| 1. |
- Lis, D. C., et al.
(författare)
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Herschel/HIFI discovery of interstellar chloronium (H2Cl+)
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the first detection of chloronium, H_2Cl^+, in the interstellar medium, using the HIFI instrument aboard the Herschel Space Observatory. The 2_12-1_01 lines of ortho-H\_2^35Cl^+ and ortho-H\_2^37Cl^+ are detected in absorption towards NGC 6334I, and the 1_11-0_00 transition of para-H\_2^35Cl^+ is detected in absorption towards NGC 6334I and Sgr B2(S). The H_2Cl^+ column densities are compared to those of the chemically-related species HCl. The derived HCl/H_2Cl^+ column density ratios, ~1-10, are within the range predicted by models of diffuse and dense photon dominated regions (PDRs). However, the observed H_2Cl^+ column densities, in excess of 10^13 cm^-2, are significantly higher than the model predictions. Our observations demonstrate the outstanding spectroscopic capabilities of HIFI for detecting new interstellar molecules and providing key constraints for astrochemical models.
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| 2. |
- Vastel, C., et al.
(författare)
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Ortho-to-para ratio of interstellar heavy water
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1, s. Article Number: L31 -
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Tidskriftsartikel (refereegranskat)abstract
- Context. Despite the low elemental deuterium abundance in the Galaxy, enhanced molecular D/H ratios have been found in the environments of low-mass star-forming regions, and in particular the Class 0 protostar IRAS 16293-2422. Aims. The CHESS (Chemical HErschel Surveys of Star forming regions) key program aims to study the molecular complexity of the interstellar medium. The high sensitivity and spectral resolution of the Herschel/HIFI instrument provide a unique opportunity to observe the fundamental 1(1,1)-0(0,0) transition of the ortho-D2O molecule, which is inaccessible from the ground, and determine the ortho-to-para D2O ratio. Methods. We detected the fundamental transition of the ortho-D2O molecule at 607.35 GHz towards IRAS 16293-2422. The line is seen in absorption with a line opacity of 0.62 +/- 0.11 (1 sigma). From the previous ground-based observations of the fundamental 1(1,0)-1(0,1) transition of para-D2O seen in absorption at 316.80 GHz, we estimate a line opacity of 0.26 +/- 0.05 (1 sigma). Results. We show that the observed absorption is caused by the cold gas in the envelope of the protostar. Using these new observations, we estimate for the first time the ortho-to-para D2O ratio to be lower than 2.6 at a 3 sigma level of uncertainty, which should be compared with the thermal equilibrium value of 2:1.
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| 3. |
- Ceccarelli, C., et al.
(författare)
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Herschel spectral surveys of star- forming regions Overview of the 555-636 GHz range
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L22-
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Tidskriftsartikel (refereegranskat)abstract
- High resolution line spectra of star-forming regions are mines of information: they provide unique clues to reconstruct the chemical, dynamical, and physical structure of the observed source. We present the first results from the Herschel key project " Chemical HErschel Surveys of Star forming regions", CHESS. We report and discuss observations towards five CHESS targets, one outflow shock spot and four protostars with luminosities bewteen 20 and 2 x 105 L similar to : L1157-B1, IRAS 16293-2422, OMC2-FIR4, AFGL 2591, and NGC 6334I. The observations were obtained with the heterodyne spectrometer HIFI on board Herschel, with a spectral resolution of 1 MHz. They cover the frequency range 555-636 GHz, a range largely unexplored before the launch of the Herschel satellite. A comparison of the five spectra highlights spectacular differences in the five sources, for example in the density of methanol lines, or the presence./absence of lines from S-bearing molecules or deuterated species. We discuss how these differences can be attributed to the different star-forming mass or evolutionary status.
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| 4. |
- Codella, C., et al.
(författare)
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The CHESS spectral survey of star forming regions : Peering into the protostellar shock L1157-B1. I. Shock chemical complexity
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L112-
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Tidskriftsartikel (refereegranskat)abstract
- We present the first results of the unbiased survey of the L1157-B1 bow shock, obtained with HIFI in the framework of the key program Chemical HErschel Survey of Star forming regions (CHESS). The L1157 outflow is driven by a low-mass Class 0 protostar and is considered the prototype of the so-called chemically active outflows. The bright blue-shifted bow shock B1 is the ideal laboratory for studying the link between the hot (~1000-2000 K) component traced by H2 IR-emission and the cold (~10-20 K) swept-up material. The main aim is to trace the warm gas chemically enriched by the passage of a shock and to infer the excitation conditions in L1157-B1. A total of 27 lines are identified in the 555-636 GHz region, down to an average 3σ level of 30 mK. The emission is dominated by CO(5-4) and H2O(110-101) transitions, as discussed by Lefloch et al. in this volume. Here we report on the identification of lines from NH3, H2CO, CH3OH, CS, HCN, and HCO+. The comparison between the profiles produced by molecules released from dust mantles (NH3, H2CO, CH3OH) and that of H2O is consistent with a scenario in which water is also formed in the gas-phase in high-temperature regions where sputtering or grain-grain collisions are not efficient. The high excitation range of the observed tracers allows us to infer, for the first time for these species, the existence of a warm (≥200 K) gas component coexisting in the B1 bow structure with the cold and hot gas detected from ground. Herschel is an ESA space observatory with science instruments provided by European-led principal Investigator consortia and with important participation from NASA.Table 1 is only available in electronic form at http://www.aanda.org
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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. |
- Gerin, M., et al.
(författare)
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Interstellar OH+, H2O+ and H3O+ along the sight-line to G10.6-0.4
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:4, s. 110-
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection of absorption lines by the reactive ions OH+, H2O+ and H3O+ along the line of sight to the submillimeter continuum source G10.6$-$0.4 (W31C). We used the Herschel HIFI instrument in dual beam switch mode to observe the ground state rotational transitions of OH+ at 971 GHz, H2O+ at 1115 and 607 GHz, and H3O+ at 984 GHz. The resultant spectra show deep absorption over a broad velocity range that originates in the interstellar matter along the line of sight to G10.6$-$0.4 as well as in the molecular gas directly associated with that source. The OH+ spectrum reaches saturation over most velocities corresponding to the foreground gas, while the opacity of the H2O+ lines remains lower than 1 in the same velocity range, and the H3O+ line shows only weak absorption. For LSR velocities between 7 and 50 kms$^{-1}$ we estimate total column densities of $N$(OH+) $> 2.5 \times 10^{14}$ cm$^{-2}$, $N$(H2O+) $\sim 6 \times 10^{13}$ cm$^{-2}$ and $N$(H3O+) $\sim 4.0 \times 10^{13}$ cm$^{-2}$. These detections confirm the role of O$^+$ and OH$^+$ in initiating the oxygen chemistry in diffuse molecular gas and strengthen our understanding of the gas phase production of water. The high ratio of the OH+ by the H2O+ column density implies that these species predominantly trace low-density gas with a small fraction of hydrogen in molecular form.
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| 7. |
- Roelfsema, P. R., et al.
(författare)
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In-orbit performance of Herschel-HIFI
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 537
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Tidskriftsartikel (refereegranskat)abstract
- Aims: In this paper the calibration and in-orbit performance of the Heterodyne Instrument for the Far-Infrared (HIFI) is described.Methods: The calibration of HIFI is based on a combination of ground and in-flight tests. Dedicated ground tests to determine those instrument parameters that can only be measured accurately using controlled laboratory stimuli were carried out in the instrument level test (ILT) campaign. Special in-flight tests during the commissioning phase (CoP) and performance verification (PV) allowed the determination of the remaining instrument parameters. The various instrument observing modes, as specified in astronomical observation templates (AOTs), were validated in parallel during PV by observing selected celestial sources.Results: The initial calibration and in-orbit performance of HIFI has been established. A first estimate of the calibration budget is given. The overall in-flight instrument performance agrees with the original specification. Issues remain at only a few frequencies. 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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| 8. |
- Falgarone, E., et al.
(författare)
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CH+(1-0) and 13CH+(1-0) absorption lines in the direction of massive star-forming regions
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection of the ground-state rotational transition of the methylidyne cation CH+ and its isotopologue (CH+)-C-13 toward the remote massive star-forming regions W33A, W49N, and W51 with the HIFI instrument onboard the Herschel satellite. Both lines are seen only in absorption against the dust continuum emission of the star-forming regions. The CH+ absorption is saturated over almost the entire velocity ranges sampled by the lines-of-sight that include gas associated with the star-forming regions (SFR) and Galactic foreground material. The CH+ column densities are inferred from the optically thin components. A lower limit of the isotopic ratio [(CH+)-C-12]/[(CH+)-C-13]> 35.5 is derived from the absorptions of foreground material toward W49N. The column density ratio, N(CH+)/N(HCO+), is found to vary by at least a factor 10, between 4 and > 40, in the Galactic foreground material. Line-of-sight 12CH+ average abundances relative to total hydrogen are estimated. Their average value, N(CH+)/NH > 2.6 x 10(-8), is higher than that observed in the solar neighborhood and confirms the high abundances of CH+ in the Galactic interstellar medium. We compare this result to the predictions of turbulent dissipation regions (TDR) models and find that these high abundances can be reproduced for the inner Galaxy conditions. It is remarkable that the range of predicted N(CH+)/ N(HCO+) ratios, from 1 to similar to 50, is comparable to that observed.
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| 9. |
- Neufeld, D. A., et al.
(författare)
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Herschel/HIFI observations of interstellar OH+ and H2O+ towards W49N: a probe of diffuse clouds with a small molecular fraction
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1, s. Article Number: L10-
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection of absorption by interstellar hydroxyl cations and water cations, along the sight-line to the bright continuum source W49N. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 972 GHz N = 1-0 transition of OH+ and the 1115 GHz 1(11)-0(00) transition of ortho-H2O+. The resultant spectra show absorption by ortho-H2O+, and strong absorption by OH+, in foreground material at velocities in the range 0 to 70 km s(-1) with respect to the local standard of rest. The inferred OH+/H2O+ abundance ratio ranges from similar to 3 to similar to 15, implying that the observed OH+ arises in clouds of small molecular fraction, in the 2-8% range. This conclusion is confirmed by the distribution of OH+ and H2O+ in Doppler velocity space, which is similar to that of atomic hydrogen, as observed by means of 21 cm absorption measurements, and dissimilar from that typical of other molecular tracers. The observed OH+/H abundance ratio of a few x10(-8) suggests a cosmic ray ionization rate for atomic hydrogen of 0.6-2.4 x 10(-16) s(-1), in good agreement with estimates inferred previously for diffuse clouds in the Galactic disk from observations of interstellar H-3(+) and other species.
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| 10. |
- Shipman, R., et al.
(författare)
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Data processing pipeline for Herschel HIFI
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 608, s. A49-
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Tidskriftsartikel (refereegranskat)abstract
- Context. The HIFI instrument on the Herschel Space Observatory performed over 9100 astronomical observations, almost 900 of which were calibration observations in the course of the nearly four-year Herschel mission. The data from each observation had to be converted from raw telemetry into calibrated products and were included in the Herschel Science Archive. Aims. The HIFI pipeline was designed to provide robust conversion from raw telemetry into calibrated data throughout all phases of the HIFI missions. Pre-launch laboratory testing was supported as were routine mission operations. Methods. A modular software design allowed components to be easily added, removed, amended and / or extended as the understanding of the HIFI data developed during and after mission operations. Results. The HIFI pipeline processed data from all HIFI observing modes within the Herschel automated processing environment as well as within an interactive environment. The same software can be used by the general astronomical community to reprocess any standard HIFI observation. The pipeline also recorded the consistency of processing results and provided automated quality reports. Many pipeline modules were in use since the HIFI pre-launch instrument level testing. Conclusions. Processing in steps facilitated data analysis to discover and address instrument artefacts and uncertainties. The availability of the same pipeline components from pre-launch throughout the mission made for well-understood, tested, and stable processing. A smooth transition from one phase to the next significantly enhanced processing reliability and robustness.
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