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Sökning: WFRF:(Caselli P.)

  • Resultat 1-10 av 70
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3.
  • Garatti, A. Caratti o., et al. (författare)
  • The GRAVITY young stellar object survey: II. First spatially resolved observations of the CO bandhead emission in a high-mass YSO
  • 2020
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 635
  • Tidskriftsartikel (refereegranskat)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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4.
  • Lis, D. C., et al. (författare)
  • Herschel/HIFI discovery of interstellar chloronium (H2Cl+)
  • 2010
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 521:1, s. L9+-
  • 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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5.
  • Lefloch, B., et al. (författare)
  • The CHESS spectral survey of star forming regions : Peering into the protostellar shock L1157-B1. II. Shock dynamics
  • 2010
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 518, s. L113-
  • 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.
  • Vastel, C., et al. (författare)
  • Ortho-to-para ratio of interstellar heavy water
  • 2010
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 521:1, s. Article Number: L31 -
  • 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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7.
  • Ceccarelli, C., et al. (författare)
  • Herschel spectral surveys of star- forming regions Overview of the 555-636 GHz range
  • 2010
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 521, s. L22-
  • 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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8.
  • Codella, C., et al. (författare)
  • The CHESS spectral survey of star forming regions : Peering into the protostellar shock L1157-B1. I. Shock chemical complexity
  • 2010
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 518, s. L112-
  • 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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9.
  • Koutoulaki, M., et al. (författare)
  • The GRAVITY young stellar object survey: IV. The CO overtone emission in 51 Oph at sub-au scales
  • 2021
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 645
  • Tidskriftsartikel (refereegranskat)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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10.
  • Marseille, M. G., et al. (författare)
  • Water abundances in high-mass protostellar envelopes : Herschel observations with HIFI
  • 2010
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 521, s. L32-
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims: We derive the dense core structure and the water abundance in four massive star-forming regions in the hope of understanding the earliest stages of massive star formation. Methods: We present Herschel/HIFI observations of the para-H2O 111-000 and 202-111 and the para-H_218O 111-000 transitions. The envelope contribution to the line profiles is separated from contributions by outflows and foreground clouds. The envelope contribution is modeled with Monte-Carlo radiative transfer codes for dust and molecular lines (MC3D and RATRAN), and the water abundance and the turbulent velocity width as free parameters. Results: While the outflows are mostly seen in emission in high-J lines, envelopes are seen in absorption in ground-state lines, which are almost saturated. The derived water abundances range from 5×10-10 to 4×10-8 in the outer envelopes. We detect cold clouds surrounding the protostar envelope, thanks to the very high quality of the Herschel/HIFI data and the unique ability of water to probe them. Several foreground clouds are also detected along the line of sight. Conclusions: The low H2O abundances in massive dense cores are in accordance with the expectation that high densities and low temperatures lead to freeze-out of water on dust grains. The spread in abundance values is not clearly linked to physical properties of the sources. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation of NASA.Appendix (pages 6 to 7) is only available in electronic form at http://www.aanda.org
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