C. Vastel

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

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Publications (104)221.32 Total impact

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    ABSTRACT: The rotational spectral lines of c-C$_3$H$_2$ and two kinds of the $^{13}$C isotopic species, c-$^{13}$CCCH$_2$ ($C_{2v}$ symmetry) and c-CC$^{13}$CH$_2$ ($C_s$ symmetry) have been observed in the 1-3 mm band toward the low-mass star-forming region L1527. We have detected 7, 3, and 6 lines of c-C$_3$H$_2$, c-$^{13}$CCCH$_2$ , and c-CC$^{13}$CH$_2$, respectively, with the Nobeyama 45 m telescope, and 34, 6, and 13 lines, respectively, with the IRAM 30 m telescope, where 7, 2, and 2 transitions, respectively, are observed with the both telescopes. With these data, we have evaluated the column densities of the normal and $^{13}$C isotopic species. The [c-C$_3$H$_2$]/[c-$^{13}$CCCH$_2$] ratio is determined to be $310\pm80$, while the [c-C$_3$H$_2$]/[c-CC$^{13}$CH$_2$] ratio is determined to be $61\pm11$. The [c-C$_3$H$_2$]/[c-$^{13}$CCCH$_2$] and [c-C$_3$H$_2$]/[c-CC$^{13}$CH$_2$] ratios expected from the elemental $^{12}$C/$^{13}$C ratio are 60-70 and 30-35, respectively, where the latter takes into account the statistical factor of 2 for the two equivalent carbon atoms in c-C$_3$H$_2$. Hence, this observation further confirms the dilution of the $^{13}$C species in carbon-chain molecules and their related molecules, which are thought to originate from the dilution of $^{13}$C$^+$ in the gas-phase C$^+$ due to the isotope exchange reaction: $\mathrm{^{13}C^++CO\rightarrow{}^{13}CO+C^+}$. Moreover, the abundances of the two $^{13}$C isotopic species are different from each other. The ratio of c-$\mathrm{^{13}CCCH_2}$ species relative to c-$\mathrm{CC^{13}CH_2}$ is determined to be $0.20\pm0.05$. If $^{13}$C were randomly substituted for the three carbon atoms, the [c-$\mathrm{^{13}CCCH_2}$]/[c-$\mathrm{CC^{13}CH_2}$] ratio would be 0.5. Hence, the observed ratio indicates that c-$\mathrm{CC^{13}CH_2}$ exists more favorably. Possible origins of the different abundances are discussed.
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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 present 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: Complex organic molecules (COMs) have been detected in a variety of environments, including cold prestellar cores. Given the low temperature of these objects, these last detections challenge existing models. We report here new observations towards the prestellar core L1544. They are based on an unbiased spectral survey of the 3mm band at the IRAM-30m telescope, as part of the Large Program ASAI. The observations allow us to provide the full census of the oxygen bearing COMs in this source. We detected tricarbon monoxide, methanol, acetaldehyde, formic acid, ketene, and propyne with abundances varying from 5e-11 to 6e-9. The non-LTE analysis of the methanol lines shows that they are likely emitted at the border of the core, at a radius of ~8000 AU where T~10 K and nH2~2e4 cm-3. Previous works have shown that water vapour is enhanced in the same region because of the photodesorption of water ices. We propose that a non-thermal desorption mechanism is also responsible for the observed emission of methanol and COMs from the same layer. The desorbed oxygen and a tiny amount of desorbed methanol and ethene are enough to reproduce the abundances of tricarbon monoxide, methanol, acetaldehyde and ketene measured in L1544. These new findings open the possibility that COMs in prestellar cores originate in a similar outer layer rather than in the dense inner cores, as previously assumed, and that their formation is driven by the non-thermally desorbed species.
    The Astrophysical Journal Letters 09/2014; 795(1). DOI:10.1088/2041-8205/795/1/L2 · 5.60 Impact Factor
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    ABSTRACT: Understanding water deuterium fractionation is important for constraining the mechanisms of water formation in interstellar clouds. Observations of HDO and H$_2^{18}$O transitions were carried out towards the high-mass star-forming region G34.26+0.15 with the HIFI instrument onboard the Herschel Space Observatory, as well as with ground-based single-dish telescopes. Ten HDO lines and three H$_2^{18}$O lines covering a broad range of upper energy levels (22-204 K) were detected. We used a non-LTE 1D analysis to determine the HDO/H$_2$O ratio as a function of radius in the envelope. Models with different water abundance distributions were considered in order to reproduce the observed line profiles. The HDO/H$_2$O ratio is found to be lower in the hot core ($\sim$3.5 $\times$ 10$^{-4}$ - 7.5 $\times$ 10$^{-4}$) than in the colder envelope ($\sim$1.0 $\times$ 10$^{-3}$ - 2.2 $\times$ 10$^{-3}$). This is the first time that a radial variation of the HDO/H$_2$O ratio has been found to occur in a high-mass source. The chemical evolution of this source was modeled as a function of its radius and the observations are relatively well reproduced. The comparison between the chemical model and the observations leads to an age of $\sim$10$^5$ years after the infrared dark cloud stage.
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    ABSTRACT: Subarcsecond images of the rotational line emissions of CCH, CS, H2CO, and CH3OH have been obtained toward the low-mass protostar IRAS 04368+2557 in L1527 as one of the early science projects of the Atacama Large Millimeter/submillimeter Array. The intensity distributions of CCH and CS show a double-peaked structure along the edge-on envelope with a dip toward the protostar position, whereas those of H2CO and CH3OH are centrally peaked. By analyzing the position-velocity diagrams along the envelope, CCH and CS are found to reside mainly in the envelope, where the gas is infalling with conservation of its angular momentum. They are almost absent inward of the centrifugal barrier (a half of the centrifugal radius). Although H2CO exists in the infalling rotating envelope, it also resides in the disk component inside the centrifugal barrier to some extent. On the other hand, CH3OH seems to exist around the centrifugal barrier and in the disk component. Hence, the drastic chemical change occurs at the centrifugal barrier. A discontinuous infalling motion as well as the gas-grain interaction would be responsible for the chemical change. This result will put an important constraint on initial chemical compositions for chemical evolution of protostellar disks.
    The Astrophysical Journal Letters 08/2014; 791(2):L38. DOI:10.1088/2041-8205/791/2/L38 · 5.60 Impact Factor
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    ABSTRACT: Water plays a crucial role both in the interstellar medium and on Earth. To constrain its formation mechanisms and its evolution through the star formation process, the determination of the water deuterium fractionation ratios is particularly suitable. Previous studies derived HDO/H$_2$O ratios in the warm inner regions of low-mass protostars. We here report a detection of the D$_2$O 1$_{1,0}$-1$_{0,1}$ transition toward the low-mass protostar NGC1333 IRAS2A with the Plateau de Bure interferometer: this represents the first interferometric detection of D$_2$O - and only the second solar-type protostar for which this isotopologue is detected. Using the observations of the HDO 5$_{4,2}$-6$_{3,3}$ transition simultaneously detected and three other HDO lines previously observed, we show that the HDO line fluxes are well reproduced with a single excitation temperature of 218$\pm$21 K and a source size of $\sim$0.5 arcsec. The D$_2$O/HDO ratio is $\sim$(1.2$\pm$0.5) $\times$ 10$^{-2}$, while the use of previous H$_2^{18}$O observations give an HDO/H$_2$O ratio of $\sim$(1.7$\pm$0.8) $\times$ 10$^{-3}$, i.e. a factor of 7 lower than the D$_2$O/HDO ratio. These results contradict the predictions of current grain surface chemical models and indicate that either the surface deuteration processes are poorly understood or that both sublimation of grain mantles and water formation at high temperatures ($\gtrsim$230 K) take place in the inner regions of this source. In the second scenario, the thermal desorption of the grain mantles would explain the high D$_2$O/HDO ratio, while water formation at high temperature would explain significant extra production of H$_2$O leading to a decrease of the HDO/H$_2$O ratio.
    The Astrophysical Journal Letters 07/2014; 792(1). DOI:10.1088/2041-8205/792/1/L5 · 5.60 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) × 105 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.
    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: IRAS 04368+2557 is a solar-type (low-mass) protostar embedded in a protostellar core (L1527) in the Taurus molecular cloud, which is only 140 parsecs away from Earth, making it the closest large star-forming region. The protostellar envelope has a flattened shape with a diameter of a thousand astronomical units (1 au is the distance from Earth to the Sun), and is infalling and rotating. It also has a protostellar disk with a radius of 90 au (ref. 6), from which a planetary system is expected to form. The interstellar gas, mainly consisting of hydrogen molecules, undergoes a change in density of about three orders of magnitude as it collapses from the envelope into the disk, while being heated from 10 kelvin to over 100 kelvin in the mid-plane, but it has hitherto not been possible to explore changes in chemical composition associated with this collapse. Here we report that the unsaturated hydrocarbon molecule cyclic-C3H2 resides in the infalling rotating envelope, whereas sulphur monoxide (SO) is enhanced in the transition zone at the radius of the centrifugal barrier (100 ± 20 au), which is the radius at which the kinetic energy of the infalling gas is converted to rotational energy. Such a drastic change in chemistry at the centrifugal barrier was not anticipated, but is probably caused by the discontinuous infalling motion at the centrifugal barrier and local heating processes there.
    Nature 02/2014; 507(7490). DOI:10.1038/nature13000 · 42.35 Impact Factor
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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 [HDO]/[H2O] ratio is a crucial parameter for probing the history of water formation. So far, it has been measured for only three solar type protostars and yielded different results, possibly pointing to a substantially different history in their formation. In the present work, we report new interferometric observations of the HDO 4 2,2 - 4 2,3 line for two solar type protostars, IRAS2A and IRAS4A, located in the NGC1333 region. In both sources, the detected HDO emission originates from a central compact unresolved region. Comparison with previously published interferometric observations of the H218$O 3 1,3 - 2 2,0 line shows that the HDO and H$_2$O lines mostly come from the same region. A non-LTE LVG analysis of the HDO and H218$O line emissions, combined with published observations, provides a [HDO]/[H2O] ratio of 0.3 - 8 % in IRAS2A and 0.5 - 3 % in IRAS4A. First, the water fractionation is lower than that of other molecules such as formaldehyde and methanol in the same sources. Second, it is similar to that measured in the solar type protostar prototype, IRAS16293-2422, and, surprisingly enough, larger than that measured in NGC1333 IRAS4B. {The comparison of the measured values towards IRAS2A and IRAS4A with the predictions of our gas-grain model GRAINOBLE gives similar conclusions to those for IRAS 16293, arguing that these protostars {share} a similar chemical history, although they are located in different clouds.
    The Astrophysical Journal Letters 04/2013; 768(2). DOI:10.1088/2041-8205/768/2/L29 · 5.60 Impact Factor
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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 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: 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 key program Chemical HErschel Surveys of Star forming regions (CHESS) aims at studying 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 ortho-D2O at 607 GHz and the higher energy 2_{1,2}-1_{0,1} transition of para-D2O at 898 GHz, both of which are inaccessible from the ground. Methods: The ortho-D2O transition at 607 GHz was previously detected. We present in this paper the first tentative detection for the para-D2O transition at 898 GHz. The spherical Monte Carlo radiative transfer code RATRAN was used to reproduce the observed line profiles of D2O with the same method that was used to reproduce the HDO and H2-18O line profiles in IRAS 16293-2422. Results: As for HDO, the absorption component seen on the D2O lines can only be reproduced by adding an external absorbing layer, possibly created by the photodesorption of the ices at the edges of the molecular cloud. The D2O column density is found to be about 2.5e12 cm^{-2} in this added layer, leading to a D2O/H2O ratio of about 0.5%. At a 3 sigma uncertainty, upper limits of 0.03% and 0.2% are obtained for this ratio in the hot corino and the colder envelope of IRAS 16293-2422, respectively. Conclusions: The deuterium fractionation derived in our study suggests that the ices present in IRAS 16293-2422 formed on warm dust grains (~15-20 K) in dense (~1e4-5e4 cm^{-3}) translucent clouds. These results allow us to address the earliest phases of star formation and the conditions in which ices form.
    Astronomy and Astrophysics 03/2013; 553:A75. DOI:10.1051/0004-6361/201220967 · 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.

Publication Stats

1k Citations
221.32 Total Impact Points

Institutions

  • 2013–2015
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2014
    • University of Grenoble
      Grenoble, Rhône-Alpes, France
    • Research Institute in Astrophysics and Planetology
      Tolosa de Llenguadoc, Midi-Pyrénées, France
  • 2011–2014
    • University of Toulouse
      Tolosa de Llenguadoc, Midi-Pyrénées, France
    • Leiden University
      • Leiden Observartory
      Leyden, South Holland, Netherlands
  • 2008
    • Muséum de Toulouse
      Tolosa de Llenguadoc, Midi-Pyrénées, France
    • University of Waterloo
      • Department of Physics and Astronomy
      Waterloo, Ontario, Canada
  • 2002–2008
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
    • Paul Sabatier University - Toulouse III
      Tolosa de Llenguadoc, Midi-Pyrénées, France
  • 2007
    • Université Bordeaux 1
      Talence, Aquitaine, France
  • 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