Bertrand Lefloch - Academia.edu (original) (raw)

Papers by Bertrand Lefloch

Research paper thumbnail of Discovery of a Hot Corino in the Bok Globule B335

The Astrophysical Journal, 2016

Research paper thumbnail of The Spatial Distribution of Complex Organic Molecules in the L1544 Pre-Stellar Core

The Astrophysical Journal, 2016

The detection of complex organic molecules (COMs) toward cold sources such as pre-stellar cores (... more The detection of complex organic molecules (COMs) toward cold sources such as pre-stellar cores (with T<10 K), has challenged our understanding of the formation processes of COMs in the interstellar medium. Recent modelling on COM chemistry at low temperatures has provided new insight into these processes predicting that COM formation depends strongly on parameters such as visual extinction and the level of CO freeze out. We report deep observations of COMs toward two positions in the L1544 pre-stellar core: the dense, highly-extinguished continuum peak with A V ≥30 mag within the inner 2700 au; and a low-density shell with average A V ~7.5-8 mag located at 4000 au from the core's center and bright in CH3OH. Our observations show that CH3O, CH3OCH3 and CH3CHO are more abundant (by factors ~2-10) toward the low-density shell than toward the continuum peak. Other COMs such as CH3OCHO, c-C3H2O, HCCCHO, CH2CHCN and HCCNC show slight enhancements (by factors ≤3) but the associated uncertainties are large. This suggests that COMs are actively formed and already present in the low-density shells of pre-stellar cores. The modelling of the chemistry of O-bearing COMs in L1544 indicates that these species are enhanced in this shell because i) CO starts freezing out onto dust grains driving an active surface chemistry; ii) the visual extinction is sufficiently high to prevent the UV photo-dissociation of COMs by the external interstellar radiation field; and iii) the density is still moderate to prevent severe depletion of COMs onto grains.

Research paper thumbnail of H2S in the L1157-B1 Bow Shock

Monthly Notices of the Royal Astronomical Society, 2016

Research paper thumbnail of Subarcsecond Analysis of the Infalling–Rotating Envelope Around the Class I Protostar Iras 04365+2535

The Astrophysical Journal, 2016

Research paper thumbnail of Search for glycine in the solar type protostar IRAS 16293-2422

Astronomy and Astrophysics, Sep 29, 2000

Research paper thumbnail of Detection of H_2D^+: Measuring the Midplane Degree of Ionization in the Disks of DM Tauri and TW Hydrae

Research paper thumbnail of Star Formation in the Trifid Nebula

Aims: We aim to characterize the properties of the prestellar and protostellar condensations to u... more Aims: We aim to characterize the properties of the prestellar and protostellar condensations to understand the star formation processes at work in a young HII region Methods: We have obtained maps of the 1.25 mm thermal dust emission and the molecular gas emission over a region of 20' × 10' around the Trifid Nebula (M 20), with the IRAM 30 m and the CSO telescopes as well as in the mid-infrared wavelength with ISO and SPITZER. Our survey is sensitive to features down to N (H2) ~ 1022 cm-2 in column density. Results: The cloud material is distributed in fragmented dense gas filaments (n (H2) of a few 103 cm-3) with sizes ranging from 1 to 10 pc. A massive filament, WF, with properties typical of Infra Red Dark Clouds, connects M 20 to the W28 supernova remnant. We find that these filaments pre-exist the formation of the Trifid and were originally self-gravitating. The fragments produced are very massive (typically 100M_⊙ or more) and are the progenitors of the cometary globules observed at the border of the HII region. We could identify 33 cores, 16 of which are currently forming stars. Most of the starless cores have typical H2 densities of a few 104 cm-3. They are usually gravitationally unbound and have low masses of a few M_⊙. The densest starless cores (several 105 cm-3) are located in condensation TC0, currently hit by the ionization front, and may be the site for the next generation of stars. The physical gas and dust properties of the cometary globules have been studied in detail and have been found very similar. They all are forming stars. Several intermediate-mass protostars have been detected in the cometary globules and in the deeply embedded cores. Evidence of clustering has been found in the shocked massive cores TC3-TC4-TC5. Conclusions: M 20 is a good example of massive-star forming region in a turbulent, filamentary molecular cloud. Photoionization appears to play a minor role in the formation of the cores. The observed fragmentation is well explained by MHD-driven instabilities and is usually not related to M 20. We propose that the nearby supernova remnant W28 could have triggered the formation of protostellar clusters in nearby dense cores of the Trifid. Table 5 and Appendices A-C are only available in electronic form at http://www.aanda.org

Research paper thumbnail of Infalling–Rotating Motion and Associated Chemical Change in the Envelope of Iras 16293–2422 Source a Studied with Alma

The Astrophysical Journal, 2016

We have analyzed rotational spectral line emission of OCS, CH 3 OH, HCOOCH 3 , and H 2 CS observe... more We have analyzed rotational spectral line emission of OCS, CH 3 OH, HCOOCH 3 , and H 2 CS observed toward the low-mass Class 0 protostellar source IRAS 16293–2422 Source A at a sub-arcsecond resolution (∼0 6 × 0 5) with ALMA. Significant chemical differentiation is found on a scale of 50 au. The OCS line is found to trace well the infalling–rotating envelope in this source. On the other hand, the distributions of CH 3 OH and HCOOCH 3 are found to be concentrated around the inner part of the infalling–rotating envelope. With a simple ballistic model of the infalling–rotating envelope, the radius of the centrifugal barrier (a half of the centrifugal radius) and the protostellar mass are evaluated from the OCS data to be from 40 to 60 au and from 0.5 to 1.0 M e , respectively, assuming the inclination angle of the envelope/disk structure to be 60° (90° for the edge-on configuration). Although the protostellar mass is correlated with the inclination angle, the radius of the centrifugal barrier is not. This is the first indication of the centrifugal barrier of the infalling–rotating envelope in a hot corino source. CH 3 OH and HCOOCH 3 may be liberated from ice mantles by weak accretion shocks around the centrifugal barrier and/or by protostellar heating. The H 2 CS emission seems to come from the disk component inside the centrifugal barrier in addition to the envelope component. The centrifugal barrier plays a central role not only in the formation of a rotationally supported disk but also in the chemical evolution from the envelope to the protoplanetary disk.

Research paper thumbnail of Methanol and deuterium fractionation in prestellar cores

Research paper thumbnail of Are Formaldehyde and Methanol Formed on Grain Surfaces in Pre-Stellar Cores?

Protostars and Planets V Posters, 2005

Research paper thumbnail of Extended Far-Infrared CO Emission in the OMC-1 Core of Orion

The Astrophysical Journal Letters, Feb 20, 2000

We report on sensitive far-infrared observations of 12CO pure rotational transitions in the OMC-1... more We report on sensitive far-infrared observations of 12CO pure rotational transitions in the OMC-1 core of Orion. The lines were observed with the long-wavelength spectrometer in the grating mode on board the Infrared Space Observatory, covering the 43-197 mum wavelength range. The transitions from Jup=14 up to Jup=19 have been identified across the whole OMC-1 core, and lines up to Jup=43 have been detected toward the central region, KL/IRc2. In addition, we have taken high-quality spectra in the Fabry-Perot mode of some of the CO lines. In KL/IRc2, the lines are satisfactorily accounted for by a three-temperature model describing the plateau and ridge emission. The fluxes detected in the high-J transitions (Jup>34) reveal the presence of a very hot and dense gas component [T=1500-2500 K; N(CO)=2x1017 cm-2], probably originating from some of the embedded sources previously observed in the H2 near-infrared lines. At all other positions in the OMC-1 core, we estimate kinetic temperatures >=80 K and as high as 150 K at some positions around IRc2, from a simple large-velocity gradient model.

Research paper thumbnail of Hot corinos in NGC1333-IRAS4B and IRAS2A

(Abridged) We aim to enlarge the number of known hot corinos and carry out a first comparative st... more (Abridged) We aim to enlarge the number of known hot corinos and carry out a first comparative study with hot cores. The ultimate goal is to understand whether complex organic molecules form in the gas phase or on grain surfaces, and what the possible key parameters are. We observed millimeter rotational transitions of HCOOH, HCOOCH3, CH3OCH3, CH3CN, and C2H5CN in a sample of low-mass protostars with the IRAM-30m. Using the rotational diagram method coupled with the information about the sources' structure, we calculate the abundances of the observed molecules. To interpret these abundances, we review the proposed formation processes of the above molecules. We report the detection of HCOOCH3 and/or CH3CN towards NGC1333-IRAS4B and NGC1333-IRAS2A. We find that abundance ratios of O-bearing molecules to methanol or formaldehyde in hot corinos are comparable and about unity, and are relatively (depending on how the ratios are determined) higher than those in hot cores and in Galactic center clouds. So far, complex organic molecules were detected in all the hot corinos where they were searched for, suggesting that it is a common phase for low-mass protostars. While some evidence points to grain-surface synthesis (either in the cold or warm-up phase) of these molecules (in particular for HCOOH and HCOOCH3), the present data do not allow us to disregard gas-phase formation. More observational, laboratory, and theoretical studies are required to improve our understanding of hot corinos.

Research paper thumbnail of The H2CO abundance in the inner warm regions of low mass protostellar envelopes

Astron Astrophys, 2004

We present a survey of the formaldehyde emission in a sample of eight Class 0 protostars obtained... more We present a survey of the formaldehyde emission in a sample of eight Class 0 protostars obtained with the IRAM and JCMT millimeter telescopes. The range of energies of the observed transitions allows us to probe the physical and chemical conditions across the protostellar envelopes. The data have been analyzed with three different methods with increasing level of sophistication. We first analyze the observed emission in the LTE approximation, and derive rotational temperatures between 11 and 40 K, and column densities between 1 and 20 × 1013 cm-2. Second, we use a LVG code and derive higher kinetic temperatures, between 30 and 90 K, consistent with subthermally populated levels and densities from 1 to 6 × 105 cm-3. The column densities from the LVG modeling are within a factor of 10 with respect to those derived in the LTE approximation. Finally, we analyze the observations based upon detailed models for the envelopes surrounding the protostars, using temperature and density profiles previously derived from continuum observations. We approximate the formaldehyde abundance across the envelope with a jump function, the jump occurring when the dust temperature reaches 100 K, the evaporation temperature of the grain mantles. The observed formaldehyde emission is well reproduced only if there is a jump of more than two orders of magnitude, in four sources. In the remaining four sources the data are consistent with a formaldehyde abundance jump, but the evidence is more marginal (≤ 2 σ). The inferred inner H2CO abundance varies between 1 × 10-8 and 6 × 10-6. The absolute values of the jump in the H2CO abundance are uncertain by about one order of magnitude, because of the uncertainties in the density, ortho to para ratio, temperature and velocity profiles of the inner region, as well as the evaporation temperature of the ices. We discuss the implications of these jumps for our understanding of the origin and evolution of ices in low mass star forming regions. Finally, we give predictions for the submillimeter H2CO lines, which are particularly sensitive to the abundance jumps. Appendices A and B are only available in electronic form at http://www.edpsciences.org

Research paper thumbnail of Discovery of deuterated water in a young proto-planetary disk

We report the first detection of the ground transition of the deuterated water at 464 GHz in the ... more We report the first detection of the ground transition of the deuterated water at 464 GHz in the young proto-planetary disk surrounding the solar type protostar DM Tau. The line is observed in absorption against the continuum from the cold dust in the disk midplane, with a line to continuum ratio close to unity. The observation implies that deuterated gaseous water is present, with a relatively large abundance ($\sim 3\times10^{-9}$), in the outer disk above the midplane, where the density is, within a factor ten, sim106\sim 10^6sim106 cm$^{-3}$ and the temperature is lower than about 25 K. In these conditions, the H$_2$O condensation timescale is much smaller than the DM Tau disk age, and, therefore, water should be fully frozen onto the grain mantles. We suggest that UV photons and/or X-rays sublimate part of the mantles re-injecting the ices into the gas phase. Even though there is currently no measurement of H$_2$O, we provide arguments that the HDO/H$_2$O ratio should be about 0.01 or larger, which would be hundreds of times larger than the values measured in Solar System objects. This suggests the need of strong caution in comparing and linking the HDO/H$_2$O in Solar System and star forming environments.

Research paper thumbnail of Testing grain surface chemistry : a survey of deuterated formaldehyde and methanol in low-mass Class 0 protostars

Astronomy and Astrophysics, Mar 6, 2006

Research paper thumbnail of The density structure of the L1157 molecular outflow

Monthly Notices of the Royal Astronomical Society, 2014

Research paper thumbnail of Detection of deuterated water in a young proto-planetary disks

Proceedings of the International Astronomical Union, 2005

It is generally assumed that the terrestrial water came from the outer Solar System, brought by c... more It is generally assumed that the terrestrial water came from the outer Solar System, brought by colliding bodies after the Earth formation, either comets and/or meteorites from the outer asteroid belt. One of the most important constraints is provided by the HDO/H2O abundance ratio in ocean water, compared to the values obtained from meteorite analysis, and from the observations of comets. Both meteorites and comets are remnants of the proto-planetary disk from which the Solar System originated, so their HDO/H2O ratio is linked to the HDO/H2O ratio across the disk. Until present, nothing has been known about the content and distribution of HDO and water in proto-planetary disks around other stars similar to the Sun. Theoretical arguments predict that water should be mostly frozen at radii larger than about 30 AU in disks 1 Myr old. Here we report the first detections of HDO in proto-planetary disks around the solar-type protostars, proving, for the first time, the presence of abundant water vapor in disks in contradictions with the theoretical predictions. Furthermore, the analysis of the present observations suggests that the HDO/H2O ratio is re-set during the proto-planetary phase. Thus, very likely the HDO/H2O ratio observed in comets and meteorites, and consequently in the oceans, does not reflect the pristine HDO/H2O ratio observed in the Inter-Stellar-Medium and/or the embedded protostar phase.

Research paper thumbnail of Sulphur-bearing species in the star forming region L1689N

Astronomy and Astrophysics a European Journal, 2004

Research paper thumbnail of Deuterated Methanol in Low-Mass Protostars

Research paper thumbnail of Observations of deuterated formaldehyde and nethanol in low-mass protostars. Evidence for grain surface chemistry?

Proceedings of the International Astronomical Union, 2005

We present observations of deuterated formaldehyde (HDCO and D2CO), methanol (CH2DOH and CH3OD) a... more We present observations of deuterated formaldehyde (HDCO and D2CO), methanol (CH2DOH and CH3OD) as well as doubly-deuterated methanol CHD2OH towards a sample of low-mass protostars. Such multi-isotope study provides strong constraints on grain chemistry models that propose to explain methanol formation. Our observations point to the formation of methanol on the grain surfaces, while formaldehyde formation may be dominated by gas-phase reactions and/or strongly affected by abstraction reactions on grains. 1. Observations Using the IRAM 30-meter telescope (Pico Veleta, Spain), we observed the five deuterated species HDCO, D2CO, CH2DOH, CH3OD and CHD2OH towards the seven low- mass protostars IRAS16293-2422, NGC1333-IRAS4A, -IRAS4B, -IRAS2, L1448N, L1448mm and L1157mm.We also present observations of deuterated formaldehyde (HDCO and D2CO) towards L1527. We detected the two deuterated formaldehyde isotopes (HDCO and D2CO) towards all the sources of our sample. Regarding methanol, only the four sources IRAS16293-2422, NGC1333-IRAS4A, -IRAS4B and -IRAS2 have good detections. This is consistent with the study by Maret et al. (2005) that shows that these three sources are indeed the brightest ones for CH3OH emission. CH2DOH was detected in all sources it was searched for, but only the low-lying transition was detected in the case of L1448N, L1448mm and L1157mm. CH3OD was detected only towards IRAS16293, IRAS4A, IRAS4B, L1448mm and L1157mm, with only one transition detected in the two last sources. Finally, doubly-deuterated methanol was detected towards IRAS16293, IRAS4A, IRAS4B and IRAS2. Upper limits were derived for the other sources. 2. Analysis - Comparison to grain chemistry models We computed all column densities of the different isotopes using the population diagrams method, assuming a source size of 10". H2CO and CH3OH column densities were recomputed by the same method from the data from Maret et al. 2004 and Maret et al. 2005, correcting for the the opacities whenever the 13C transitions had been observed. Methanol is thought to be formed on the grains by successive hydrogenations of CO. An intermediate product of these reactions is formaldehyde. Deuterium fractionation studies of formaldehyde and methanol thus provide a useful tool for confirming the grain chemistry scenario. To understand if formaldehyde and methanol are formed simultanuously on the grains, and to unveil a possible contribution of gas-phase processes in the formation of formaldehyde, we compared the observed fractionations to the predictions of the grain chemistry model from Stantcheva et al. (2003), which only considers successive hydrogenations/deuterations but no abstraction reactions (such as H2CO + H → HCO). Fig. 1 presents, in dashed lines, the HDCO, D2CO, CH2DOH, CH3OD et CHD2OH fractionations predicted by the grain model, as a function of the gas-phase atomic D/H ratio at the time of mantle formation. The observed fractionations with their error bars have been superimposed for each source. This allows to infer the required D/H ratio required for the formation of each molecule.

Research paper thumbnail of Discovery of a Hot Corino in the Bok Globule B335

The Astrophysical Journal, 2016

Research paper thumbnail of The Spatial Distribution of Complex Organic Molecules in the L1544 Pre-Stellar Core

The Astrophysical Journal, 2016

The detection of complex organic molecules (COMs) toward cold sources such as pre-stellar cores (... more The detection of complex organic molecules (COMs) toward cold sources such as pre-stellar cores (with T<10 K), has challenged our understanding of the formation processes of COMs in the interstellar medium. Recent modelling on COM chemistry at low temperatures has provided new insight into these processes predicting that COM formation depends strongly on parameters such as visual extinction and the level of CO freeze out. We report deep observations of COMs toward two positions in the L1544 pre-stellar core: the dense, highly-extinguished continuum peak with A V ≥30 mag within the inner 2700 au; and a low-density shell with average A V ~7.5-8 mag located at 4000 au from the core's center and bright in CH3OH. Our observations show that CH3O, CH3OCH3 and CH3CHO are more abundant (by factors ~2-10) toward the low-density shell than toward the continuum peak. Other COMs such as CH3OCHO, c-C3H2O, HCCCHO, CH2CHCN and HCCNC show slight enhancements (by factors ≤3) but the associated uncertainties are large. This suggests that COMs are actively formed and already present in the low-density shells of pre-stellar cores. The modelling of the chemistry of O-bearing COMs in L1544 indicates that these species are enhanced in this shell because i) CO starts freezing out onto dust grains driving an active surface chemistry; ii) the visual extinction is sufficiently high to prevent the UV photo-dissociation of COMs by the external interstellar radiation field; and iii) the density is still moderate to prevent severe depletion of COMs onto grains.

Research paper thumbnail of H2S in the L1157-B1 Bow Shock

Monthly Notices of the Royal Astronomical Society, 2016

Research paper thumbnail of Subarcsecond Analysis of the Infalling–Rotating Envelope Around the Class I Protostar Iras 04365+2535

The Astrophysical Journal, 2016

Research paper thumbnail of Search for glycine in the solar type protostar IRAS 16293-2422

Astronomy and Astrophysics, Sep 29, 2000

Research paper thumbnail of Detection of H_2D^+: Measuring the Midplane Degree of Ionization in the Disks of DM Tauri and TW Hydrae

Research paper thumbnail of Star Formation in the Trifid Nebula

Aims: We aim to characterize the properties of the prestellar and protostellar condensations to u... more Aims: We aim to characterize the properties of the prestellar and protostellar condensations to understand the star formation processes at work in a young HII region Methods: We have obtained maps of the 1.25 mm thermal dust emission and the molecular gas emission over a region of 20' × 10' around the Trifid Nebula (M 20), with the IRAM 30 m and the CSO telescopes as well as in the mid-infrared wavelength with ISO and SPITZER. Our survey is sensitive to features down to N (H2) ~ 1022 cm-2 in column density. Results: The cloud material is distributed in fragmented dense gas filaments (n (H2) of a few 103 cm-3) with sizes ranging from 1 to 10 pc. A massive filament, WF, with properties typical of Infra Red Dark Clouds, connects M 20 to the W28 supernova remnant. We find that these filaments pre-exist the formation of the Trifid and were originally self-gravitating. The fragments produced are very massive (typically 100M_⊙ or more) and are the progenitors of the cometary globules observed at the border of the HII region. We could identify 33 cores, 16 of which are currently forming stars. Most of the starless cores have typical H2 densities of a few 104 cm-3. They are usually gravitationally unbound and have low masses of a few M_⊙. The densest starless cores (several 105 cm-3) are located in condensation TC0, currently hit by the ionization front, and may be the site for the next generation of stars. The physical gas and dust properties of the cometary globules have been studied in detail and have been found very similar. They all are forming stars. Several intermediate-mass protostars have been detected in the cometary globules and in the deeply embedded cores. Evidence of clustering has been found in the shocked massive cores TC3-TC4-TC5. Conclusions: M 20 is a good example of massive-star forming region in a turbulent, filamentary molecular cloud. Photoionization appears to play a minor role in the formation of the cores. The observed fragmentation is well explained by MHD-driven instabilities and is usually not related to M 20. We propose that the nearby supernova remnant W28 could have triggered the formation of protostellar clusters in nearby dense cores of the Trifid. Table 5 and Appendices A-C are only available in electronic form at http://www.aanda.org

Research paper thumbnail of Infalling–Rotating Motion and Associated Chemical Change in the Envelope of Iras 16293–2422 Source a Studied with Alma

The Astrophysical Journal, 2016

We have analyzed rotational spectral line emission of OCS, CH 3 OH, HCOOCH 3 , and H 2 CS observe... more We have analyzed rotational spectral line emission of OCS, CH 3 OH, HCOOCH 3 , and H 2 CS observed toward the low-mass Class 0 protostellar source IRAS 16293–2422 Source A at a sub-arcsecond resolution (∼0 6 × 0 5) with ALMA. Significant chemical differentiation is found on a scale of 50 au. The OCS line is found to trace well the infalling–rotating envelope in this source. On the other hand, the distributions of CH 3 OH and HCOOCH 3 are found to be concentrated around the inner part of the infalling–rotating envelope. With a simple ballistic model of the infalling–rotating envelope, the radius of the centrifugal barrier (a half of the centrifugal radius) and the protostellar mass are evaluated from the OCS data to be from 40 to 60 au and from 0.5 to 1.0 M e , respectively, assuming the inclination angle of the envelope/disk structure to be 60° (90° for the edge-on configuration). Although the protostellar mass is correlated with the inclination angle, the radius of the centrifugal barrier is not. This is the first indication of the centrifugal barrier of the infalling–rotating envelope in a hot corino source. CH 3 OH and HCOOCH 3 may be liberated from ice mantles by weak accretion shocks around the centrifugal barrier and/or by protostellar heating. The H 2 CS emission seems to come from the disk component inside the centrifugal barrier in addition to the envelope component. The centrifugal barrier plays a central role not only in the formation of a rotationally supported disk but also in the chemical evolution from the envelope to the protoplanetary disk.

Research paper thumbnail of Methanol and deuterium fractionation in prestellar cores

Research paper thumbnail of Are Formaldehyde and Methanol Formed on Grain Surfaces in Pre-Stellar Cores?

Protostars and Planets V Posters, 2005

Research paper thumbnail of Extended Far-Infrared CO Emission in the OMC-1 Core of Orion

The Astrophysical Journal Letters, Feb 20, 2000

We report on sensitive far-infrared observations of 12CO pure rotational transitions in the OMC-1... more We report on sensitive far-infrared observations of 12CO pure rotational transitions in the OMC-1 core of Orion. The lines were observed with the long-wavelength spectrometer in the grating mode on board the Infrared Space Observatory, covering the 43-197 mum wavelength range. The transitions from Jup=14 up to Jup=19 have been identified across the whole OMC-1 core, and lines up to Jup=43 have been detected toward the central region, KL/IRc2. In addition, we have taken high-quality spectra in the Fabry-Perot mode of some of the CO lines. In KL/IRc2, the lines are satisfactorily accounted for by a three-temperature model describing the plateau and ridge emission. The fluxes detected in the high-J transitions (Jup>34) reveal the presence of a very hot and dense gas component [T=1500-2500 K; N(CO)=2x1017 cm-2], probably originating from some of the embedded sources previously observed in the H2 near-infrared lines. At all other positions in the OMC-1 core, we estimate kinetic temperatures >=80 K and as high as 150 K at some positions around IRc2, from a simple large-velocity gradient model.

Research paper thumbnail of Hot corinos in NGC1333-IRAS4B and IRAS2A

(Abridged) We aim to enlarge the number of known hot corinos and carry out a first comparative st... more (Abridged) We aim to enlarge the number of known hot corinos and carry out a first comparative study with hot cores. The ultimate goal is to understand whether complex organic molecules form in the gas phase or on grain surfaces, and what the possible key parameters are. We observed millimeter rotational transitions of HCOOH, HCOOCH3, CH3OCH3, CH3CN, and C2H5CN in a sample of low-mass protostars with the IRAM-30m. Using the rotational diagram method coupled with the information about the sources' structure, we calculate the abundances of the observed molecules. To interpret these abundances, we review the proposed formation processes of the above molecules. We report the detection of HCOOCH3 and/or CH3CN towards NGC1333-IRAS4B and NGC1333-IRAS2A. We find that abundance ratios of O-bearing molecules to methanol or formaldehyde in hot corinos are comparable and about unity, and are relatively (depending on how the ratios are determined) higher than those in hot cores and in Galactic center clouds. So far, complex organic molecules were detected in all the hot corinos where they were searched for, suggesting that it is a common phase for low-mass protostars. While some evidence points to grain-surface synthesis (either in the cold or warm-up phase) of these molecules (in particular for HCOOH and HCOOCH3), the present data do not allow us to disregard gas-phase formation. More observational, laboratory, and theoretical studies are required to improve our understanding of hot corinos.

Research paper thumbnail of The H2CO abundance in the inner warm regions of low mass protostellar envelopes

Astron Astrophys, 2004

We present a survey of the formaldehyde emission in a sample of eight Class 0 protostars obtained... more We present a survey of the formaldehyde emission in a sample of eight Class 0 protostars obtained with the IRAM and JCMT millimeter telescopes. The range of energies of the observed transitions allows us to probe the physical and chemical conditions across the protostellar envelopes. The data have been analyzed with three different methods with increasing level of sophistication. We first analyze the observed emission in the LTE approximation, and derive rotational temperatures between 11 and 40 K, and column densities between 1 and 20 × 1013 cm-2. Second, we use a LVG code and derive higher kinetic temperatures, between 30 and 90 K, consistent with subthermally populated levels and densities from 1 to 6 × 105 cm-3. The column densities from the LVG modeling are within a factor of 10 with respect to those derived in the LTE approximation. Finally, we analyze the observations based upon detailed models for the envelopes surrounding the protostars, using temperature and density profiles previously derived from continuum observations. We approximate the formaldehyde abundance across the envelope with a jump function, the jump occurring when the dust temperature reaches 100 K, the evaporation temperature of the grain mantles. The observed formaldehyde emission is well reproduced only if there is a jump of more than two orders of magnitude, in four sources. In the remaining four sources the data are consistent with a formaldehyde abundance jump, but the evidence is more marginal (≤ 2 σ). The inferred inner H2CO abundance varies between 1 × 10-8 and 6 × 10-6. The absolute values of the jump in the H2CO abundance are uncertain by about one order of magnitude, because of the uncertainties in the density, ortho to para ratio, temperature and velocity profiles of the inner region, as well as the evaporation temperature of the ices. We discuss the implications of these jumps for our understanding of the origin and evolution of ices in low mass star forming regions. Finally, we give predictions for the submillimeter H2CO lines, which are particularly sensitive to the abundance jumps. Appendices A and B are only available in electronic form at http://www.edpsciences.org

Research paper thumbnail of Discovery of deuterated water in a young proto-planetary disk

We report the first detection of the ground transition of the deuterated water at 464 GHz in the ... more We report the first detection of the ground transition of the deuterated water at 464 GHz in the young proto-planetary disk surrounding the solar type protostar DM Tau. The line is observed in absorption against the continuum from the cold dust in the disk midplane, with a line to continuum ratio close to unity. The observation implies that deuterated gaseous water is present, with a relatively large abundance ($\sim 3\times10^{-9}$), in the outer disk above the midplane, where the density is, within a factor ten, sim106\sim 10^6sim106 cm$^{-3}$ and the temperature is lower than about 25 K. In these conditions, the H$_2$O condensation timescale is much smaller than the DM Tau disk age, and, therefore, water should be fully frozen onto the grain mantles. We suggest that UV photons and/or X-rays sublimate part of the mantles re-injecting the ices into the gas phase. Even though there is currently no measurement of H$_2$O, we provide arguments that the HDO/H$_2$O ratio should be about 0.01 or larger, which would be hundreds of times larger than the values measured in Solar System objects. This suggests the need of strong caution in comparing and linking the HDO/H$_2$O in Solar System and star forming environments.

Research paper thumbnail of Testing grain surface chemistry : a survey of deuterated formaldehyde and methanol in low-mass Class 0 protostars

Astronomy and Astrophysics, Mar 6, 2006

Research paper thumbnail of The density structure of the L1157 molecular outflow

Monthly Notices of the Royal Astronomical Society, 2014

Research paper thumbnail of Detection of deuterated water in a young proto-planetary disks

Proceedings of the International Astronomical Union, 2005

It is generally assumed that the terrestrial water came from the outer Solar System, brought by c... more It is generally assumed that the terrestrial water came from the outer Solar System, brought by colliding bodies after the Earth formation, either comets and/or meteorites from the outer asteroid belt. One of the most important constraints is provided by the HDO/H2O abundance ratio in ocean water, compared to the values obtained from meteorite analysis, and from the observations of comets. Both meteorites and comets are remnants of the proto-planetary disk from which the Solar System originated, so their HDO/H2O ratio is linked to the HDO/H2O ratio across the disk. Until present, nothing has been known about the content and distribution of HDO and water in proto-planetary disks around other stars similar to the Sun. Theoretical arguments predict that water should be mostly frozen at radii larger than about 30 AU in disks 1 Myr old. Here we report the first detections of HDO in proto-planetary disks around the solar-type protostars, proving, for the first time, the presence of abundant water vapor in disks in contradictions with the theoretical predictions. Furthermore, the analysis of the present observations suggests that the HDO/H2O ratio is re-set during the proto-planetary phase. Thus, very likely the HDO/H2O ratio observed in comets and meteorites, and consequently in the oceans, does not reflect the pristine HDO/H2O ratio observed in the Inter-Stellar-Medium and/or the embedded protostar phase.

Research paper thumbnail of Sulphur-bearing species in the star forming region L1689N

Astronomy and Astrophysics a European Journal, 2004

Research paper thumbnail of Deuterated Methanol in Low-Mass Protostars

Research paper thumbnail of Observations of deuterated formaldehyde and nethanol in low-mass protostars. Evidence for grain surface chemistry?

Proceedings of the International Astronomical Union, 2005

We present observations of deuterated formaldehyde (HDCO and D2CO), methanol (CH2DOH and CH3OD) a... more We present observations of deuterated formaldehyde (HDCO and D2CO), methanol (CH2DOH and CH3OD) as well as doubly-deuterated methanol CHD2OH towards a sample of low-mass protostars. Such multi-isotope study provides strong constraints on grain chemistry models that propose to explain methanol formation. Our observations point to the formation of methanol on the grain surfaces, while formaldehyde formation may be dominated by gas-phase reactions and/or strongly affected by abstraction reactions on grains. 1. Observations Using the IRAM 30-meter telescope (Pico Veleta, Spain), we observed the five deuterated species HDCO, D2CO, CH2DOH, CH3OD and CHD2OH towards the seven low- mass protostars IRAS16293-2422, NGC1333-IRAS4A, -IRAS4B, -IRAS2, L1448N, L1448mm and L1157mm.We also present observations of deuterated formaldehyde (HDCO and D2CO) towards L1527. We detected the two deuterated formaldehyde isotopes (HDCO and D2CO) towards all the sources of our sample. Regarding methanol, only the four sources IRAS16293-2422, NGC1333-IRAS4A, -IRAS4B and -IRAS2 have good detections. This is consistent with the study by Maret et al. (2005) that shows that these three sources are indeed the brightest ones for CH3OH emission. CH2DOH was detected in all sources it was searched for, but only the low-lying transition was detected in the case of L1448N, L1448mm and L1157mm. CH3OD was detected only towards IRAS16293, IRAS4A, IRAS4B, L1448mm and L1157mm, with only one transition detected in the two last sources. Finally, doubly-deuterated methanol was detected towards IRAS16293, IRAS4A, IRAS4B and IRAS2. Upper limits were derived for the other sources. 2. Analysis - Comparison to grain chemistry models We computed all column densities of the different isotopes using the population diagrams method, assuming a source size of 10". H2CO and CH3OH column densities were recomputed by the same method from the data from Maret et al. 2004 and Maret et al. 2005, correcting for the the opacities whenever the 13C transitions had been observed. Methanol is thought to be formed on the grains by successive hydrogenations of CO. An intermediate product of these reactions is formaldehyde. Deuterium fractionation studies of formaldehyde and methanol thus provide a useful tool for confirming the grain chemistry scenario. To understand if formaldehyde and methanol are formed simultanuously on the grains, and to unveil a possible contribution of gas-phase processes in the formation of formaldehyde, we compared the observed fractionations to the predictions of the grain chemistry model from Stantcheva et al. (2003), which only considers successive hydrogenations/deuterations but no abstraction reactions (such as H2CO + H → HCO). Fig. 1 presents, in dashed lines, the HDCO, D2CO, CH2DOH, CH3OD et CHD2OH fractionations predicted by the grain model, as a function of the gas-phase atomic D/H ratio at the time of mantle formation. The observed fractionations with their error bars have been superimposed for each source. This allows to infer the required D/H ratio required for the formation of each molecule.