    Moretti, E.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Rydström, S.
    Takahashi, H.
    Lind, J.
    Strömberg, J. -E.
    Welin, O.
    Iyudin, A.
    Shifrin, D.
    Pearce, M.
    The design and flight performance of the PoGOLite Pathfinder balloon-borne hard X-ray polarimeter2016In: Experimental astronomy (Print), ISSN 0922-6435, E-ISSN 1572-9508, Vol. 41, no 1, p. 17-41Article in journal (Refereed)
    Abstract [en]

    In the 50 years since the advent of X-ray astronomy there have been many scientific advances due to the development of new experimental techniques for detecting and characterising X-rays. Observations of X-ray polarisation have, however, not undergone a similar development. This is a shortcoming since a plethora of open questions related to the nature of X-ray sources could be resolved through measurements of the linear polarisation of emitted X-rays. The PoGOLite Pathfinder is a balloon-borne hard X-ray polarimeter operating in the 25-240 keV energy band from a stabilised observation platform. Polarisation is determined using coincident energy deposits in a segmented array of plastic scintillators surrounded by a BGO anticoincidence system and a polyethylene neutron shield. The PoGOLite Pathfinder was launched from the SSC Esrange Space Centre in July 2013. A near-circumpolar flight was achieved with a duration of approximately two weeks. The flight performance of the Pathfinder design is discussed for the three Crab observations conducted. The signal-to-background ratio for the observations is shown to be 0.25 +/- 0.03 and the Minimum Detectable Polarisation (99 % C.L.) is (28.4 +/- 2.2) %. A strategy for the continuation of the PoGOLite programme is outlined based on experience gained during the 2013 maiden flight.

  • 16. Clayton, Geoffrey C.
    et al.
    Sugerman, Ben E. K.
    Stanford, S. Adam
    Whitney, B. A.
    Honor, J.
    Babler, B.
    Barlow, M. J.
    Gordon, K. D.
    Andrews, J. E.
    Geballe, T. R.
    Bond, Howard E.
    De Marco, O.
    Lawson, W. A.
    Sibthorpe, B.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Polehampton, E.
    Gomez, H. L.
    Matsuura, M.
    Hargrave, P. C.
    Ivison, R. J.
    Wesson, R.
    Leeks, S. J.
    Swinyard, B. M.
    Lim, T. L.
    THE CIRCUMSTELLAR ENVIRONMENT OF R CORONAE BOREALIS: WHITE DWARF MERGER OR FINAL-HELIUM-SHELL FLASH?2011In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 743, no 1, p. 44-Article in journal (Refereed)
    Abstract [en]

    In 2007, R Coronae Borealis (R CrB) went into a historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 mu m with Gemini/GMOS, Hubble Space Telescope/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around R CrB are cometary globules caused by wind from the star streaming past dense blobs. The estimated dust mass of the knots is consistent with their being responsible for the R CrB declines if they form along the line of sight to the star. In addition, there is a large diffuse shell extending up to 4 pc away from the star containing cool 25 K dust that is detected all the way out to 500 mu m. The spectral energy distribution of R CrB can be well fitted by a 150 AU disk surrounded by a very large diffuse envelope which corresponds to the size of the observed nebulosity. The total masses of the disk and envelope are 10(-4) and 2M(circle dot), respectively, assuming a gas-to-dust ratio of 100. The evidence pointing toward a white dwarf merger or a final-helium-shell flash origin for R CrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that R CrB shows significant lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of R CrB and its high fluorine abundance support a white dwarf merger.

  • 17. Covino, S.
    et al.
    Andra, 14
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Andra, 39
    The complex light curve of the afterglow of GRB071010A2008In: Monthly Notices of the Royal Astronomical Society, Vol. 388, no 1, p. 347-356Article in journal (Refereed)
    Abstract [en]

    We present and discuss the results of an extensive observational campaign devoted to GRB071010A, a long-duration gamma-ray burst detected by the Swift satellite. This event was followed for almost a month in the optical/near-infrared (NIR) with various telescopes starting from about 2min after the high-energy event. Swift XRT observations started only later at about 0.4d. The light-curve evolution allows us to single out an initial rising phase with a maximum at about 7min, possibly the afterglow onset in the context of the standard fireball model, which is then followed by a smooth decay interrupted by a sharp rebrightening at about 0.6d. The rebrightening was visible in both the optical/NIR and X-rays and can be interpreted as an episode of discrete energy injection, although various alternatives are possible. A steepening of the afterglow light curve is recorded at about 1d. The entire evolution of the optical/NIR afterglow is consistent with being achromatic. This could be one of the few identified GRB afterglows with an achromatic break in the X-ray through the optical/NIR bands. Polarimetry was also obtained at about 1d, just after the rebrightening and almost coincident with the steepening. This provided a fairly tight upper limit of 0.9 per cent for the polarized-flux fraction.

  • 18. Danilovich, T.
    et al.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Black, J. H.
    Justtanont, K.
    Olofsson, H.
    Classifying the secondary component of the binary star W Aquilae2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 574, article id A23Article in journal (Refereed)
    Abstract [en]

    Aims. The object W Aql is an asymptotic giant branch (AGB) star with a faint companion. By determining more carefully the properties of the companion, we hope to better constrain the properties of the AGB star. Methods. We present new spectral observations of the binary star W Aql at minimum and maximum brightness and new photometric observations of W Aql at minimum brightness. Results. The composite spectrum near minimum light is predominantly from the companion at wavelengths lambda 6000 angstrom. This spectrum can be classified as F8 to G0, and the brightness of the companion is that of a dwarf star. Therefore, it can be concluded that the companion is a main sequence star. From this, we are able to constrain the mass of the AGB component to 1.04-3 M-circle dot and the mass of the W Aql system to 2.1-4.1 M-circle dot. Our photometric results are broadly consistent with this classification and suggest that the main sequence component suffers from approximately 2 mag of extinction in the V band primarily due to the dust surrounding the AGB component.

  • 19. de Vries, B. L.
    et al.
    Acke, B.
    Blommaert, J. A. D. L.
    Waelkens, C.
    Waters, L. B. F. M.
    Vandenbussche, B.
    Min, M.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Dominik, C.
    Decin, L.
    Barlow, M. J.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Di Francesco, J.
    Glauser, A. M.
    Greaves, J.
    Harvey, P. M.
    Holland, W. S.
    Ivison, R. J.
    Liseau, R.
    Pantin, E. E.
    Pilbratt, G. L.
    Royer, P.
    Sibthorpe, B.
    Comet-like mineralogy of olivine crystals in an extrasolar proto-Kuiper belt2012In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 490, no 7418, p. 74-76Article in journal (Refereed)
    Abstract [en]

    Some planetary systems harbour debris disks containing planetesimals such as asteroids and comets(1). Collisions between such bodies produce small dust particles(2), the spectral features of which reveal their composition and, hence, that of their parent bodies. A measurement of the composition of olivine crystals (Mg2-2xFe2xSiO4) has been done for the protoplanetary disk HD 100546 (refs 3, 4) and for olivine crystals in the warm inner parts of planetary systems. The latter compares well with the iron-rich olivine in asteroids(5,6) (x approximate to 0.29). In the cold outskirts of the beta Pictoris system, an analogue to the young Solar System, olivine crystals were detected(7) but their composition remained undetermined, leaving unknown how the composition of the bulk of Solar System cometary olivine grains compares with that of extrasolar comets(8,9). Here we report the detection of the 69-micrometre-wavelength band of olivine crystals in the spectrum of beta Pictoris. Because the disk is optically thin, we can associate the crystals with an extrasolar proto-Kuiper belt a distance of 15-45 astronomical units from the star (one astronomical unit is the Sun-Earth distance), determine their magnesium-rich composition (x = 0.01 +/- 0.001) and show that they make up 3.6 +/- 1.0 per cent of the total dust mass. These values are strikingly similar to those for the dust emitted by the most primitive comets in the Solar System(8-10), even though beta Pictoris is more massive and more luminous and has a different planetary system architecture.

  • 20. Decin, L.
    et al.
    Agundez, M.
    Barlow, M. J.
    Daniel, F.
    Cernicharo, J.
    Lombaert, R.
    De Beck, E.
    Royer, P.
    Vandenbussche, B.
    Wesson, R.
    Polehampton, E. T.
    Blommaert, J. A. D. L.
    De Meester, W.
    Exter, K.
    Feuchtgruber, H.
    Gear, W. K.
    Gomez, H. L.
    Groenewegen, M. A. T.
    Guelin, M.
    Hargrave, P. C.
    Huygen, R.
    Imhof, P.
    Ivison, R. J.
    Jean, C.
    Kahane, C.
    Kerschbaum, F.
    Leeks, S. J.
    Lim, T.
    Matsuura, M.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Posch, T.
    Regibo, S.
    Savini, G.
    Sibthorpe, B.
    Swinyard, B. M.
    Yates, J. A.
    Waelkens, C.
    Warm water vapour in the sooty outflow from a luminous carbon star2010In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 467, no 7311, p. 64-67Article in journal (Refereed)
    Abstract [en]

    The detection(1) of circumstellar water vapour around the ageing carbon star IRC + 10216 challenged the current understanding of chemistry in old stars, because water was predicted(2) to be almost absent in carbon-rich stars. Several explanations for the water were postulated, including the vaporization of icy bodies (comets or dwarf planets) in orbit around the star(1), grain surface reactions(3), and photochemistry in the outer circumstellar envelope(4). With a single water line detected so far from this one carbon-rich evolved star, it is difficult to discriminate between the different mechanisms proposed. Here we report the detection of dozens of water vapour lines in the far-infrared and sub-millimetre spectrum of IRC + 10216 using the Herschel satellite(5). This includes some high-excitation lines with energies corresponding to similar to 1,000 K, which can be explained only if water is present in the warm inner sooty region of the envelope. A plausible explanation for the warm water appears to be the penetration of ultraviolet photons deep into a clumpy circumstellar envelope. This mechanism also triggers the formation of other molecules, such as ammonia, whose observed abundances(6) are much higher than hitherto predicted(7).

  • 21. Decin, L.
    et al.
    Cernicharo, J.
    Barlow, M. J.
    Royer, P.
    Vandenbussche, B.
    Wesson, R.
    Polehampton, E. T.
    De Beck, E.
    Agundez, M.
    Blommaert, J. A. D. L.
    Cohen, M.
    Daniel, F.
    De Meester, W.
    Exter, K.
    Feuchtgruber, H.
    Fonfria, J. P.
    Gear, W. K.
    Goicoechea, J. R.
    Gomez, H. L.
    Groenewegen, M. A. T.
    Hargrave, P. C.
    Huygen, R.
    Imhof, P.
    Ivison, R. J.
    Jean, C.
    Kerschbaum, F.
    Leeks, S. J.
    Lim, T.
    Matsuura, M.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Posch, T.
    Regibo, S.
    Savini, G.
    Sibthorpe, B.
    Swinyard, B. M.
    Tercero, B.
    Waelkens, C.
    Witherick, D. K.
    Yates, J. A.
    Silicon in the dust formation zone of IRC+102162010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, p. L143-Article in journal (Refereed)
    Abstract [en]

    The interstellar medium is enriched primarily by matter ejected from evolved low and intermediate mass stars. The outflows from these stars create a circumstellar envelope in which a rich gas-phase and dust-nucleation chemistry takes place. We observed the nearest carbon-rich evolved star, IRC + 10216, using the PACS (55-210 mu m) and SPIRE (194-672 mu m) spectrometers on board Herschel. We find several tens of lines from SiS and SiO, including lines from the v = 1 vibrational level. For SiS these transitions range up to J = 124-123, corresponding to energies around 6700 K, while the highest detectable transition is J = 90-89 for SiO, which corresponds to an energy around 8400 K. Both species trace the dust formation zone of IRC + 10216, and the broad energy ranges involved in their detected transitions permit us to derive the physical properties of the gas and the particular zone in which each species has been formed. This allows us to check the accuracy of chemical thermodynamical equilibrium models and the suggested depletion of SiS and SiO due to accretion onto dust grains.

  • 22. Djupvik, A. A.
    et al.
    André, Philippe
    Bontemps, Sylvain
    Motte, F.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Gålfalk, Magnus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    A multi-wavelength census of star formation activity in the young embedded cluster around Serpens/G3-G62006In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 458, no 3, p. 789-803Article in journal (Refereed)
    Abstract [en]

    Aims.The aim of this paper is to characterise the star formation activity in the poorly studied embedded cluster Serpens/G3-G6, located ~45 arcmin (3 pc) to the south of the Serpens Cloud Core, and to determine the luminosity and mass functions of its population of Young Stellar Objects (YSOs).

    Methods: .Multi-wavelength broadband photometry was obtained to sample the near and mid-IR spectral energy distributions to separate YSOs from field stars and classify the YSO evolutionary stage. ISOCAM mapping in the two filters LW2 (5-8.5 μm) and LW3 (12-18 μm) of a 19 arcmin × 16 arcmin field was combined with JHKS data from 2MASS, KS data from Arnica/NOT, and L arcmin data from SIRCA/NOT. Continuum emission at 1.3 mm (IRAM) and 3.6 cm (VLA) was mapped to study the cloud structure and the coldest/youngest sources. Deep narrow band imaging at the 2.12 μm S(1) line of H2 from NOTCam/NOT was obtained to search for signs of bipolar outflows.

    Results: .We have strong evidence for a stellar population of 31 Class II sources, 5 flat-spectrum sources, 5 Class I sources, and two Class 0 sources. Our method does not sample the Class III sources. The cloud is composed of two main dense clumps aligned along a ridge over ~0.5 pc plus a starless core coinciding with absorption features seen in the ISOCAM maps. We find two S-shaped bipolar collimated flows embedded in the NE clump, and propose the two driving sources to be a Class 0 candidate (MMS3) and a double Class I (MMS2). For the Class II population we find a best age of ~2 Myr and compatibility with recent Initial Mass Functions (IMFs) by comparing the observed Class II luminosity function (LF), which is complete to 0.08 Lȯ, to various model LFs with different star formation scenarios and input IMFs.

  • 23. Eiroa, C.
    et al.
    Fedele, D.
    Maldonado, J.
    Gonzalez-Garcia, B. M.
    Rodmann, J.
    Heras, A. M.
    Pilbratt, G. L.
    Augereau, J. -Ch.
    Mora, A.
    Montesinos, B.
    Ardila, D.
    Bryden, G.
    Liseau, R.
    Stapelfeldt, K.
    Launhardt, R.
    Solano, E.
    Bayo, A.
    Absil, O.
    Arevalo, M.
    Barrado, D.
    Beichmann, C.
    Danchi, W.
    del Burgo, C.
    Ertel, S.
    Fridlund, M.
    Fukagawa, M.
    Gutierrez, R.
    Gruen, E.
    Kamp, I.
    Krivov, A.
    Lebreton, J.
    Loehne, T.
    Lorente, R.
    Marshall, J.
    Martinez-Arnaiz, R.
    Meeus, G.
    Montes, D.
    Morbidelli, A.
    Mueller, S.
    Mutschke, H.
    Nakagawa, T.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Ribas, I.
    Roberge, A.
    Sanz-Forcada, J.
    Thebault, P.
    Walker, H.
    White, G. J.
    Wolf, S.
    Cold DUst around NEarby Stars (DUNES). First results A resolved exo-Kuiper belt around the solar-like star zeta(2) Ret2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, p. L131-Article in journal (Refereed)
    Abstract [en]

    We present the first far-IR observations of the solar-type stars delta Pav, HR 8501, 51 Peg and zeta(2) Ret, taken within the context of the DUNES Herschel open time key programme (OTKP). This project uses the PACS and SPIRE instruments with the objective of studying infrared excesses due to exo-Kuiper belts around nearby solar-type stars. The observed 100 mu m fluxes from delta Pav, HR 8501, and 51 Peg agree with the predicted photospheric fluxes, excluding debris disks brighter than L-dust/L-star similar to 5 x 10(-7) (1 sigma level) around those stars. A flattened, disk-like structure with a semi-major axis of similar to 100 AU in size is detected around zeta(2) Ret. The resolved structure suggests the presence of an eccentric dust ring, which we interpret as an exo-Kuiper belt with L-dust/L-star approximate to 10(-5).

  • 24. Galfalk, Magnus
    et al.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bastviken, David
    Making methane visible2016In: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 6, no 4, p. 426-430Article in journal (Refereed)
    Abstract [en]

    Methane (CH4) is one of the most important greenhouse gases, and an important energy carrier in biogas and natural gas. Its large-scale emission patterns have been unpredictable and the source and sink distributions are poorly constrained. Remote assessment of CH4 with high sensitivity at a m(2) spatial resolution would allow detailed mapping of the near-ground distribution and anthropogenic sources in landscapes but has hitherto not been possible. Here we show that CH4 gradients can be imaged on the <m(2) scale at ambient levels (similar to 1.8 ppm) and filmed using optimized infrared (IR) hyperspectral imaging. Our approach allows both spectroscopic confirmation and quantification for all pixels in an imaged scene simultaneously. It also has the ability to map fluxes for dynamic scenes. This approach to mapping boundary layer CH4 offers a unique potential way to improve knowledge about greenhouse gases in landscapes and a step towards resolving source-sink attribution and scaling issues.

  • 25. Greaves, J. S.
    et al.
    Sibthorpe, B.
    Acke, B.
    Pantin, E. E.
    Vandenbussche, B.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Dominik, C.
    Barlow, M. J.
    Bendo, G. J.
    Blommaert, J. A. D. L.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    de Vries, Bernard L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Dent, W. R. F.
    Di Francesco, J.
    Fridlund, M.
    Gear, W. K.
    Harvey, P. M.
    Hogerheijde, M. R.
    Holland, W. S.
    Ivison, R. J.
    Liseau, R.
    Matthews, B. C.
    Pilbratt, G. L.
    Walker, H. J.
    Waelkens, C.
    EXTREME CONDITIONS IN A CLOSE ANALOG TO THE YOUNG SOLAR SYSTEM: HERSCHEL OBSERVATIONS OF is an element of ERIDANI2014In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 791, no 1, p. L11-Article in journal (Refereed)
    Abstract [en]

    Far-infrared Herschel images of the is an element of Eridani system, seen at a fifth of the Sun's present age, resolve two belts of debris emission. Fits to the 160 mu m PACS image yield radial spans for these belts of 12-16 and 54-68 AU. The south end of the outer belt is approximate to 10% brighter than the north end in the PACS+SPIRE images at 160, 250, and 350 mu m, indicating a pericenter glow attributable to a planet c From this asymmetry and an upper bound on the offset of the belt center, this second planet should be mildly eccentric (e(c) approximate to 0.03-0.3). Compared to the asteroid and Kuiper Belts of the young Sun, the is an element of Eri belts are intermediate in brightness and more similar to each other, with up to 20 km sized collisional fragments in the inner belt totaling approximate to 5% of an Earth mass. This reservoir may feed the hot dust close to the star and could send many impactors through the Habitable Zone, especially if it is being perturbed by the suspected planet is an element of Eri b, at semi-major axis approximate to 3 AU.

  • 26. Griffin, M. J.
    et al.
    Abergel, A.
    Abreu, A.
    Ade, P. A. R.
    Andre, P.
    Augueres, J. -L
    Babbedge, T.
    Bae, Y.
    Baillie, T.
    Baluteau, J. -P
    Barlow, M. J.
    Bendo, G.
    Benielli, D.
    Bock, J. J.
    Bonhomme, P.
    Brisbin, D.
    Brockley-Blatt, C.
    Caldwell, M.
    Cara, C.
    Castro-Rodriguez, N.
    Cerulli, R.
    Chanial, P.
    Chen, S.
    Clark, E.
    Clements, D. L.
    Clerc, L.
    Coker, J.
    Communal, D.
    Conversi, L.
    Cox, P.
    Crumb, D.
    Cunningham, C.
    Daly, F.
    Davis, G. R.
    De Antoni, P.
    Delderfield, J.
    Devin, N.
    Di Giorgio, A.
    Didschuns, I.
    Dohlen, K.
    Donati, M.
    Dowell, A.
    Dowell, C. D.
    Duband, L.
    Dumaye, L.
    Emery, R. J.
    Ferlet, M.
    Ferrand, D.
    Fontignie, J.
    Fox, M.
    Franceschini, A.
    Frerking, M.
    Fulton, T.
    Garcia, J.
    Gastaud, R.
    Gear, W. K.
    Glenn, J.
    Goizel, A.
    Griffin, D. K.
    Grundy, T.
    Guest, S.
    Guillemet, L.
    Hargrave, P. C.
    Harwit, M.
    Hastings, P.
    Hatziminaoglou, E.
    Herman, M.
    Hinde, B.
    Hristov, V.
    Huang, M.
    Imhof, P.
    Isaak, K. J.
    Israelsson, U.
    Ivison, R. J.
    Jennings, D.
    Kiernan, B.
    King, K. J.
    Lange, A. E.
    Latter, W.
    Laurent, G.
    Laurent, P.
    Leeks, S. J.
    Lellouch, E.
    Levenson, L.
    Li, B.
    Li, J.
    Lilienthal, J.
    Lim, T.
    Liu, S. J.
    Lu, N.
    Madden, S.
    Mainetti, G.
    Marliani, P.
    McKay, D.
    Mercier, K.
    Molinari, S.
    Morris, H.
    Moseley, H.
    Mulder, J.
    Mur, M.
    Naylor, D. A.
    Nguyen, H.
    O'Halloran, B.
    Oliver, S.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, H. -G
    Stockholm University, Faculty of Science, Department of Astronomy.
    Orfei, R.
    Page, M. J.
    Pain, I.
    Panuzzo, P.
    Papageorgiou, A.
    Parks, G.
    Parr-Burman, P.
    Pearce, A.
    Pearson, C.
    Perez-Fournon, I.
    Pinsard, F.
    Pisano, G.
    Podosek, J.
    Pohlen, M.
    Polehampton, E. T.
    Pouliquen, D.
    Rigopoulou, D.
    Rizzo, D.
    Roseboom, I. G.
    Roussel, H.
    Rowan-Robinson, M.
    Rownd, B.
    Saraceno, P.
    Sauvage, M.
    Savage, R.
    Savini, G.
    Sawyer, E.
    Scharmberg, C.
    Schmitt, D.
    Schneider, N.
    Schulz, B.
    Schwartz, A.
    Shafer, R.
    Shupe, D. L.
    Sibthorpe, B.
    Sidher, S.
    Smith, A.
    Smith, A. J.
    Smith, D.
    Spencer, L.
    Stobie, B.
    Sudiwala, R.
    Sukhatme, K.
    Surace, C.
    Stevens, J. A.
    Swinyard, B. M.
    Trichas, M.
    Tourette, T.
    Triou, H.
    Tseng, S.
    Tucker, C.
    Turner, A.
    Vaccari, M.
    Valtchanov, I.
    Vigroux, L.
    Virique, E.
    Voellmer, G.
    Walker, H.
    Ward, R.
    Waskett, T.
    Weilert, M.
    Wesson, R.
    White, G. J.
    Whitehouse, N.
    Wilson, C. D.
    Winter, B.
    Woodcraft, A. L.
    Wright, G. S.
    Xu, C. K.
    Zavagno, A.
    Zemcov, M.
    Zhang, L.
    Zonca, E.
    The Herschel-SPIRE instrument and its in-flight performance2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, p. L3-Article in journal (Refereed)
    Abstract [en]

    The Spectral and Photometric Imaging REceiver (SPIRE), is the Herschel Space Observatory`s submillimetre camera and spectrometer. It contains a three-band imaging photometer operating at 250, 350 and 500 mu m, and an imaging Fourier-transform spectrometer (FTS) which covers simultaneously its whole operating range of 194-671 mu m (447-1550 GHz). The SPIRE detectors are arrays of feedhorn-coupled bolometers cooled to 0.3 K. The photometer has a field of view of 4' x 8', observed simultaneously in the three spectral bands. Its main operating mode is scan-mapping, whereby the field of view is scanned across the sky to achieve full spatial sampling and to cover large areas if desired. The spectrometer has an approximately circular field of view with a diameter of 2.6'. The spectral resolution can be adjusted between 1.2 and 25 GHz by changing the stroke length of the FTS scan mirror. Its main operating mode involves a fixed telescope pointing with multiple scans of the FTS mirror to acquire spectral data. For extended source measurements, multiple position offsets are implemented by means of an internal beam steering mirror to achieve the desired spatial sampling and by rastering of the telescope pointing to map areas larger than the field of view. The SPIRE instrument consists of a cold focal plane unit located inside the Herschel cryostat and warm electronics units, located on the spacecraft Service Module, for instrument control and data handling. Science data are transmitted to Earth with no on-board data compression, and processed by automatic pipelines to produce calibrated science products. The in-flight performance of the instrument matches or exceeds predictions based on pre-launch testing and modelling: the photometer sensitivity is comparable to or slightly better than estimated pre-launch, and the spectrometer sensitivity is also better by a factor of 1.5-2.

  • 27. Griffin, Matt
    et al.
    Andra, 16
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Andra, 30
    Herschel-SPIRE: design, ground test results, and predicted performance2008In: Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter, 2008, p. 701006-701006Conference paper (Other academic)
  • 28.
    Griffin, Matthew
    et al.
    School of Physics and Astronomy, Cardiff University.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    The Herschel-SPIRE instrument and its capabilities for extragalactic astronomy2007In: Advances in Space Research, Vol. 40, no 5, p. 612-619Article in journal (Refereed)
    Abstract [en]

    SPIRE, the Spectral and Photometric Imaging Receiver, is one of three instruments to fly on the European Space Agency's Herschel Space Observatory. It contains a three-band imaging photometer operating at 250, 350 and 500 μm, and an imaging Fourier transform spectrometer covering 194-672 μm. The SPIRE detectors are arrays of feedhorn-coupled bolometers cooled to 0.3 K. The photometer has a field of view of 4 × 8′, observed simultaneously in the three spectral bands. The spectrometer has an approximately circular field of view with a diameter of 2.6′ The spectral resolution can be adjusted between 0.04 and 2 cm‑1 (resolving power of 20-1000 at 250 μm). SPIRE will be used for many galactic and extragalactic science programmes, a number of which will be implemented as Herschel Key Projects. The SPIRE consortium's Guaranteed Time (GT) programme will devote more than 1000 h to Key Projects covering the high-redshift universe and local galaxies, which will be carried out in coordination with other GT programmes, especially that of the PACS consortium. It is also expected that substantial amounts of Herschel Open Time will be used for further extragalactic investigations. The high-redshift part of the SPIRE GT programme will focus on blank-field surveys with a range of depths and areas optimised to sample the luminosity-redshift plane and characterize the bolometric luminosity density of the universe at high-redshift. Fields will be selected that are well covered by Spitzer, SCUBA-2, PACS-GT and near-IR surveys, to facilitate source identifications and enable detailed studies of the redshifts, spectral energy distributions, and other properties of detected galaxies. The local galaxies programme will include a detailed spectral and photometric study of a sample of well resolved nearby galaxies, a survey of more than 300 local galaxies designed to provide a statistical survey of dust in the nearby universe, and a study of the ISM in low-metallicity environments, bridging the gap between the local universe and primordial galaxies.

  • 29. Groenewegen, M. A. T.
    et al.
    Barlow, M. J.
    Blommaert, J. A. D. L.
    Cernicharo, J.
    Decin, L.
    Gomez, H. L.
    Hargrave, P. C.
    Kerschbaum, F.
    Ladjal, D.
    Lim, T. L.
    Matsuura, M.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sibthorpe, B.
    Swinyard, B. M.
    Ueta, T.
    Yates, J.
    An independent distance estimate to cw leonis2012In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 543, p. L8-Article in journal (Refereed)
    Abstract [en]

    CW Leo has been observed six times between October 2009 and June 2012 with the SPIRE instrument on board the Herschel satellite. Variability has been detected in the flux emitted by the central star with a period of 639 +/- 4 days, in good agreement with determinations in the literature. Variability is also detected in the bow shock around CW Leo that had previously been detected in the ultraviolet and Herschel PACS/SPIRE data. Although difficult to prove directly, our working hypothesis is that this variability is directly related to that of the central star. In this case, fitting a sine curve with the period fixed to 639 days results in a time-lag in the variability between bow shock and the central star of 402 +/- 37 days. The orientation of the bow shock relative to the plane of the sky is unknown (but see below). For an inclination angle of zero degrees, the observed time-lag translates into a distance to CW Leo of 130 +/- 13 pc, and for non-zero inclination angles the distance is smaller. Fitting the shape of the bow shock with an analytical model (Wilkin 1996, ApJ, 459, L31), the effect of the inclination angle on the distance may be estimated. Making the additional assumption that the relative peculiar velocity between the interstellar medium (ISM) and CW Leo is determined entirely by the star space velocity with respect to the local standard of rest (i.e. a stationary ISM), the inclination angle is found to be (-33.3 +/- 0.8)degrees based on the observed proper motion and radial velocity. Using the Wilkin model, our current best estimate of the distance to CW Leo is 123 +/- 14 pc. For a distance of 123 pc, we derive a mean luminosity of 7790 +/- 150 L-circle dot (internal error).

  • 30. Groenewegen, M. A. T.
    et al.
    Waelkens, C.
    Barlow, M. J.
    Kerschbaum, F.
    Garcia-Lario, P.
    Cernicharo, J.
    Blommaert, J. A. D. L.
    Bouwman, J.
    Cohen, M.
    Cox, N.
    Decin, L.
    Exter, K.
    Gear, W. K.
    Gomez, H. L.
    Hargrave, P. C.
    Henning, Th.
    Hutsemekers, D.
    Ivison, R. J.
    Jorissen, A.
    Krause, O.
    Ladjal, D.
    Leeks, S. J.
    Lim, T. L.
    Matsuura, M.
    Naze, Y.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Ottensamer, R.
    Polehampton, E.
    Posch, T.
    Rauw, G.
    Royer, P.
    Sibthorpe, B.
    Swinyard, B. M.
    Ueta, T.
    Vamvatira-Nakou, C.
    Vandenbussche, B.
    Van de Steene, G. C.
    Van Eck, S.
    van Hoof, P. A. M.
    Van Winckel, H.
    Verdugo, E.
    Wesson, R.
    MESS (Mass-loss of Evolved StarS), a Herschel key program2011In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 526, p. A162-Article in journal (Refereed)
    Abstract [en]

    MESS (Mass-loss of Evolved StarS) is a guaranteed time key program that uses the PACS and SPIRE instruments on board the Herschel space observatory to observe a representative sample of evolved stars, that include asymptotic giant branch (AGB) and post-AGB stars, planetary nebulae and red supergiants, as well as luminous blue variables, Wolf-Rayet stars and supernova remnants. In total, of order 150 objects are observed in imaging and about 50 objects in spectroscopy. This paper describes the target selection and target list, and the observing strategy. Key science projects are described, and illustrated using results obtained during Herschel's science demonstration phase. Aperture photometry is given for the 70 AGB and post-AGB stars observed up to October 17, 2010, which constitutes the largest single uniform database of far-IR and sub-mm fluxes for late-type stars.

  • 31.
    Gålfalk, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    A detailed study of the L1641N star formation region2008In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 489, no 3, p. 1409-1439Article in journal (Refereed)
    Abstract [en]

    Aims. We search for young stellar objects (YSOs) in the L1641N cluster and characterize the star formation activity through determination of the age distribution, mass function, spatial distribution, and the star formation history.Methods. Multi-wavelength broad band photometry both from space and the ground are used to look for IR excess in order to separate field stars from YSOs and to sample the spectral energy distributions. Space-based observations were obtained using the ISO satellite (ISOCAM) in two filters, centred at 6.7 and 14.3 m, and Spitzer (IRAC) at 3.6, 4.5, 5.8, and 8.0 m. Our ground-based observations were made with the Nordic Optical Telescope (NOT) using ALFOSC (I band), NOTCam (J, and 2.12 m H2), and SIRCA (L'). More than 50 of the brightest I-band sources were then studied with follow-up optical spectroscopy (5780-8340 Å) to check for signs of accretion (H in emission) and youth (Li I

    in absorption) and to determine their effective temperatures. By comparing theoretical evolution tracks with our YSO sample in the H-R diagram, we calculated an age, luminosity, and mass distribution.Results. We detect a total of 216 (Spitzer or I band) sources in L1641N, 89 of which are YSO candidates. Most of the spectra are of M-type with H strongly in emission, and many have Li 6707 in absorption. The four brightest I band sources (F and G stars) are suggested as foreground stars, and the L1641N IRAS source is shown to be the combined flux of at least four sources. We find that the interstellar extinction is well-fit in the optical and near-IR by a power law with an exponent of 1.58, although in the mid-IR the Spitzer observations show a higher extinction than expected from theory. The median age of the YSO sample is ~1 Myr and the resulting MF has a flat distribution for low masses down to the completeness limit. There is evidence of a constant star formation rate of one star in 3.7  104 yr during the past few Myr. We find 11 sources older than 10 Myr and a spatial separation between younger and older YSOs, suggesting that many of the older stars formed in L1641N could have left the cluster, giving the appearance of an increased star formation rate with time.

  • 32.
    Gålfalk, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Herbig-Haro flows in B3352007In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 475, no 1, p. 281-300Article in journal (Refereed)
    Abstract [en]

    Aims.To study the Herbig-Haro flows in the nearby dark globule B335. To find new HH objects and H2 knots, make a proper motion map of the flow activity and investigate physical properties through shock models. Methods: We have observed optical (Hα and [SII]) and near-IR (2.12 μm H2) deep fields and taken optical spectra using the 2.56 m Nordic Optical Telescope, as well as a near-UV deep field (U band) using the 3.58 m NTT. In addition we present new SPITZER / IRAC (3.5-8.0 μm) and MIPS (24 μm) observations. We use previous Hα and 2.12 μm H2 observations taken 15 and 9 years earlier to make proper motion maps. We then investigate the shock physics by matching our spectra with planar shock models. Results: We discover five new HH objects (HH 119 D-H) in the eastern and one (HH 119 I) in the western lobe of the outflow. From proper motions we find an optically bright, roughly E-W oriented group with high space velocities (200-280 km s-1) and a near-IR bright, slower group (15-75 km s-1) moving to the ESE. We also find a system of at least 15 H2 knots in the western lobe. This (WNW) counterflow suggests the possibility of a binary outflow source, giving rise to two outflow axes with slightly different orientations. We find that the E-W flow is symmetrical with evidence for two outbursts. We make the first detection of [OI] λλ 6300/63 in HH 119 B and Hβ in HH 119 A and B and find their extinctions to be AV ≈ 1.4 and 4.4, respectively. HH 119 A is found to expand much faster than expected from linear expansion with distance from the outflow source. Using planar shock models we find shock velocities of ~60 km s-1 (A) and ~35 km s-1 (B and C). This agrees with A being of higher excitation than B and C. In our U image we detect three of the HH objects and propose that the emission arise from the [OII] λ3728 line and the blue continuum. New SPITZER / IRAC and MIPS observations show most of the HH objects at 4.5 μm and a E-W elongated hour-glass shaped structure at the outflow source. Even at 24 μm it is not clear whether most of the light is direct or reflected.

    Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Based on observations made with the New Technology Telescope, ESO (La Silla) under programme ID 077.C-0524. NOT and NTT images in FITS format are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/475/281

  • 33.
    Gålfalk, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Herbig-Haro flows in L1641N2007In: Astronomy & Astrophysics, Vol. 466, no 2, p. 579-587Article in journal (Refereed)
    Abstract [en]

    Aims.To study the Herbig-Haro (HH) flows in L1641N, an active star formation region in the southern part of the Orion GMC and one of the most densely populated regions of HH objects in the entire sky. By mapping the velocities of these HH objects, combined with mid-IR observations of the young stars, the major flows in the region and the corresponding outflow sources can be revealed. Methods: We have used the 2.56 m Nordic Optical Telescope (NOT) to observe two deep fields in L1641N, selected on the basis of previous shock studies, using the 2.12 μm transition of H2 (and a KS filter to sample the continuum) for a total exposure time of 4.6 h (72 min K_S) in the overlapping region. The resulting high-resolution mosaic (0.23 arcsec pixel size, 0.75 arcsec seeing) shows numerous new shocks and resolves many known shocks into multiple components. Using previous observations taken 9 yr earlier we calculate a proper motion map and combine this with Spitzer 24 μm observations of the embedded young stars. Results: The combined H2 mosaic shows many new shocks and faint structures in the HH flows. From the proper motion map we find that most HH objects belong to two major bi-polar HH flows, the large-scale roughly North-South oriented flow from central L1641N and a previously unseen HH flow in eastern L1641N. Combining the tangential velocity map with the mid-IR Spitzer images, two very likely outflow sources are found. The outflow source of the eastern flow, L1641N-172, is found to be the currently brightest mid-IR source in L1641N and seem to have brightened considerably during the past 20 yr. We make the first detection of this source in the near-IR (K_S) and also find a near-IR reflection nebula pointing at the source, probably the illuminated walls of a cone-shaped cavity cleared out by the eastern lobe of the outflow. Extending a line from the eastern outflow source along the proper motion vector we find that HH 301 and HH 302 (almost 1 pc away) belong to this new HH flow.

    Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

    This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

  • 34. Gålfalk, Magnus
    et al.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bastviken, David
    Approaches for hyperspectral remote flux quantification and visualization of GHGs in the environment2017In: Remote Sensing of Environment, ISSN 0034-4257, E-ISSN 1879-0704, Vol. 191, p. 81-94Article in journal (Refereed)
    Abstract [en]

    Methane (CH4) and nitrous oxide (N2O) are two very potent greenhouse gases, with highly heterogeneous distributions in both space and time. Mapping hot-spots and source areas, and measuring fluxes in different environments has so far not been possible on a local scale using direct measurements. We have developed a method for simultaneous mapping of methane (CH4) and nitrous oxide (N2O), also including water vapor (H2O), using ground-based remote sensing on a landscape-sized scale by utilizing Imaging Fourier Transform Spectrometers (IFTS) with high spectral resolution and imaging rates. The approach uses calculated libraries of transmission spectra at the spectroscopic resolutions of the IFTS, based on the HITRAN database of spectroscopic lines and our own line-by-line radiative transfer model (LBLRTM). For each species, 1024 spectra have been made, resulting in 10243 combinations of column densities. Using an adaptive grid, solutions are found for each line of sight at a spectral resolution of up to 0.25 cm(-1) using the full spectral region of the detector. The modeling is multi-layered, calculating temperatures of the background, air, and any additional gas layers, also accounting for reflected cold sky. Background distances can be mapped from the amount of water vapor in each line of sight. The described approach can be used to identify sources, quantify gas distributions, and to calculate fluxes. Visualizations can produce gas distribution images, as well as air motion videos, which are used to map fluxes using the same data set, without the need for additional instruments for wind measurements.

  • 35. Hennemann, M.
    et al.
    Motte, F.
    Bontemps, S.
    Schneider, N.
    Csengeri, T.
    Balog, Z.
    Di Francesco, J.
    Zavagno, A.
    Andre, Ph.
    Men'shchikov, A.
    Abergel, A.
    Ali, B.
    Baluteau, J. -P
    Bernard, J. -Ph.
    Cox, P.
    Didelon, P.
    di Giorgio, A. -M
    Griffin, M.
    Hargrave, P.
    Hill, T.
    Horeau, B.
    Huang, M.
    Kirk, J.
    Leeks, S.
    Li, J. Z.
    Marston, A.
    Martin, P.
    Molinari, S.
    Luong, Q. Nguyen
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Persi, P.
    Pezzuto, S.
    Russeil, D.
    Saraceno, P.
    Sauvage, M.
    Sibthorpe, B.
    Spinoglio, L.
    Testi, L.
    Ward-Thompson, D.
    White, G.
    Wilson, C.
    Woodcraft, A.
    Herschel observations of embedded protostellar clusters in the Rosette molecular cloud2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, p. L84-Article in journal (Refereed)
    Abstract [en]

    The Herschel OB young stellar objects survey (HOBYS) has observed the Rosette molecular cloud, providing an unprecedented view of its star formation activity. These new far-infrared data reveal a population of compact young stellar objects whose physical properties we aim to characterise. We compiled a sample of protostars and their spectral energy distributions that covers the near-infrared to submillimetre wavelength range. These were used to constrain key properties in the protostellar evolution, bolometric luminosity, and envelope mass and to build an evolutionary diagram. Several clusters are distinguished including the cloud centre, the embedded clusters in the vicinity of luminous infrared sources, and the interaction region. The analysed protostellar population in Rosette ranges from 0.1 to about 15 M-circle dot with luminosities between 1 and 150 L-circle dot, which extends the evolutionary diagram from low-mass protostars into the high-mass regime. Some sources lack counterparts at near-to mid-infrared wavelengths, indicating extreme youth. The central cluster and the Phelps & Lada 7 cluster appear less evolved than the remainder of the analysed protostellar population. For the central cluster, we find indications that about 25% of the protostars classified as Class I from near-to mid-infrared data are actually candidate Class 0 objects. As a showcase for protostellar evolution, we analysed four protostars of low-to intermediate-mass in a single dense core, and they represent different evolutionary stages from Class 0 to Class I. Their mid-to far-infrared spectral slopes flatten towards the Class I stage, and the 160 to 70 mu m flux ratio is greatest for the presumed Class 0 source. This shows that the Herschel observations characterise the earliest stages of protostellar evolution in detail.

  • 36. Hjalmarson, Å.
    et al.
    Frisk, U.
    Olberg, M.
    Bergman, P.
    Bernath, P.
    Biver, N.
    Black, J. H.
    Booth, R. S.
    Buat, V.
    Crovisier, J.
    Curry, C. L.
    Dahlgren, M.
    Encrenaz, P. J.
    Falgarone, E.
    Feldman, P. A.
    Fich, M.
    Florén, H. G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fredrixon, M.
    Gerin, M.
    Gregersen, E. M.
    Hagström, M.
    Harju, J.
    Hasegawa, T.
    Horellou, C.
    Johansson, L. E. B.
    Kyrölä, E.
    Kwok, S.
    Larsson, B.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lecacheux, A.
    Liljeström, T.
    Lindqvist, M.
    Liseau, R.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Llewellyn, E. J.
    Mattila, K.
    Mégie, G.
    Mitchell, G. F.
    Murtagh, D.
    Nyman, L.-Å.
    Nordh, H. L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, A. O. H.
    Olofsson, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, H.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pagani, L.
    Persson, G.
    Plume, R.
    Rickman, H.
    Ristorcelli, I.
    Rydbeck, G.
    Sandqvist, Aa.
    Stockholm University, Faculty of Science, Department of Astronomy.
    von Schéele, F.
    Serra, G.
    Torchinsky, S.
    Tothill, N. F.
    Volk, K.
    Wiklind, T.
    Wilson, C. D.
    Winnberg, A.
    Witt, G.
    Highlights from the first year of Odin observations2003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 402, p. L39-L46Article in journal (Refereed)
    Abstract [en]

    Key Odin operational and instrumental features and highlights from our sub-millimetre and millimetre wave observations of H2O, H218O, NH3, 15NH3 and O2 are presented, with some insights into accompanying Odin Letters in this A&A issue. We focus on new results where Odin's high angular resolution, high frequency resolution, large spectrometer bandwidths, high sensitivity or/and frequency tuning capability are crucial: H2O mapping of the Orion KL, W3, DR21, S140 regions, and four comets; H2O observations of Galactic Centre sources, of shock enhanced H2O towards the SNR IC443, and of the candidate infall source IRAS 16293-2422; H218O detections in Orion KL and in comet Ikeya-Zhang; sub-mm detections of NH3 in Orion KL (outflow, ambient cloud and bar) and ρ Oph, and very recently, of 15NH3 in~Orion KL. Simultaneous sensitive searches for the 119 GHz line of O2 have resulted in very low abundance limits, which are difficult to accomodate in chemical models. We also demonstrate, by means of a quantitative comparison of Orion KL H2O results, that the Odin and SWAS observational data sets are very consistently calibrated. Odin is a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes), and the Centre National d'études Spatiales (CNES, France). The Swedish Space Corporation (SSC) has been the prime industrial contractor, and is also responsible for the satellite operation from its Odin Mission Control Centre at SSC in Solna and its Odin Control Centre at ESRANGE near Kiruna in northern Sweden. See also the SNSB Odin web page: http://www.snsb.se/eng_odin_intro.shtml

  • 37. Kiss, M.
    et al.
    Larsson, Stefan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Astronomy.
    Bettolo, C.
    Bogaert, G.
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Astronomy.
    Fukazawa, Y.
    Gunji, S.
    Hjalmarsdotter, Linnea
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Astronomy.
    Kamae, T.
    Kanai, Y.
    Kataoka, J.
    Kawai, N.
    Klamra, W.
    Kurita, K.
    Madejski, G.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Astronomy.
    Pearce, Mark
    Ryde, Felix
    Rydström, S.
    Tajima, H.
    Takahashi, H.
    Takahashi, T.
    Tanaka, T.
    Ueno, M.
    Umeki, Y.
    Varner, G.
    Yoshida, H.
    The PoGOLite balloon-borne soft gamma-ray polarimeter2008In: COOL DISCS, HOT FLOWS: The Varying Faces of Accreting Compact Objects, 2008, p. 225-232Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Linearly polarized radiation in the hard X-ray/soft gamma-ray band is expected from a large variety of astronomical sources. We discuss the importance of polarimetric studies for several classes of sources-pulsars, accreting black holes, magnetic neutron stars and jets from active galaxies-and then describe PoGOLite, a balloon-borne instrument which is currently under construction and will be able to measure the polarization of electromagnetic radiation from such extra-solar objects in the energy range 25-80 keV.

  • 38. Ladjal, D.
    et al.
    Barlow, M. J.
    Groenewegen, M. A. T.
    Ueta, T.
    Blommaert, J. A. D. L.
    Cohen, M.
    Decin, L.
    De Meester, W.
    Exter, K.
    Gear, W. K.
    Gomez, H. L.
    Hargrave, P. C.
    Huygen, R.
    Ivison, R. J.
    Jean, C.
    Kerschbaum, F.
    Leeks, S. J.
    Lim, T. L.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Polehampton, E.
    Posch, T.
    Regibo, S.
    Royer, P.
    Sibthorpe, B.
    Swinyard, B. M.
    Vandenbussche, B.
    Waelkens, C.
    Wesson, R.
    Herschel PACS and SPIRE imaging of CW Leonis2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, p. L141-Article in journal (Refereed)
    Abstract [en]

    Herschel PACS and SPIRE images have been obtained over a 30' x 30' area around the well-known carbon star CW Leo (IRC + 10 216). An extended structure is found in an incomplete arc of similar to 22' diameter, which is cospatial with the termination shock due to interaction with the interstellar medium (ISM) as defined by Sahai & Chronopoulos from ultraviolet GALEX images. Fluxes are derived in the 70, 160, 250, 350, and 550 mu m bands in the region where the interaction with the ISM takes place, and this can be fitted with a modified black body with a temperature of 25 +/- 3 K. Using the published proper motion and radial velocity for the star, we derive a heliocentric space motion of 25.1 km s(-1). Using the PACS and SPIRE data and the analytical formula of the bow shock structure, we infer a de-projected standoff distance of the bow shock of R-0 = (8.0 +/- 0.3) x 10(17) cm. We also derive a relative velocity of the star with respect to the ISM of (106.6 +/- 8.7)/ root n(ISM) km s (1), where n(ISM) is the number density of the local ISM.

  • 39.
    Larsson, B.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Liseau, R.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bergman, P.
    Bernath, P.
    Black, J. H.
    Booth, R. S.
    Buat, V.
    Curry, C. L.
    Encrenaz, P.
    Falgarone, E.
    Feldman, P.
    Fich, M.
    Florén, H. G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Frisk, U.
    Gerin, M.
    Gregersen, E. M.
    Harju, J.
    Hasegawa, T.
    Johansson, L. E. B.
    Kwok, S.
    Lecacheux, A.
    Liljeström, T.
    Mattila, K.
    Mitchell, G. F.
    Nordh, L. H.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olberg, M.
    Olofsson, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pagani, L.
    Plume, R.
    Ristorcelli, I.
    Sandqvist, Aa.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Schéele, F. v.
    Tothill, N. F. H.
    Volk, K.
    Wilson, C. D.
    Hjalmarson, Å.
    First NH3 detection of the Orion Bar2003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 402, p. L69-L72Article in journal (Refereed)
    Abstract [en]

    Odin has successfully observed three regions in the Orion A cloud, i.e. Ori KL, Ori S and the Orion Bar, in the 572.5 GHz rotational ground state line of ammonia, ortho-NH3 (J,K) = (1,0) -> (0,0), and the result for the Orion Bar represents the first detection in an ammonia line. Several velocity components are present in the data. Specifically, the observed line profile from the Orion Bar can be decomposed into two components, which are in agreement with observations in high-J CO lines by Wilson et al. (\cite{wilson01}). Using the source model for the Orion Bar by these authors, our Odin observation implies a total ammonia abundance of NH3/H2 = 5x 10-9. Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Études Spatiales (CNES). The Swedish Space Corporation has been the industrial prime contractor.

  • 40.
    Larsson, B.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Liseau, R.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Men'shchikov, A. B.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Caux, E.
    Ceccarelli, C.
    Lorenzetti, D.
    Molinari, S.
    Nisini, B.
    Nordh, L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Saraceno, P.
    Sibille, F.
    Spinoglio, L.
    White, G. J.
    Stockholm University, Faculty of Science, Department of Astronomy.
    The ISO-LWS map of the Serpens cloud core. I. The SEDs of the IR/SMM sources2000In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 363, p. 253-268Article in journal (Refereed)
    Abstract [en]

    Iso-Lws mapping observations of the Serpens molecular cloud core are presented. The spectral range is 50 - 200 μ m and the map size is 8',x 8'. These observations suffer from severe source confusion at Fir wavelengths and we employ a Maximum Likelihood Method for the spectro-spatial deconvolution. The strong and fairly isolated source SMM 1/FIRS 1 presented a test case, whose modelled spectral energy distribution (SED), within observational errors, is identical to the observed one. The model results for the other infrared and submillimetre sources are therefore likely to represent their correct SEDs. Simulations demonstrating the reliability and potential of the developed method support this view. It is found that some sources do not exhibit significant Fir emission and others are most likely not pointlike at long wavelengths. In contrast, the SEDs of a number of SMMs are well fit by modified single-temperature blackbodies over the entire accessible spectral range. For the majority of sources the peak of the SEDs is found within the spectral range of the Lws and derived temperatures are generally higher (>= 30 K) than have been found by earlier deconvolution attempts using Iras data. SMM sizes are found to be only a few arcsec in diameter. In addition, the SMMs are generally optically thick even at Lws wavelengths, i.e. estimated lambda (TAu=1) are in the range 160-270 μ m. The Rayleigh-Jeans tails are less steep than expected for optically thin dust emission. This indicates that the SMMs are optically thick out to longer wavelengths than previously assumed, an assertion confirmed by self-consistent radiative transfer calculations. Models were calculated for five sources, for which sufficient data were available, viz. SMM 1, 2, 3, 4 and 9. These models are optically thick out to millimetre wavelengths (wavelength of unit optical depth 900 to 1 400 μ m). Envelope masses for these SMMs are in the range 2-6 Msun, which is of course considerably more massive than estimates based on the optically thin assumption. The luminosities are in the range 10-70 Lsun, suggesting the formation of low-mass to intermediate mass stars, so that the existence of such massive envelopes argues for extreme youth of the SMMs in the Serpens cloud core. Finally, we present, for the first time, the full infrared SEDs for the outburst source DEOS, both at high and low intensity states. Based on observations with Iso, an Esa project with instruments funded by Esa Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of Isas and Nasa.

  • 41.
    Larsson, Bengt
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Liseau, Rene
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pagani, Laurent
    Bergman, Per
    Bernath, Peter
    Biver, Nicolas
    Black, John
    Booth, Roy
    Buat, Veronique
    Crovisier, Jacques
    Curry, Charles
    Dahlgren, Magnus
    Encrenaz, Pierre
    Falgarone, Edith
    Feldman, Paul
    Fish, Michel
    Florén, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fredrixon,
    Frisk, Urban
    Gahm, Gösta
    Stockholm University, Faculty of Science, Department of Astronomy.
    Gerin, Maryvonne
    Hagström, Magne
    Harju, Jorma
    Hasegawa, Tatsuhiko
    Hjalmarsson, Åke
    Johansson, Lars
    Justtanout, Kay
    Stockholm University, Faculty of Science, Department of Astronomy.
    Klotz, Alain
    Kytölä, Erikii
    Kwok, Sun
    Lecacheux, Alain
    Liljeström, Tarja
    Llewellyn, Edward
    Lundin, Stefan
    Mégie, Gérard
    Mitchell, Gary
    Murtagh, Donal
    Nordh, Lennart
    Nyman, Lars-Åke
    Olberg, Michael
    Olofsson, Henrik
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Hans
    Stockholm University, Faculty of Science, Department of Astronomy.
    Persson, Glen
    Plume, Rene
    Rickman, Hans
    Ristorcelli, Isabelle
    Rydbeck, Gustaf
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    von Scheele, Fredrik
    Serra, Guy
    Torchinsky, Steve
    Tothill, Nick
    Volk, Kevin
    Wiklind, Tommy
    Wilson, Christine
    Winnberg, Anders
    Witt, George
    Department of Meteorology.
    Molecular oxygen in the rho Ophiuchi cloud2007In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 466, no 3, p. 5-Article in journal (Refereed)
    Abstract [en]

    Context: Molecular oxygen, O2, has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O2 emission.

    Aims: The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium. Methods: The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O2. Starting in 2002, the star forming molecular cloud core ρ Oph A was observed with Odin for 34 days during several observing runs.

    Results: We detect a spectral line at v_LSR =+3.5 km s-1 with Δ v_FWHM=1.5 km s-1, parameters which are also common to other species associated with ρ Oph A. This feature is identified as the O2 (NJ = 11 - 1_0) transition at 118 750.343 MHz.

    Conclusions: The abundance of molecular oxygen, relative to H{2} , is 5 × 10-8 averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits.

    Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Étude Spatiale (CNES). The Swedish Space Corporation has been the industrial prime contractor and also is operating the satellite. Appendix A is only available in electronic form at http://www.aanda.org

  • 42. Lawler, S. M.
    et al.
    Di Francesco, J.
    Kennedy, G. M.
    Sibthorpe, B.
    Booth, M.
    Vandenbussche, B.
    Matthews, B. C.
    Holland, W. S.
    Greaves, J.
    Wilner, D. J.
    Tuomi, M.
    Blommaert, J. A. D. L.
    de Vries, Bernard L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Dominik, C.
    Fridlund, M.
    Gear, W.
    Heras, A. M.
    Ivison, R.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    The debris disc of solar analogue tau Ceti: Herschel observations and dynamical simulations of the proposed multiplanet system2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 444, no 3, p. 2665-2675Article in journal (Refereed)
    Abstract [en]

    tau Ceti is a nearby, mature G-type star very similar to our Sun, with a massive Kuiper Belt analogue and possible multiplanet system that has been compared to our Solar system. We present Herschel Space Observatory images of the debris disc, finding the disc is resolved at 70 mu m and 160 mu m, and marginally resolved at 250 mu m. The Herschel images and infrared photometry from the literature are best modelled using a wide dust annulus with an inner edge between 1 and 10 au and an outer edge at similar to 55 au, inclined from face-on by 35 degrees +/- 10 degrees, and with no significant azimuthal structure. We model the proposed tightly packed planetary system of five super-Earths and find that the innermost dynamically stable disc orbits are consistent with the inner edge found by the observations. The photometric modelling, however, cannot rule out a disc inner edge as close to the star as 1 au, though larger distances produce a better fit to the data. Dynamical modelling shows that the five-planet system is stable with the addition of a Neptune or smaller mass planet on an orbit outside 5 au, where the radial velocity data analysis would not have detected a planet of this mass.

  • 43. Liseau, R.
    et al.
    Goldsmith, P. F.
    Larsson, Bengt
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pagani, L.
    Bergman, P.
    Le Bourlot, J.
    Bell, T. A.
    Benz, A. O.
    Bergin, E. A.
    Bjerkeli, P.
    Black, J. H.
    Bruderer, S.
    Caselli, P.
    Caux, E.
    Chen, J. -H
    de Luca, M.
    Encrenaz, P.
    Falgarone, E.
    Gerin, M.
    Goicoechea, J. R.
    Hjalmarson, A.
    Hollenbach, D. J.
    Justtanont, K.
    Kaufman, M. J.
    Le Petit, F.
    Li, D.
    Lis, D. C.
    Melnick, G. J.
    Nagy, Z.
    Olofsson, A. O. H.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Roueff, E.
    Sandqvist, Aage
    Stockholm University, Faculty of Science, Department of Astronomy.
    Snell, R. L.
    van der Tak, F. F. S.
    van Dishoeck, E. F.
    Vastel, C.
    Viti, S.
    Yildiz, U. A.
    Multi-line detection of O-2 toward rho Ophiuchi A2012In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 541, p. A73-Article in journal (Refereed)
    Abstract [en]

    Context. Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict relatively high levels of molecular oxygen, O-2, and water, H2O. These high abundances imply high cooling rates, leading to relatively short timescales for the evolution of gravitationally unstable dense cores, forming stars and planets. Contrary to expectations, the dedicated space missions SWAS and Odin typically found only very small amounts of water vapour and essentially no O-2 in the dense star-forming interstellar medium. Aims. Only toward rho OphA did Odin detect a very weak line of O-2 at 119 GHz in a beam of size 10 arcmin. The line emission of related molecules changes on angular scales of the order of some tens of arcseconds, requiring a larger telescope aperture such as that of the Herschel Space Observatory to resolve the O-2 emission and pinpoint its origin. Methods. We use the Heterodyne Instrument for the Far Infrared (HIFI) aboard Herschel to obtain high resolution O-2 spectra toward selected positions in the rho Oph A core. These data are analysed using standard techniques for O2 excitation and compared to recent PDR-like chemical cloud models. Results. The N-J = 3(3)-1(2) line at 487.2 GHz is clearly detected toward all three observed positions in the rho Oph A core. In addition, an oversampled map of the 5(4)-3(4) transition at 773.8 GHz reveals the detection of the line in only half of the observed area. On the basis of their ratios, the temperature of the O-2 emitting gas appears to vary quite substantially, with warm gas (greater than or similar to 50 K) being adjacent to a much colder region, of temperatures lower than 30 K. Conclusions. The exploited models predict that the O-2 column densities are sensitive to the prevailing dust temperatures, but rather insensitive to the temperatures of the gas. In agreement with these models, the observationally determined O-2 column densities do not seem to depend strongly on the derived gas temperatures, but fall into the range N(O-2) = 3 to greater than or similar to 6 x 10(15) cm(-2). Beam-averaged O-2 abundances are about 5 x 10(-8) relative to H-2. Combining the HIFI data with earlier Odin observations yields a source size at 119 GHz in the range of 4 to 5 arcmin, encompassing the entire rho Oph A core. We speculate that one of the reasons for the generally very low detection rate of O-2 is the short period of time during which O-2 molecules are reasonably abundant in molecular clouds.

  • 44.
    Liseau, R.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Larsson, B.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Brandeker, A.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bergman, P.
    Bernath, P.
    Black, J. H.
    Booth, R.
    Buat, V.
    Curry, C.
    Encrenaz, P.
    Falgarone, E.
    Feldman, P.
    Fich, M.
    Florén, H.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Frisk, U.
    Gerin, M.
    Gregersen, E.
    Harju, J.
    Hasegawa, T.
    Hjalmarson, Å.
    Johansson, L.
    Kwok, S.
    Lecacheux, A.
    Liljeström, T.
    Mattila, K.
    Mitchell, G.
    Nordh, L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olberg, M.
    Olofsson, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pagani, L.
    Plume, R.
    Ristorcelli, I.
    Sandqvist, Aa.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Schéele, F. v.
    Serra, G.
    Tothill, N.
    Volk, K.
    Wilson, C.
    First detection of NH3 (10 -> 00) from a low mass cloud core. On the low ammonia abundance of the rho Oph A core2003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 402, p. L73-L76Article in journal (Refereed)
    Abstract [en]

    Odin has successfully observed the molecular core rho Oph A in the 572.5 GHz rotational ground state line of ammonia, NH3 (JK = 10 -> 00). The interpretation of this result makes use of complementary molecular line data obtained from the ground (C17O and CH3OH) as part of the Odin preparatory work. Comparison of these observations with theoretical model calculations of line excitation and transfer yields a quite ordinary abundance of methanol, X(CH3OH)= 3 x 10-9. Unless NH3 is not entirely segregated from C17O and CH3OH, ammonia is found to be significantly underabundant with respect to typical dense core values, viz. X(NH3) = 8 x 10-10. Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Études Spatiales (CNES). The Swedish Space Corporation has been the industrial prime contractor. and based on observations collected with the Swedish ESO Submillimeter Telescope, SEST, in La Silla, Chile.

  • 45. Liseau, R.
    et al.
    Larsson, Bengt
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lunttila, T.
    Olberg, M.
    Rydbeck, G.
    Bergman, P.
    Justtanont, K.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    de Vries, Bernard L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Gas and dust in the star-forming region rho Oph A The dust opacity exponent beta and the gas-to-dust mass ratio g2d2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 578, article id A131Article in journal (Refereed)
    Abstract [en]

    Aims. We aim at determining the spatial distribution of the gas and dust in star-forming regions and address their relative abundances in quantitative terms. We also examine the dust opacity exponent beta for spatial and/or temporal variations. Methods. Using mapping observations of the very dense rho Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimetre (submm) continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N2H+, which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N2H+ (J = 3-2) and (J = 6-5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H-2), hence the surface density distribution of the gas. Results. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM 1. The global average, = 88, is not far from the canonical value of 100, however. In rho Oph A, the exponent beta of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class -1 sources to low values close to 0 for the disk-dominated emission in Class III objects. beta assumes intermediate values for evolutionary classes in between. Conclusions. Since beta is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like (CO)-O-18, also N2H+ is frozen onto the grains.

  • 46. Liseau, R.
    et al.
    Montesinos, B.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bryden, G.
    Marshall, J. P.
    Ardila, D.
    Aran, A. Bayo
    Danchi, W. C.
    del Burgo, C.
    Eiroa, C.
    Ertel, S.
    Fridlund, M. C. W.
    Krivov, A. V.
    Pilbratt, G. L.
    Roberge, A.
    Thebault, P.
    Wiegert, J.
    White, G. J.
    Alpha centauri a in the far infrared first measurement of the temperature minimum of a star other than the sun2013In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 549, p. L7-Article in journal (Refereed)
    Abstract [en]

    Context. Chromospheres and coronae are common phenomena on solar-type stars. Understanding the energy transfer to these heated atmospheric layers requires direct access to the relevant empirical data. Study of these structures has, by and large, been limited to the Sun thus far. Aims. The region of the temperature reversal can be directly observed only in the far infrared and submillimetre spectral regime. We aim at determining the characteristics of the atmosphere in the region of the temperature minimum of the solar sister star alpha Cen A. As a bonus this will also provide a detailed mapping of the spectral energy distribution, i.e. knowledge that is crucial when searching for faint, Kuiper belt-like dust emission around other stars. Methods. For the nearby binary system alpha Cen, stellar parameters are known with high accuracy from measurements. For the basic model parameters T-eff, log g and [Fe/H], we interpolate stellar model atmospheres in the grid of Gaia/PHOENIX and compute the corresponding model for the G2 V star alpha Cen A. Comparison with photometric measurements shows excellent agreement between observed photospheric data in the optical and infrared. For longer wavelengths, the modelled spectral energy distribution is compared to Spitzer-MIPS, Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry. A specifically tailored Uppsala model based on the MARCS code and extending further in wavelength is used to gauge the emission characteristics of alpha Cen A in the far infared. Results. Similar to the Sun, the far infrared (FIR) emission of alpha Cen A originates in the minimum temperature region above the stellar photosphere in the visible. However, in comparison with the solar case, the FIR photosphere of alpha Cen A appears marginally cooler, T-min similar to T-160 (mu m) = 3920 +/- 375 K. Beyond the minimum near 160 mu m, the brightness temperatures increase, and this radiation very likely originates in warmer regions of the chromosphere of alpha Cen A. Conclusions. To the best of our knowledge, this is the first time a temperature minimum has been directly measured on a main-sequence star other than the Sun.

  • 47. Liseau, Rene
    et al.
    Risacher, Christophe
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    Eiroa, Carlos
    Fridlund, Malcolm
    Nilsson, Ricky
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pilbratt, Göran L.
    Thébault, Philippe
    q1 Eridani: a solar-type star with a planet and a dust belt2008In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 480, no 3, p. L47-L50Article in journal (Refereed)
    Abstract [en]

    Context. Far-infrared excess emission from main-sequence stars is due to dust produced by orbiting minor bodies. In these disks, larger bodies, such as planets, may also be present and the understanding of their incidence and influence currently presents a challenge.

    Aims. Only very few solar-type stars exhibiting an infrared excess and harbouring planets are known to date. Indeed, merely a single case of a star-planet-disk system has previously been detected at submillimeter (submm) wavelengths. Consequently, one of our aims is to understand the reasons for these poor statistics, i.e., whether these results reflected the composition and/or the physics of the planetary disks or were simply due to observational bias and selection effects. Finding more examples would be very significant.

    Methods. The selected target, q(1) Eri, is a solar-type star, which was known to possess a planet, q(1) Eri b, and to exhibit excess emission at IRAS wavelengths, but had remained undetected in the millimeter regime. Therefore, submm flux densities would be needed to better constrain the physical characteristics of the planetary disk. Consequently, we performed submm imaging observations of q(1) Eri.

    Results. The detected dust toward q(1) Eri at 870 mu m exhibits the remarkable fact that the entire SED, from the IR to mm-wavelengths, is fit by a single-temperature blackbody function (60 K). This would imply that the emitting regions are confined to a narrow region (ring) at radial distances much larger than the orbital distance of q(1) Eri b, and that the emitting particles are considerably larger than some hundred micron. However, the 870 mu m source is extended, with a full-width-half-maximum of roughly 600AU. Therefore, a physically more compelling model also invokes a belt of cold dust (17 K), located at 300AU from the star and about 60AU wide.

    Conclusions. The minimum mass of 0.04 M-circle plus (3 M-Moon) of 1 mm-size icy ring-particles is considerable, given the stellar age of >= 1Gyr. These big grains form an inner edge at about 25 AU, which may suggest the presence of an unseen outer planet (q(1) Eri c).

  • 48.
    Lundqvist, Natalia
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Björnsson, Claes-Ingvar
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pires, S.
    Shibanov, Yu. A.
    Zyuzin, D. A.
    Spectral evolution and polarization of variable structures in the pulsar wind nebula of PSR B0540-69.32011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 413, no 1, p. 611-627Article in journal (Refereed)
    Abstract [en]

    We present high spatial resolution optical imaging and polarization observations of the PSR B0540-69.3 and its highly dynamical pulsar wind nebula (PWN) performed with Hubble Space Telescope, and compare them with X-ray data obtained with the Chandra X-ray Observatory. In particular, we have studied the bright region south-west of the pulsar where a bright 'blob' is seen in 1999. In a recent paper by De Luca et al. it was argued that the 'blob' moves away from the pulsar at high speed. We show that it may instead be a result of local energy deposition around 1999, and that the emission from this then faded away rather than moved outward. Polarization data from 2007 show that the polarization properties show dramatic spatial variations at the 1999 blob position arguing for a local process. Several other positions along the pulsar-'blob' orientation show similar changes in polarization, indicating previous recent local energy depositions. In X-rays, the spectrum steepens away from the 'blob' position, faster orthogonal to the pulsar-'blob' direction than along this axis of orientation. This could indicate that the pulsar-'blob' orientation is an axis along where energy in the PWN is mainly injected, and that this is then mediated to the filaments in the PWN by shocks. We highlight this by constructing an [S ii]-to-[O iii]-ratio map, and comparing this to optical continuum and X-ray emission maps. We argue, through modelling, that the high [S ii]/[O iii] ratio is not due to time-dependent photoionization caused by possible rapid X-ray emission variations in the 'blob' region. We have also created a multiwavelength energy spectrum for the 'blob' position showing that one can, to within 2 Sigma, connect the optical and X-ray emission by a single power law. The slope of that power law (defined from <file name=mnr_18159_mu1.gif type=gif/>) would be alpha(nu) = 0.74 +/- 0.03, which is marginally different from the X-ray spectral slope alone with alpha(nu) = 0.65 +/- 0.03. A single power law for most of the PWN is, however, not be possible. We obtain best power-law fits for the X-ray spectrum if we include 'extra' oxygen, in addition to the oxygen column density in the interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen is most naturally explained by the oxygen-rich ejecta of the supernova remnant. The oxygen needed likely places the progenitor mass in the 20-25 M(circle dot) range, i.e. in the upper mass range for progenitors of Type IIP supernovae.

  • 49. Maercker, M.
    et al.
    Ramstedt, S.
    Leal-Ferreira, M. L.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Floren, Hans-Gustav
    Stockholm University, Faculty of Science, Department of Astronomy.
    The detached dust shells around the carbon AGB stars R Sculptoris and V644 Scorpii2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 570, p. A101-Article in journal (Refereed)
    Abstract [en]

    Context. The morphology of the circumstellar envelopes (CSE) around asymptotic giant branch (AGB) stars gives information on the mass-loss process from the star, its evolution and wind, and on the effect of binary interaction. However, determining the distribution of dust in the circumstellar envelopes is difficult. Observations of polarised, dust-scattered stellar light in the optical have produced images with high-spatial resolution of the envelopes around evolved stars. For sources with detached shells in particular, this method has proven extremely successful. Detached shells are believed to be created during a thermal pulse, and studying them can constrain the time scales and physical properties of one of the main drivers of late stellar evolution. Aims. We aim at determining the morphology of the detached shells around the carbon AGB stars R Scl and V644 Sco. In particular, we attempt to constrain the radii and widths of the detached dust shells around the stars and compare them to observations of the detached gas shells. Methods. We observed the polarised, dust-scattered stellar light around the carbon AGB stars R Scl and V644 Sco using the PolCor instrument mounted on the ESO 3.6 m telescope. Observations were done with a coronographic mask to block out the direct stellar light. The polarised images clearly show the detached shells around R Scl and V644 Sco. Using a dust radiative transfer code to model the dust-scattered polarised light, we constrained the radii and widths of the shells. Results. We determine radii of 19 ''.5 and 9 ''.4 for the detached dust shells around R Scl and V644 Sco, respectively. Both shells have an overall spherical symmetry and widths of approximate to 2 ''. For R Scl, we can compare the observed dust emission directly with high spatialresolution maps of CO(3-2) emission from the shell observed with ALMA. We find that the dust and gas coincide almost exactly, indicating a common evolution. The data presented here for R Scl are the most detailed observations of the entire dusty detached shell to date. For V644 Sco, these are the first direct measurements of the detached shell. Also here we find that the dust most likely coincides with the gas shell. Conclusions. The observations are consistent with a scenario where the detached shells are created during a thermal pulse. The determined radii and widths will constrain hydrodynamical models describing the pre-pulse mass loss, the thermal pulse, and postpulse evolution of the star.

  • 50. Malisani, Daniel
    et al.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    GRB 070612A: NOT observations.2007Report (Other academic)
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