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  • 201. Beckman, J. E.
    et al.
    Fathi, K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Piñol, N.
    Toonen, S.
    Hernandez, O.
    Carignan, C.
    The Tremaine-Weinberg Method for Pattern Speeds Using Hα Emission from Ionized Gas2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Fabry-Perot interferometer FaNTOmM was used at the 3.6-m CFHT and the 1.6-m Mont Mégantic Telescope to obtain data cubes in Hα of 9 nearby spiral galaxies from which maps in integrated intensity, velocity, and velocity dispersion were derived. We then applied the Tremaine-Weinberg method, in which the pattern speed can be deduced from its velocity field, by finding the integrated value of the mean velocity along a slit parallel to the major axis weighted by the intensity and divided by the weighted mean distance of the velocity points from the tangent point measured along the slit. The measured variables can be used either to make separate calculations of the pattern speed and derive a mean, or in a plot of one against the other for all the points on all slits, from which a best fit value can be derived. Linear fits were found for all the galaxies in the sample. For two galaxies a clearly separate inner pattern speed with a higher value, was also identified and measured.

  • 202. Beckman, John
    et al.
    Fathi, Kambiz
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Piñol, Núria
    Toonen, Silvia
    Hernandez, Olivier
    Carignan, Claude
    The Tremaine-Weinberg method for pattern speeds using H-alpha emission from ionized gas2008Ingår i: Formation and Evolution of Galaxy Disks, Astronomical Society of the Pacific , 2008, s. 353-Konferensbidrag (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    The Fabry-Perot interferometer FaNTOmM was used at the 3.6m Canada France Hawaii Telescope and the 1.6m Mont Megantic Telescope to obtain data cubes in H-alpha of 9 nearby spiral galaxies from which maps in integrated intensity, velocity, and velocity dispersion were derived. We then applied the Tremaine-Weinberg method, in which the pattern speed can be deduced from its velocity field, by finding the integrated value of the mean velocity along a slit parallel to the major axis weighted by the intensity and divided by the weighted mean distance of the velocity points from the tangent point measured along the slit. The measured variables can be used either to make separate calculations of the pattern speed and derive a mean, or in a plot of one against the other for all the points on all slits, from which a best fit value can be derived. Linear fits were found for all the galaxies in the sample. For two galaxies a clearly separate inner pattern speed with a higher value, was also identified and measured.

  • 203. Bejarano, Cecilia
    et al.
    Gomez, Daniel O.
    Brandenburg, Axel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    SHEAR-DRIVEN INSTABILITIES IN HALL-MAGNETOHYDRODYNAMIC PLASMAS2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 737, nr 2, s. 62-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The large-scale dynamics of plasmas is well described within the framework of magnetohydrodynamics (MHD). However, whenever the ion density of the plasma becomes sufficiently low, the Hall effect is likely to become important. The role of the Hall effect has been studied in several astrophysical plasma processes, such as magnetic reconnection, magnetic dynamo, MHD turbulence, or MHD instabilities. In particular, the development of small-scale instabilities is essential to understand the transport properties in a number of astrophysical plasmas. The magneto-rotational instability (MRI), which takes place in differentially rotating accretion disks embedded in relatively weak magnetic fields, is just one example. The influence of the large-scale velocity flows on small-scale instabilities is often approximated by a linear shear flow. In this paper, we quantitatively study the role of the Hall effect on plasmas embedded in large-scale shear flows. More precisely, we show that an instability develops when the Hall effect is present, which we therefore term as the Hall magneto-shear instability. As a particular case, we recover the so-called MRI and quantitatively assess the role of the Hall effect on its development and evolution.

  • 204. Bellm, Eric C.
    et al.
    Kulkarni, Shrinivas R.
    Graham, Matthew J.
    Dekany, Richard
    Smith, Roger M.
    Riddle, Reed
    Masci, Frank J.
    Helou, George
    Prince, Thomas A.
    Adams, Scott M.
    Barbarino, Cristina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Barlow, Tom
    Bauer, James
    Beck, Ron
    Belicki, Justin
    Biswas, Rahul
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Blagorodnova, Nadejda
    Bodewits, Dennis
    Bolin, Bryce
    Brinnel, Valery
    Brooke, Tim
    Bue, Brian
    Bulla, Mattia
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Burruss, Rick
    Cenko, S. Bradley
    Chang, Chan-Kao
    Connolly, Andrew
    Coughlin, Michael
    Cromer, John
    Cunningham, Virginia
    De, Kishalay
    Delacroix, Alex
    Desai, Vandana
    Duev, Dmitry A.
    Eadie, Gwendolyn
    Farnham, Tony L.
    Feeney, Michael
    Feindt, Ulrich
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Flynn, David
    Franckowiak, Anna
    Frederick, S.
    Fremling, C.
    Gal-Yam, Avishay
    Gezari, Suvi
    Giomi, Matteo
    Goldstein, Daniel A.
    Golkhou, V. Zach
    Goobar, Ariel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Groom, Steven
    Hacopians, Eugean
    Hale, David
    Henning, John
    Ho, Anna Y. Q.
    Hover, David
    Howell, Justin
    Hung, Tiara
    Huppenkothen, Daniela
    Imel, David
    Ip, Wing-Huen
    Ivezic, Zeljko
    Jackson, Edward
    Jones, Lynne
    Juric, Mario
    Kasliwal, Mansi M.
    Kaspi, S.
    Kaye, Stephen
    Kelley, Michael S. P.
    Kowalski, Marek
    Kramer, Emily
    Kupfer, Thomas
    Landry, Walter
    Laher, Russ R.
    Lee, Chien-De
    Lin, Hsing Wen
    Lin, Zhong-Yi
    Lunnan, Ragnhild
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Giomi, Matteo
    Mahabal, Ashish
    Mao, Peter
    Miller, Adam A.
    Monkewitz, Serge
    Murphy, Patrick
    Ngeow, Chow-Choong
    Nordin, Jakob
    Nugent, Peter
    Ofek, Eran
    Patterson, Maria T.
    Penprase, Bryan
    Porter, Michael
    Rauch, Ludwig
    Rebbapragada, Umaa
    Reiley, Dan
    Rigault, Mickael
    Rodriguez, Hector
    van Roestel, Jan
    Rusholme, Ben
    van Santen, Jakob
    Schulze, S.
    Shupe, David L.
    Singer, Leo P.
    Soumagnac, Maayane T.
    Stein, Robert
    Surace, Jason
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Szkody, Paula
    Taddia, Francesco
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Terek, Scott
    Van Sistine, Angela
    van Velzen, Sjoert
    Vestrand, W. Thomas
    Walters, Richard
    Ward, Charlotte
    Ye, Quan-Zhi
    Yu, Po-Chieh
    Yan, Lin
    Zolkower, Jeffry
    The Zwicky Transient Facility: System Overview, Performance, and First Results2019Ingår i: Publications of the Astronomical Society of the Pacific, ISSN 0004-6280, E-ISSN 1538-3873, Vol. 131, nr 995, artikel-id 018002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Zwicky Transient Facility (ZTF) is a new optical time-domain survey that uses the Palomar 48 inch Schmidt telescope. A custom-built wide-field camera provides a 47 deg(2) field of view and 8 s readout time, yielding more than an order of magnitude improvement in survey speed relative to its predecessor survey, the Palomar Transient Factory. We describe the design and implementation of the camera and observing system. The ZTF data system at the Infrared Processing and Analysis Center provides near-real-time reduction to identify moving and varying objects. We outline the analysis pipelines, data products, and associated archive. Finally, we present on-sky performance analysis and first scientific results from commissioning and the early survey. ZTF's public alert stream will serve as a useful precursor for that of the Large Synoptic Survey Telescope.

  • 205. Ben-Ami, Sagi
    et al.
    Hachinger, Stephan
    Gal-Yam, Avishay
    Mazzali, Paolo A.
    Filippenko, Alexei V.
    Horesh, Assaf
    Matheson, Thomas
    Modjaz, Maryam
    Sauer, Daniel N.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Silverman, Jeffrey M.
    Smith, Nathan
    Yaron, Ofer
    ULTRAVIOLET SPECTROSCOPY OF TYPE IIB SUPERNOVAE: DIVERSITY AND THE IMPACT OF CIRCUMSTELLAR MATERIAL2015Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 803, nr 1, artikel-id 40Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present new Hubble Space Telescope (HST) multi-epoch ultraviolet (UV) spectra of the bright Type IIb SN 2013df, and undertake a comprehensive analysis of the set of four SNe IIb for which HST UV spectra are available (SN 1993J, SN 2001ig, SN 2011dh, and SN 2013df). We find strong diversity in both continuum levels and line features among these objects. We use radiative-transfer models that fit the optical part of the spectrum well, and find that in three of these four events we see a UV continuum flux excess, apparently unaffected by line absorption. We hypothesize that this emission originates above the photosphere, and is related to interaction with circumstellar material (CSM) located in close proximity to the SN progenitor. In contrast, the spectra of SN 2001ig are well fit by single-temperature models, display weak continuum and strong reverse-fluorescence features, and are similar to spectra of radioactive 56Ni-dominated SNe Ia. A comparison of the early shock-cooling components in the observed light curves with the UV continuum levels which we assume trace the strength of CSM interaction suggests that events with slower cooling have stronger CSM emission. The radio emission from events having a prominent UV excess is perhaps consistent with slower blast-wave velocities, as expected if the explosion shock was slowed down by the CSM that is also responsible for the strong UV, but this connection is currently speculative as it is based on only a few events.

  • 206. Benetti, S.
    et al.
    Nicholl, M.
    Cappellaro, E.
    Pastorello, A.
    Smartt, S. J.
    Elias-Rosa, N.
    Drake, A. J.
    Tomasella, L.
    Turatto, M.
    Harutyunyan, A.
    Taubenberger, S.
    Hachinger, S.
    Morales-Garoffolo, A.
    Chen, T. -W
    Djorgovski, S. G.
    Fraser, M.
    Gal-Yam, A.
    Inserra, C.
    Mazzali, P.
    Pumo, M. L.
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Valenti, S.
    Young, D. R.
    Dennefeld, M.
    Le Guillou, L.
    Fleury, M.
    Leget, P. -F
    The supernova CSS121015:004244+132827: a clue for understanding superluminous supernovae2014Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 441, nr 1, s. 289-303Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present optical photometry and spectra of the superluminous Type II/IIn supernova (SN) CSS121015: 004244+132827 (z = 0.2868) spanning epochs from -30 d (rest frame) to more than 200 d after maximum. CSS121015 is one of the more luminous SNe ever found and one of the best observed. The photometric evolution is characterized by a relatively fast rise to maximum (similar to 40 d in the SN rest frame), and by a linear post-maximum decline. The light curve shows no sign of a break to an exponential tail. A broad Ha is first detected at similar to+40 d (rest frame). Narrow, barely resolved Balmer and [O III] 5007 angstrom lines, with decreasing strength, are visible along the entire spectral evolution. The spectra are very similar to other superluminous supernovae (SLSNe) with hydrogen in their spectrum, and also to SN 2005gj, sometimes considered Type Ia interacting with H-rich circumstellar medium. The spectra are also similar to a subsample of H-deficient SLSNe. We propose that the properties of CSS121015 are consistent with the interaction of the ejecta with a massive, extended, opaque shell, lost by the progenitor decades before the final explosion, although a magnetar-powered model cannot be excluded. Based on the similarity of CSS121015 with other SLSNe (with and without H), we suggest that the shocked-shell scenario should be seriously considered as a plausible model for both types of SLSN.

  • 207. Bento, J.
    et al.
    Schmidt, B.
    Hartman, J. D.
    Bakos, G. A.
    Ciceri, Simona
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Max Plank Institute for Astronomy, Heidelberg, Germany.
    Brahm, R.
    Bayliss, D.
    Espinoza, N.
    Zhou, G.
    Rabus, M.
    Bhatti, W.
    Penev, K.
    Csubry, Z.
    Jordan, A.
    Mancini, L.
    Henning, T.
    de Val-Borro, M.
    Tinney, C. G.
    Wright, D. J.
    Durkan, S.
    Suc, V.
    Noyes, R.
    Lazar, J.
    Papp, I.
    Sari, P.
    HATS-22b, HATS-23b and HATS-24b: three new transiting super-Jupiters from the HATSouth project2017Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 468, nr 1, s. 835-848Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the discovery of three moderately high-mass transiting hot Jupiters from the HATSouth survey: HATS-22b, HATS-23b and HATS-24b. These planets add to the number of known planets in the similar to 2MJ regime. HATS-22b is a 2.74 +/- 0.11MJ mass and 0.953(-0.029)(+0.048) R-J radius planet orbiting a V = 13.455 +/- 0.040 sub-solar mass (M-* = 0.759 +/- 0.019M(circle dot); R-* = 0.759 +/- 0.019 R-circle dot) K-dwarf host star on an eccentric (e = 0.079 +/- 0.026) orbit. This planet's high planet-to-stellar mass ratio is further evidence that migration mechanisms for hot Jupiters may rely on exciting orbital eccentricities that bring the planets closer to their parent stars followed by tidal circularization. HATS-23b is a 1.478 +/- 0.080M(J) mass and 1.69 +/- 0.24 R-J radius planet on a grazing orbit around a V = 13.901 +/- 0.010 G-dwarf with properties very similar to those of the Sun (M* = 1.115 +/- 0.054; R-* = 1.145 +/- 0.070). HATS24b orbits a moderately bright V = 12.830 +/- 0.010 F-dwarf star (M-* = 1.218 +/- 0.036M circle dot; R-* = 1.194(-0.041)(+0.066) R circle dot). This planet has a mass of 2.39+0.21 -0.12MJ and an inflated radius of 1.516(-0.065)(+0.085) R-J.

  • 208. Benz, A. O.
    et al.
    Bruderer, S.
    van Dishoeck, E. F.
    Stäuber, P.
    Wampfler, S. F.
    Melchior, M.
    Dedes, C.
    Wyrowski, F.
    Doty, S. D.
    van der Tak, F.
    Bächtold, W.
    Csillaghy, A.
    Megej, A.
    Monstein, C.
    Soldati, M.
    Bachiller, R.
    Baudry, A.
    Benedettini, M.
    Bergin, E.
    Bjerkeli, P.
    Blake, G. A.
    Bontemps, S.
    Braine, J.
    Caselli, P.
    Cernicharo, J.
    Codella, C.
    Daniel, F.
    di Giorgio, A. M.
    Dieleman, P.
    Dominik, C.
    Encrenaz, P.
    Fich, M.
    Fuente, A.
    Giannini, T.
    Goicoechea, J. R.
    de Graauw, Th.
    Helmich, F.
    Herczeg, G. J.
    Herpin, F.
    Hogerheijde, M. R.
    Jacq, T.
    Jellema, W.
    Johnstone, D.
    Jørgensen, J. K.
    Kristensen, L. E.
    Larsson, Bengt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Lis, D.
    Liseau, R.
    Marseille, M.
    McCoey, C.
    Melnick, G.
    Neufeld, D.
    Nisini, B.
    Olberg, M.
    Ossenkopf, V.
    Parise, B.
    Pearson, J. C.
    Plume, R.
    Risacher, C.
    Santiago-García, J.
    Saraceno, P.
    Schieder, R.
    Shipman, R.
    Stutzki, J.
    Tafalla, M.
    Tielens, A. G. G. M.
    van Kempen, T. A.
    Visser, R.
    Yıldız, U. A.
    Hydrides in young stellar objects: Radiation tracers in a protostar-disk-outflow system2010Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 521, s. L35-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Hydrides of the most abundant heavier elements are fundamental molecules in cosmic chemistry. Some of them trace gas irradiated by UV or X-rays. Aims: We explore the abundances of major hydrides in W3 IRS5, a prototypical region of high-mass star formation. Methods: W3 IRS5 was observed by HIFI on the Herschel Space Observatory with deep integration (≃2500 s) in 8 spectral regions. Results: The target lines including CH, NH, H3O+, and the new molecules SH+, H2O+, and OH+ are detected. The H2O+ and OH+ J = 1-0 lines are found mostly in absorption, but also appear to exhibit weak emission (P-Cyg-like). Emission requires high density, thus originates most likely near the protostar. This is corroborated by the absence of line shifts relative to the young stellar object (YSO). In addition, H2O+ and OH+ also contain strong absorption components at a velocity shifted relative to W3 IRS5, which are attributed to foreground clouds. Conclusions: The molecular column densities derived from observations correlate well with the predictions of a model that assumes the main emission region is in outflow walls, heated and irradiated by protostellar UV radiation. Herschel is an ESA space observatory with science instruments provided by a European-led Principal Investigator consortia and with important participation from NASA.Appendix (page 5) is only available in electronic form at http://www.aanda.org

  • 209. Berger, E.
    et al.
    Soderberg, A. M.
    Chevalier, R. A.
    Fransson, C.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Foley, R. J.
    Leonard, D. C.
    Debes, J. H.
    Diamond-Stanic, A. M.
    Dupree, A. K.
    Ivans, I. I.
    Simmerer, J.
    Thompson, I. B.
    Tremonti, C. A.
    An Intermediate Luminosity Transient in NGC 300: The Eruption of a Dust-Enshrouded Massive Star2009Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 699, s. 1850-1865Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present multi-epoch high-resolution optical spectroscopy, UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an intermediate luminosity optical transient recently discovered in the nearby galaxy NGC 300. We find that the transient (NGC 300 OT2008-1) has a peak absolute magnitude of M bol ≈ -11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN 2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (~200-1000 km s-1) hydrogen Balmer lines and Ca II emission and absorption lines that point to a complex circumstellar environment, reminiscent of the yellow hypergiant IRC+10420. In particular, we detect asymmetric Ca II H&K absorption with a broad red wing extending to ~103 km s-1, indicative of gas inflow at high velocity (possibly the wind of a massive binary companion). The low luminosity, intermediate velocities, and overall similarity to a known eruptive star indicate that the event did not result in a complete disruption of the progenitor. We identify the progenitor in archival Spitzer observations, with deep upper limits from Hubble data. The spectral energy distribution points to a dust-enshrouded star with a luminosity of about 6 × 104 L sun, indicative of a ~10-20 M sun progenitor (or binary system). This conclusion is in good agreement with our interpretation of the outburst and circumstellar properties. The lack of significant extinction in the transient spectrum indicates that the dust surrounding the progenitor was cleared by the outburst. We thus predict that the progenitor should be eventually visible with Hubble if the transient event marks an evolutionary transition to a dust-free state, or with Spitzer if the event marks a cyclical process of dust formation.

  • 210. Berger, Thomas
    et al.
    Rouppe van der Voort, Luc
    Löfdahl, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Contrast analysis of solar faculae and magnetic bright points2007Ingår i: Astrophysical Journal, Vol. 661, nr 2, s. 1272-1288Artikel i tidskrift (Refereegranskat)
  • 211. Berger, Thomas
    et al.
    Title, A.
    Tarbell, T.
    Rouppe van der Voort, Luc
    Löfdahl, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Scharmer, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    What are 'Faculae'?2007Ingår i: New Solar Physics with Solar-B Mission, 2007, s. 103-Konferensbidrag (Övrigt vetenskapligt)
  • 212. Bergfors, C.
    et al.
    Brandner, W.
    Bonnefoy, M.
    Schlieder, J.
    Janson, Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Henning, Th.
    Chauvin, G.
    Characterization of close visual binaries from the AstraLux Large M Dwarf Survey2016Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 456, nr 3, s. 2576-2585Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present Very Large Telescope/Spectrograph for INtegral Field Observations in the Near Infrared (VLT/SINFONI) J, H + K spectra of seven close visual pairs in M dwarf binary/triple systems, discovered or observed by the AstraLux M dwarf survey. We determine the spectral types to within +/- 1.0 subclasses from comparison to template spectra and the strength of K-band water absorption, and derive effective temperatures. The results are compared to optical spectral types of the unresolved binary/multiple systems, and we confirm that our photometric method to derive spectral types in the AstraLux M dwarf survey is accurate. We look for signs of youth such as chromospheric activity and low surface gravity, and find an age in the range 0.25-1 Gyr for the GJ 852 system. Strong Li absorption is detected in optical spectra of the triple system J024902 obtained with the Fiberfed Extended Range Optical Spectrograph (FEROS) at the European Southern Observatory (ESO)-Max-Planck-Gesellschaft (MPG) 2.2 m telescope. The equivalent width of the absorption suggests an age consistent with the beta Pic moving group. However, further observations are needed to establish group membership. Ongoing orbital monitoring will provide dynamical masses and thus calibration of evolutionary models for low mass stars.

  • 213. Bergin, E. A.
    et al.
    Hogerheijde, M. R.
    Brinch, C.
    Fogel, J.
    Yildiz, U. A.
    Kristensen, L. E.
    van Dishoeck, E. F.
    Bell, T. A.
    Blake, G. A.
    Cernicharo, J.
    Dominik, C.
    Lis, D.
    Melnick, G.
    Neufeld, D.
    Panic, O.
    Pearson, J. C.
    Bachiller, R.
    Baudry, A.
    Benedettini, M.
    Benz, A. O.
    Bjerkeli, P.
    Bontemps, S.
    Braine, J.
    Bruderer, S.
    Caselli, P.
    Codella, C.
    Daniel, F.
    di Giorgio, A. M.
    Doty, S. D.
    Encrenaz, P.
    Fich, M.
    Fuente, A.
    Giannini, T.
    Goicoechea, J. R.
    de Graauw, Th
    Helmich, F.
    Herczeg, G. J.
    Herpin, F.
    Jacq, T.
    Johnstone, D.
    Jorgensen, J. K.
    Larsson, Bengt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Liseau, R.
    Marseille, M.
    Mc Coey, C.
    Nisini, B.
    Olberg, M.
    Parise, B.
    Plume, R.
    Risacher, C.
    Santiago-Garcia, J.
    Saraceno, P.
    Shipman, R.
    Tafalla, M.
    van Kempen, T. A.
    Visser, R.
    Wampfler, S. F.
    Wyrowski, F.
    van der Tak, F.
    Jellema, W.
    Tielens, A. G. G. M.
    Hartogh, P.
    Stuetzki, J.
    Szczerba, R.
    Sensitive limits on the abundance of cold water vapor in the DM Tauri protoplanetary disk2010Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 521, s. L33-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We performed a sensitive search for the ground-state emission lines of ortho-and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument. No strong lines are detected down to 3 sigma levels in 0.5 km s(-1) channels of 4.2 mK for the 1(10)-1(01) line and 12.6 mK for the 1(11)-0(00) line. We report a very tentative detection, however, of the 1(10)-1(01) line in the wide band spectrometer, with a strength of T-mb = 2.7 mK, a width of 5.6 km s(-1) and an integrated intensity of 16.0 mK km s(-1). The latter constitutes a 6 sigma detection. Regardless of the reality of this tentative detection, model calculations indicate that our sensitive limits on the line strengths preclude efficient desorption of water in the UV illuminated regions of the disk. We hypothesize that more than 95-99% of the water ice is locked up in coagulated grains that have settled to the midplane.

  • 214. Bergman, P.
    et al.
    Parise, B.
    Liseau, R.
    Larsson, Bengt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Deuterated formaldehyde in rho Ophiuchi A2011Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 527, s. A39-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Formaldehyde is an organic molecule that is abundant in the interstellar medium. High deuterium fractionation is a common feature in low-mass star-forming regions. Observing several isotopologues of molecules is an excellent tool for understanding the formation paths of the molecules. Aims. We seek an understanding of how the various deuterated isotopologues of formaldehyde are formed in the dense regions of low-mass star formation. More specifically, we adress the question of how the very high deuteration levels (several orders of magnitude above the cosmic D/H ratio) can occur using H(2)CO data of the nearby rho Oph A molecular cloud. Methods. From mapping observations of H(2)CO, HDCO, and D(2)CO, we have determined how the degree of deuterium fractionation changes over the central 3' x 3' region of rho Oph A. The multi-transition data of the various H(2)CO isotopologues, as well as from other molecules (e. g., CH(3)OH and N(2)D(+)) present in the observed bands, were analysed using both the standard type rotation diagram analysis and, in selected cases, a more elaborate method of solving the radiative transfer for optically thick emission. In addition to molecular column densities, the analysis also estimates the kinetic temperature and H(2) density. Results. Toward the SM1 core in rho Oph A, the H(2)CO deuterium fractionation is very high. In fact, the observed D(2)CO/HDCO ratio is 1.34 +/- 0.19, while the HDCO/H(2)CO ratio is 0.107 +/- 0.015. This is the first time, to our knowledge, that the D(2)CO/HDCO abundance ratio is observed to be greater than 1. The kinetic temperature is in the range 20-30 K in the cores of rho Oph A, and the H(2) density is (6-10) x 10(5) cm(-3). We estimate that the total H(2) column density toward the deuterium peak is (1-4) x 10(23) cm(-2). As depleted gas-phase chemistry is not adequate, we suggest that grain chemistry, possibly due to abstraction and exchange reactions along the reaction chain H(2)CO --> HDCO --> D(2)CO, is at work to produce the very high deuterium levels observed.

  • 215. Bergman, P.
    et al.
    Parise, B.
    Liseau, R.
    Larsson, Bengt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, H.
    Menten, K. M.
    Guesten, R.
    Detection of interstellar hydrogen peroxide2011Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 531, s. L8-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The molecular species hydrogen peroxide, HOOH, is likely to be a key ingredient in the oxygen and water chemistry in the interstellar medium. Aims. Our aim with this investigation is to determine how abundant HOOH is in the cloud core rho Oph A. Methods. By observing several transitions of HOOH in the (sub)millimeter regime we seek to identify the molecule and also to determine the excitation conditions through a multilevel excitation analysis. Results. We have detected three spectral lines toward the SM1 position of rho Oph A at velocity-corrected frequencies that coincide very closely with those measured from laboratory spectroscopy of HOOH. A fourth line was detected at the 4 sigma level. We also found through mapping observations that the HOOH emission extends (about 0.05 pc) over the densest part of the rho Oph A cloud core. We derive an abundance of HOOH relative to that of H(2) in the SM1 core of about 1 x 10(-10). Conclusions. To our knowledge, this is the first reported detection of HOOH in the interstellar medium.

  • 216. Bergvall, N.
    et al.
    Leitet, E.
    Zackrisson, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Marquart, T.
    Lyman continuum leaking galaxies: search strategies and local candidates2013Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 554, artikel-id A38Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Star-forming dwarf galaxies may have played an important role in the reionization of the Universe, provided that some fraction of their ionizing radiation were able to escape into the intergalactic medium. Local galaxies exhibiting such Lyman-continuum (LyC) leakage could potentially shed light on the escape mechanisms involved, but only two low-redshift cases of LyC leakage have been identified so far. Here, we argue that this meager harvest may be caused by unsuitable selection criteria. Candidates for LyC leakage are normally selected by indicators of starburst activity, one of which is a high equivalent width in H alpha. Such a criterion will guarantee a high production of LyC photons but will also bias the selection in favour of a high column density in the neutral gas, effectively ruling out LyC escape. Aims. In this work we want to investigate whether the lack of local LyC emitters can be caused in part by biased selection criteria, and we present a novel method of selecting targets with high escape fractions. By applying these criteria, we assemble a sample of observation targets to study their basic properties. Methods. We introduce a new selection strategy here where the potential LyC leakers are selected by their blue colours and weak emission lines. The selection is based on data from the Sloan Digital Sky Survey (SDSS). We also take a closer look at the properties of 8 LyC leaking candidates at z similar to 0.03 which we have observed with ESO/NTT in broadband B and H alpha. Results. We find that 7 of the 8 target galaxies are involved in interaction with neighbours or show signs of mergers. In 7 cases the young stellar population is clearly displaced relative to the main body of these galaxies, often directly bordering the halo region. In about half of our targets the absorption spectra show young post-starburst signatures. Comparing the scale lengths in H alpha with those of the stellar continua shows that the scale lengths in H alpha typically are 30% smaller, which is characteristic of galaxies influenced by ram pressure stripping. We tentatively identify a few mechanisms that could improve the conditions for leakage: 1) the combined effects of ram pressure stripping with supernova winds from young stars formed in the front, 2) merger events that increase the star formation rate and displace stars from gas, 3) starbursts in the centres of post-starburst galaxies, whose previous activity has cleared channels for leakage into the intergalactic medium, and 4) a low dust content. Although our target galaxies are rare species in the local universe, we argue that related types could have played a major role in producing ionizing radiation at high redshifts.

  • 217. Bergvall, Nils
    et al.
    Marquart, Thomas
    Way, Michael J.
    Blomqvist, Anna
    Holst, Emma
    Östlin, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Zackrisson, Erik
    Local starburst galaxies and their descendants Statistics from the Sloan Digital Sky Survey2016Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, artikel-id A72Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims. Despite strong interest in the starburst phenomenon in extragalactic astronomy, the concept remains ill-defined. Here we use a strict definition of starburst to examine the statistical properties of starburst galaxies in the local universe. We also seek to establish links between starburst galaxies, post-starburst (hereafter postburst) galaxies, and active galaxies.

    Methods. Data were selected from the Sloan Digital Sky Survey DR7. We applied a novel method of treating dust attenuation and derive star formation rates, ages, and stellar masses assuming a two-component stellar population model. Dynamical masses are calculated from the width of the H alpha line. These masses agree excellently with the photometric masses. The mass (gas + stars) range is similar to 10(9)-10(11.5) M-circle dot. As a selection criterion for starburst galaxies, we use, the birthrate parameter, b = SFR/< SFR >, requiring that b >= 3. For postburst galaxies, we use, the equivalent width of H delta in absorption with the criterion EWH delta,abs >= 6 angstrom.

    Results. We find that only 1% of star-forming galaxies are starburst galaxies. They contribute 3 6% to the stellar production and are therefore unimportant for the local star formation activity. The median starburst age is 70 Myr roughly independent of mass, indicating that star formation is mainly regulated by local feedback processes. The b-parameter strongly depends on burst age. Values close to b = 60 are found at ages similar to 10 Myr, while almost no starbursts are found at ages >1 Gyr. The median baryonic burst mass fraction of sub-L* galaxies is 5% and decreases slowly towards high masses. The median mass fraction of the recent burst in the postburst sample is 5-10%. A smaller fraction of the postburst galaxies, however, originates in non-bursting galaxies. The age-mass distribution of the postburst progenitors (with mass fractions >3%) is bimodal with a break at log M (M-circle dot) similar to 10.6, above which the ages are doubled. The starburst and postburst luminosity functions (LFs) follow each other closely until M-r similar to -21, when active galactic nuclei (AGNs) begin to dominate. The postburst LF continues to follow the AGN LF, while starbursts become less significant. This suggests that the number of luminous starbursts is underestimated by about one dex at high luminosities, because of having large amounts of dust and/or being outshone by an AGN. It also indicates that the starburst phase preceded the AGN phase. Finally, we look at the conditions for global gas outflow caused by stellar feedback and find that massive starburst galaxies are susceptible to such outflows.

  • 218. Bergvall, Nils
    et al.
    Zackrisson, Erik
    Andersson, B.-G.
    Arneberg, D.
    Masegosa, J.
    Östlin, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    First detection of Lyman continuum escape from a local starburst galaxy. I. Observations of the luminous blue compact galaxy Haro 11 with the Far Ultraviolet Spectroscopic Explorer (FUSE)2006Ingår i: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 448, nr 2, s. 513-524Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context: The dominating reionization source in the young universe has not yet been identified. Possible candidates include metal poor dwarf galaxies with starburst properties.

    Aims. We selected an extreme starburst dwarf, the Blue Compact Galaxy Haro 11, with the aim of determining the Lyman continuum escape fraction from UV spectroscopy.

    Methods. Spectra of Haro 11 were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). A weak signal shortwards of the Lyman break is identified as Lyman continuum (LyC) emission escaping from the ongoing starburst. From profile fitting to weak metal lines we derive column densities of the low ionization species. Adopting a metallicity typical of the H II regions of Haro 11, these data correspond to a hydrogen column density of ~10^19cm^-2. This relatively high value indicates that most of the LyC photons escape through transparent holes in the interstellar medium. We then use spectral evolutionary models to constrain the escape fraction of the produced LyC photons.

    Results. Assuming a normal Salpeter initial mass function we obtain a Lyman continuum escape fraction of f_esc˜ 4-10%. We argue that in a hierarchical galaxy formation scenario, the upper limit we derive for the escape rate allows for a substantial contribution to cosmic reionization by starburst dwarf galaxies at high redshifts.

  • 219. Bergvall, Nils
    et al.
    Zackrisson, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Caldwell, Brady
    The red haloes of SDSS low surface brightness disc galaxies2010Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 405, nr 4, s. 2697-2716Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The faint stellar haloes of galaxies contain key information about the oldest stars and the process of galaxy formation. A previous study of stacked SDSS images of disc galaxies has revealed a halo with an abnormally red r - i colour, seemingly inconsistent with our current understanding of the stellar populations inhabiting stellar haloes. Measurements of this type are, however, plagued by large uncertainties which calls for follow-up studies. Here, we investigate the statistical properties of the faint envelopes of low surface brightness disc galaxies to look for further support for a red excess. A total of 1510 nearly edge-on, bulgeless low surface brightness galaxies were selected from the SDSS Data Release 5, rescaled to the same apparent size, aligned and stacked. This procedure allows us to reach a surface brightness of mu(r) similar to 31 mag arcsec-2. After a careful assessment of instrumental light scattering effects in the stacked images, we derive median and average radial surface brightness and colour profiles in g, r and i. The sample is then divided into three subsamples according to g - r colour. All three samples exhibit a red colour excess in r - i in the thick disc/halo region. The halo colours of the full sample, g - r = 0.60 +/- 0.15 and r - i = 0.80 +/- 0.15, are found to be incompatible with the colours of any normal type of stellar population. The fact that no similar colour anomaly is seen at comparable surface brightness levels along the disc rules out a sky subtraction residual as the source of the extreme colours. A number of possible explanations for these abnormally red haloes are discussed. We find that two different scenarios - dust extinction of extragalactic background light and a stellar population with a very bottom-heavy initial mass function - appear to be broadly consistent with our observations and with similar red excesses reported in the haloes of other types of galaxies.

  • 220.
    Berkefeld, Thomas
    et al.
    Kiepenheuer-Institut für Sonnenphysik.
    Betonvil, Felix
    Univ. Utrecht.
    Collados, Manuel
    Instituto de Astrofísica de Canarias.
    López, R.
    Instituto de Astrofísica de Canarias.
    Martín, Y.
    Instituto de Astrofísica de Canarias.
    Peñate, J.
    Instituto de Astrofísica de Canarias.
    Pérez, A.
    Instituto de Astrofísica de Canarias.
    Scharmer, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Sliepen, Guus
    Univ. Utrecht.
    Soltau, Dirk
    Kiepenheuer-Institut für Sonnenphysik.
    Waldmann, Torsten
    Kiepenheuer-Institut für Sonnenphysik.
    van Werkhoven, T.I.M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Site-seeing measurements for the European Solar Telescope2010Ingår i: Ground-based and Airborne Telescopes III / [ed] Stepp, Larry M.; Gilmozzi, Roberto; Hall, Helen J., 2010, s. 77334I-Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Seeing measurements are crucial for the optimum design of (multi-conjugate) adaptive optics systems operating at solar telescopes. For the design study of the 4-meter European Solar Telescope, to be located in the Canary Islands, several instruments have been constructed and operated, at the Observatorio del Roque de los Muchachos (La Palma) and at the Observatorio del Teide (Tenerife), to measure the properties of the ground layer and medium-high altitude turbulence. Several units of short (42.34 cm) and two long (323.06 cm) scintillometer bars are, or are to be, installed at both observatories. In addition to them, two wide-field wavefront sensors will be attached to the optical beams of the Swedish tower, on La Palma, and of the German VTT, on Tenerife, simultaneously used with the normal operation of the telescopes. These wavefront sensors are of Shack-Hartmann type with ~1 arcminute field of view. In this contribution, the instruments setup and their performance are described.

  • 221.
    Berkefeld, Thomas
    et al.
    Kiepenheuer-Institut für Sonnenphysik.
    Soltau, Dirk
    Kiepenheuer-Institut für Sonnenphysik.
    Del Moro, Dario
    Univ. degli Studi di Roma Tor Vergata.
    Löfdahl, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Wavefront sensing and wavefront reconstruction for the 4m European Solar Telescope EST2010Ingår i: Adaptive Optics Systems II / [ed] Ellerbroek, Brent L.; Hart, Michael; Hubin, Norbert; Wizinowich, Peter L, 2010, s. 77362J-Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We give an overview of the Adaptive Optics (AO) and Multi-conjugate Adaptive Optics (MCAO) system of the planned 4m European Solar Telescope (EST). The parameter space and the problems of solar MCAO working in the visible are explained. The wavefront reconstruction schemes presently being considered are explained. First estimates of the expected MCAO performance for varying parameter sets are given.

  • 222. Berry, Michael
    et al.
    Gawiser, Eric
    Guaita, Lucia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Padilla, Nelson
    Treister, Ezequiel
    Blanc, Guillermo A.
    Ciardullo, Robin
    Francke, Harold
    Gronwall, Caryl
    STACKED REST-FRAME ULTRAVIOLET SPECTRA OF Ly alpha-EMITTING AND CONTINUUM-SELECTED GALAXIES AT 2 < z < 3.52012Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 749, nr 1, s. 4-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present properties of individual and composite rest-UV spectra of continuum-and narrowband-selected star-forming galaxies (SFGs) at a redshift of 2 < z < 3.5 discovered by the MUSYC collaboration in the Extended Chandra Deep Field-South. Among our sample of 81 UV-bright SFGs, 59 have R < 25.5, of which 32 have rest-frame equivalent widths of W-Ly alpha > 20 angstrom, the canonical limit to be classified as an Ly alpha-emitting galaxy. We divide our data set into subsamples based on properties that we are able to measure for each individual galaxy: Ly alpha equivalent width, rest-frame UV colors, and redshift. Among our subsample of galaxies with R < 25.5, those with rest frame W-Ly alpha > 20 angstrom have bluer UV continua, weaker low-ionization interstellar absorption lines, weaker C IV absorption, and stronger Si II* nebular emission than those with W-Ly alpha < 20 angstrom. We measure a velocity offset of Delta nu similar to 600 km s(-1) between Ly alpha emission and low-ionization absorption, which does not vary substantially among any of our subsamples. We find that the interstellar component, as opposed to the stellar component, dominates the high-ionization absorption line profiles. We find that the low-and high-ionization Si ionization states have similar kinematic properties, yet the low-ionization absorption is correlated with Ly alpha emission and the high-ionization absorption is not. These trends are consistent with outflowing neutral gas being in the form of neutral clouds embedded in ionized gas as previously suggested by Steidel et al. Moreover, our galaxies with bluer UV colors have stronger Ly alpha emission, weaker low-ionization absorption, and more prominent nebular emission line profiles. From a redshift of 2.7 < z < 3.5 to 2.0 < z < 2.7, our subsample of galaxies with W-Ly alpha < 20 angstrom shows no significant evolution in their physical properties or the nature of their outflows. Among our data set, UV-bright galaxies with W-Ly alpha > 20 angstrom exhibit weaker Ly alpha emission at lower redshifts, although we caution that this could be caused by spectroscopic confirmation of low Ly alpha equivalent width galaxies being harder at z similar to 3 than z similar to 2.

  • 223. Bersten, Melina C.
    et al.
    Benvenuto, Omar G.
    Nomoto, Ken'ichi
    Ergon, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Folatelli, Gaston
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Benetti, Stefano
    Botticella, Maria Teresa
    Fraser, Morgan
    Kotak, Rubina
    Maeda, Keiichi
    Ochner, Paolo
    Tomasella, Lina
    THE TYPE IIb SUPERNOVA 2011dh FROM A SUPERGIANT PROGENITOR2012Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 757, nr 1, artikel-id 31Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star-with R similar to 200 R-circle dot-is needed to reproduce the early light curve (LC) of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the supernova (SN) in deep pre-explosion images is the progenitor star. From the main peak of the bolometric LC and expansion velocities, we constrain the mass of the ejecta to be approximate to 2 M-circle dot, the explosion energy to be E = (6-10) x 10(50) erg, and the Ni-56 mass to be approximately 0.06 M-circle dot. The progenitor star was composed of a helium core of 3-4 M-circle dot and a thin hydrogen-rich envelope of approximate to 0.1M(circle dot) with a main-sequence mass estimated to be in the range of 12-15 M-circle dot. Our models rule out progenitors with helium-core masses larger than 8 M-circle dot, which correspond to M-ZAMS greater than or similar to 25M(circle dot). This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.

  • 224. Beswick, R. J.
    et al.
    Perez-Torres, M. A.
    Mattila, S.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Garrington, S. T.
    Kankare, E.
    Ryder, S.
    Alberdi, A.
    Romero-Canizales, C.
    MERLIN radio observations of two recent supernovae in Arp299: SN2010O & SN2010P2010Rapport (Övrigt vetenskapligt)
    Abstract [en]

    We report MERLIN radio observations of the two recent supernovae in Arp299; SN2010P and SN2010O (CBET #2145 and CBET #2144, respectively). Observations of Arp299 were made between 1900UT 29th Jan 2010 and 0150UT 1st Feb 2010 at 4994MHz. The previously known compact radio structure of Arp299, including the nuclear starburst components associated with A=IC694 and B1=the southernmost nucleus of NGC3690 are detected (Neff, Ulvestad & Teng 2004, ApJ, 611, 186; Ulvestad 2009 AJ, 138, 152; Perez-Torres et al 2009, A&A 507, 17).

  • 225. Betoule, M.
    et al.
    Kessler, R.
    Guy, J.
    Mosher, J.
    Hardin, D.
    Biswas, R.
    Astier, P.
    El-Hage, P.
    Konig, M.
    Kuhlmann, S.
    Marriner, J.
    Pain, R.
    Regnault, N.
    Balland, C.
    Bassett, B. A.
    Brown, P. J.
    Campbell, H.
    Carlberg, R. G.
    Cellier-Holzern, F.
    Cinabro, D.
    Conley, A.
    D'Andrea, C. B.
    DePoy, D. L.
    Doi, M.
    Ellis, R. S.
    Fabbro, S.
    Filippenko, A. V.
    Foley, R. J.
    Frieman, J. A.
    Fouchez, D.
    Galbany, L.
    Goobar, Ariel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Gupta, R. R.
    Hill, G. J.
    Hlozek, R.
    Hogan, C. J.
    Hook, I. M.
    Howell, D. A.
    Jha, S. W.
    Le Guillou, L.
    EGENLeloudas, G.
    Lidrnan, C.
    Marshall, J. L.
    Moeller, A.
    Mourao, A. M.
    Neveu, J.
    Nichol, R.
    Olmstead, M. D.
    Palanque-Delabrouille, N.
    Perlinutter, S.
    Prieto, J. L.
    Pritchet, C. J.
    Richinond, M.
    Riess, A. G.
    Ruhlmann-Kleider, V.
    Sako, M.
    Sehahmaneche, K.
    Schneider, D. P.
    Smith, M.
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Sullivan, M.
    Walton, N. A.
    Wheeler, C. J.
    Improved cosmological constraints from a joint analysis of the SDSS-II and SNLS supernova samples2014Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 568, s. A22-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims. We present cosmological constraints from a joint analysis of type la supernova (SN Ia) observations obtained by the SDSS-II and SNLS collaborations. The dataset includes several low-redshift samples (z < 0.1), all three seasons from the SDSS-11 (0.05 < z < 0.4), and three years from SNLS (0.2 < z < 1), and it totals 740 spectroscopically confirmed type la supernovae with high quality light curves. Methods. We followed the methods and assumptions of the SNLS three-year data analysis except for the following important improvements: I) the addition of the full SDSS-II spectroscopically-confirmed SN la sample in both the training of the SALT2 light-curve model and in the Hubble diagram analysis (374 SNe); 2) intercalibration of the SNLS and SDSS surveys and reduced systematic uncertainties in the photometric calibration, performed blindly with respect to the cosmology analysis; and 3) a thorough investigation of systematic errors associated with the SALT2 modeling of SN la light curves. Results. We produce recalibrated SN la light curves and associated distances for the SDSS-II and SNLS samples. The large SOSS-II sample provides an effective, independent, low -z anchor for the Hubble diagram and reduces the systematic error from calibration systematics in the low -z SN sample. For a flat ACDM cosmology, we find Omega(m), = 0.295 0.034 (stat+sys), a value consistent with the most recent cosmic microwave background (CMB) measurement from the Planck and WMAP experiments. Our result is 1.8 sigma (stat+sys) different than the previously published result of SNLS three-year data. The change is due primarily to improvements in the SNLS photometric calibration. When combined with CMB constraints, we measure a constant dark energy equation of state parameter omega = -1.018 +/- 0,057 (sral+sys) for a fiat universe. Adding baryon acoustic oscillation distance measurements gives similar constraints: omega = 59 -1.027 0.055. Our supernova measurements provide the most stringent constraints to date on the nature of dark energy.

  • 226.
    Bhat, Pallavi
    et al.
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). Inter University Centre for Astronomy and Astrophysics, India; Princeton University, USA.
    Brandenburg, Axel
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. University of Colorado, USA.
    Hydraulic effects in a radiative atmosphere with ionization2016Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, artikel-id A90Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. In his 1978 paper, Eugene Parker postulated the need for hydraulic downward motion to explain magnetic flux concentrations at the solar surface. A similar process has also recently been seen in simplified (e.g., isothermal) models of flux concentrations from the negative effective magnetic pressure instability (NEMPI).

    Aims. We study the effects of partial ionization near the radiative surface on the formation of these magnetic flux concentrations.

    Methods. We first obtain one-dimensional (1D) equilibrium solutions using either a Kramers-like opacity or the H-opacity. The resulting atmospheres are then used as initial conditions in two-dimensional (2D) models where flows are driven by an imposed gradient force that resembles a localized negative pressure in the form of a blob. To isolate the effects of partial ionization and radiation, we ignore turbulence and convection.

    Results. Because of partial ionization, an unstable stratification always forms near the surface. We show that the extrema in the specific entropy profiles correspond to the extrema in the degree of ionization. In the 2D models without partial ionization, strong flux concentrations form just above the height where the blob is placed. Interestingly, in models with partial ionization, such flux concentrations always form at the surface well above the blob. This is due to the corresponding negative gradient in specific entropy. Owing to the absence of turbulence, the downflows reach transonic speeds.

    Conclusions. We demonstrate that, together with density stratification, the imposed source of negative pressure drives the formation of flux concentrations. We find that the inclusion of partial ionization affects the entropy profile dramatically, causing strong flux concentrations to form closer to the surface. We speculate that turbulence effects are needed to limit the strength of flux concentrations and homogenize the specific entropy to a stratification that is close to marginal.

  • 227. Bhat, Pallavi
    et al.
    Subramanian, Kandaswamy
    Brandenburg, Axel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). University of Colorado, USA.
    A unified large/small-scale dynamo in helical turbulence2016Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 461, nr 1, s. 240-247Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We use high resolution direct numerical simulations (DNS) to show that helical turbulence can generate significant large-scale fields even in the presence of strong small-scale dynamo action. During the kinematic stage, the unified large/ small-scale dynamo grows fields with a shapeinvariant eigenfunction, with most power peaked at small scales or large k, as in Subramanian & Brandenburg. Nevertheless, the large-scale field can be clearly detected as an excess power at small k in the negatively polarized component of the energy spectrum for a forcing with positively polarized waves. Its strength (B) over bar, relative to the total rms field Brms, decreases with increasing magnetic Reynolds number, Re-M. However, as the Lorentz force becomes important, the field generated by the unified dynamo orders itself by saturating on successively larger scales. The magnetic integral scale for the positively polarized waves, characterizing the smallscale field, increases significantly from the kinematic stage to saturation. This implies that the small-scale field becomes as coherent as possible for a given forcing scale, which averts the Re-M-dependent quenching of (B) over bar /B-rms. These results are obtained for 1024(3) DNS with magnetic Prandtl numbers of PrM = 0.1 and 10. For PrM = 0.1, B/ Brms grows from about 0.04 to about 0.4 at saturation, aided in the final stages by helicity dissipation. For Pr-M = 10, (B) over bar /B-rms grows from much less than 0.01 to values of the order the 0.2. Our results confirm that there is a unified large/ small-scale dynamo in helical turbulence.

  • 228.
    Bik, Adrianus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Max-Planck-Institut für Astronomie, Germany.
    Henning, Th.
    Wu, S.-W.
    Zhang, M.
    Brandner, W.
    Pasquali, A.
    Stolte, A.
    Near-infrared spectroscopy of the massive stellar population of W51: evidence for multi-seeded star formation2019Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 624, artikel-id A63Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The interplay between the formation of stars, stellar feedback and cloud properties strongly influences the star formation history of giant molecular clouds. The formation of massive stars leads to a variety of stellar clusters, ranging from low stellar density OB associations to dense, gravitationally bound starburst clusters.

    Aims. We aimed at identifying the massive stellar content and reconstructing the star formation history of the W51 giant molecular cloud.

    Methods. We performed near-infrared imaging and K-band spectroscopy of the massive stars in W51. We analysed the stellar populations using colour-magnitude and colour-colour diagrams and compared the properties of the spectroscopically identified stars with stellar evolution models.

    Results. We derive the ages of the different sub-clusters in W51 and, based on our spectroscopy derive an age for W51 of 3 Myr or less. The age of the P Cygni star LS1 and the presence of two still forming proto-clusters suggests that the star formation history of W51 is more complex than a single burst.

    Conclusions. We did not find evidence for triggered star formation and we concluded that the star formation in W51 is multi seeded. We finally concluded that W51 is an OB association where different sub-clusters form over a time span of at least 3-5 Myr.

  • 229.
    Bik, Adrianus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Östlin, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Hayes, Matthew
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Adamo, Angela
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Melinder, Jens
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Amram, P.
    VLT/MUSE view of the highly ionized outflow cones in the nearby starburst ESO338-IG042015Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 576, artikel-id L13Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The Lya line is an important diagnostic for star formation at high redshift, but interpreting its flux and line profile is difficult because of the resonance nature of Lya. Trends between the escape of Lya photons and dust and properties of the interstellar medium (ISM) have been found, but detailed comparisons between Lya emission and the properties of the gas in local high-redshift analogs are vital for understanding the relation between Lya emission and galaxy properties. Aims. For the first time, we can directly infer the properties of the ionized gas at the same location and similar spatial scales of the extended Lya halo around the local Lya emitter and Lyman-break galaxy analog ESO338-IG04. Methods. We obtained VLT/MUSE integral field spectra. We used ionization parameter mapping of the [S II]/[O III] line ratio and the kinematics of Ha to study the ionization state and kinematics of the ISM of ESO 338-IG04. Results. The velocity map reveals two outflows, one toward the north, the other toward the south of ESO338. The ionization parameter mapping shows that the entire central area of the galaxy is highly ionized by photons leaking from the HII regions around the youngest star clusters. Three highly ionized cones have been identified, of which one is associated with an outflow detected in the Ha. We propose a scenario where the outflows are created by mechanical feedback of the older clusters, while the highly ionized gas is caused by the hard ionizing photons emitted by the youngest clusters. A comparison with the Lya map shows that the (approximately bipolar) asymmetries observed in the Lya emission are consistent with the base of the outflows detected in Ha. No clear correlation with the ionization cones is found. Conclusions. The mechanical and ionization feedback of star clusters significantly changes the state of the ISM by creating ionized cones and outflows. The comparison with Lya suggests that especially the outflows could facilitate the escape of Lya photons.

  • 230.
    Bik, Adrianus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Östlin, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Menacho, Veronica
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Adamo, Angela
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Hayes, Matthew
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Herenz, Edmund Christian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Melinder, Jens
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Super star cluster feedback driving ionization, shocks and outflows in the halo of the nearby starburst ESO 338-IG042018Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 619, artikel-id A131Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Stellar feedback strongly affects the interstellar medium (ISM) of galaxies. Stellar feedback in the first galaxies likely plays a major role in enabling the escape of LyC photons, which contribute to the re-ionization of the Universe. Nearby starburst galaxies serve as local analogues allowing for a spatially resolved assessment of the feedback processes in these galaxies. Aims. We aim to characterize the feedback effects from the star clusters in the local high-redshift analogue ESO 338-IG04 on the ISM and compare the results with the properties of the most massive clusters. Methods. We used high quality VLT/MUSE optical integral field data to derive the physical properties of the ISM such as ionization, density, shocks, and performed new fitting of the spectral energy distributions of the brightest clusters in ESO 338-IG04 from HST imaging. Results. We find that ESO 338-IG04 has a large ionized halo which we detect to a distance of 9 kpc. We identify four Wolf-Rayet (WR) clusters based on the blue and red WR bump. We follow previously identified ionization cones and find that the ionization of the halo increases with distance. Analysis of the galaxy kinematics shows two complex outflows driven by the numerous young clusters in the galaxy. We find a ring of shocked emission traced by an enhanced [O-I]/H alpha ratio surrounding the starburst and at the end of the outflow. Finally we detect nitrogen enriched gas associated with the outflow, likely caused by the WR stars in the massive star clusters. Conclusions. Photoionization dominates the central starburst and sets the ionization structure of the entire halo, resulting in a density bounded halo, facilitating the escape of LyC photons. Outside the central starburst, shocks triggered by an expanding super bubble become important. The shocks at the end of the outflow suggest interaction between the hot outflowing material and the more quiescent halo gas.

  • 231. Biver, N. ...
    et al.
    Floren, H.G. ...
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Sandqvist, Aa. et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Odin observations of water emission variation in comet 103P/Hartley 22010Ingår i: Central Bureau Electronic Telegrams (CBET), Vol. CBET, nr 2524Artikel i tidskrift (Övrigt vetenskapligt)
  • 232. Biver, N.
    et al.
    Bockelee-Morvan, D.
    Crovisier, J.
    Lecacheux, A.
    Lis, D.C.
    Bossier, J.
    Colom, P.
    Dello-Russo, N.
    Floren, H.-G.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholm Observatory.
    Frisk, U.
    Hjalmarson, Å.
    Kwok, S.
    Menten, K.
    Moreno, R.
    Olberg, M.
    Parise, B.
    Paubert, G.
    Sandqvist, Aa.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholm Observatory.
    Vervack, R. J.
    Weaver, H. A.
    Winnberg, A.
    In-depth investigation of the fragmenting comet 73P/Schwassmann-Wachmann3 at radio wavelengths with the Nancay, IRAM, CSO, APEX and Odin Radio Telscopes2008Ingår i: Asteroids, Comets, Meteors 2008, 2008Konferensbidrag (Refereegranskat)
  • 233. Biver, N. et al.
    et al.
    Floren, H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Sandqvist, Aa.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Radio monitoring of 9P/Tempel 1 outgassing and and gas released by the Impact2009Ingår i: Deep Impact as a World Observatory Event: Synergies in Space, Time and Wavelength, ESO Astrophysics Symposia, Volume, ISSN 978-3-540-76958-3, s. 233-241Artikel, recension (Övrigt vetenskapligt)
  • 234. Biver, N. et al.
    et al.
    Sandqvist, Aa.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Periodic variation in the water production of comet C/2001 Q4 (NEAT) observed with the Odin satellite2009Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 501, s. 359-366Artikel i tidskrift (Refereegranskat)
  • 235. Biver, N.
    et al.
    Lellouch, E.
    Sandqvist, Aage
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Florén, H.G.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Observation of Saturn and the Enceladus water torus at 557 GHz with Odin2011Ingår i: EPSC Abstracts, 2011, s. 912-1-2Konferensbidrag (Refereegranskat)
  • 236. Biver, N.
    et al.
    Moreno, R.
    Bockelée-Morvan, D.
    Sandqvist, Aage
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Colom, P.
    Crovisier, J.
    Lis, D. C.
    Boissier, J.
    Debout, V.
    Paubert, G.
    Milam, S.
    Hjalmarson, A.
    Lundin, S.
    Karlsson, T.
    Battelino, M.
    Frisk, U.
    Murtagh, D.
    Isotopic ratios of H, C, N, O, and S in comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy)2016Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 589, artikel-id A78Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The apparition of bright comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy) in March-April 2013 and January 2015, combined with the improved observational capabilities of submillimeter facilities, offered an opportunity to carry out sensitive compositional and isotopic studies of the volatiles in their coma. We observed comet Lovejoy with the IRAM 30 m telescope between 13 and 26 January 2015, and with the Odin submillimeter space observatory on 29 January-3 February 2015. We detected 22 molecules and several isotopologues. The (H2O)-O-16 and (H2O)-O-18 production rates measured with Odin follow a periodic pattern with a period of 0.94 days and an amplitude of similar to 25%. The inferred isotope ratios in comet Lovejoy are O-16/O-18 = 499 +/- 24 and D/H = 1.4 +/- 0.4 x 10(-4) in water, S-32/S-34 = 24.7 +/- 3.5 in CS, all compatible with terrestrial values. The ratio C-12/C-13 = 109 +/- 14 in HCN is marginally higher than terrestrial and N-14/N-15 = 145 +/- 12 in HCN is half the Earth ratio. Several upper limits for D/H or C-12/C-13 in other molecules are reported. From our observation of HDO in comet C/2014 Q2 (Lovejoy), we report the first D/H ratio in an Oort Cloud comet that is not larger than the terrestrial value. On the other hand, the observation of the same HDO line in the other Oort-cloud comet, C/2012 F6 (Lemmon), suggests a D/H value four times higher. Given the previous measurements of D/H in cometary water, this illustrates that a diversity in the D/H ratio and in the chemical composition, is present even within the same dynamical group of comets, suggesting that current dynamical groups contain comets formed at very different places or times in the early solar system.

  • 237. Biver, N.,....
    et al.
    Sandqvist, Aage
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Floren, H.-G.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Molecular composition and outgassing variability of 103P/Hartley 2 from mm and submm observations2011Ingår i: EPSC Abstracts, EPSC , 2011, s. 938-1-2Konferensbidrag (Refereegranskat)
  • 238. Biver, Nicolas
    et al.
    Bockelée-Morvan, Dominique
    Moreno, Raphaël
    Crovisier, Jacques
    Colom, Pierre
    Lis, Dariusz C.
    Sandqvist, Aage
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Boissier, Jérémie
    Despois, Didier
    Milam, Stefanie N.
    Ethyl alcohol and sugar in comet C/2014 Q2 (Lovejoy)2015Ingår i: Science Advances, ISSN 2375-2548, Vol. 1, nr 9, s. 1-5, artikel-id e1500863Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The presence of numerous complex organic molecules (COMs; defined as those containing six or more atoms) around protostars shows that star formation is accompanied by an increase of molecular complexity. These COMs may be part of the material from which planetesimals and, ultimately, planets formed. Comets represent some of the oldest and most primitive material in the solar system, including ices, and are thus our best window into the volatile composition of the solar protoplanetary disk. Molecules identified to be present in cometary ices include water, simple hydrocarbons, oxygen, sulfur, and nitrogen-bearing species, as well as a few COMs, such as ethylene glycol and glycine. We report the detection of 21 molecules in comet C/2014 Q2 (Lovejoy), including the first identification of ethyl alcohol (ethanol, C2H5OH) and the simplest monosaccharide sugar glycolaldehyde (CH2OHCHO) in a comet. The abundances of ethanol and glycolaldehyde, respectively 5 and 0.8% relative to methanol (0.12 and 0.02% relative to water), are somewhat higher than the values measured in solar-type protostars. Overall, the high abundance of COMs in cometary ices supports the formation through grain-surface reactions in the solar system protoplanetary disk.

  • 239. Biver, Nicolas
    et al.
    Florén, Hans-Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Sandqvist, Aage
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Radio observations of Comet 9P/Tempel 1 before and after Deep Impact2007Ingår i: Icarus, Vol. 187, nr 1, s. 253-271Artikel i tidskrift (Refereegranskat)
  • 240. Biver, Nicolas
    et al.
    Florén, Hans-Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Sandqvist, Aage
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Radio observations of Comet 9P/Tempel 1 before and after Deep Impact2007Ingår i: Icarus (Supplement), Vol. 191, nr 2, s. 494-512Artikel i tidskrift (Refereegranskat)
  • 241. Biver, Nicolas
    et al.
    Florén, Hans-Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Sandqvist, Aage
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Submillimetre observations of comets with Odin: 2001 20052007Ingår i: Planetary and Space Science, Vol. 55, nr 9, s. 1058-1068Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Odin satellite, launched in February 2001, is equipped with a 1.1-m submillimetre telescope. Odin was used to observe the 557 GHz line of water with high spectral resolution in 12 comets between 2001 and 2005. Line shapes and spatial mapping provide information on the anisotropy of the outgassing and constraints on water excitation, enabling accurate measurements of the water production rate. Five comets were regularly observed over periods of more than one month to monitor the variation of their water outgassing rate with heliocentric distance. Observing campaigns have been generally coordinated with ground-based observations of molecular lines at Nançay, CSO or IRAM 30-m telescopes to obtain molecular abundances relative to water. Thanks to Odin's frequency coverage, it was also possible to detect the H218O 548 GHz line, first in comet 153P/Ikeya Zhang in April 2002 [Lecacheux, A., Biver, N., Crovisier, J. et al., 2003, Observations of water in comets with Odin. Astron. Astrophys. 402, L55 L58.] and then in comets C/2002 T7 (LINEAR), C/2001 Q4 (NEAT) and C/2004 Q2 (Machholz). The 16O/18O isotopic ratio (≈450) is consistent with the terrestrial value. Ammonia has been searched for in three comets through its J=1 0 line at 572 GHz and was tentatively detected in C/2001 Q4 and C/2002 T7. The derived abundances of NH3 relative to water are 0.5% and 0.3%, respectively, similar to values obtained in other comets with different techniques.

  • 242. Bjerkeli, P., et al.
    et al.
    Larsson, Bengt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Sandqvist, Aage
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Odin observations of water in molecular outflows and shocks2009Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 507, s. 1455-1466Artikel i tidskrift (Refereegranskat)
  • 243. Bjerkeli, P.
    et al.
    Liseau, R.
    Brinch, C.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Santangelo, G.
    Cabrit, S.
    Benedettini, M.
    Black, J. H.
    Herczeg, G.
    Justtanont, K.
    Kristensen, L. E.
    Larsson, Bengt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Nisini, B.
    Tafalla, M.
    Resolving the shocked gas in HH54 with Herschel CO line mapping at high spatial and spectral resolution2014Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 571, artikel-id A90Artikel i tidskrift (Refereegranskat)
    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.

  • 244. Bjerkeli, P.
    et al.
    Liseau, R.
    Larsson, Bengt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Rydbeck, G.
    Nisini, B.
    Tafalla, M.
    Antoniucci, S.
    Benedettini, M.
    Bergman, P.
    Cabrit, S.
    Giannini, T.
    Melnick, G.
    Neufeld, D.
    Santangelo, G.
    van Dishoeck, E. F.
    H2O line mapping at high spatial and spectral resolution Herschel observations of the VLA 1623 outflow2012Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 546, s. A29-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Apart from being an important coolant, water is known to be a tracer of high-velocity molecular gas. Recent models predict relatively high abundances behind interstellar shockwaves. The dynamical and physical conditions of the water emitting gas, however, are not fully understood yet. Using the Herschel Space Observatory, it is now possible to observe water emission from supersonic molecular outflows at high spectral and spatial resolution. Several molecular outflows from young stars are currently being observed as part of the WISH (Water In Star-forming regions with Herschel) key program. Aims. We aim to determine the abundance and distribution of water, its kinematics, and the physical conditions of the gas responsible for the water emission. The observed line profile shapes help us understand the dynamics in molecular outflows. Methods. We mapped the VLA1623 outflow, in the ground-state transitions of o-H2O, with the HIFI and PACS instruments. We also present observations of higher energy transitions of o-H2O and p-H2O obtained with HIFI and PACS towards selected outflow positions. From comparison with non-LTE radiative transfer calculations, we estimate the physical parameters of the water emitting regions. Results. The observed water emission line profiles vary over the mapped area. Spectral features and components, tracing gas in different excitation conditions, allow us to constrain the density and temperature of the gas. The water emission originates in a region where temperatures are comparable to that of the warm H-2 gas (T greater than or similar to 200 K). Thus, the water emission traces a gas component significantly warmer than the gas responsible for the low-J CO emission. The water column densities at the CO peak positions are low, i.e. N(H2O) similar or equal to (0.03-10) x 10(14) cm(-2). Conclusions. The water abundance with respect to H-2 in the extended outflow is estimated at X(H2O) < 1 x 10(-6), significantly lower than what would be expected from most recent shock models. The H2O emission traces a gas component moving at relatively high velocity compared to the low-J CO emitting gas. However, other dynamical quantities such as the momentum rate, energy, and mechanical luminosity are estimated to be the same, independent of the molecular tracer used, CO or H2O.

  • 245. Bjerkeli, P.
    et al.
    Liseau, R.
    Nisini, B.
    Tafalla, M.
    Benedettini, M.
    Bergman, P.
    Dionatos, O.
    Giannini, T.
    Herczeg, G.
    Justtanont, K.
    Larsson, Bengt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    McCoey, C.
    Olberg, M.
    Olofsson, A. O. H.
    Herschel observations of the Herbig-Haro objects HH52-542011Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 533Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The emission from Herbig-Haro objects and supersonic molecular outflows is understood as cooling radiation behind shocks, which are initiated by a (proto-)stellar wind or jet. Within a given object, one often observes both dissociative (J-type) and non-dissociative (C-type) shocks, owing to the collective effects of internally varying shock velocities. Aims. We aim at the observational estimation of the relative contribution to the cooling by CO and H(2)O, as this provides decisive information for understanding the oxygen chemistry behind interstellar shock waves. Methods. The high sensitivity of HIFI, in combination with its high spectral resolution capability, allowed us to trace the H(2)O outflow wings at an unprecedented signal-to-noise ratio. From the observation of spectrally resolved H(2)O and CO lines in the HH52-54 system, both from space and from the ground, we arrived at the spatial and velocity distribution of the molecular outflow gas. Solving the statistical equilibrium and non-LTE radiative transfer equations provides us with estimates of the physical parameters of this gas, including the cooling rate ratios of the species. The radiative transfer is based on an accelerated lambda iteration code, where we use the fact that variable shock strengths, distributed along the front, are naturally implied by a curved surface. Results. Based on observations of CO and H(2)O spectral lines, we conclude that the emission is confined to the HH54 region. The quantitative analysis of our observations favours a ratio of the CO-to-H(2)O-cooling-rate >> 1. Formally, we derived the ratio A(CO)/A(o-H(2)O) = 10, which is in good agreement with earlier determination of 7 based on ISO-LWS observations. From the best-fit model to the CO emission, we arrive at an H(2)O abundance close to 1 x 10(-5). The line profiles exhibit two components, one that is triangular and another that is a superposed, additional feature. This additional feature is likely to find its origin in a region that is smaller than the beam where the ortho-water abundance is smaller than in the quiescent gas. Conclusions. Comparison with recent shock models indicate that a planar shock cannot easily explain the observed line strengths and triangular line profiles. We conclude that the geometry can play an important role. Although abundances support a scenario where J-type shocks are present, higher cooling rate ratios are derived than predicted by these types of shocks.

  • 246.
    Björnsson, C. -I.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    JOINING RADIO WITH X-RAYS: A REVISED MODEL FOR SN 1993J2015Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 813, nr 1, artikel-id 43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A joint analysis is done of the radio and X-ray observations of SN 1993J. It is argued that neither synchrotron cooling behind the forward shock nor thermal cooling behind the reverse shock is supported by observations. In order for adiabatic models to be consistent, a reinterpretation of the radius of the spatially resolved very long baseline interferometry-source (VLBI) is needed during the first few hundred days. Instead of reflecting the position of the forward shock, it is then associated with the expansion of the Rayleigh-Taylor unstable region emanating from the contact discontinuity. Although observations imply a constant ratio between the energy densities in magnetic fields and relativistic electrons, they do not appear to scale individually with the thermal energy density behind the forward shock; rather, in adiabatic models, the evolution of the magnetic field strength is best understood as scaling inversely with the supernova radius.

  • 247.
    Björnsson, Claes-Ingvar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Circular Polarization in Compact Radio Sources: Constraints on Particle Acceleration and Electron-Positron Pairs2019Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 873, nr 1, artikel-id 55Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is shown that the frequency distribution of the degree of circular polarization for a homogeneous source is sensitive to the properties of the synchrotron emitting plasma. Most of the circular polarization comes from the region around the turnover frequency, where the synchrotron radiation becomes optically thick. However, nearly circular characteristic waves result in circular polarization dominated by frequencies above the turnover frequency, while in the case of nearly linear characteristic waves, it is dominated by frequencies below. Observations argue in favor of nearly circular characteristic waves. This implies a low-energy cutoff in the electron distribution that is substantially below that corresponding to the turnover frequency and simultaneously provides an upper limit to the fraction of electron-positron pairs.

  • 248.
    Björnsson, Claes-Ingvar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    GRB 060218: THE NATURE OF THE OPTICAL-UV COMPONENT2008Ingår i: The Astrophysical Journal, Vol. 672Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The optical-UV component in GRB 060218 is assumed to be due to optically thick cyclotron emission. The key aspect of this model is the high temperature of the absorbing electrons. The heat input derives from nuclei accelerated in semirelativistic internal shocks, like in ordinary gamma-ray bursts. Coulomb collisions transfer part of that energy to electrons. Inverse Compton cooling on the X-ray photons leads to electron temperatures around ~100 keV. Such a high brightness temperature for the optical-UV emission implies an emitting area roughly equal to that of the thermal X-ray component. This suggests a model in which the radio, optical-UV, and thermal X-ray emission are closely related. Although the optical-UV and thermal X-ray emission are two separate spectral components, it is argued that they both come from the photosphere of a quasi-spherical, continuous outflow, whose interaction with the circumstellar medium gives rise to the radio emission. The properties of GRB 060218, as measured in the comoving frame, are similar to those of ordinary gamma-ray bursts; i.e., the main difference is the much lower value of the bulk Lorentz factor in GRB 060218. The cyclotron absorption implies a magnetic field in rough equipartition with the matter energy density in the outflow. Hence, the magnetic field could have a dynamically important role, possibly with a magnetar as the central engine.

  • 249.
    Björnsson, Claes-Ingvar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    GRB 060218: The nature of the optical-UV component2007Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The optical-UV component in GRB 060218 is assumed to be due to optically thick cyclotron emission. The key aspect of this model is the high temperature of the absorbing electrons. The heat input derives from nuclei accelerated in semi-relativistic internal shocks, like in ordinary gamma-ray bursts. Coulomb collisions transfer part of that energy to electrons. Inverse Compton cooling on the X-ray photons leads to electron temperatures around 100 keV. Such a high brightness temperature for the optical-UV emission implies an emitting area roughly equal to that of the thermal X-ray component. This suggests a model in which the radio, optical-UV and thermal X-ray emission are closely related: Although the optical-UV and thermal X-ray emission are two separate spectral components, it is argued that they both come from the photosphere of a quasi-spherical, continuous outflow, whose interaction with the circumstellar medium gives rise to the radio emission. The properties of GRB 060218, as measured in the co-moving frame, are similar to those of ordinary gamma-ray burst; i.e., the main difference is the much lower value of the bulk Lorentz factor in GRB 060218. The cyclotron absorption implies a magnetic field in rough equipartition with the matter energy density in the outflow. Hence, the magnetic field could have a dynamically important role, possibly with a magnetar as the central engine.

  • 250.
    Björnsson, Claes-Ingvar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    INHOMOGENEITIES IN TYPE Ib/c SUPERNOVAE: AN INVERSE COMPTON SCATTERING ORIGIN OF THE X-RAY EMISSION2013Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 769, nr 1, s. 65-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Inhomogeneities in a synchrotron source can severely affect the conclusions drawn from observations regarding the source properties. However, their presence is not always easy to establish, since several other effects can give rise to similar observed characteristics. It is argued that the recently observed broadening of the radio spectra and/or light curves in some Type Ib/c supernovae is a direct indication of inhomogeneities. As compared to a homogeneous source, this increases the deduced velocity of the forward shock and the observed correlation between total energy and shock velocity could in part be due to a varying covering factor. The X-ray emission from at least some Type Ib/c supernovae is unlikely to be synchrotron radiation from an electron distribution accelerated in a nonlinear shock. Instead it is shown that the observed correlation during the first few hundred days between the radio, X-ray, and bolometric luminosities indicates that the X-ray emission is inverse Compton scattering of the photospheric photons. Inhomogeneities are consistent with equipartition between electrons and magnetic fields in the optically thin synchrotron emitting regions.

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