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3.
  • Lis, D. C., et al. (author)
  • Herschel/HIFI discovery of interstellar chloronium (H2Cl+)
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1
  • Journal article (peer-reviewed)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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6.
  • Lacour, S., et al. (author)
  • The mass of β Pictoris c from β Pictoris b orbital motion
  • 2021
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 654
  • Journal article (peer-reviewed)abstract
    • Aims. We aim to demonstrate that the presence and mass of an exoplanet can now be effectively derived from the astrometry of another exoplanet.Methods. We combined previous astrometry of β Pictoris b with a new set of observations from the GRAVITY interferometer. The orbital motion of β Pictoris b is fit using Markov chain Monte Carlo simulations in Jacobi coordinates. The inner planet, β Pictoris c, was also reobserved at a separation of 96 mas, confirming the previous orbital estimations.Results. From the astrometry of planet b only, we can (i) detect the presence of β Pictoris c and (ii) constrain its mass to 10.04(-3.10)(+4.53) M-Jup. If one adds the astrometry of β Pictoris c, the mass is narrowed down to 9.15(-1.06)(+1.08) M-Jup. The inclusion of radial velocity measurements does not affect the orbital parameters significantly, but it does slightly decrease the mass estimate to 8.89(-0.75)(+0.75) M-Jup. With a semimajor axis of 2.68 +/- 0.02 au, a period of 1221 +/- 15 days, and an eccentricity of 0.32 +/- 0.02, the orbital parameters of β Pictoris c are now constrained as precisely as those of β Pictoris b. The orbital configuration is compatible with a high-order mean-motion resonance (7:1). The impact of the resonance on the planets' dynamics would then be negligible with respect to the secular perturbations, which might have played an important role in the eccentricity excitation of the outer planet.
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7.
  • Vastel, C., et al. (author)
  • Ortho-to-para ratio of interstellar heavy water
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1, s. Article Number: L31 -
  • Journal article (peer-reviewed)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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8.
  • Ceccarelli, C., et al. (author)
  • Herschel spectral surveys of star- forming regions Overview of the 555-636 GHz range
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L22-
  • Journal article (peer-reviewed)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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9.
  • Codella, C., et al. (author)
  • The CHESS spectral survey of star forming regions : Peering into the protostellar shock L1157-B1. I. Shock chemical complexity
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L112-
  • Journal article (peer-reviewed)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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10.
  • Garcia-Lopez, R., et al. (author)
  • A measure of the size of the magnetospheric accretion region in TW Hydrae
  • 2020
  • In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 584:7822, s. 547-550
  • Journal article (peer-reviewed)abstract
    • Stars form by accreting material from their surrounding disks. There is a consensus that matter flowing through the disk is channelled onto the stellar surface by the stellar magnetic field. This is thought to be strong enough to truncate the disk close to the corotation radius, at which the disk rotates at the same rate as the star. Spectro-interferometric studies in young stellar objects show that hydrogen emission (a well known tracer of accretion activity) mostly comes from a region a few milliarcseconds across, usually located within the dust sublimation radius1–3. The origin of the hydrogen emission could be the stellar magnetosphere, a rotating wind or a disk. In the case of intermediate-mass Herbig AeBe stars, the fact that Brackett γ (Brγ) emission is spatially resolved rules out the possibility that most of the emission comes from the magnetosphere4–6 because the weak magnetic fields (some tenths of a gauss) detected in these sources7,8 result in very compact magnetospheres. In the case of T Tauri sources, their larger magnetospheres should make them easier to resolve. The small angular size of the magnetosphere (a few tenths of a milliarcsecond), however, along with the presence of winds9,10 make the interpretation of the observations challenging. Here we report optical long-baseline interferometric observations that spatially resolve the inner disk of the T Tauri star TW Hydrae. We find that the near-infrared hydrogen emission comes from a region approximately 3.5 stellar radii across. This region is within the continuum dusty disk emitting region (7 stellar radii across) and also within the corotation radius, which is twice as big. This indicates that the hydrogen emission originates in the accretion columns (funnel flows of matter accreting onto the star), as expected in magnetospheric accretion models, rather than in a wind emitted at much larger distance (more than one astronomical unit).
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11.
  • Koutoulaki, M., et al. (author)
  • The GRAVITY young stellar object survey: IV. The CO overtone emission in 51 Oph at sub-au scales
  • 2021
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 645
  • Journal article (peer-reviewed)abstract
    • Context. 51 Oph is a Herbig Ae/Be star that exhibits strong near-infrared CO ro-vibrational emission at 2.3 μm, most likely originating in the innermost regions of a circumstellar disc. Aims. We aim to obtain the physical and geometrical properties of the system by spatially resolving the circumstellar environment of the inner gaseous disc. Methods. We used the second-generation Very Large Telescope Interferometer instrument GRAVITY to spatially resolve the continuum and the CO overtone emission. We obtained data over 12 baselines with the auxiliary telescopes and derive visibilities, and the differential and closure phases as a function of wavelength. We used a simple local thermal equilibrium ring model of the CO emission to reproduce the spectrum and CO line displacements. Results. Our interferometric data show that the star is marginally resolved at our spatial resolution, with a radius of ∼10.58 ± 2.65R·. The K-band continuum emission from the disc is inclined by 63° ± 1°, with a position angle of 116° ± 1°, and 4 ± 0.8 mas (0.5 ± 0.1 au) across. The visibilities increase within the CO line emission, indicating that the CO is emitted within the dust-sublimation radius. By modelling the CO bandhead spectrum, we derive that the CO is emitted from a hot (T = 1900-2800 K) and dense (NCO = (0.9-9) × 1021 cm-2) gas. The analysis of the CO line displacement with respect to the continuum allows us to infer that the CO is emitted from a region 0.10 ± 0.02 au across, well within the dust-sublimation radius. The inclination and position angle of the CO line emitting region is consistent with that of the dusty disc. Conclusions. Our spatially resolved interferometric observations confirm the CO ro-vibrational emission within the dust-free region of the inner disc. Conventional disc models exclude the presence of CO in the dust-depleted regions of Herbig AeBe stars. Ad hoc models of the innermost disc regions, that can compute the properties of the dust-free inner disc, are therefore required.
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12.
  • Lefloch, B., et al. (author)
  • The CHESS spectral survey of star forming regions : Peering into the protostellar shock L1157-B1. II. Shock dynamics
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L113-
  • Journal article (peer-reviewed)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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13.
  • van Dishoeck, E. F., et al. (author)
  • Water in Star-forming Regions with the Herschel Space Observatory (WISH). I. Overview of Key Program and First Results
  • 2011
  • In: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 123:900, s. 138-170
  • Journal article (peer-reviewed)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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14.
  • van Kempen, T. A., et al. (author)
  • Origin of the hot gas in low-mass protostars Herschel-PACS spectroscopy of HH 46
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L121
  • Journal article (peer-reviewed)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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15.
  • Caselli, P., et al. (author)
  • Water vapor toward starless cores : The Herschel view
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L29-
  • Journal article (peer-reviewed)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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16.
  • Cosentino, Giuliana, 1990, et al. (author)
  • Negative and positive feedback from a supernova remnant with SHREC. a detailed study of the shocked gas in IC443
  • 2022
  • In: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 511:1, s. 953-963
  • Journal article (peer-reviewed)abstract
    • Supernova remnants (SNRs) contribute to regulate the star formation efficiency and evolution of galaxies. As they expand into the interstellar medium (ISM), they transfer vast amounts of energy and momentum that displace, compress, and heat the surrounding material. Despite the extensive work in galaxy evolution models, it remains to be observationally validated to what extent the molecular ISM is affected by the interaction with SNRs. We use the first results of the ESO-ARO Public Spectroscopic Survey SHREC to investigate the shock interaction between the SNR IC443 and the nearby molecular clump G. We use high-sensitivity SiO(2-1) and (HCO+)-C-13 (1-0) maps obtained by SHREC together with SiO(1-0) observations obtained with the 40-m telescope at the Yebes Observatory. We find that the bulk of the SiO emission is arising from the ongoing shock interaction between IC443 and clump G. The shocked gas shows a well-ordered kinematic structure, with velocities blue-shifted with respect to the central velocity of the SNR, similar to what observed towards other SNR-cloud interaction sites. The shock compression enhances the molecular gas density, n(H-2), up to >10(5) cm(-3), a factor of >10 higher than the ambient gas density and similar to values required to ignite star formation. Finally, we estimate that up to 50 per cent of the momentum injected by IC443 is transferred to the interacting molecular material. Therefore, the molecular ISM may represent an important momentum carrier in sites of SNR-cloud interactions.
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17.
  • Fich, M., et al. (author)
  • Herschel-PACS spectroscopy of the intermediate mass protostar NGC 7129 FIRS 2
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L86
  • Journal article (peer-reviewed)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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18.
  • Kristensen, L., et al. (author)
  • Water in star-forming regions with Herschel (WISH) II. Evolution of 557 GHz 1(10)-1(01) emission in low-mass protostars
  • 2012
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 542
  • Journal article (peer-reviewed)abstract
    • Context. Water is a key tracer of dynamics and chemistry in low-mass star-forming regions, but spectrally resolved observations have so far been limited in sensitivity and angular resolution, and only data from the brightest low-mass protostars have been published. Aims. The first systematic survey of spectrally resolved water emission in 29 low-mass (L 10 km s(-1)). The water abundance in the outer cold envelope is low, greater than or similar to 10(-10). The different H2O profile components show a clear evolutionary trend: in the younger Class 0 sources the emission is dominated by outflow components originating inside an infalling envelope. When large-scale infall diminishes during the Class I phase, the outflow weakens and H2O emission all but disappears.
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19.
  • Marseille, M. G., et al. (author)
  • Water abundances in high-mass protostellar envelopes : Herschel observations with HIFI
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L32-
  • Journal article (peer-reviewed)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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20.
  • Nisini, B., et al. (author)
  • Water cooling of shocks in protostellar outflows. Herschel-PACS map of L1157
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L120-
  • Journal article (peer-reviewed)abstract
    • Context. The far-IR/sub-mm spectral mapping facility provided by the Herschel-PACS and HIFI instruments has made it possible to obtain, for the first time, images of H2O emission with a spatial resolution comparable to ground based mm/sub-mm observations. Aims: In the framework of the Water In Star-forming regions with Herschel (WISH) key program, maps in water lines of several outflows from young stars are being obtained, to study the water production in shocks and its role in the outflow cooling. This paper reports the first results of this program, presenting a PACS map of the o-H2O 179 μm transition obtained toward the young outflow L1157. Methods: The 179 μm map is compared with those of other important shock tracers, and with previous single-pointing ISO, SWAS, and Odin water observations of the same source that allow us to constrain the H2O abundance and total cooling. Results: Strong H2O peaks are localized on both shocked emission knots and the central source position. The H2O 179 μm emission is spatially correlated with emission from H2 rotational lines, excited in shocks leading to a significant enhancement of the water abundance. Water emission peaks along the outflow also correlate with peaks of other shock-produced molecular species, such as SiO and NH3. A strong H2O peak is also observed at the location of the proto-star, where none of the other molecules have significant emission. The absolute 179 μm intensity and its intensity ratio to the H2O 557 GHz line previously observed with Odin/SWAS indicate that the water emission originates in warm compact clumps, spatially unresolved by PACS, having a H2O abundance of the order of 10-4. This testifies that the clumps have been heated for a time long enough to allow the conversion of almost all the available gas-phase oxygen into water. The total H2O cooling is ~10-1 L_ȯ, about 40% of the cooling due to H2 and 23% of the total energy released in shocks along the L1157 outflow. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important partecipation from NASA.
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21.
  • Paciaroni, M., et al. (author)
  • Timing of initiation of oral anticoagulants in patients with acute ischemic stroke and atrial fibrillation comparing posterior and anterior circulation strokes
  • 2020
  • In: European Stroke Journal. - : SAGE Publications. - 2396-9873 .- 2396-9881.
  • Journal article (peer-reviewed)abstract
    • Introduction: The aim of this study in patients with acute posterior ischaemic stroke (PS) and atrial fibrillation (AF) was to evaluate (1) the risks of recurrent ischaemic event and severe bleeding and (2) these risks in relation with oral anticoagulant therapy (OAT) and its timing. Materials and Methods: Patients with PS were prospectively included; the outcome events of these patients were compared with those of patients with anterior stroke (AS) which were taken from previous registries. The primary outcome was the composite of stroke recurrence, transient ischaemic attack, symptomatic systemic embolism, symptomatic cerebral bleeding and major extracranial bleeding occurring within 90 days from acute stroke. Results: A total of 2470 patients were available for the analysis: 473 (19.1%) with PS and 1997 (80.9%) with AS. Over 90 days, 213 (8.6%) primary outcome events were recorded: 175 (8.7%) in patients with AS and 38 (8.0%) in those with PS. In patients who initiated OAT within 2 days, the primary outcome occurred in 5 out of 95 patients (5.3%) with PS compared to 21 out of 373 patients (4.3%) with AS (OR 1.07; 95% CI 0.39-2.94). In patients who initiated OAT between days 3 and 7, the primary outcome occurred in 3 out of 103 patients (2.9%) with PS compared to 26 out of 490 patients (5.3%) with AS (OR 0.54; 95% CI 0.16-1.80). Discussion: our findings suggest that, when deciding the time to initiate oral anticoagulation, the location of stroke, either anterior or posterior, does not predict the risk of outcome events. Conclusions: Patients with PS or AS and AF appear to have similar risks of ischaemic or haemorrhagic events at 90 days with no difference concerning the timing of initiation of OAT.
  •  
22.
  • van der Tak, F. F. S., et al. (author)
  • Water abundance variations around high-mass protostars: HIFI observations of the DR21 region
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L107
  • Journal article (peer-reviewed)abstract
    • Context. Water is a key molecule in the star formation process, but its spatial distribution in star-forming regions is not well known. Aims. We study the distribution of dust continuum and H2O and (CO)-C-13 line emission in DR21, a luminous star-forming region with a powerful outflow and a compact H II region. Methods. Herschel-HIFI spectra near 1100 GHz show narrow (CO)-C-13 10-9 emission and H2O 1(11)-0(00) absorption from the dense core and broad emission from the outflow in both lines. The H2O line also shows absorption by a foreground cloud known from ground-based observations of low-J CO lines. Results. The dust continuum emission is extended over 36 '' FWHM, while the (CO)-C-13 and H2O lines are confined to approximate to 24 '' or less. The foreground absorption appears to peak further North than the other components. Radiative transfer models indicate very low abundances of similar to 2 x 10(-10) for H2O and similar to 8 x 10(-7) for (CO)-C-13 in the dense core, and higher H2O abundances of similar to 4 x 10(-9) in the foreground cloud and similar to 7 x 10(-7) in the outflow. Conclusions. The high H2O abundance in the warm outflow is probably due to the evaporation of water-rich icy grain mantles, while the H2O abundance is kept down by freeze-out in the dense core and by photodissociation in the foreground cloud.
  •  
23.
  • van Dishoeck, E. F., et al. (author)
  • Water in star-forming regions: Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
  • 2021
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 648
  • Journal article (peer-reviewed)abstract
    • 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 ∼80 sources along the two axes of luminosity and evolutionary stage: from low- to high-mass protostars (luminosities from <1 to > 10Lpdbl) 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 (> 10cm-3, 300-1000 K, v ∼ 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 Jup > 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/H2 abundance of 4 × 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 ∼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 × 10-6 to a few × 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 102-10times 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 μm-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 (Eup < 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.
  •  
24.
  • Wampfler, S. F., et al. (author)
  • Herschel observations of the hydroxyl radical (OH) in young stellar objects
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L36-
  • Journal article (peer-reviewed)abstract
    • Aims: “Water In Star-forming regions with Herschel” (WISH) is a Herschel key program investigating the water chemistry in young stellar objects (YSOs) during protostellar evolution. Hydroxyl (OH) is one of the reactants in the chemical network most closely linked to the formation and destruction of H2O. High-temperature (T ⪆ 250 K) chemistry connects OH and H2O through the OH + H2 Leftrightarrow H2O + H reactions. Formation of H2O from OH is efficient in the high-temperature regime found in shocks and the innermost part of protostellar envelopes. Moreover, in the presence of UV photons, OH can be produced from the photo-dissociation of H2O through H2O + γUV Rightarrow OH + H. Methods: High-resolution spectroscopy of the 163.12 μm triplet of OH towards HH 46 and NGC 1333 IRAS 2A was carried out with the Heterodyne Instrument for the Far Infrared (HIFI) on board the Herschel Space Observatory. The low- and intermediate-mass protostars HH 46, TMR 1, IRAS 15398-3359, DK Cha, NGC 7129 FIRS 2, and NGC 1333 IRAS 2A were observed with the Photodetector Array Camera and Spectrometer (PACS) on Herschel in four transitions of OH and two [O i] lines. Results: The OH transitions at 79, 84, 119, and 163 μm and [O i] emission at 63 and 145 μm were detected with PACS towards the class I low-mass YSOs as well as the intermediate-mass and class I Herbig Ae sources. No OH emission was detected from the class 0 YSO NGC 1333 IRAS 2A, though the 119 μm was detected in absorption. With HIFI, the 163.12 μm was not detected from HH 46 and only tentatively detected from NGC 1333 IRAS 2A. The combination of the PACS and HIFI results for HH 46 constrains the line width (FWHM ⪆ 11 km s-1) and indicates that the OH emission likely originates from shocked gas. This scenario is supported by trends of the OH flux increasing with the [O i] flux and the bolometric luminosity, as found in our sample. Similar OH line ratios for most sources suggest that OH has comparable excitation temperatures despite the different 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 from NASA.Appendices (page 6) are only available in electronic form at http://www.aanda.org
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25.
  • Benz, A. O., et al. (author)
  • Hydrides in young stellar objects : Radiation tracers in a protostar-disk-outflow system
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L35-
  • Journal article (peer-reviewed)abstract
    • 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
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26.
  • Bergin, E. A., et al. (author)
  • Sensitive limits on the abundance of cold water vapor in the DM Tauri protoplanetary disk
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L33-
  • Journal article (peer-reviewed)abstract
    • 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.
  •  
27.
  • Bruderer, S., et al. (author)
  • Herschel/HIFI detections of hydrides towards AFGL 2591. Envelope emission versus tenuous cloud absorption
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L44-
  • Journal article (peer-reviewed)abstract
    • The Heterodyne Instrument for the Far Infrared (HIFI) onboard the Herschel Space Observatory allows the first observations of light diatomic molecules at high spectral resolution and in multiple transitions. Here, we report deep integrations using HIFI in different lines of hydrides towards the high-mass star forming region AFGL 2591. Detected are CH, CH+, NH, OH+, H2O+, while NH+ and SH+ have not been detected. All molecules except for CH and CH+ are seen in absorption with low excitation temperatures and at velocities different from the systemic velocity of the protostellar envelope. Surprisingly, the CH(JF,P = 3/22,- - 1/21,+ ) and CH+(J = 1-0, J = 2-1) lines are detected in emission at the systemic velocity. We can assign the absorption features to a foreground cloud and an outflow lobe, while the CH and CH+ emission stems from the envelope. The observed abundance and excitation of CH and CH+ can be explained in the scenario of FUV irradiated outflow walls, where a cavity etched out by the outflow allows protostellar FUV photons to irradiate and heat the envelope at larger distances driving the chemical reactions that produce these molecules. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Apppendices and Table 1 (pages 6 to 7) are only available in electronic form at http://www.aanda.org
  •  
28.
  • Chavarria, L., et al. (author)
  • Water in massive star-forming regions : HIFI observations of W3 IRS5
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L37-
  • Journal article (peer-reviewed)abstract
    • We present Herschel observations of the water molecule in the massive star-forming region W3 IRS5. The o-(H2O)-O-17 1(10)-1(01), p-(H2O)-O-18 1(11)-0(00), p-H2O 2(02)-1(11), p-H2O 1(11)-0(00), o-H2O 2(21)-2(12), and o-H2O 2(12)-1(01) lines, covering a frequency range from 552 up to 1669 GHz, have been detected at high spectral resolution with HIFI. The water lines in W3 IRS5 show well-defined high-velocity wings that indicate a clear contribution by outflows. Moreover, the systematically blue-shifted absorption in the H2O lines suggests expansion, presumably driven by the outflow. No infall signatures are detected. The p-H2O 1(11)-0(00) and o-H2O 2(12)-1(01) lines show absorption from the cold material (T similar to 10 K) in which the high-mass protostellar envelope is embedded. One-dimensional radiative transfer models are used to estimate water abundances and to further study the kinematics of the region. We show that the emission in the rare isotopologues comes directly from the inner parts of the envelope (T greater than or similar to 100 K) where water ices in the dust mantles evaporate and the gas-phase abundance increases. The resulting jump in the water abundance (with a constant inner abundance of 10(-4)) is needed to reproduce the o-(H2O)-O-17 1(10)-1(01) and p-(H2O)-O-18 1(11)-0(00) spectra in our models. We estimate water abundances of 10(-8) to 10(-9) in the outer parts of the envelope (T less than or similar to 100 K). The possibility of two protostellar objects contributing to the emission is discussed.
  •  
29.
  • Johnstone, D., et al. (author)
  • Herschel/HIFI spectroscopy of the intermediate mass protostar NGC7129 FIRS 2
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L41-
  • Journal article (peer-reviewed)abstract
    • Herschel/HIFI observations of water from the intermediate mass protostar NGC 7129 FIRS 2 provide a powerful diagnostic of the physical conditions in this star formation environment. Six spectral settings, covering four (H2O)-O-16 and two (H2O)-O-18 lines, were observed and all but one (H2O)-O-18 line were detected. The four (H2O)-O-16 lines discussed here share a similar morphology: a narrower, approximate to 6kms(-1), component centered slightly redward of the systemic velocity of NGC7129 FIRS 2 and a much broader, approximate to 25 km s(-1) component centered blueward and likely associated with powerful outflows. The narrower components are consistent with emission from water arising in the envelope around the intermediate mass protostar, and the abundance of H2O is constrained to approximate to 10(-7) for the outer envelope. Additionally, the presence of a narrow self-absorption component for the lowest energy lines is likely due to self-absorption from colder water in the outer envelope. The broader component, where the H2O/CO relative abundance is found to be approximate to 0.2, appears to be tracing the same energetic region that produces strong CO emission at high J.
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30.
  • Karska, A., et al. (author)
  • Water in star-forming regions with Herschel (WISH) III. Far-infrared cooling lines in low-mass young stellar objects
  • 2013
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 552
  • Journal article (peer-reviewed)abstract
    • Context. Understanding the physical phenomena involved in the earlierst stages of protostellar evolution requires knowledge of the heating and cooling processes that occur in the surroundings of a young stellar object. Spatially resolved information from its constituent gas and dust provides the necessary constraints to distinguish between different theories of accretion energy dissipation into the envelope.Aims. Our aims are to quantify the far-infrared line emission from low-mass protostars and the contribution of different atomic and molecular species to the gas cooling budget, to determine the spatial extent of the emission, and to investigate the underlying excitation conditions. Analysis of the line cooling will help us characterize the evolution of the relevant physical processes as the protostar ages.Methods. Far-infrared Herschel-PACS spectra of 18 low-mass protostars of various luminosities and evolutionary stages are studied in the context of the WISH key program. For most targets, the spectra include many wavelength intervals selected to cover specific CO, H2O, OH, and atomic lines. For four targets the spectra span the entire 55-200 mu m region. The PACS field-of-view covers similar to 47 '' with the resolution of 9.4 ''.Results. Most of the protostars in our sample show strong atomic and molecular far-infrared emission. Water is detected in 17 out of 18 objects (except TMC1A), including 5 Class I sources. The high-excitation H2O 8(18)-7(07) 63.3 mu m line (E-u/k(B) = 1071 K) is detected in 7 sources. CO transitions from J = 14-13 up to J = 49-48 are found and show two distinct temperature components on Boltzmann diagrams with rotational temperatures of similar to 350 K and similar to 700 K. H2O has typical excitation temperatures of similar to 150 K. Emission from both Class 0 and I sources is usually spatially extended along the outflow direction but with a pattern that depends on the species and the transition. In the extended sources, emission is stronger off source and extended on >= 10 000 AU scales; in the compact sample, more than half of the flux originates within 1000 AU of the protostar. The H2O line fluxes correlate strongly with those of the high-J CO lines, both for the full array and for the central position, as well as with the bolometric luminosity and envelope mass. They correlate less strongly with OH fluxes and not with [O I] fluxes. In contrast, [O I] and OH often peak together at the central position.Conclusions. The PACS data probe at least two physical components. The H2O and CO emission very likely arises in non-dissociative (irradiated) shocks along the outflow walls with a range of pre-shock densities. Some OH is also associated with this component, most likely resulting from H2O photodissociation. UV-heated gas contributes only a minor fraction to the CO emission observed by PACS, based on the strong correlation between the shock-dominated CO 24-23 line and the CO 14-13 line. [O I] and some of the OH emission probe dissociative shocks in the inner envelope. The total far-infrared cooling is dominated by H2O and CO, with the fraction contributed by [O I] increasing for Class I sources. Consistent with previous studies, the ratio of total far-infrared line emission over bolometric luminosity decreases with the evolutionary state.
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31.
  • Kristensen, L. E., et al. (author)
  • Water in low-mass star-forming regions with Herschel . HIFI spectroscopy of NGC 1333
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L30-
  • Journal article (peer-reviewed)abstract
    • “Water In Star-forming regions with Herschel” (WISH) is a key programme dedicated to studying the role of water and related species during the star-formation process and constraining the physical and chemical properties of young stellar objects. The Heterodyne Instrument for the Far-Infrared (HIFI) on the Herschel Space Observatory observed three deeply embedded protostars in the low-mass star-forming region NGC 1333 in several H_216O, H_218O, and CO transitions. Line profiles are resolved for five H_216O transitions in each source, revealing them to be surprisingly complex. The line profiles are decomposed into broad (>20 km s-1), medium-broad (~5-10 km s-1), and narrow (<5 km s-1) components. The H_218O emission is only detected in broad 110-101 lines (>20 km s-1), indicating that its physical origin is the same as for the broad H_216O component. In one of the sources, IRAS4A, an inverse P Cygni profile is observed, a clear sign of infall in the envelope. From the line profiles alone, it is clear that the bulk of emission arises from shocks, both on small (⪉1000 AU) and large scales along the outflow cavity walls (~10 000 AU). The H2O line profiles are compared to CO line profiles to constrain the H2O abundance as a function of velocity within these shocked regions. The H2O/CO abundance ratios are measured to be in the range of ~0.1-1, corresponding to H2O abundances of ~10-5-10-4 with respect to H2. Approximately 5-10% of the gas is hot enough for all oxygen to be driven into water in warm post-shock gas, mostly at high velocities. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Tables 2 and 3 (page 6) are only available in electronic form at http://www.aanda.org
  •  
32.
  •  
33.
  • Taquet, V, et al. (author)
  • Seeds of Life in Space (SOLIS) VI. Chemical evolution of sulfuretted species along the outflows driven by the low-mass protostellar binary NGC1333-IRAS4A
  • 2020
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 637
  • Journal article (peer-reviewed)abstract
    • Context. Low-mass protostars drive powerful molecular outflows that can be observed with millimetre and submillimetre telescopes. Various sulfuretted species are known to be bright in shocks and could be used to infer the physical and chemical conditions throughout the observed outflows. Aims. The evolution of sulfur chemistry is studied along the outflows driven by the NGC1333-IRAS4A protobinary system located in the Perseus cloud to constrain the physical and chemical processes at work in shocks. Methods. We observed various transitions from OCS, CS, SO, and SO2 towards NGC1333-IRAS4A in the 1.3, 2, and 3mm bands using the IRAM NOrthern Extended Millimeter Array and we interpreted the observations through the use of the Paris-Durham shock model. Results. The targeted species clearly show different spatial emission along the two outflows driven by IRAS4A. OCS is brighter on small and large scales along the south outflow driven by IRAS4A1, whereas SO2 is detected rather along the outflow driven by IRAS4A2 that is extended along the north east-south west direction. SO is detected at extremely high radial velocity up to +25 km s 1 relative to the source velocity, clearly allowing us to distinguish the two outflows on small scales. Column density ratio maps estimated from a rotational diagram analysis allowed us to confirm a clear gradient of the OCS/SO2 column density ratio between the IRAS4A1 and IRAS4A2 outflows. Analysis assuming non Local Thermodynamic Equilibrium of four SO2 transitions towards several SiO emission peaks suggests that the observed gas should be associated with densities higher than 105 cm 3 and relatively warm (T > 100 K) temperatures in most cases. Conclusions. The observed chemical differentiation between the two outflows of the IRAS4A system could be explained by a different chemical history. The outflow driven by IRAS4A1 is likely younger and more enriched in species initially formed in interstellar ices, such as OCS, and recently sputtered into the shock gas. In contrast, the longer and likely older outflow triggered by IRAS4A2 is more enriched in species that have a gas phase origin, such as SO2.
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34.
  • Wyrowski, F., et al. (author)
  • Variations in H2O+/H2O ratios toward massive star-forming regions
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L34-
  • Journal article (peer-reviewed)abstract
    • Early results from the Herschel Space Observatory revealed the water cation H2O+ to be an abundant ingredient of the interstellar medium. Here we present new observations of the H2O and H2O+ lines at 1113.3 and 1115.2 GHz using the Herschel Space Observatory toward a sample of high-mass star-forming regions to observationally study the relation between H2O and H2O+. Nine out of ten sources show absorption from H2O+ in a range of environments: the molecular clumps surrounding the forming and newly formed massive stars, bright high-velocity outflows associated with the massive protostars, and unrelated low-density clouds along the line of sight. Column densities per velocity component of H2O+ are found in the range of 10(12) to a few 10(13) cm(-2). The highest N(H2O+) column densities are found in the outflows of the sources. The ratios of H2O+/H2O are determined in a range from 0.01 to a few and are found to differ strongly between the observed environments with much lower ratios in the massive (proto) cluster envelopes (0.01-0.1) than in outflows and diffuse clouds. Remarkably, even for source components detected in H2O in emission, H2O+ is still seen in absorption.
  •  
35.
  • Yildiz, U. A., et al. (author)
  • Herschel/HIFI observations of high-J CO lines in the NGC 1333 low-mass star-forming region
  • 2010
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L40-
  • Journal article (peer-reviewed)abstract
    • Herschel/HIFI observations of high-J lines (up to J(u) = 10) of (CO)-C-12, (CO)-C-13 and (CO)-O-18 are presented toward three deeply embedded low-mass protostars, NGC 1333 IRAS 2A, IRAS 4A, and IRAS 4B, obtained as part of the Water In Star-forming regions with Herschel (WISH) key program. The spectrally-resolved HIFI data are complemented by ground-based observations of lower-J CO and isotopologue lines. The (CO)-C-12 10-9 profiles are dominated by broad (FWHM 25-30 km s(-1)) emission. Radiative transfer models are used to constrain the temperature of this shocked gas to 100-200 K. Several CO and (CO)-C-13 line profiles also reveal a medium-broad component (FWHM5-10 km s(-1)), seen prominently in H2O lines. Column densities for both components are presented, providing a reference for determining abundances of other molecules in the same gas. The narrow (CO)-O-18 9-8 lines probe the warmer part of the quiescent envelope. Their intensities require a jump in the CO abundance at an evaporation temperature around 25 K, thus providing new direct evidence for a CO ice evaporation zone around low-mass protostars.
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36.
  • Barnes, A. T., et al. (author)
  • ALMA-IRDC: dense gas mass distribution from cloud to core scales
  • 2021
  • In: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 503:3, s. 4601-4626
  • Journal article (peer-reviewed)abstract
    • Infrared dark clouds (IRDCs) are potential hosts of the elusive early phases of high mass star formation (HMSF). Here, we conduct an in-depth analysis of the fragmentation properties of a sample of 10 IRDCs, which have been highlighted as some of the best candidates to study HMSF within the Milky Way. To do so, we have obtained a set of large mosaics covering these IRDCs with Atacama Large Millimeter/submillimeter Array (ALMA) at Band 3 (or 3 mm). These observations have a high angular resolution (similar to 3 arcsec; similar to 0.05 pc), and high continuum and spectral line sensitivity (similar to 0.15 mJy beam(-1) and similar to 0.2 K per 0.1 km s(-1) channel at the N2H+ (1 - 0) transition). From the dust continuum emission, we identify 96 cores ranging from low to high mass (M = 3.4-50.9M(circle dot)) that are gravitationally bound (alpha(vir) = 0.3-1.3) and which would require magnetic field strengths of B = 0.3-1.0 mG to be in virial equilibrium. We combine these results with a homogenized catalogue of literature cores to recover the hierarchical structure within these clouds over four orders of magnitude in spatial scale (0.01-10 pc). Using supplementary observations at an even higher angular resolution, we find that the smallest fragments (<0.02 pc) within this hierarchy do not currently have the mass and/or the density required to form high-mass stars. None the less, the new ALMA observations presented in this paper have facilitated the identification of 19 (6 quiescent and 13 star-forming) cores that retain >16M(circle dot) without further fragmentation. These high-mass cores contain trans-sonic non-thermal motions, are kinematically sub-virial, and require moderate magnetic field strengths for support against collapse. The identification of these potential sites of HMSF represents a key step in allowing us to test the predictions from high-mass star and cluster formation theories.
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37.
  • Benz, A. O., et al. (author)
  • Water in star-forming regions with Herschel (WISH): VI. Constraints on UV and X-ray irradiation from a survey of hydrides in low- to high-mass young stellar objects
  • 2016
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 590, s. Art. no. A105-
  • Journal article (peer-reviewed)abstract
    • Context. Hydrides are simple compounds containing one or a few hydrogen atoms bonded to a heavier atom. They are fundamental precursor molecules in cosmic chemistry and many hydride ions have become observable in high quality for the first time thanks to the Herschel Space Observatory. Ionized hydrides such as CH+ and OH+ (and also HCO+), which affect the chemistry of molecules such as water, provide complementary information on irradiation by far-UV (FUV) or X-rays and gas temperature. Aims. We explore hydrides of the most abundant heavier elements in an observational survey covering young stellar objects (YSOs) with different mass and evolutionary state. The focus is on hydrides associated with the dense protostellar envelope and outflows, contrary to previous work that focused on hydrides in diffuse foreground clouds. Methods. Twelve YSOs were observed with HIFI on Herschel in six spectral settings providing fully velocity-resolved line profiles as part of the Water in star-forming regions with Herschel (WISH) program. The YSOs include objects of low (Class 0 and I), intermediate, and high mass, with luminosities ranging from 4 L? to 2 × 105 L?. Results. The targeted lines of CH+, OH+, H2O+, C+, and CH are detected mostly in blue-shifted absorption. H3O+ and SH+ are detected in emission and only toward some high-mass objects. The observed line parameters and correlations suggest two different origins related to gas entrained by the outflows and to the circumstellar envelope. The derived column densities correlate with bolometric luminosity and envelope mass for all molecules, best for CH, CH+, and HCO+. The column density ratios of CH+/OH+ are estimated from chemical slab models, assuming that the H2 density is given by the specific density model of each object at the beam radius. For the low-mass YSOs the observed ratio can be reproduced for an FUV flux of 2-400 times the interstellar radiation field (ISRF) at the location of the molecules. In two high-mass objects, the UV flux is 20-200 times the ISRF derived from absorption lines, and 300-600 ISRF using emission lines. Upper limits for the X-ray luminosity can be derived from H3O+ observations for some low-mass objects. Conclusions. If the FUV flux required for low-mass objects originates at the central protostar, a substantial FUV luminosity, up to 1.5 L?, is required. There is no molecular evidence for X-ray induced chemistry in the low-mass objects on the observed scales of a few 1000 AU. For high-mass regions, the FUV flux required to produce the observed molecular ratios is smaller than the unattenuated flux expected from the central object(s) at the Herschel beam radius. This is consistent with an FUV flux reduced by circumstellar extinction or by bloating of the protostar.
  •  
38.
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39.
  • Bulut, N., et al. (author)
  • Gas phase Elemental abundances in Molecular cloudS (GEMS): III. Unlocking the CS chemistry: The CS+O reaction
  • 2021
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 646
  • Journal article (peer-reviewed)abstract
    • Context. Carbon monosulphide (CS) is among the most abundant gas-phase S-bearing molecules in cold dark molecular clouds. It is easily observable with several transitions in the millimeter wavelength range, and has been widely used as a tracer of the gas density in the interstellar medium in our Galaxy and external galaxies. However, chemical models fail to account for the observed CS abundances when assuming the cosmic value for the elemental abundance of sulfur. Aims. The CS+O → CO + S reaction has been proposed as a relevant CS destruction mechanism at low temperatures, and could explain the discrepancy between models and observations. Its reaction rate has been experimentally measured at temperatures of 150-400 K, but the extrapolation to lower temperatures is doubtful. Our goal is to calculate the CS+O reaction rate at temperatures <150 K which are prevailing in the interstellar medium. Methods. We performed ab initio calculations to obtain the three lowest potential energy surfaces (PES) of the CS+O system. These PESs are used to study the reaction dynamics, using several methods (classical, quantum, and semiclassical) to eventually calculate the CS + O thermal reaction rates. In order to check the accuracy of our calculations, we compare the results of our theoretical calculations for T ~ 150-400 K with those obtained in the laboratory. Results. Our detailed theoretical study on the CS+O reaction, which is in agreement with the experimental data obtained at 150-400 K, demonstrates the reliability of our approach. After a careful analysis at lower temperatures, we find that the rate constant at 10 K is negligible, below 10-15 cm s-1, which is consistent with the extrapolation of experimental data using the Arrhenius expression. Conclusions. We use the updated chemical network to model the sulfur chemistry in Taurus Molecular Cloud 1 (TMC 1) based on molecular abundances determined from Gas phase Elemental abundances in Molecular CloudS (GEMS) project observations. In our model, we take into account the expected decrease of the cosmic ray ionization rate, ζH2, along the cloud. The abundance of CS is still overestimated when assuming the cosmic value for the sulfur abundance.
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40.
  • Garatti, A. Caratti o., et al. (author)
  • The GRAVITY young stellar object survey: II. First spatially resolved observations of the CO bandhead emission in a high-mass YSO
  • 2020
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 635
  • Journal article (peer-reviewed)abstract
    • Context. The inner regions of the discs of high-mass young stellar objects (HMYSOs) are still poorly known due to the small angular scales and the high visual extinction involved. Aims. We deploy near-infrared spectro-interferometry to probe the inner gaseous disc in HMYSOs and investigate the origin and physical characteristics of the CO bandhead emission (2.3-2.4 m). Methods. We present the first GRAVITY/VLTI observations at high spectral (R = 4000) and spatial (mas) resolution of the CO overtone transitions in NGC2024 IRS 2. Results. The continuum emission is resolved in all baselines and is slightly asymmetric, displaying small closure phases (8). Our best ellipsoid model provides a disc inclination of 34 1, a disc major axis position angle (PA) of 166 1, and a disc diameter of 3:99 0:09 mas (or 1.69 0.04 au, at a distance of 423 pc). The small closure phase signals in the continuum are modelled with a skewed rim, originating from a pure inclination effect. For the first time, our observations spatially and spectrally resolve the first four CO bandheads. Changes in visibility, as well as differential and closure phases across the bandheads are detected. Both the size and geometry of the CO-emitting region are determined by fitting a bidimensional Gaussian to the continuum-compensated CO bandhead visibilities. The CO-emitting region has a diameter of 2.740:08 0:07 mas (1.16 0.03 au), and is located in the inner gaseous disc, well within the dusty rim, with inclination and PA matching the dusty disc geometry, which indicates that both dusty and gaseous discs are coplanar. Physical and dynamical gas conditions are inferred by modelling the CO spectrum. Finally, we derive a direct measurement of the stellar mass of M 14:7 M by combining our interferometric and spectral modelling results.
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41.
  • Liseau, René, 1949, et al. (author)
  • Multi-line detection of O2 toward rho Ophiuchi A
  • 2012
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 541
  • Journal article (peer-reviewed)abstract
    • Context. Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict relatively high levels of molecular oxygen, O-2, and water, H2O. These high abundances imply high cooling rates, leading to relatively short timescales for the evolution of gravitationally unstable dense cores, forming stars and planets. Contrary to expectations, the dedicated space missions SWAS and Odin typically found only very small amounts of water vapour and essentially no O-2 in the dense star-forming interstellar medium. Aims. Only toward rho OphA did Odin detect a very weak line of O-2 at 119 GHz in a beam of size 10 arcmin. The line emission of related molecules changes on angular scales of the order of some tens of arcseconds, requiring a larger telescope aperture such as that of the Herschel Space Observatory to resolve the O-2 emission and pinpoint its origin. Methods. We use the Heterodyne Instrument for the Far Infrared (HIFI) aboard Herschel to obtain high resolution O-2 spectra toward selected positions in the rho Oph A core. These data are analysed using standard techniques for O2 excitation and compared to recent PDR-like chemical cloud models. Results. The N-J = 3(3)-1(2) line at 487.2 GHz is clearly detected toward all three observed positions in the rho Oph A core. In addition, an oversampled map of the 5(4)-3(4) transition at 773.8 GHz reveals the detection of the line in only half of the observed area. On the basis of their ratios, the temperature of the O-2 emitting gas appears to vary quite substantially, with warm gas (greater than or similar to 50 K) being adjacent to a much colder region, of temperatures lower than 30 K. Conclusions. The exploited models predict that the O-2 column densities are sensitive to the prevailing dust temperatures, but rather insensitive to the temperatures of the gas. In agreement with these models, the observationally determined O-2 column densities do not seem to depend strongly on the derived gas temperatures, but fall into the range N(O-2) = 3 to greater than or similar to 6 x 10(15) cm(-2). Beam-averaged O-2 abundances are about 5 x 10(-8) relative to H-2. Combining the HIFI data with earlier Odin observations yields a source size at 119 GHz in the range of 4 to 5 arcmin, encompassing the entire rho Oph A core. We speculate that one of the reasons for the generally very low detection rate of O-2 is the short period of time during which O-2 molecules are reasonably abundant in molecular clouds.
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42.
  • Rodríguez-Baras, M., et al. (author)
  • Gas phase Elemental abundances in Molecular cloudS (GEMS): IV. Observational results and statistical trends
  • 2021
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 648
  • Journal article (peer-reviewed)abstract
    • Gas phase Elemental abundances in Molecular CloudS (GEMS) is an IRAM 30 m Large Program designed to provide estimates of the S, C, N, and O depletions and gas ionization degree, X(e-), in a selected set of star-forming filaments of Taurus, Perseus, and Orion. Our immediate goal is to build up a complete and large database of molecular abundances that can serve as an observational basis for estimating X(e-) and the C, O, N, and S depletions through chemical modeling. We observed and derived the abundances of 14 species (13CO, C18O, HCO+, H13CO+, HC18O+, HCN, H13CN, HNC, HCS+, CS, SO, 34SO, H2S, and OCS) in 244 positions, covering the AV ~3 to ~100 mag, n(H2) ~ a few 103 to 106 cm-3, and Tk ~10 to ~30 K ranges in these clouds, and avoiding protostars, HII regions, and bipolar outflows. A statistical analysis is carried out in order to identify general trends between different species and with physical parameters. Relations between molecules reveal strong linear correlations which define three different families of species: (1) 13CO and C18O isotopologs; (2) H13CO+, HC18O+, H13 CN, and HNC; and (3) the S-bearing molecules. The abundances of the CO isotopologs increase with the gas kinetic temperature until TK ~ 15 K. For higher temperatures, the abundance remains constant with a scatter of a factor of ~3. The abundances of H13 CO+, HC18 O+, H13 CN, and HNC are well correlated with each other, and all of them decrease with molecular hydrogen density, following the law ∝ n(H2)-0.8  ±  0.2. The abundances of S-bearing species also decrease with molecular hydrogen density at a rate of (S-bearing/H)gas ∝ n(H2)-0.6  ±  0.1. The abundances of molecules belonging to groups 2 and 3 do not present any clear trend with gas temperature. At scales of molecular clouds, the C18O abundance is the quantity that better correlates with the cloud mass. We discuss the utility of the 13CO/C18O, HCO+/H13CO+, and H13 CO+/H13CN abundance ratios as chemical diagnostics of star formation in external galaxies.
  •  
43.
  • Barnes, Ashley T., et al. (author)
  • Mother of dragons: A massive, quiescent core in the dragon cloud (IRDC G028.37+00.07)
  • 2023
  • In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 675
  • Journal article (peer-reviewed)abstract
    • Context. Core accretion models of massive star formation require the existence of massive, starless cores within molecular clouds. Yet, only a small number of candidates for such truly massive, monolithic cores are currently known. Aims. Here we analyse a massive core in the well-studied infrared-dark cloud (IRDC) called the dragon clouda'(also known as G028.37+00.07 or Cloud Ca). This core (C2c1) sits at the end of a chain of a roughly equally spaced actively star-forming cores near the center of the IRDC. Methods. We present new high-angular-resolution 1 mm ALMA dust continuum and molecular line observations of the massive core. Results. The high-angular-resolution observations show that this region fragments into two cores, C2c1a and C2c1b, which retain significant background-subtracted masses of 23 M· and 2 M· (31 M· and 6 M· without background subtraction), respectively. The cores do not appear to fragment further on the scales of our highest-angular-resolution images (0.2 , 0.005 pc ∼ 1000 AU). We find that these cores are very dense (nH2 > 106 cm-3) and have only trans-sonic non-thermal motions ( 3s ∼ 1). Together the mass, density, and internal motions imply a virial parameter of
  •  
44.
  • Börjesson, Mats, 1965, et al. (author)
  • Brief recommendations for participation in leisure time or competitive sports in athletes-patients with coronary artery disease: Summary of a Position Statement from the Sports Cardiology Section of the European Association of Preventive Cardiology (EAPC)
  • 2020
  • In: European Journal of Preventive Cardiology. - : Oxford University Press (OUP). - 2047-4873 .- 2047-4881. ; 27:7, s. 770-776
  • Journal article (peer-reviewed)abstract
    • This paper presents a brief summary of the recommendations from the Sports Cardiology section of the European Association of Preventive Cardiology (EAPC) on sports-participation in patients with coronary artery disease, coronary artery anomalies or spontaneous dissection of the coronary arteries, all entities being associated with myocardial ischaemia.1 Given the wealth of evidence supporting the benefits of exercise for primary and secondary prevention of coronary artery disease, individuals should be restricted from competitive sport only when a substantial risk of adverse event or disease progression is present. These recommendations aim to encourage regular physical activity including participation in sports and, with reasonable precaution, ensure a high level of safety for all individuals with coronary artery disease. The present document is based on available current evidence, but in most instances because of lack of evidence, also on clinical experience and expert opinion.
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45.
  •  
46.
  • Coppin, K. E. K., et al. (author)
  • Herschel-PACS observations of [O I]63 μm towards submillimetre galaxies at z~1
  • 2012
  • In: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 427:1, s. 520-532
  • Journal article (peer-reviewed)abstract
    • We present Herschel-PACS spectroscopy of the [O I]63 μm far-infrared cooling line from a sample of six unlensed and spectroscopically confirmed 870 μm selected submillimetre (submm) galaxies (SMGs) at 1.1
  •  
47.
  • Fuente, A., et al. (author)
  • Gas phase Elemental abundances in Molecular cloudS (GEMS) I. The prototypical dark cloud TMC 1
  • 2019
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 624
  • Journal article (peer-reviewed)abstract
    • GEMS is an IRAM 30 m Large Program whose aim is determining the elemental depletions and the ionization fraction in a set of prototypical star-forming regions. This paper presents the first results from the prototypical dark cloud Taurus molecular cloud (TMC) 1. Extensive millimeter observations have been carried out with the IRAM 30 m telescope (3 and 2mm) and the 40 m Yebes telescope (1.3 cm and 7 mm) to determine the fractional abundances of CO, HCO+, HCN, CS, SO, HCS+, and N2H+ in three cuts which intersect the dense filament at the well-known positions TMC 1-CP, TMC 1-NH3, and TMC 1-C, covering a visual extinction range from A(v) similar to 3 to similar to 20 mag. Two phases with differentiated chemistry can be distinguished: (i) the translucent envelope with molecular hydrogen densities of 1-5 x 10(3) cm(-3); and (ii) the dense phase, located at A(v) > 10 mag, with molecular hydrogen densities >10(4) cm(-3). Observations and modeling show that the gas phase abundances of C and O progressively decrease along the C+/C/CO transition zone (A(v) similar to 3 mag) where C/H similar to 8 x 10(-5) and C/O similar to 0.8-1, until the beginning of the dense phase at A(v) similar to 10 mag. This is consistent with the grain temperatures being below the CO evaporation temperature in this region. In the case of sulfur, a strong depletion should occur before the translucent phase where we estimate an S/H similar to (0.4-2.2) x 10(-6), an abundance similar to 7-40 times lower than the solar value. A second strong depletion must be present during the formation of the thick icy mantles to achieve the values of S/H measured in the dense cold cores (S/H similar to 8 x 10(-8)). Based on our chemical modeling, we constrain the value of zeta(H2) to similar to(0.5-1.8) x 10(-16) s(-1) in the translucent cloud.
  •  
48.
  • Garcia-Lopez, R., et al. (author)
  • The GRAVITY young stellar object survey XII. The hot gas disk component in Herbig Ae/Be stars
  • 2024
  • In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 684
  • Journal article (peer-reviewed)abstract
    • Context. The region of protoplanetary disks closest to a star (within 1–2 au) is shaped by a number of different processes, from accretion of the disk material onto the central star to ejection in the form of winds and jets. Optical and near-IR emission lines are potentially good tracers of inner disk processes if very high spatial and/or spectral resolution are achieved. Aims. In this paper, we exploit the capabilities of the VLTI-GRAVITY near-IR interferometer to determine the location and kinematics of the hydrogen emission line Brγ. Methods. We present VLTI-GRAVITY observations of the Brγ line for a sample of 26 stars of intermediate mass (HAEBE), the largest sample so far analysed with near-IR interferometry. Results. The Brγ line was detected in 17 objects. The emission is very compact (in most cases only marginally resolved), with a size of 10–30 R∗(1–5 mas). About half of the total flux comes from even smaller regions, which are unresolved in our data. For eight objects, it was possible to determine the position angle (PA) of the line-emitting region, which is generally in agreement with that of the inner-dusty disk emitting the K-band continuum. The position-velocity pattern of the Brγ line-emitting region of the sampled objects is roughly consistent with Keplerian rotation. The exception is HD 45677, which shows more extended emission and more complex kinematics. The most likely scenario for the Brγ origin is that the emission comes from an MHD wind launched very close to the central star, in a region well within the dust sublimation radius. An origin in the bound gas layer at the disk surface cannot be ruled out, while accreting matter provides only a minor fraction of the total flux. Conclusions. These results show the potential of near-IR spectro-interferometry to study line emission in young stellar objects.
  •  
49.
  • Goldsmith, Paul F., et al. (author)
  • Herschel Measurements of Molecular Oxygen in Orion
  • 2011
  • In: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 737:2, s. 96 (1-17)
  • Journal article (peer-reviewed)abstract
    • We report observations of three rotational transitions of molecular oxygen (O2) in emission from the H2 Peak 1 position of vibrationally excited molecular hydrogen in Orion. We observed the 487 GHz, 774 GHz, and 1121 GHz lines using the Heterodyne Instrument for the Far Infrared on the Herschel Space Observatory, having velocities of 11 km s–1 to 12 km s–1 and widths of 3 km s–1. The beam-averaged column density is N(O2) = 6.5 × 1016 cm–2, and assuming that the source has an equal beam-filling factor for all transitions (beam widths 44, 28, and 19''), the relative line intensities imply a kinetic temperature between 65 K and 120 K. The fractional abundance of O2 relative to H2 is (0.3-7.3) × 10–6. The unusual velocity suggests an association with a ~5'' diameter source, denoted Peak A, the Western Clump, or MF4. The mass of this source is ~10 Msun and the dust temperature is ≥150 K. Our preferred explanation of the enhanced O2 abundance is that dust grains in this region are sufficiently warm (T ≥ 100 K) to desorb water ice and thus keep a significant fraction of elemental oxygen in the gas phase, with a significant fraction as O2. For this small source, the line ratios require a temperature ≥180 K. The inferred O2 column density sime5 × 1018 cm–2 can be produced in Peak A, having N(H2) sime 4 × 1024 cm–2. An alternative mechanism is a low-velocity (10-15 km s–1) C-shock, which can produce N(O2) up to 1017 cm–2.
  •  
50.
  • Mottram, J. C., et al. (author)
  • Water in star-forming regions with Herschel (WISH)
  • 2014
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 572
  • Journal article (peer-reviewed)abstract
    • Context. Outflows are an important part of the star formation process as both the result of ongoing active accretion and one of the main sources of mechanical feedback on small scales. Water is the ideal tracer of these effects because it is present in high abundance for the conditions expected in various parts of the protostar, particularly the outflow. Aims. We constrain and quantify the physical conditions probed by water in the outflow-jet system for Class 0 and I sources. Methods. We present velocity-resolved Herschel HIFI spectra of multiple water-transitions observed towards 29 nearby Class 0/I protostars as part of the WISH guaranteed time key programme. The lines are decomposed into different Gaussian components, with each component related to one of three parts of the protostellar system; quiescent envelope, cavity shock and spot shocks in the jet and at the base of the outflow. We then use non-LTE radex models to constrain the excitation conditions present in the two outflow-related components. Results. Water emission at the source position is optically thick but effectively thin, with line ratios that do not vary with velocity, in contrast to CO. The physical conditions of the cavity and spot shocks are similar, with post-shock H-2 densities of order 10(5) -10(8) cm(-3) and H2O column densities of order 10(16) -10(18) cm(-2). H2O emission originates in compact emitting regions: for the spot shocks these correspond to point sources with radii of order 10-200 AU, while for the cavity shocks these come from a thin layer along the outflow cavity wall with thickness of order 1-30 AU. Conclusions. Water emission at the source position traces two distinct kinematic components in the outflow; J shocks at the base of the outflow or in the jet, and C shocks in a thin layer in the cavity wall. The similarity of the physical conditions is in contrast to off-source determinations which show similar densities but lower column densities and larger filling factors. We propose that this is due to the differences in shock properties and geometry between these positions. Class I sources have similar excitation conditions to Class 0 sources, but generally smaller line-widths and emitting region sizes. We suggest that it is the velocity of the wind driving the outflow, rather than the decrease in envelope density or mass, that is the cause of the decrease in H2O intensity between Class 0 and I sources.
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