C. Vastel

French National Centre for Scientific Research, Lutetia Parisorum, Île-de-France, France

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Publications (87)236.83 Total impact

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    ABSTRACT: Formamide (NH2CHO) has been proposed as a pre-biotic precursor with a key role in the emergence of life on Earth. While this molecule has been observed in space, most of its detections correspond to high-mass star-forming regions. Motivated by this lack of investigation in the low-mass regime, we searched for formamide, as well as isocyanic acid (HNCO), in 10 low- and intermediate-mass pre-stellar and protostellar objects. The present work is part of the IRAM Large Programme ASAI (Astrochemical Surveys At IRAM), which makes use of unbiased broadband spectral surveys at millimetre wavelengths. We detected HNCO in all the sources and NH2CHO in five of them. We derived their abundances and analysed them together with those reported in the literature for high-mass sources. For those sources with formamide detection, we found a tight and almost linear correlation between HNCO and NH2CHO abundances, with their ratio being roughly constant -between 3 and 10- across 6 orders of magnitude in luminosity. This suggests the two species are chemically related. The sources without formamide detection, which are also the coldest and devoid of hot corinos, fall well off the correlation, displaying a much larger amount of HNCO relative to NH2CHO. Our results suggest that, while HNCO can be formed in the gas phase during the cold stages of star formation, NH2CHO forms most efficiently on the mantles of dust grains at these temperatures, where it remains frozen until the temperature rises enough to sublimate the icy grain mantles. We propose hydrogenation of HNCO as a likely formation route leading to NH2CHO.
    Monthly Notices of the Royal Astronomical Society 02/2015; 449(3). DOI:10.1093/mnras/stv377 · 5.23 Impact Factor
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    ABSTRACT: IRAS 16293-2422 is a well-studied low-mass protostar characterized by a strong level of deuterium fractionation. In the line of sight of the protostellar envelope, an additional absorption layer, rich in singly and doubly deuterated water has been discovered by a detailed multiline analysis of HDO. To model the chemistry in this source, the gas–grain chemical code Nautilus has been used with an extended deuterium network. For the protostellar envelope, we solve the chemical reaction network in infalling fluid parcels in a protostellar core model. For the foreground cloud, we explored several physical conditions (density, cosmic ionization rate, C/O ratio). The main results of the paper are that gas-phase abundances of H2O, HDO and D2O observed in the inner regions of IRAS16293-2422 are lower than those predicted by a 1D dynamical/chemical (hot corino) model in which the ices are fully evaporated. The abundance in the outer part of the envelope presents chaotic profiles due to adsorption/evaporation competition, very different from the constant abundance assumed for the analysis of the observations. We also found that the large abundances of gas-phase H2O, HDO and D2O observed in the absorption layer are more likely explained by exothermic surface reactions rather than photodesorption processes.
    Monthly Notices of the Royal Astronomical Society 10/2014; 445(3). DOI:10.1093/mnras/stu1920 · 5.23 Impact Factor
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    ABSTRACT: While recent studies of the solar-mass protostar IRAS 16293-2422 have focused on its inner arcsecond, the wealth of Herschel/Heterodyne Instrument for the Far-Infrared (HIFI) data has shown that the structure of the outer envelope and of the transition region to the more diffuse interstellar medium is not clearly constrained. We use rotational ground-state transitions of CH (methylidyne), as a tracer of the lower density envelope. Assuming local thermodynamic equilibrium, we perform a χ2 minimization of the high spectral resolution HIFI observations of the CH transitions at ̃532 and ̃536 GHz in order to derive column densities in the envelope and in the foreground cloud. We obtain column densities of (7.7 ± 0.2) × 1013 cm-2 and (1.5 ± 0.3) × 1013 cm-2, respectively. The chemical modelling predicts column densities of (0.5 - 2) × 1013 cm-2 in the envelope (depending on the cosmic ray ionization rate), and 5 × 1011 to 2.5 × 1014 cm-2 in the foreground cloud (depending on time). Both observed abundances are reproduced by the model at a satisfactory level. The constraints set by these observations on the physical conditions in the foreground cloud are however weak. Furthermore, the CH abundance in the envelope is strongly affected by the rate coefficient of the reaction H+CH→C+H2; further investigation of its value at low temperature would be necessary to facilitate the comparison between the model and the observations.
    Monthly Notices of the Royal Astronomical Society 06/2014; 441(3). DOI:10.1093/mnras/stu700 · 5.23 Impact Factor
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    ABSTRACT: In the framework of the Herschel/PRISMAS guaranteed time key program, the line of sight to the distant ultracompact H ii region W51e2 has been observed using several selected molecular species. Most of the detected absorption features are not associated with the background high-mass star-forming region and probe the diffuse matter along the line of sight. We present here the detection of an additional narrow absorption feature at ~70 km s-1 in the observed spectra of HDO, NH3 and C3. The 70 km s-1 feature is not uniquely identifiable with the dynamic components (the main cloud and the large-scale foreground filament) so-far identified toward this region. The narrow absorption feature is similar to the one found toward low-mass protostars, which is characteristic of the presence of a cold external envelope. The far-infrared spectroscopic data were combined with existing ground-based observations of 12CO, 13CO, CCH, CN, and C3H2 to characterize the 70 km s-1 component. Using a non-LTE analysis of multiple transitions of NH3 and CN, we estimated the density (n(H2) ~ (1-5) × 10^5 cm-3) and temperature (10-30 K) for this narrow feature. We used a gas-grain warm-up based chemical model with physical parameters derived from the NH3 data to explain the observed abundances of the different chemical species. We propose that the 70 km s-1 narrow feature arises in a dense and cold clump that probably undergoes collapse to form a low-mass protostar, formed on the trailing side of the high-velocity filament, which is thought to be interacting with the W51 main cloud. While the fortuitous coincidence of the dense clump along the line of sight with the continuum-bright W51e2 compact H ii region has contributed to its nondetection in the continuum images, this same attribute makes it an appropriate source for absorption studies and in particular for ice studies of star-forming regions. Based on data acquired with Herschel and IRAM observatories. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
    Astronomy and Astrophysics 06/2014; 566:A61. DOI:10.1051/0004-6361/201323131 · 4.48 Impact Factor
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    ABSTRACT: While recent studies of the solar-mass protostar IRAS16293-2422 have focused on its inner arcsecond, the wealth of Herschel/HIFI data has shown that the structure of the outer envelope and of the transition region to the more diffuse ISM is not clearly constrained. We use rotational ground-state transitions of CH (methylidyne), as a tracer of the lower-density envelope. Assuming LTE, we perform a $\chi^2$ minimization of the high spectral resolution HIFI observations of the CH transitions at ~532 and ~536 GHz in order to derive column densities in the envelope and in the foreground cloud. We obtain column densities of (7.7$\pm$0.2)$\times10^{13}$ cm$^{-2}$ and (1.5$\pm$0.3)$\times10^{13}$ cm$^{-2}$, respectively. The chemical modeling predicts column densities of (0.5-2)$\times10^{13}$ cm$^{-2}$ in the envelope (depending on the cosmic-ray ionization rate), and 5$\times10^{11}$ to 2.5$\times10^{14}$ cm$^{-2}$ in the foreground cloud (depending on time). Both observed abundances are reproduced by the model at a satisfactory level. The constraints set by these observations on the physical conditions in the foreground cloud are however weak. Furthermore, the CH abundance in the envelope is strongly affected by the rate coefficient of the reaction H+CH$\rightarrow$C+H$_2$ ; further investigation of its value at low temperature would be necessary to facilitate the comparison between the model and the observations.
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    ABSTRACT: Aims. The aim of this paper is to study deuterated water in the solar-type protostars NGC1333 IRAS4A and IRAS4B, compare their HDO abundance distribution with other star-forming regions and constrain their HDO/H2O ratios. Methods. Using the Herschel/HIFI instrument as well as ground-based telescopes, we observed several HDO lines covering a large excitation range (Eup/k=22-168 K) towards these protostars and an outflow position. Non-LTE radiative transfer codes were then used to determine the HDO abundance profiles in these sources. Results. The HDO fundamental line profiles show a very broad component, tracing the molecular outflows, in addition to a narrower emission component as well as a narrow absorbing component. In the protostellar envelope of NGC1333 IRAS4A, the HDO inner (T>100 K) and outer (T<100 K) abundances with respect to H2 are estimated at 7.5x10^{-9} and 1.2x10^{-11} respectively, whereas, in NGC1333 IRAS4B, they are 1.0x10^{-8} and 1.2x10^{-10} respectively. Similarly to the low-mass protostar IRAS16293-2422, an absorbing outer layer with an enhanced abundance of deuterated water is required to reproduce the absorbing components seen in the fundamental lines at 465 and 894 GHz in both sources. This water-rich layer is probably extended enough to encompass the two sources as well as parts of the outflows. In the outflows emanating from NGC1333 IRAS4A, the HDO column density is estimated at about (2-4)x10^{13} cm^{-2}, leading to an abundance of about (0.7-1.9)x10^{-9}. An HDO/H2O ratio between 7x10^{-4} and 9x10^{-2} is derived in the outflows. In the warm inner regions of these two sources, we estimate the HDO/H2O ratios at about 1x10^{-4}-4x10^{-3}. This ratio seems higher (a few %) in the cold envelope of IRAS4A, whose possible origin is discussed in relation to formation processes of HDO and H2O.
    Astronomy and Astrophysics 10/2013; 560. DOI:10.1051/0004-6361/201322400 · 4.48 Impact Factor
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    ABSTRACT: The tables present the experimental frequencies of rotational transitions for the symmetric and asymmetric conformers of mono-deuterated dimethylether up to 1THz and the predicted frequencies up to 1.2THz. (4 data files).
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    ABSTRACT: Context. Dimethyl ether is one of the most abundant complex organic molecules (COMs) in star-forming regions. Like other COMs, its formation process is not yet clearly established, but the relative abundances of its deuterated isotopomers may provide crucial hints in studying its chemistry and tracing the source history. The mono-deuterated species (CH2DOCH3) is still a relatively light molecule compared to other COMs. Its spectrum is the most intense in the THz domain in the 100-150 K temperature regime, tracing the inner parts of the low-mass star-forming region. Therefore, it is necessary to measure and assign its transitions in this range in order to be able to compute accurate predictions required by astronomical observations, in particular with the telescope operating in the submm range, such as ALMA. Aims. We present the analysis of mono-deuterated dimethyl ether in its ground-vibrational state, based on an effective Hamiltonian for an asymmetric rotor molecules with internal rotors. The analysis covers the frequency range 150-990 GHz. Methods. The laboratory rotational spectrum of this species was measured with a submillimeter spectrometer (50-990 GHz) using solid-state sources. For the astronomical detection, we used the IRAM 30 m telescope to observe a total range of 27 GHz, in 4 frequency bands from 100 GHz to 219 GHz. Results. New sets of spectroscopic parameters have been determined by a least squares fit with the ERHAM code for both conformers. These parameters have permitted the first identification in space of both mono-deuterated DME isomers via detection of twenty transitions in the solar-type protostar IRAS 16293-2422 with the IRAM 30 m telescope. The DME deuteration ratio in this source appears as high as observed for methanol and formaldehyde, two species known to play an important role in the COMs formation history.
    Astronomy and Astrophysics 04/2013; 552:117-. DOI:10.1051/0004-6361/201220826 · 4.48 Impact Factor
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    ABSTRACT: The H3+ ion plays a key role in the chemistry of dense interstellar gas clouds where stars and planets are forming. The low temperatures and high extinctions of such clouds make direct observations of H3+ impossible, but lead to large abundances of H2D+ and D2H+, which are very useful probes of the early stages of star and planet formation. The ground-state rotational ortho-D2H+ 111-000 transition at 1476.6 GHz in the prestellar core 16293E has been searched for with the Herschel/HIFI instrument, within the CHESS (Chemical HErschel Surveys of Star forming regions) Key Program. The line has not been detected at the 21 mK km/s level (3 sigma integrated line intensity). We used the ortho-H2D+ 110-111 transition and para-D2H+ 110-101 transition detected in this source to determine an upper limit on the ortho-to-para D2H+ ratio as well as the para-D2H+/ortho-H2D+ ratio from a non-LTE analysis. The comparison between our chemical modeling and the observations suggests that the CO depletion must be high (larger than 100), with a density between 5e5 and 1e6 cm-3. Also the upper limit on the ortho-D2H+ line is consistent with a low gas temperature (~ 11 K) with a ortho-to-para ratio of 6 to 9, i.e. 2 to 3 times higher than the value estimated from the chemical modeling, making it impossible to detect this high frequency transition with the present state of the art receivers.
    Astronomy and Astrophysics 10/2012; 547. DOI:10.1051/0004-6361/201219616 · 4.48 Impact Factor
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    ABSTRACT: The ground-state rotational ortho-D2H+(1,1,1-0,0,0) transition at 1476.6GHz in the prestellar core 16293E has been searched for with the Herschel/HIFI instrument, within the CHESS (Chemical HErschel Surveys of Star forming regions) Key Program. The line has not been detected at the 21mK.km/s level (3 sigma integrated line intensity). We used the ortho-H2D+ 110-111 transition and para-D2H+ 110-101 transition detected in this source to determine an upper limit on the ortho-to-para D2H+ ratio as well as the para-D2H+/ortho-H2D+ ratio from a non-LTE analysis. We then compared our chemical modeling with the observations in order to estimate the CO depletion as well as the H2 density and kinetic temperature at the position observed. The chemical network is provided in the kida.dat file. (1 data file).
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    ABSTRACT: We present the results of the HIFI observations of the pre-stellar cores L1544 and 16293E, as part of the CHESS Key Program. Pre-stellar cores, being cold and dense, have a chemistry dominated by the freeze-out of molecular species and enhanced deuteration, both phenomena being linked. L1544 is a well-studied prototypical pre-stellar core and 16293E is one of the very few source where the species para-D_2H^+ and ortho-H_2D^+ were both detected. These ions play a key role in the deuteration process. We report here the detection of HDO and ND in 16293E (together with their hydrogenated counterparts H_2O and NH). This is the first time these species have been observed in pre-stellar cores. Both species represent particularly interesting cases since they have completely different behaviours with respect to freeze-out. In L1544, we report the detection of high critical density transitions of NH_2D, tracing the very inner parts of the core. We discuss the implications of the species' abundances and deuterium fractionation on our understanding of pre-stellar core chemistry.
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    ABSTRACT: Context. Water is a primordial species in the emergence of life, and comets may have brought a large fraction to Earth to form the oceans. To understand the evolution of water from the first stages of star formation to the formation of planets and comets, the HDO/H2O ratio is a powerful diagnostic. Aims: Our aim is to determine precisely the abundance distribution of HDO towards the low-mass protostar IRAS 16293-2422 and learn more about the water formation mechanisms by determining the HDO/H2O abundance ratio. Methods: A spectral survey of the source IRAS 16293-2422 was carried out in the framework of the CHESS (Chemical Herschel Surveys of Star forming regions) Herschel key program with the HIFI (Heterodyne Instrument for the Far-Infrared) instrument, allowing detection of numerous HDO lines. Other transitions have been observed previously with ground-based telescopes. The spherical Monte Carlo radiative transfer code RATRAN was used to reproduce the observed line profiles of HDO by assuming an abundance jump. To determine the H2O abundance throughout the envelope, a similar study was made of the H218O observed lines, as the H2O main isotope lines are contaminated by the outflows. Results: It is the first time that so many HDO and H218O transitions have been detected towards the same source with high spectral resolution. We derive an inner HDO abundance (T ≥ 100 K) of about 1.7 × 10-7 and an outer HDO abundance (T < 100 K) of about 8 × 10-11. To reproduce the HDO absorption lines observed at 894 and 465 GHz, it is necessary to add an absorbing layer in front of the envelope. It may correspond to a water-rich layer created by the photodesorption of the ices at the edges of the molecular cloud. At a 3σ uncertainty, the HDO/H2O ratio is 1.4-5.8% in the hot corino, whereas it is 0.2-2.2% in the outer envelope. It is estimated at ~4.8% in the added absorbing layer. Conclusions: Although it is clearly higher than the cosmic D/H abundance, the HDO/H2O ratio remains lower than the D/H ratio derived for other deuterated molecules observed in the same source. The similarity of the ratios derived in the hot corino and in the added absorbing layer suggests that water formed before the gravitational collapse of the protostar, contrary to formaldehyde and methanol, which formed later once the CO molecules had depleted on the grains. Based on Herschel/HIFI observations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
    Astronomy and Astrophysics 03/2012; 539:132-. DOI:10.1051/0004-6361/201117627 · 4.48 Impact Factor
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    ABSTRACT: Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict relatively high levels of molecular oxygen, O2, and water, H2O. Contrary to expectation, the space missions SWAS and Odin found only very small amounts of water vapour and essentially no O2 in the dense star-forming interstellar medium. Only toward rho Oph A did Odin detect a weak line of O2 at 119 GHz in a beam size of 10 arcmin. A larger telescope aperture such as that of the Herschel Space Observatory is required to resolve the O2 emission and to pinpoint its origin. We use the Heterodyne Instrument for the Far Infrared aboard Herschel to obtain high resolution O2 spectra toward selected positions in rho Oph A. These data are analysed using standard techniques for O2 excitation and compared to recent PDR-like chemical cloud models. The 487.2GHz line was clearly detected toward all three observed positions in rho Oph A. In addition, an oversampled map of the 773.8GHz transition revealed the detection of the line in only half of the observed area. Based on their ratios, the temperature of the O2 emitting gas appears to vary quite substantially, with warm gas (> 50 K) adjacent to a much colder region, where temperatures are below 30 K. The exploited models predict O2 column densities to be sensitive to the prevailing dust temperatures, but rather insensitive to the temperatures of the gas. In agreement with these model, the observationally determined O2 column densities seem not to depend strongly on the derived gas temperatures, but fall into the range N(O2) = (3 to >6)e15/cm^2. Beam averaged O2 abundances are about 5e-8 relative to H2. Combining the HIFI data with earlier Odin observations yields a source size at 119 GHz of about 4 - 5 arcmin, encompassing the entire rho Oph A core.
    Astronomy and Astrophysics 02/2012; 541:73. DOI:10.1051/0004-6361/201118575 · 4.48 Impact Factor
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    ABSTRACT: VizieR On-line Data Catalog: J/A+A/532/A23. Originally published in: 2011A&A...532A..23C
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    ABSTRACT: Aims. In this paper the calibration and in-orbit performance of the Heterodyne Instrument for the Far-Infrared (HIFI) is described. Methods. The calibration of HIFI is based on a combination of ground and in-flight tests. Dedicated ground tests to determine those instrument parameters that can only be measured accurately using controlled laboratory stimuli were carried out in the instrument level test (ILT) campaign. Special in-flight tests during the commissioning phase (CoP) and performance verification (PV) allowed the determination of the remaining instrument parameters. The various instrument observing modes, as specified in astronomical observation templates (AOTs), were validated in parallel during PV by observing selected celestial sources. Results. The initial calibration and in-orbit performance of HIFI has been established. A first estimate of the calibration budget is given. The overall in-flight instrument performance agrees with the original specification. Issues remain at only a few frequencies.
    Astronomy and Astrophysics 01/2012; 537:A17. DOI:10.1051/0004-6361/201015120 · 4.48 Impact Factor
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    ABSTRACT: While unbiased surveys observable from ground-based telescopes have previously been obtained towards several high mass protostars, very little exists on low mass protostars. To fill up this gap, we carried out a complete spectral survey of the bands at 3, 2, 1 and 0.8 mm towards the solar type protostar IRAS16293-2422. The observations covered about 200\,GHz and were obtained with the IRAM-30m and JCMT-15m telescopes. Particular attention was devoted to the inter-calibration of the obtained spectra with previous observations. All the lines detected with more than 3 sigma and free from obvious blending effects were fitted with Gaussians to estimate their basic kinematic properties. More than 4000 lines were detected (with sigma \geq 3) and identified, yielding a line density of approximatively 20 lines per GHz, comparable to previous surveys in massive hot cores. The vast majority (~2/3) of the lines are weak and due to complex organic molecules. The analysis of the profiles of more than 1000 lines belonging 70 species firmly establishes the presence of two distinct velocity components, associated with the two objects, A and B, forming the IRAS16293-2422 binary system. In the source A, the line widths of several species increase with the upper level energy of the transition, a behavior compatible with gas infalling towards a ~1 Mo object. The source B, which does not show this effect, might have a much lower central mass of ~0.1 Mo. The difference in the rest velocities of both objects is consistent with the hypothesis that the source B rotates around the source A. This spectral survey, although obtained with single-dish telescope with a low spatial resolution, allows to separate the emission from 2 different components, thanks to the large number of lines detected. The data of the survey are public and can be retrieved on the web site http://www-laog.obs.ujf-grenoble.fr/heberges/timasss.
    Astronomy and Astrophysics 03/2011; 532. DOI:10.1051/0004-6361/201015399 · 4.48 Impact Factor
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    ABSTRACT: We have examined methanol emission from Orion KL with of the {\em Herschel}/HIFI instrument, and detected two methanol bands centered at 524 GHz and 1061 GHz. The 524 GHz methanol band (observed in HIFI band 1a) is dominated by the isolated $\Delta$J$=$0, K$=-4\rightarrow$-3, v$_t$$=$0 Q branch, and includes 25 E-type and 2 A-type transitions. The 1061 GHz methanol band (observed in HIFI band 4b) is dominated by the $\Delta$J$=$0, K$=7\rightarrow$6, v$_t$$=$0 Q branch transitions which are mostly blended. We have used the isolated E-type v$_t$$=$0 methanol transitions to explore the physical conditions in the molecular gas. With HIFI's high velocity resolution, the methanol emission contributed by different spatial components along the line of sight toward Orion KL (hot core, low velocity flow, and compact ridge) can be distinguished and studied separately. The isolated transitions detected in these bands cover a broad energy range (upper state energy ranging from 80 K to 900 K), which provides a unique probe of the thermal structure in each spatial component. The observations further show that the compact ridge is externally heated. These observations demonstrate the power of methanol lines as probes of the physical conditions in warm regions in close proximity to young stars.
    Astronomy and Astrophysics 01/2011; 527. DOI:10.1051/0004-6361/201015079 · 4.48 Impact Factor
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    ABSTRACT: Hot cores are key targets for present day research in Astronomy because of both their extreme chemical richness and their role in the process of high-mass star formation. Several papers have dealt with the Ultra Compact HII region W31C, also known as G10.62-0.39, in the last few years, revealing a complex source presenting evidences for infalling material from the molecular envelope, multiple outflowing activity from high-mass protostars, methanol masers and a rotating dense toroid. Herschel-HIFI high resolution (1.1 MHz) sub-millimeter spectra have been taken in the framework of the PRISMAS Herschel key programme, aiming at the absorption features of hydride molecules due to foreground diffuse clouds. These data contain also precious information on the W31C massive core itself because of the abundance of emission lines arising from all the environments characterizing the region, from the compact hot core to the surrounding molecular cloud, with clear signatures of outflowing activity. We will present preliminary results of our attempt of modeling the HIFI spectra, in combination with IRAM-30m data, in both LTE and non-LTE approximations, with particular focus on key molecular species like methanol, formaldehyde, CO, CS, SO, SO2 and CN-bearing molecules (and isotopologues). We will also discuss the compatibility of our results with previous studies of the same region.
    Proceedings of the International Astronomical Union 01/2011; 280.
  • E. Caux · S. Bottinelli · C. Vastel · J. M. Glorian
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    ABSTRACT: CASSIS (Centre d'Analyse Scientifique de Spectres Infrarouges et Submillimetriques) is a software package aimed to speed-up the scientific analysis of high spectral resolution observations, particularly suited for broad-band spectral surveys. CASSIS is written in Java and can be ran on any platform. It has been extensively tested on Mac OSX, Linux and Windows operating systems. CASSIS is regularly enhanced, and can be easily installed and updated on any modern laptop. It uses a fast Sql-lite access to a local spectroscopic database made of the two molecular spectroscopic databases JPL and CDMS, as well as the atomic spectroscopic database NIST. The tools available in the currently distributed version (2.6) include a LTE model and the RADEX model connected to the LAMDA molecular collisional database. A module allows to build a line list fitting the various transitions of a given species and to directly produce rotational diagrams from these lists. CASSIS has been recently fully integrated into HIPE, the Herschel Interactive Processing Environment, as a plug-in (from version 5.1).
    Proceedings of the International Astronomical Union 01/2011; 280.

Publication Stats

1k Citations
236.83 Total Impact Points

Institutions

  • 2002–2015
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
    • Paul Sabatier University - Toulouse III
      Tolosa de Llenguadoc, Midi-Pyrénées, France
  • 2010–2014
    • University of Toulouse
      Tolosa de Llenguadoc, Midi-Pyrénées, France
  • 2002–2008
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
  • 2001
    • Institute for Advanced Study
      Princeton Junction, New Jersey, United States
    • Netherlands Institute for Space Research, Utrecht
      Utrecht, Utrecht, Netherlands
  • 2000
    • The Ecological Society of America
      ISO, North Carolina, United States