| 1. |
- Gupta, H., et al.
(författare)
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Detection of OH+ and H2O+ towards Orion KL
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L47-
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Tidskriftsartikel (refereegranskat)abstract
- We report observations of the reactive molecular ions OH+, H2O+, and H3O+ towards Orion KL with Herschel/HIFI. All three N = 1-0 fine-structure transitions of OH+ at 909, 971, and 1033 GHz and both fine-structure components of the doublet ortho-H2O+ 111-000 transition at 1115 and 1139 GHz were detected; an upper limit was obtained for H3O+. OH+ and H2O+ are observed purely in absorption, showing a narrow component at the source velocity of 9 km s-1, and a broad blueshifted absorption similar to that reported recently for HF and para-H218O, and attributed to the low velocity outflow of Orion KL. We estimate column densities of OH+ and H2O+ for the 9 km s-1 component of 9 ± 3 × 1012 cm-2 and 7 ± 2 × 1012 cm-2, and those in the outflow of 1.9 ± 0.7 × 1013 cm-2 and 1.0 ± 0.3 × 1013 cm-2. Upper limits of 2.4 × 1012 cm-2 and 8.7 × 1012 cm-2 were derived for the column densities of ortho and para-H3O+ from transitions near 985 and 1657 GHz. The column densities of the three ions are up to an order of magnitude lower than those obtained from recent observations of W31C and W49N. The comparatively low column densities may be explained by a higher gas density despite the assumption of a very high ionization rate.
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| 2. |
- de Graauw, Th., et al.
(författare)
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The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI)
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L6-
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Tidskriftsartikel (refereegranskat)abstract
- Aims: This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods: The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s-1. Results: After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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| 3. |
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| 4. |
- Rolffs, R., et al.
(författare)
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Reversal of infall in SgrB2(M) revealed by Herschel/HIFI observations of HCN lines at THz frequencies
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1, s. Article Number: L46 -
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Tidskriftsartikel (refereegranskat)abstract
- Aims. To investigate the accretion and feedback processes in massive star formation, we analyze the shapes of emission lines from hot molecular cores, whose asymmetries trace infall and expansion motions. Methods. The high-mass star forming region SgrB2(M) was observed with Herschel/HIFI (HEXOS key project) in various lines of HCN and its isotopologues, complemented by APEX data. The observations are compared to spherically symmetric, centrally heated models with density power-law gradient and different velocity fields (infall or infall+expansion), using the radiative transfer code RATRAN. Results. The HCN line profiles are asymmetric, with the emission peak shifting from blue to red with increasing J and decreasing line opacity (HCN to (HCN)-C-13). This is most evident in the HCN 12-11 line at 1062 GHz. These line shapes are reproduced by a model whose velocity field changes from infall in the outer part to expansion in the inner part. Conclusions. The qualitative reproduction of the HCN lines suggests that infall dominates in the colder, outer regions, but expansion dominates in the warmer, inner regions. We are thus witnessing the onset of feedback in massive star formation, starting to reverse the infall and finally disrupting the whole molecular cloud. To obtain our result, the THz lines uniquely covered by HIFI were critically important.
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| 5. |
- Lefloch, B., et al.
(författare)
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The CHESS spectral survey of star forming regions : Peering into the protostellar shock L1157-B1. II. Shock dynamics
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L113-
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Tidskriftsartikel (refereegranskat)abstract
- Context. The outflow driven by the low-mass class 0 protostar L1157 is the prototype of the so-called chemically active outflows. The bright bowshock B1 in the southern outflow lobe is a privileged testbed of magneto-hydrodynamical (MHD) shock models, for which dynamical and chemical processes are strongly interdependent. Aims: We present the first results of the unbiased spectral survey of the L1157-B1 bowshock, obtained in the framework of the key program “Chemical HErschel Surveys of star forming regions” (CHESS). The main aim is to trace the warm and chemically enriched gas and to infer the excitation conditions in the shock region. Methods: The CO 5-4 and o-H2O 110-101 lines have been detected at high-spectral resolution in the unbiased spectral survey of the HIFI-band 1b spectral window (555-636 GHz), presented by Codella et al. in this volume. Complementary ground-based observations in the submm window help establish the origin of the emission detected in the main-beam of HIFI and the physical conditions in the shock. Results: Both lines exhibit broad wings, which extend to velocities much higher than reported up to now. We find that the molecular emission arises from two regions with distinct physical conditions : an extended, warm (100 K), dense (3 × 105 cm-3) component at low-velocity, which dominates the water line flux in Band 1; a secondary component in a small region of B1 (a few arcsec) associated with high-velocity, hot (>400 K) gas of moderate density ((1.0-3.0) × 104 cm-3), which appears to dominate the flux of the water line at 179μm observed with PACS. The water abundance is enhanced by two orders of magnitude between the low- and the high-velocity component, from 8 × 10-7 up to 8 × 10-5. The properties of the high-velocity component agree well with the predictions of steady-state C-shock models. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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| 6. |
- van Dishoeck, E. F., et al.
(författare)
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Water in Star-forming Regions with the Herschel Space Observatory (WISH). I. Overview of Key Program and First Results
- 2011
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 123:900, s. 138-170
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Tidskriftsartikel (refereegranskat)abstract
- Water In Star-forming regions with Herschel (WISH) is a key program on the Herschel Space Observatory designed to probe the physical and chemical structures of young stellar objects using water and related molecules and to follow the water abundance from collapsing clouds to planet-forming disks. About 80 sources are targeted, covering a wide ranee of luminosities-from low ( 10(5) L-circle dot)-and a wide range of evolutionary stages-from cold prestellar cores to warm protostellar envelopes and outflows to disks around young stars. Both the HIFI and PACS instruments are used to observe a variety of lines of H2O, (H2O)-O-18 and chemically related species at the source position and in small maps around the protostars and selected outflow positions. In addition, high-frequency lines of CO, (CO)-C-13, and (CO)-O-18 are obtained with Herschel and are complemented by ground-based observations of dust continuum, HDO, CO and its isotopologs, and other molecules to ensure a self-consistent data set for analysis. An overview of the scientific motivation and observational strategy of the program is given, together with the modeling approach and analysis tools that have been developed. Initial science results are presented. These include a lack of water in cold gas at abundances that are lower than most predictions, strong water emission from shocks in protostellar environments, the importance of UV radiation in heating the gas along outflow walls across the full range of luminosities, and surprisingly widespread detection of the chemically related hydrides OH+ and H2O+ in outflows and foreground gas. Quantitative estimates of the energy budget indicate that H2O is generally not the dominant coolant in the warm dense gas associated with protostars. Very deep limits on the cold gaseous water reservoir in the outer regions of protoplanetary disks are obtained that have profound implications for our understanding of grain growth and mixing in disks.
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| 7. |
- van Kempen, T. A., et al.
(författare)
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Origin of the hot gas in low-mass protostars Herschel-PACS spectroscopy of HH 46
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L121
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Tidskriftsartikel (refereegranskat)abstract
- Aims. "Water In Star-forming regions with Herschel" (WISH) is a Herschel key programme aimed at understanding the physical and chemical structure of young stellar objects (YSOs) with a focus on water and related species. Methods. The low-mass protostar HH 46 was observed with the Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory to measure emission in H2O, CO, OH, [O I], and [C II] lines located between 63 and 186 mu m. The excitation and spatial distribution of emission can disentangle the different heating mechanisms of YSOs, with better spatial resolution and sensitivity than previously possible. Results. Far-IR line emission is detected at the position of the protostar and along the outflow axis. The OH emission is concentrated at the central position, CO emission is bright at the central position and along the outflow, and H2O emission is concentrated in the outflow. In addition, [O I] emission is seen in low-velocity gas, assumed to be related to the envelope, and is also seen shifted up to 170 km s(-1) in both the red-and blue-shifted jets. Envelope models are constructed based on previous observational constraints. They indicate that passive heating of a spherical envelope by the protostellar luminosity cannot explain the high-excitation molecular gas detected with PACS, including CO lines with upper levels at >2500 K above the ground state. Instead, warm CO and H2O emission is probably produced in the walls of an outflow-carved cavity in the envelope, which are heated by UV photons and non-dissociative C-type shocks. The bright OH and [O I] emission is attributed to J-type shocks in dense gas close to the protostar. In the scenario described here, the combined cooling by far-IR lines within the central spatial pixel is estimated to be 2 x 10(-2) L-circle dot, with 60-80% attributed to J- and C-type shocks produced by interactions between the jet and the envelope.
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| 8. |
- Caselli, P., et al.
(författare)
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Water vapor toward starless cores : The Herschel view
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L29-
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Tidskriftsartikel (refereegranskat)abstract
- Aims: Previous studies by the satellites SWAS and Odin provided stringent upper limits on the gas phase water abundance of dark clouds (x(H2O) < 7 × 10-9). We investigate the chemistry of water vapor in starless cores beyond the previous upper limits using the highly improved angular resolution and sensitivity of Herschel and measure the abundance of water vapor during evolutionary stages just preceding star formation. Methods: High spectral resolution observations of the fundamental ortho water (o-H2O) transition (557 GHz) were carried out with the Heterodyne Instrument for the Far Infrared onboard Herschel toward two starless cores: Barnard 68 (hereafter B68), a Bok globule, and LDN 1544 (L1544), a prestellar core embedded in the Taurus molecular cloud complex. Detailed radiative transfer and chemical codes were used to analyze the data. Results: The RMS in the brightness temperature measured for the B68 and L1544 spectra is 2.0 and 2.2 mK, respectively, in a velocity bin of 0.59 km s-1. The continuum level is 3.5 ± 0.2 mK in B68 and 11.4 ± 0.4 mK in L1544. No significant feature is detected in B68 and the 3σ upper limit is consistent with a column density of o-H2O N(o-H2O) < 2.5 × 1013 cm-2, or a fractional abundance x(o-H2O) < 1.3 × 10-9, more than an order of magnitude lower than the SWAS upper limit on this source. The L1544 spectrum shows an absorption feature at a 5σ level from which we obtain the first value of the o-H2O column density ever measured in dark clouds: N(o-H2O) = (8 ± 4) × 1012 cm-2. The corresponding fractional abundance is x(o-H2O) ≃ 5 × 10-9 at radii >7000 AU and ≃2 × 10-10 toward the center. The radiative transfer analysis shows that this is consistent with a x(o-H2O) profile peaking at ≃10-8, 0.1 pc away from the core center, where both freeze-out and photodissociation are negligible. Conclusions: Herschel has provided the first measurement of water vapor in dark regions. Column densities of o-H2O are low, but prestellar cores such as L1544 (with their high central densities, strong continuum, and large envelopes) appear to be very promising tools to finally shed light on the solid/vapor balance of water in molecular clouds and oxygen chemistry in the earliest stages of star formation. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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| 9. |
- Fich, M., et al.
(författare)
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Herschel-PACS spectroscopy of the intermediate mass protostar NGC 7129 FIRS 2
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L86
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We present preliminary results of the first Herschel spectroscopic observations of NGC 7129 FIRS2, an intermediate mass star-forming region. We attempt to interpret the observations in the framework of an in-falling spherical envelope. Methods. The PACS instrument was used in line spectroscopy mode ( R = 1000-5000) with 15 spectral bands between 63 and 185 mu m. This provided good detections of 26 spectral lines seen in emission, including lines of H2O, CO, OH, O I, and C II. Results. Most of the detected lines, particularly those of H2O and CO, are substantially stronger than predicted by the spherical envelope models, typically by several orders of magnitude. In this paper we focus on what can be learned from the detected CO emission lines. Conclusions. It is unlikely that the much stronger than expected line emission arises in the (spherical) envelope of the YSO. The region hot enough to produce such high excitation lines within such an envelope is too small to produce the amount of emission observed. Virtually all of this high excitation emission must arise in structures such as as along the walls of the outflow cavity with the emission produced by a combination of UV photon heating and/or non-dissociative shocks.
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| 10. |
- Marseille, M. G., et al.
(författare)
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Water abundances in high-mass protostellar envelopes : Herschel observations with HIFI
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L32-
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Tidskriftsartikel (refereegranskat)abstract
- Aims: We derive the dense core structure and the water abundance in four massive star-forming regions in the hope of understanding the earliest stages of massive star formation. Methods: We present Herschel/HIFI observations of the para-H2O 111-000 and 202-111 and the para-H_218O 111-000 transitions. The envelope contribution to the line profiles is separated from contributions by outflows and foreground clouds. The envelope contribution is modeled with Monte-Carlo radiative transfer codes for dust and molecular lines (MC3D and RATRAN), and the water abundance and the turbulent velocity width as free parameters. Results: While the outflows are mostly seen in emission in high-J lines, envelopes are seen in absorption in ground-state lines, which are almost saturated. The derived water abundances range from 5×10-10 to 4×10-8 in the outer envelopes. We detect cold clouds surrounding the protostar envelope, thanks to the very high quality of the Herschel/HIFI data and the unique ability of water to probe them. Several foreground clouds are also detected along the line of sight. Conclusions: The low H2O abundances in massive dense cores are in accordance with the expectation that high densities and low temperatures lead to freeze-out of water on dust grains. The spread in abundance values is not clearly linked to physical properties of the sources. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation of NASA.Appendix (pages 6 to 7) is only available in electronic form at http://www.aanda.org
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