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Larsson, Bengt
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Sandqvist, A., Hjalmarson, Å., Larsson, B., Frisk, U., Lundin, S. & Rydbeck, G. (2021). Herschel and Odin observations of H2O, CO, CH, CH+, and [NII] in the barred spiral galaxy NGC 1365 Bar-induced activity in the outer and inner circumnuclear tori. Astronomy and Astrophysics, 647, Article ID A86.
Öppna denna publikation i ny flik eller fönster >>Herschel and Odin observations of H2O, CO, CH, CH+, and [NII] in the barred spiral galaxy NGC 1365 Bar-induced activity in the outer and inner circumnuclear tori
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2021 (Engelska)Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 647, artikel-id A86Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Context. The Odin satellite is now into its twentieth year of operation, much surpassing its design life of two years. One of its major astronomical pursuits was the search for and study of water vapor in diverse regions of the Solar System and the Milky Way galaxy. The Herschel space observatory was needed to detect water vapor in external galaxies.

Aims. Our goal is to study the distribution and excitation of water vapor and other molecules in the barred spiral galaxy NGC 1365.

Methods. Herschel has observed the central region of NGC 1365 in two positions, and both its SPIRE and PACS observations are available in the Herschel Science Archive. Herschel PACS images have been produced of the 70 and 160 mu m infrared emission from the whole galaxy, and also of the cold dust distribution as obtained from the ratio of the 160 to 70 mu m images. The Herschel SPIRE observations have been used to produce simultaneously observed maps of the 557 GHz o-H2O, 752 GHz p-H2O, 691 GHz CO(6-5), 1037 GHz CO(9-8), 537 GHz CH, 835 GHz CH', and the 1461 GHz [N IT] lines (efficiently probing the warm ionized medium) in the inner bar and circumnuclear torus region; - however, these observations have no effective velocity resolution. For this reason Odin has recently observed the 557 GHz ortho-H2O ground state line in the central region with high (5 km s(-1)) spectral resolution.

Results. The emission and absorption of H2O at 557 GHz, with a velocity resolution of 5 km s(-1), has been marginally detected in NGC 1365 with Odin. The water vapor is predominantly located in a shocked 15 '' (1.3 kpc) region near some central compact radio sources and hot-spot HIT regions, close to the northeast component of the molecular torus surrounding the nucleus. An analysis of the H2O line intensities and velocities indicates that a shock-region is located here. This is corroborated by a statistical image deconvolution of our SEST CO(3-2) observations, yielding 5 '' resolution, and a study of our Very Large Array HI absorption observations, as well as comparisons with published interferometric CO observations. Additionally, an enticing 20 '' HI ridge is found to extend south-southeast from the nucleus, coinciding in position with the southern edge of an O III outflow cone, emanating from the nucleus. The molecular chemistry of the shocked central region of NGC 1365 is analyzed with special emphasis on the CO, H2O and CH, CH+ results.

Conclusions. The dominating activity near the northeast (NE) torus component may have been triggered by the rapid bar-driven inflow into the circumnuclear torus causing cloud-cloud collisions and shocks, leading to the formation of stellar superclusters and, hence, also to more efficient PDR chemistry, which, here, may also benefit from cosmic ray focusing caused by the observed aligned magnetic field. The very high activity near the NE torus component may reflect the fact that the eastern bar-driven gas inflow into the NE region is much more massive than the corresponding western gas inflow into the southwest region. The H2O and CH+ emissions peak in the NE torus region, but the CO and CH emissions are more evenly distributed across the whole circumnuclear torus. The higher energy CO spectral line energy distribution (SLED) is nicely modeled by a low velocity (10 km s(-1)) shock, which may as well explain the required CH excitation and its high abundance in denser gas. The higher velocity (40 km s(-1)) shock required to model the H2O SLED in the NE torus region, paired with the intense UV radiation from the observed massive young stellar superclusters, may also explain the high abundance of CH+ in this region. The nuclear H I ridge may have been created by the action of outflow-driving X-ray photons colliding with ice-covered dust grains. A precessing nuclear engine, as is suggested by the tilted massive inner gas torus, may be necessary to explain the various nuclear outflows encountered.

Nyckelord
galaxies: ISM, galaxies: individual: NGC 1365, galaxies: Seyfert, galaxies: nuclei
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-193217 (URN)10.1051/0004-6361/202038875 (DOI)000629650600001 ()
Tillgänglig från: 2021-05-18 Skapad: 2021-05-18 Senast uppdaterad: 2022-02-25Bibliografiskt granskad
Kamp, I., Honda, M., Nomura, H., Audard, M., Fedele, D., Waters, L. B., . . . Ysard, N. (2021). The formation of planetary systems with SPICA. Publications Astronomical Society of Australia, 38, Article ID e055.
Öppna denna publikation i ny flik eller fönster >>The formation of planetary systems with SPICA
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2021 (Engelska)Ingår i: Publications Astronomical Society of Australia, ISSN 1323-3580, E-ISSN 1448-6083, Vol. 38, artikel-id e055Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

In this era of spatially resolved observations of planet-forming disks with Atacama Large Millimeter Array (ALMA) and large groundbased telescopes such as the Very Large Telescope (VLT), Keck, and Subaru, we still lack statistically relevant information on the quantity and composition of the material that is building the planets, such as the total disk gas mass, the ice content of dust, and the state of water in planetesimals. SPace Infrared telescope for Cosmology and Astrophysics (SPICA) is an infrared space mission concept developed jointly by Japan Aerospace Exploration Agency (JAXA) and European Space Agency (ESA) to address these questions. The key unique capabilities of SPICA that enable this research are (1) the wide spectral coverage 10-220 mu m, (2) the high line detection sensitivity of (1-2) x10(-19)Wm(-2) with R similar to 2 000-5 000 in the far-IR (SAFARI), and 10-20Wm(-2) with R similar to 29 000 in themid-IR (SPICA Mid-infrared Instrument (SMI), spectrally resolving line profiles), (3) the high far-IR continuum sensitivity of 0.45mJy (SAFARI), and (4) the observing efficiency for point source surveys. This paper details how mid- to far-IR infrared spectra will be unique in measuring the gas masses and water/ice content of disks and how these quantities evolve during the planet-forming period. These observations will clarify the crucial transition when disks exhaust their primordial gas and further planet formation requires secondary gas produced from planetesimals. The high spectral resolution mid-IR is also unique for determining the location of the snowline dividing the rocky and icy mass reservoirs within the disk and how the divide evolves during the build-up of planetary systems. Infrared spectroscopy (mid- to far-IR) of key solid-state bands is crucial for assessing whether extensive radial mixing, which is part of our Solar System history, is a general process occurring in most planetary systems and whether extrasolar planetesimals are similar to our Solar System comets/asteroids. We demonstrate that the SPICA mission concept would allow us to achieve the above ambitious science goals through large surveys of several hundred disks within similar to 2.5 months of observing time.

Nyckelord
comets: general, infrared: planetary systems, Kuiper belt: general, minor planets, asteroids: general, protoplanetary disks
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-200125 (URN)10.1017/pasa.2021.31 (DOI)000721318200001 ()
Tillgänglig från: 2021-12-28 Skapad: 2021-12-28 Senast uppdaterad: 2021-12-28Bibliografiskt granskad
van Dishoeck, E. F., Kristensen, L. E., Mottram, J. C., Benz, A. O., Bergin, E. A., Caselli, P., . . . Yildiz, U. (2021). Water in star-forming regions: physics and chemistry from clouds to disks as probed by Herschel spectroscopy. Astronomy and Astrophysics, 648, Article ID A24.
Öppna denna publikation i ny flik eller fönster >>Water in star-forming regions: physics and chemistry from clouds to disks as probed by Herschel spectroscopy
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2021 (Engelska)Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 648, artikel-id A24Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Context. Water is a key molecule in the physics and chemistry of star and planet formation, but it is difficult to observe from Earth. The Herschel Space Observatory provided unprecedented sensitivity as well as spatial and spectral resolution to study water. The Water In Star-forming regions with Herschel (WISH) key program was designed to observe water in a wide range of environments and provide a legacy data set to address its physics and chemistry.

Aims. The aim of WISH is to determine which physical components are traced by the gas-phase water lines observed with Herschel and to quantify the excitation conditions and water abundances in each of these components. This then provides insight into how and where the bulk of the water is formed in space and how it is transported from clouds to disks, and ultimately comets and planets.

Methods. Data and results from WISH are summarized together with those from related open time programs. WISH targeted similar to 80 sources along the two axes of luminosity and evolutionary stage: from low- to high-mass protostars (luminosities from <1 to > 10(5)L(circle dot)) and from pre-stellar cores to protoplanetary disks. Lines of H2O and its isotopologs, HDO, OH, CO, and [O I], were observed with the HIFI and PACS instruments, complemented by other chemically-related molecules that are probes of ultraviolet, X-ray, or grain chemistry. The analysis consists of coupling the physical structure of the sources with simple chemical networks and using non-LTE radiative transfer calculations to directly compare models and observations.

Results. Most of the far-infrared water emission observed with Herschel in star-forming regions originates from warm outflowing and shocked gas at a high density and temperature (> 10(5) cm(-3), 300-1000 K, v similar to 25 km s(-1)), heated by kinetic energy dissipation. This gas is not probed by single-dish low-J CO lines, but only by CO lines with J(up) > 14. The emission is compact, with at least two different types of velocity components seen. Water is a significant, but not dominant, coolant of warm gas in the earliest protostellar stages. The warm gas water abundance is universally low: orders of magnitude below the H2O/H-2 abundance of 4 x 10(-4) expected if all volatile oxygen is locked in water. In cold pre-stellar cores and outer protostellar envelopes, the water abundance structure is uniquely probed on scales much smaller than the beam through velocity-resolved line profiles. The inferred gaseous water abundance decreases with depth into the cloud with an enhanced layer at the edge due to photodesorption of water ice. All of these conclusions hold irrespective of protostellar luminosity. For low-mass protostars, a constant gaseous HDO/H2O ratio of similar to 0.025 with position into the cold envelope is found. This value is representative of the outermost photodesorbed ice layers and cold gas-phase chemistry, and much higher than that of bulk ice. In contrast, the gas-phase NH3 abundance stays constant as a function of position in low-mass pre- and protostellar cores. Water abundances in the inner hot cores are high, but with variations from 5 x 10(-6) to a few x 10(-4) for low- and high-mass sources. Water vapor emission from both young and mature disks is weak.

Conclusions. The main chemical pathways of water at each of the star-formation stages have been identified and quantified. Low warm water abundances can be explained with shock models that include UV radiation to dissociate water and modify the shock structure. UV fields up to 10(2)-10(3) times the general interstellar radiation field are inferred in the outflow cavity walls on scales of the Herschel beam from various hydrides. Both high temperature chemistry and ice sputtering contribute to the gaseous water abundance at low velocities, with only gas-phase (re-)formation producing water at high velocities. Combined analyses of water gas and ice show that up to 50% of the oxygen budget may be missing. In cold clouds, an elegant solution is that this apparently missing oxygen is locked up in larger mu m-sized grains that do not contribute to infrared ice absorption. The fact that even warm outflows and hot cores do not show H2O at full oxygen abundance points to an unidentified refractory component, which is also found in diffuse clouds. The weak water vapor emission from disks indicates that water ice is locked up in larger pebbles early on in the embedded Class I stage and that these pebbles have settled and drifted inward by the Class II stage. Water is transported from clouds to disks mostly as ice, with no evidence for strong accretion shocks. Even at abundances that are somewhat lower than expected, many oceans of water are likely present in planet-forming regions. Based on the lessons for galactic protostars, the low-J H2O line emission (E-up < 300 K) observed in extragalactic sources is inferred to be predominantly collisionally excited and to originate mostly from compact regions of current star formation activity. Recommendations for future mid- to far-infrared missions are made.

Nyckelord
astrochemistry, infrared: ISM, stars: formation, ISM: jets and outflows, ISM: molecules, protoplanetary disks
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-194262 (URN)10.1051/0004-6361/202039084 (DOI)000639366000001 ()
Tillgänglig från: 2021-06-17 Skapad: 2021-06-17 Senast uppdaterad: 2022-03-01Bibliografiskt granskad
Cavallius, M., Cataldi, G., Brandeker, A., Olofsson, G., Larsson, B. & Liseau, R. (2019). Upper limits on the water vapour content of the β Pictoris debris disk. Astronomy and Astrophysics, 628, Article ID A127.
Öppna denna publikation i ny flik eller fönster >>Upper limits on the water vapour content of the β Pictoris debris disk
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2019 (Engelska)Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 628, artikel-id A127Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Context. The debris disk surrounding β Pictoris has been observed with ALMA to contain a belt of CO gas with a distinct peak at ~85 au. This CO clump is thought to be the result of a region of enhanced density of solids that collide and release CO through vaporisation. The parent bodies are thought to be comparable to solar system comets, in which CO is trapped inside a water ice matrix

Aims. Since H2O should be released along with CO, we aim to put an upper limit on the H2O gas mass in the disk of β Pictoris.

Methods. We used archival data from the Heterodyne Instrument for the Far-Infrared (HIFI) aboard the Herschel Space Observatory to study the ortho-H2O 1(10)-1(01) emission line. The line is undetected. Using a python implementation of the radiative transfer code RADEX, we converted upper limits on the line flux to H2O gas masses. The resulting lower limits on the CO/H2O mass ratio are compared to the composition of solar system comets.

Results. Depending on the assumed gas spatial distribution, we find a 95% upper limit on the ortho-H2O line flux of7.5×10−20W m−2or1.2×10−19W m−2. These translate into an upper limit on the H2O mass of7.4×1016–1.1×1018kg depending on both the electron density and gas kinetic temperature. The range of derived gas-phase CO/H2O ratios is marginally consistent with low-ratio solar system comets.

Nyckelord
stars: individual: β Pictoris, submillimeter: planetary systems, methods: observational, circumstellar matter
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-173134 (URN)10.1051/0004-6361/201935655 (DOI)000482750100007 ()
Tillgänglig från: 2019-10-06 Skapad: 2019-10-06 Senast uppdaterad: 2022-02-26Bibliografiskt granskad
Roelfsema, P. R., Shibai, H., Armus, L., Arrazola, D., Audard, M., Audley, M. D., . . . Yamamura, I. (2018). SPICA-A Large Cryogenic Infrared Space Telescope: Unveiling the Obscured Universe. Publications Astronomical Society of Australia, 35, Article ID e030.
Öppna denna publikation i ny flik eller fönster >>SPICA-A Large Cryogenic Infrared Space Telescope: Unveiling the Obscured Universe
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2018 (Engelska)Ingår i: Publications Astronomical Society of Australia, ISSN 1323-3580, E-ISSN 1448-6083, Vol. 35, artikel-id e030Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Measurements in the infrared wavelength domain allow direct assessment of the physical state and energy balance of cool matter in space, enabling the detailed study of the processes that govern the formation and evolution of stars and planetary systems in galaxies over cosmic time. Previous infrared missions revealed a great deal about the obscured Universe, but were hampered by limited sensitivity. SPICA takes the next step in infrared observational capability by combining a large 2.5-meter diameter telescope. cooled to below 8 K, with instruments employing ultra-sensitive detectors. A combination of passive cooling and mechanical coolers will be used to cool both the telescope and the instruments. With mechanical coolers the mission lifetime is not limited by the supply of cryogen. With the combination of low telescope background and instruments with state-of-the-art detectors SPICA provides a huge advance on the capabilities of previous missions. SPICA instruments offer spectral resolving power ranging from R similar to 50 through 11 000 in the 17-230 mu m domain and R similar to 28.000 spectroscopy between 12 and 18 mu m.SPICA will provide efficient 30-37 mu m broad band mapping, and small field spectroscopic and polarimetric imaging at 100, 200 and 350 mu m. SPICA will provide infrared spectroscopy with an unprecedented sensitivity of similar to 5 x 10(-20) W m (-2) (5 sigma/1 h)-over two orders of magnitude improvement over what earlier missions. This exceptional performance leap, will open entirely new domains in infrared astronomy; galaxy evolution and metal production over cosmic time, dust formation and evolution from very early epochs onwards, the formation history of planetary systems.

Nyckelord
infrared: galaxies, infrared: general, infrared: planetary systems, instrumentation: photometers, instrumentation: spectrographs, space vehicles: instruments
Nationell ämneskategori
Astronomi, astrofysik och kosmologi
Identifikatorer
urn:nbn:se:su:diva-160072 (URN)10.1017/pasa.2018.15 (DOI)000442853900001 ()
Tillgänglig från: 2018-10-01 Skapad: 2018-10-01 Senast uppdaterad: 2022-02-26Bibliografiskt granskad
Larsson, B. & Liseau, R. (2017). Gas and dust in the star-forming region rho Oph A II. The gas in the PDR and in the dense cores. Astronomy and Astrophysics, 608, Article ID A133.
Öppna denna publikation i ny flik eller fönster >>Gas and dust in the star-forming region rho Oph A II. The gas in the PDR and in the dense cores
2017 (Engelska)Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 608, artikel-id A133Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Context. The evolution of interstellar clouds of gas and dust establishes the prerequisites for star formation. The pathway to the formation of stars can be studied in regions that have formed stars, but which at the same time also display the earliest phases of stellar evolution, i.e. pre-collapse/collapsing cores (Class-1), protostars (Class 0), and young stellar objects (Class I, II, III).

Aims. We investigate to what degree local physical and chemical conditions are related to the evolutionary status of various objects in star-forming media.

Methods. rho OphA displays the entire sequence of low-mass star formation in a small volume of space. Using spectrophotometric line maps of H-2, H2O, NH3, N2H+, O-2, OI, CO, and CS, we examine the distribution of the atomic and molecular gas in this dense molecular core. The physical parameters of these species are derived, as are their relative abundances in rho Oph A. Using radiative transfer models, we examine the infall status of the cold dense cores from their resolved line profiles of the ground state lines of H2O and NH3, where for the latter no contamination from the VLA 1623 outflow is observed and line overlap of the hyperfine components is explicitly taken into account.

Results. The stratified structure of this photon dominated region (PDR), seen edge-on, is clearly displayed. Polycyclic aromatic hydrocarbons (PAHs) and OI are seen throughout the region around the exciting star S 1. At the interface to the molecular core 0.05 pc away, atomic hydrogen is rapidly converted into H-2, whereas OI protrudes further into the molecular core. This provides oxygen atoms for the gas-phase formation of O-2 in the core SM1, where X(O-2) similar to 5 x 10(-8). There, the ratio of the O-2 to H2O abundance [X(H2O) similar to 5 x 10(-9)] is significantly higher than unity. Away from the core, O-2 experiences a dramatic decrease due to increasing H2O formation. Outside the molecular core rho Oph A, on the far side as seen from S 1, the intense radiation from the 0.5 pc distant early B-type star HD147889 destroys the molecules.

Conclusions. Towards the dark core SM1, the observed abundance ratio X(O-2)/X(H2O) > 1, which suggests that this object is extremely young, which would explain why O-2 is such an elusive molecule outside the solar system.

Nyckelord
ISM: individual objects: rho Oph A, ISM: molecules, ISM: abundances, photon-dominated region (PDR), stars: formation, ISM: general
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-150959 (URN)10.1051/0004-6361/201731466 (DOI)000418459900004 ()
Tillgänglig från: 2018-01-12 Skapad: 2018-01-12 Senast uppdaterad: 2022-02-28Bibliografiskt granskad
Liseau, R., Larsson, B., Lunttila, T., Olberg, M., Rydbeck, G., Bergman, P., . . . de Vries, B. L. (2015). Gas and dust in the star-forming region rho Oph A The dust opacity exponent beta and the gas-to-dust mass ratio g2d. Astronomy and Astrophysics, 578, Article ID A131.
Öppna denna publikation i ny flik eller fönster >>Gas and dust in the star-forming region rho Oph A The dust opacity exponent beta and the gas-to-dust mass ratio g2d
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2015 (Engelska)Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 578, artikel-id A131Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

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

Nyckelord
ISM: general, ISM: individual objects: rho Oph A, dust, extinction, ISM: abundances, stars: formation
Nationell ämneskategori
Astronomi, astrofysik och kosmologi
Identifikatorer
urn:nbn:se:su:diva-119753 (URN)10.1051/0004-6361/201525641 (DOI)000357502600143 ()
Tillgänglig från: 2015-08-27 Skapad: 2015-08-24 Senast uppdaterad: 2022-02-23Bibliografiskt granskad
Sandqvist, A., Larsson, B., Hjalmarson, Å., Encrenaz, P., Gerin, M., Goldsmith, P. F., . . . Viti, S. (2015). Herschel HIFI observations of the Sgr A+50 km s(-1) Cloud Deep searches for O-2 in emission and foreground absorption. Astronomy and Astrophysics, 584, Article ID A118.
Öppna denna publikation i ny flik eller fönster >>Herschel HIFI observations of the Sgr A+50 km s(-1) Cloud Deep searches for O-2 in emission and foreground absorption
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2015 (Engelska)Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 584, artikel-id A118Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Context: The Herschel Oxygen Project (HOP) is an open time key program, awarded 140 h of observing time to search for molecular oxygen (O-2) in a number of interstellar sources. To date O-2 has definitely been detected in only two sources, namely rho Oph A and Orion, reflecting the extremely low abundance of O-2 in the interstellar medium.

Aims: One of the sources in the HOP program is the + 50 km s(-1) Cloud in the Sgr A Complex in the centre of the Milky Way. Its environment is unique in the Galaxy and this property is investigated to see if it is conducive to the presence of O-2. Methods. The Herschel Heterodyne Instrument for the Far Infrared (HIFI) is used to search for the 487 and 774 GHz emission lines of O-2.

Results: No O-2 emission is detected towards the Sgr A + 50 km s(-1) Cloud, but a number of strong emission lines of methanol (CH3OH) and absorption lines of chloronium (H2Cl+) are observed.

Conclusions: A 3 sigma upper limit for the fractional abundance ratio of [O-2]/[H-2] in the Sgr A + 50 km s(-1) Cloud is found to be X(O-2) <= 5x 10(-8). However, since we can find no other realistic molecular candidate than O-2 itself, we very tentatively suggest that two weak absorption lines at 487.261 and 487.302 GHz may be caused by the 487 GHz line of O-2 in two foreground spiral arm clouds. By considering that the absorption may only be apparent, the estimated upper limit to the O-2 abundance of <=(10-20) x 10(-6) in these foreground clouds is very high, as opposed to the upper limit in the Sgr A + 50 km s(-1) Cloud itself, but similar to what has been reached in recent chemical shock models for Orion. This abundance limit was determined also using Odin non-detection limits, and assumes that O-2 fills the beam. If the absorption is due to a differential Herschel OFF-ON emission, the O-2 fractional abundance may be of the order of approximate to(5-10) x 10 (6). With the assumption of pure absorption by foreground clouds, the unreasonably high abundance of (1.4-2.8) x 10(-4) was obtained. The rotation temperatures for CH3OH-A and CH3OH-E lines in the + 50 km s(-1) Cloud are found to be approximate to 64 and 79 K, respectively, and the fractional abundance of CH3OH is approximately 5 x 10(-7).

Nyckelord
Galaxy: center, ISM: individual objects: Sgr A, ISM: molecules, ISM: clouds
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-125784 (URN)10.1051/0004-6361/201526280 (DOI)000366936800118 ()
Tillgänglig från: 2016-01-27 Skapad: 2016-01-18 Senast uppdaterad: 2022-02-23Bibliografiskt granskad
Liseau, R. & Larsson, B. (2015). Search for HOOH in Orion. Astronomy and Astrophysics, 583, Article ID A53.
Öppna denna publikation i ny flik eller fönster >>Search for HOOH in Orion
2015 (Engelska)Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 583, artikel-id A53Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Context: The abundance of key molecules determines the level of cooling that is necessary for the formation of stars and planetary systems. In this context, one needs to understand the details of the time dependent oxygen chemistry, leading to the formation of O-2 and H2O.

Aims: We aim to determine the degree of correlation between the occurrence of O-2 and HOOH (hydrogen peroxide) in star-forming molecular clouds. We first detected O-2 and HOOH in rho Oph A, we now search for HOOH in Orion OMCA, where O-2 has also been detected.

Methods: We mapped a 3' x 3' region around Orion H-2-Peak 1 with the Atacama Pathfinder Experiment (APEX). In addition to several maps in two transitions of HOOH, viz. 219.17 GHz and 251.91 GHz, we obtained single-point spectra for another three transitions towards the position of maximum emission.

Results: Line emission at the appropriate LSR-velocity (Local Standard of Rest) and at the level of >= 4 sigma was found for two transitions, with lower signal-to-noise ratio (2.8-3.5 sigma) for another two transitions, whereas for the remaining transition, only an upper limit was obtained. The emitting region, offset 18 '' south of H2-Peak 1, appeared point-like in our observations with APEX.

Conclusions: The extremely high spectral line density in Orion makes the identification of HOOH much more difficult than in rho Oph A. As a result of having to consider the possible contamination by other molecules, we left the current detection status undecided.

Nyckelord
astrochemistry, ISM: general, ISM: individual objects: Orion H2-Peak 1, ISM: molecules, ISM: abundances, stars: formation
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-124794 (URN)10.1051/0004-6361/201526830 (DOI)000365072200125 ()
Tillgänglig från: 2016-01-04 Skapad: 2016-01-04 Senast uppdaterad: 2022-02-23Bibliografiskt granskad
Cataldi, G., Brandeker, A., Olofsson, G., Larsson, B., Liseau, R., Blommaert, J., . . . Wu, Y. (2014). Herschel/HIFI observations of ionised carbon in the beta Pictoris debris disk. Astronomy and Astrophysics, 563, Article ID A66.
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2014 (Engelska)Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 563, artikel-id A66Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

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

Nyckelord
protoplanetary disks, stars: individual: beta Pictoris, planetary systems, methods: observational, circumstellar matter, infrared: general
Nationell ämneskategori
Astronomi, astrofysik och kosmologi
Forskningsämne
astronomi
Identifikatorer
urn:nbn:se:su:diva-103302 (URN)10.1051/0004-6361/201323126 (DOI)000333798000066 ()
Anmärkning

AuthorCount:12;

Tillgänglig från: 2014-05-16 Skapad: 2014-05-12 Senast uppdaterad: 2022-02-23Bibliografiskt granskad
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