E. Caux - Academia.edu (original) (raw)

Papers by E. Caux

Context. Despite the low elemental deuterium abundance in the Galaxy, enhanced molecular D/H rati... more Context. Despite the low elemental deuterium abundance in the Galaxy, enhanced molecular D/H ratios have been found in the environments of low-mass star-forming regions, and in particular the Class 0 protostar IRAS 16293-2422. Aims. The CHESS (Chemical HErschel Surveys of Star forming regions) key program aims to study the molecular complexity of the interstellar medium. The high sensitivity and spectral resolution of the Herschel/HIFI instrument provide a unique opportunity to observe the fundamental 11,1−00,0 transition of the ortho-D2O molecule, which is inaccessible from the ground, and determine the ortho-to-para D2O ratio. Methods. We detected the fundamental transition of the ortho-D2O molecule at 607.35 GHz towards IRAS 16293-2422. The line is seen in absorption with a line opacity of 0.62 ± 0.11 (1σ). From the previous ground-based observations of the fundamental 11,0−10,1 transition of para-D2O seen in absorption at 316.80 GHz, we estimate a line opacity of 0.26 ± 0.05 (1σ...

Sun like stars are born from the collapse of fragment of molecular clouds. During the first embed... more Sun like stars are born from the collapse of fragment of molecular clouds. During the first embedded phase (the so called class 0/1), the protostar is surrounded by a collapsing envelope, whose physical and chemical structure would set up the initial conditions of the proto-stellar disk which may eventually form planets. In this contribution, we show how spectroscopic far infrared to millimeter observations can be a powerful diagnostic to derive the chemical and physical structure of the innermost regions of envelopes collapsing around solar type protostars, where disk are believe to form. Our claim is based on the simultaneous modeling of the dynamics, chemistry and radiative transfer in a protostellar envelope. Here we present a study of a class 0 protostar NGC1333-IRAS4, obtained using ISO-LWS observations of water far-infrared lines. We show the derived physical and chemical structure of the protostar, namely the density and temperature profiles, as well as the water abundance a...

Context. Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict ... more Context. Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict relatively high levels of molecular oxygen, O2, and water, H2O. These high abundances imply high cooling rates, leading to relatively short timescales for the evolution of gravitationally unstable dense cores, forming stars and planets. Contrary to expectations, the dedicated space missions SWAS and Odin typically found only very small amounts of water vapour and essentially no O2 in the dense star-forming interstellar medium. Aims. Only toward ρOph A did Odin detect a very weak line of O2 at 119 GHz in a beam of size 10 arcmin. The line emission of related molecules changes on angular scales of the order of some tens of arcseconds, requiring a larger telescope aperture such as that of the Herschel Space Observatory to resolve the O2 emission and pinpoint its origin. Methods. We use the Heterodyne Instrument for the Far Infrared (HIFI) aboard Herschel to obtain high resolution O2 spectra...

We present a versatile digital autocorrelation spectrometer designed to suit the needs of HIFI, t... more We present a versatile digital autocorrelation spectrometer designed to suit the needs of HIFI, the sub-millimeter heterodyne instrument of the ESA's Herschel Space Observatory (HSO). This spectrometer will offer a set of four observation modes with different "channel spacing / total bandwidth" combinations. Each subband can be set anywhere in the 4-8 GHz input bandwidth. An original architecture made of an hybride Gallium Arsenide and Silicon technology allowed us to realize a 512 channel, low power consumption and high speed correlation module. INTRODUCTION HSO, the Herschel Space Observatory is the fourth corner stone of the European Space Agency Horizon 2000 program. It will be the first observatory studying the sub-millimeter domain from space in the range 100 m to 600 m. Herschel will be launched with an Ariane 5 rocket in the year 2007; it will be placed at the Lagrange point L2 at about 1.5 million kilometers from the Earth. Three instruments will be placed at ...

We report the detection of more than 48 velocity-resolved ground rotational state transitions of ... more We report the detection of more than 48 velocity-resolved ground rotational state transitions of H 16 2 O, H 18 2 O, and H 17 2 O – most for the first time – in both emission and absorption toward Orion KL using Herschel/HIFI. We show that a simple fit, constrained to match the known emission and absorption components along the line of sight, is in excellent agreement with the spectral profiles of all the water lines. Using the measured H 18 2 O line fluxes, which are less affected by line opacity than their H 16 2 O counterparts, and an escape probability method, the column densities of H 18 2 O associated with each emission component are derived. We infer total water abundances of 7.4× 10−5, 1.0× 10−5, and 1.6× 10−5 for the plateau, hot core, and extended warm gas, respectively. In the case of the plateau, this value is consistent with previous measures of the Orion-KL water abundance as well as those of other molecular outflows. In the case of the hot core and extended warm gas, ...

In contrast with numerous studies on the physical and chemical structure of lowand high-mass prot... more In contrast with numerous studies on the physical and chemical structure of lowand high-mass protostars, much less is known about their intermediate-mass counterparts, a class of objects that could help to elucidate the mechanisms of star formation on both ends of the mass range. We present the first results from a rich HIFI spectral dataset on an intermediate-mass protostar, OMC2-FIR4, obtained in the CHESS (Chemical HErschel Survey of Star forming regions) key programme. The more than 100 methanol lines detected between 554 and 961 GHz cover a range in upper level energy of 40 to 540 K. Our physical interpretation focusses on the hot core, but likely the cold envelope and shocked regions also play a role in reality, because an analysis of the line profiles suggests the presence of multiple emission components. An upper limit of 10−6 is placed on the methanol abundance in the hot core, using a population diagram, large-scale source model and other considerations. This value is cons...

Sun like stars are born from the collapse of fragment of molecular clouds. During the first embed... more Sun like stars are born from the collapse of fragment of molecular clouds. During the first embedded phase (the so called class 0/1), the protostar is surrounded by a collapsing envelope, whose physical and chemical structure would set up the initial conditions of the proto-stellar disk which may eventually form planets. In this contribution , we show how spectroscopic far infrared to millimeter observations can be a powerful diagnostic to derive the chemical and physical structure of the innermost regions of envelopes collapsing around solar type protostars, where disk are believe to form. Our claim is based on the simultaneous modeling of the dynamics , chemistry and radiative transfer in a protostellar envelope. Here we present a study of a class 0 protostar NGC1333-IRAS4, obtained using ISO-LWS observations of water far-infrared lines. We show the derived physical and chemical structure of the protostar, namely the density and temperature profiles, as well as the water abundance...

We report a detection of the fundamental rotational transition of hydrogen fluoride in absorption... more We report a detection of the fundamental rotational transition of hydrogen fluoride in absorption towards Orion KL using Herschel/HIFI. After the removal of contaminating features associated with common molecules (“weeds”), the HF spectrum shows a P-Cygni profile, with weak redshifted emission and strong blue-shifted absorption, associated with the low-velocity molecular outflow. We derive an estimate of 2.9 × 1013 cm−2 for the HF column density responsible for the broad absorption component. Using our best estimate of the H2 column density within the low-velocity molecular outflow, we obtain a lower limit of ∼1.6 × 10−10 for the HF abundance relative to hydrogen nuclei, corresponding to ∼0.6% of the solar abundance of fluorine. This value is close to that inferred from previous ISO observations of HF J = 2−1 absorption towards Sgr B2, but is in sharp contrast to the lower limit of 6 × 10−9 derived by Neufeld et al. for cold, foreground clouds on the line of sight towards G10.6-0.4.

MNRAS in press

The study of hot corinos in Solar-like protostars has been so far mostly limited to the Class 0 p... more The study of hot corinos in Solar-like protostars has been so far mostly limited to the Class 0 phase, hampering our understanding of their origin and evolution. In addition, recent evidence suggests that planet formation starts already during Class I phase, which, therefore, represents a crucial step in the future planetary system chemical composition. Hence, the study of hot corinos in Class I protostars has become of paramount importance. Here we report the discovery of a hot corino towards the prototypical Class I protostar L1551 IRS5, obtained within the ALMA Large Program FAUST. We detected several lines from methanol and its isopo-tologues (13 CH 3 OH and CH 2 DOH), methyl formate and ethanol. Lines are bright toward the north component of the IRS5 binary system, and a possible second hot corino may be associated with the south component. The methanol lines non-LTE analysis constrains the gas temperature (∼100 K), density (≥1.5×10 8 cm −3), and emitting size (∼10 au in radius...

We report new interferometric images of cyclopropenylidene, c–C 3 H 2 , towards the young protocl... more We report new interferometric images of cyclopropenylidene, c–C 3 H 2 , towards the young protocluster OMC–2 FIR 4. The observations were performed at 82 and 85 GHz with the NOrthern Extended Millimeter Array (NOEMA) as part of the project Seeds Of Life In Space (SOLIS). In addition, IRAM-30m data observations were used to investigate the physical structure of OMC–2 FIR 4. We find that the c–C 3 H 2 gas emits from the same region where previous SOLIS observations showed bright HC 5 N emission. From a non-LTE analysis of the IRAM-30m data, the c–C 3 H 2 gas has an average temperature of ∼40 K, a H 2 density of ∼3×10 5 cm −3 , and a c–C 3 H 2 abundance relative to H 2 of (7±1)×10 −12. In addition, the NOEMA observations provide no sign of significant c–C 3 H 2 excitation temperature gradients across the region (about 3-4 beams), with T ex in the range 8±3 up to 16±7 K. We thus infer that our observations are inconsistent with a physical interaction of the OMC–2 FIR 4 envelope with the...

The Astrophysical Journal

We present results from a comprehensive submillimeter spectral survey toward the source Orion Sou... more We present results from a comprehensive submillimeter spectral survey toward the source Orion South, based on data obtained with the HIFI instrument aboard the Herschel Space Observatory, covering the frequency range 480 to 1900 GHz. We detect 685 spectral lines with S/N > 3σ, originating from 52 different molecular and atomic species. We model each of the detected species assuming conditions of Local Thermodynamic Equilibrium. This analysis provides an estimate of the physical conditions of Orion South (column density, temperature, source size, & V LSR). We find evidence for three different cloud components: a cool (T ex ∼ 20 − 40 K), spatially extended (> 60), and quiescent (∆V F W HM ∼ 4 km s −1) component; a warmer (T ex ∼ 80 − 100 K), less spatially extended (∼ 30), and dynamic (∆V F W HM ∼ 8 km s −1) component, which is likely affected by embedded outflows; and a kinematically distinct region (T ex > 100 K; V LSR ∼ 8 km s −1), dominated by emission from species which trace ultraviolet irradiation, likely at the surface of the cloud. We find little evidence for the existence of a chemically distinct "hot core" component, likely due to the small filling factor of the hot core or hot cores within the Herschel beam. We find that the chemical composition of the gas in the cooler, quiescent component of

The results from a single-dish molecular line survey of a set of 18 deeply embedded young stellar... more The results from a single-dish molecular line survey of a set of 18 deeply embedded young stellar objects are summarized. More than 40 lines from 16 different species were observed with the JCMT, Onsala, IRAM 30m and SEST telescopes. The multi-transition data are analyzed using a temperature and density structure derived from models of the dust continuum emission. For the outer envelope (>300 AU), the data indicate a `drop' abundance profile for many species, with normal abundances in the outer- and innermost regions and highly depleted abundances in an intermediate zone. This zone is bounded at the outer than the lifetime of the core, and at the inner edge by the evaporation temperature of the species involved. In the innermost envelope (<300 AU), all ices evaporate resulting in jumps in the abundances of complex organic molecules such as CH3OH. A key project for Herschel will be to survey gas-phase water in these objects, whose abundance shows extreme variations with tem...

... Class 0 and Class I protostars are thought to correspond to the earliest stages of stellar ev... more ... Class 0 and Class I protostars are thought to correspond to the earliest stages of stellar evolution. Still heavily embedded, they are efficiently accreting their surrounding envelopes (André et al., 1993), and power energetic outflows. ... The references are: (1) André et al. ...

Monthly Notices of the Royal Astronomical Society

Although chemical models predict that the deuterium fractionation in N 2 H + is a good evolutiona... more Although chemical models predict that the deuterium fractionation in N 2 H + is a good evolutionary tracer in the star formation process, the fractionation of nitrogen is still a poorly understood process. Recent models have questioned the similar evolutionary trend expected for the two fractionation mechanisms in N 2 H + , based on a classical scenario in which ionneutral reactions occurring in cold gas should have caused an enhancement of the abundance of N 2 D + , 15 NNH + , and N 15 NH +. In the framework of the ASAI IRAM-30m large program, we have investigated the fractionation of deuterium and 15 N in N 2 H + in the best known representatives of the different evolutionary stages of the Sun-like star formation process. The goal is to ultimately confirm (or deny) the classical 'ion-neutral reactions' scenario that predicts a similar trend for D and 15 N fractionation. We do not find any evolutionary trend of the 14 N/ 15 N ratio from both the 15 NNH + and N 15 NH + isotopologues. Therefore, our findings confirm that, during the formation of a Sun-like star, the core evolution is irrelevant in the fractionation of 15 N. The independence of the 14 N/ 15 N ratio with time, found also in high-mass star-forming cores, indicates that the enrichment in 15 N revealed in comets and protoplanetary discs is unlikely to happen at core scales. Nevertheless, we have firmly confirmed the evolutionary trend expected for the H/D ratio, with the N 2 H + /N 2 D + ratio decreasing before the pre-stellar core phase, and increasing monotonically during the protostellar phase. We have also confirmed clearly that the two fractionation mechanisms are not related.

Monthly Notices of the Royal Astronomical Society

Monthly notices of the Royal Astronomical Society, Jan 14, 2018

Evidence is mounting that the small bodies of our Solar System, such as comets and asteroids, hav... more Evidence is mounting that the small bodies of our Solar System, such as comets and asteroids, have at least partially inherited their chemical composition from the first phases of the Solar System formation. It then appears that the molecular complexity of these small bodies is most likely related to the earliest stages of star formation. It is therefore important to characterize and to understand how the chemical evolution changes with solar-type protostellar evolution. We present here the Large Program "Astrochemical Surveys At IRAM" (ASAI). Its goal is to carry out unbiased millimeter line surveys between 80 and 272 GHz of a sample of ten template sources, which fully cover the first stages of the formation process of solar-type stars, from prestellar cores to the late protostellar phase. In this article, we present an overview of the surveys and results obtained from the analysis of the 3 mm band observations. The number of detected main isotopic species barely varies ...

Context. Despite the low elemental deuterium abundance in the Galaxy, enhanced molecular D/H rati... more Context. Despite the low elemental deuterium abundance in the Galaxy, enhanced molecular D/H ratios have been found in the environments of low-mass star-forming regions, and in particular the Class 0 protostar IRAS 16293-2422. Aims. The CHESS (Chemical HErschel Surveys of Star forming regions) key program aims to study the molecular complexity of the interstellar medium. The high sensitivity and spectral resolution of the Herschel/HIFI instrument provide a unique opportunity to observe the fundamental 11,1−00,0 transition of the ortho-D2O molecule, which is inaccessible from the ground, and determine the ortho-to-para D2O ratio. Methods. We detected the fundamental transition of the ortho-D2O molecule at 607.35 GHz towards IRAS 16293-2422. The line is seen in absorption with a line opacity of 0.62 ± 0.11 (1σ). From the previous ground-based observations of the fundamental 11,0−10,1 transition of para-D2O seen in absorption at 316.80 GHz, we estimate a line opacity of 0.26 ± 0.05 (1σ...

Sun like stars are born from the collapse of fragment of molecular clouds. During the first embed... more Sun like stars are born from the collapse of fragment of molecular clouds. During the first embedded phase (the so called class 0/1), the protostar is surrounded by a collapsing envelope, whose physical and chemical structure would set up the initial conditions of the proto-stellar disk which may eventually form planets. In this contribution, we show how spectroscopic far infrared to millimeter observations can be a powerful diagnostic to derive the chemical and physical structure of the innermost regions of envelopes collapsing around solar type protostars, where disk are believe to form. Our claim is based on the simultaneous modeling of the dynamics, chemistry and radiative transfer in a protostellar envelope. Here we present a study of a class 0 protostar NGC1333-IRAS4, obtained using ISO-LWS observations of water far-infrared lines. We show the derived physical and chemical structure of the protostar, namely the density and temperature profiles, as well as the water abundance a...

Context. Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict ... more Context. Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict relatively high levels of molecular oxygen, O2, and water, H2O. These high abundances imply high cooling rates, leading to relatively short timescales for the evolution of gravitationally unstable dense cores, forming stars and planets. Contrary to expectations, the dedicated space missions SWAS and Odin typically found only very small amounts of water vapour and essentially no O2 in the dense star-forming interstellar medium. Aims. Only toward ρOph A did Odin detect a very weak line of O2 at 119 GHz in a beam of size 10 arcmin. The line emission of related molecules changes on angular scales of the order of some tens of arcseconds, requiring a larger telescope aperture such as that of the Herschel Space Observatory to resolve the O2 emission and pinpoint its origin. Methods. We use the Heterodyne Instrument for the Far Infrared (HIFI) aboard Herschel to obtain high resolution O2 spectra...

We present a versatile digital autocorrelation spectrometer designed to suit the needs of HIFI, t... more We present a versatile digital autocorrelation spectrometer designed to suit the needs of HIFI, the sub-millimeter heterodyne instrument of the ESA's Herschel Space Observatory (HSO). This spectrometer will offer a set of four observation modes with different "channel spacing / total bandwidth" combinations. Each subband can be set anywhere in the 4-8 GHz input bandwidth. An original architecture made of an hybride Gallium Arsenide and Silicon technology allowed us to realize a 512 channel, low power consumption and high speed correlation module. INTRODUCTION HSO, the Herschel Space Observatory is the fourth corner stone of the European Space Agency Horizon 2000 program. It will be the first observatory studying the sub-millimeter domain from space in the range 100 m to 600 m. Herschel will be launched with an Ariane 5 rocket in the year 2007; it will be placed at the Lagrange point L2 at about 1.5 million kilometers from the Earth. Three instruments will be placed at ...

We report the detection of more than 48 velocity-resolved ground rotational state transitions of ... more We report the detection of more than 48 velocity-resolved ground rotational state transitions of H 16 2 O, H 18 2 O, and H 17 2 O – most for the first time – in both emission and absorption toward Orion KL using Herschel/HIFI. We show that a simple fit, constrained to match the known emission and absorption components along the line of sight, is in excellent agreement with the spectral profiles of all the water lines. Using the measured H 18 2 O line fluxes, which are less affected by line opacity than their H 16 2 O counterparts, and an escape probability method, the column densities of H 18 2 O associated with each emission component are derived. We infer total water abundances of 7.4× 10−5, 1.0× 10−5, and 1.6× 10−5 for the plateau, hot core, and extended warm gas, respectively. In the case of the plateau, this value is consistent with previous measures of the Orion-KL water abundance as well as those of other molecular outflows. In the case of the hot core and extended warm gas, ...

In contrast with numerous studies on the physical and chemical structure of lowand high-mass prot... more In contrast with numerous studies on the physical and chemical structure of lowand high-mass protostars, much less is known about their intermediate-mass counterparts, a class of objects that could help to elucidate the mechanisms of star formation on both ends of the mass range. We present the first results from a rich HIFI spectral dataset on an intermediate-mass protostar, OMC2-FIR4, obtained in the CHESS (Chemical HErschel Survey of Star forming regions) key programme. The more than 100 methanol lines detected between 554 and 961 GHz cover a range in upper level energy of 40 to 540 K. Our physical interpretation focusses on the hot core, but likely the cold envelope and shocked regions also play a role in reality, because an analysis of the line profiles suggests the presence of multiple emission components. An upper limit of 10−6 is placed on the methanol abundance in the hot core, using a population diagram, large-scale source model and other considerations. This value is cons...

Sun like stars are born from the collapse of fragment of molecular clouds. During the first embed... more Sun like stars are born from the collapse of fragment of molecular clouds. During the first embedded phase (the so called class 0/1), the protostar is surrounded by a collapsing envelope, whose physical and chemical structure would set up the initial conditions of the proto-stellar disk which may eventually form planets. In this contribution , we show how spectroscopic far infrared to millimeter observations can be a powerful diagnostic to derive the chemical and physical structure of the innermost regions of envelopes collapsing around solar type protostars, where disk are believe to form. Our claim is based on the simultaneous modeling of the dynamics , chemistry and radiative transfer in a protostellar envelope. Here we present a study of a class 0 protostar NGC1333-IRAS4, obtained using ISO-LWS observations of water far-infrared lines. We show the derived physical and chemical structure of the protostar, namely the density and temperature profiles, as well as the water abundance...

We report a detection of the fundamental rotational transition of hydrogen fluoride in absorption... more We report a detection of the fundamental rotational transition of hydrogen fluoride in absorption towards Orion KL using Herschel/HIFI. After the removal of contaminating features associated with common molecules (“weeds”), the HF spectrum shows a P-Cygni profile, with weak redshifted emission and strong blue-shifted absorption, associated with the low-velocity molecular outflow. We derive an estimate of 2.9 × 1013 cm−2 for the HF column density responsible for the broad absorption component. Using our best estimate of the H2 column density within the low-velocity molecular outflow, we obtain a lower limit of ∼1.6 × 10−10 for the HF abundance relative to hydrogen nuclei, corresponding to ∼0.6% of the solar abundance of fluorine. This value is close to that inferred from previous ISO observations of HF J = 2−1 absorption towards Sgr B2, but is in sharp contrast to the lower limit of 6 × 10−9 derived by Neufeld et al. for cold, foreground clouds on the line of sight towards G10.6-0.4.

MNRAS in press

The study of hot corinos in Solar-like protostars has been so far mostly limited to the Class 0 p... more The study of hot corinos in Solar-like protostars has been so far mostly limited to the Class 0 phase, hampering our understanding of their origin and evolution. In addition, recent evidence suggests that planet formation starts already during Class I phase, which, therefore, represents a crucial step in the future planetary system chemical composition. Hence, the study of hot corinos in Class I protostars has become of paramount importance. Here we report the discovery of a hot corino towards the prototypical Class I protostar L1551 IRS5, obtained within the ALMA Large Program FAUST. We detected several lines from methanol and its isopo-tologues (13 CH 3 OH and CH 2 DOH), methyl formate and ethanol. Lines are bright toward the north component of the IRS5 binary system, and a possible second hot corino may be associated with the south component. The methanol lines non-LTE analysis constrains the gas temperature (∼100 K), density (≥1.5×10 8 cm −3), and emitting size (∼10 au in radius...

We report new interferometric images of cyclopropenylidene, c–C 3 H 2 , towards the young protocl... more We report new interferometric images of cyclopropenylidene, c–C 3 H 2 , towards the young protocluster OMC–2 FIR 4. The observations were performed at 82 and 85 GHz with the NOrthern Extended Millimeter Array (NOEMA) as part of the project Seeds Of Life In Space (SOLIS). In addition, IRAM-30m data observations were used to investigate the physical structure of OMC–2 FIR 4. We find that the c–C 3 H 2 gas emits from the same region where previous SOLIS observations showed bright HC 5 N emission. From a non-LTE analysis of the IRAM-30m data, the c–C 3 H 2 gas has an average temperature of ∼40 K, a H 2 density of ∼3×10 5 cm −3 , and a c–C 3 H 2 abundance relative to H 2 of (7±1)×10 −12. In addition, the NOEMA observations provide no sign of significant c–C 3 H 2 excitation temperature gradients across the region (about 3-4 beams), with T ex in the range 8±3 up to 16±7 K. We thus infer that our observations are inconsistent with a physical interaction of the OMC–2 FIR 4 envelope with the...

The Astrophysical Journal

We present results from a comprehensive submillimeter spectral survey toward the source Orion Sou... more We present results from a comprehensive submillimeter spectral survey toward the source Orion South, based on data obtained with the HIFI instrument aboard the Herschel Space Observatory, covering the frequency range 480 to 1900 GHz. We detect 685 spectral lines with S/N > 3σ, originating from 52 different molecular and atomic species. We model each of the detected species assuming conditions of Local Thermodynamic Equilibrium. This analysis provides an estimate of the physical conditions of Orion South (column density, temperature, source size, & V LSR). We find evidence for three different cloud components: a cool (T ex ∼ 20 − 40 K), spatially extended (> 60), and quiescent (∆V F W HM ∼ 4 km s −1) component; a warmer (T ex ∼ 80 − 100 K), less spatially extended (∼ 30), and dynamic (∆V F W HM ∼ 8 km s −1) component, which is likely affected by embedded outflows; and a kinematically distinct region (T ex > 100 K; V LSR ∼ 8 km s −1), dominated by emission from species which trace ultraviolet irradiation, likely at the surface of the cloud. We find little evidence for the existence of a chemically distinct "hot core" component, likely due to the small filling factor of the hot core or hot cores within the Herschel beam. We find that the chemical composition of the gas in the cooler, quiescent component of

The results from a single-dish molecular line survey of a set of 18 deeply embedded young stellar... more The results from a single-dish molecular line survey of a set of 18 deeply embedded young stellar objects are summarized. More than 40 lines from 16 different species were observed with the JCMT, Onsala, IRAM 30m and SEST telescopes. The multi-transition data are analyzed using a temperature and density structure derived from models of the dust continuum emission. For the outer envelope (>300 AU), the data indicate a `drop' abundance profile for many species, with normal abundances in the outer- and innermost regions and highly depleted abundances in an intermediate zone. This zone is bounded at the outer than the lifetime of the core, and at the inner edge by the evaporation temperature of the species involved. In the innermost envelope (<300 AU), all ices evaporate resulting in jumps in the abundances of complex organic molecules such as CH3OH. A key project for Herschel will be to survey gas-phase water in these objects, whose abundance shows extreme variations with tem...

... Class 0 and Class I protostars are thought to correspond to the earliest stages of stellar ev... more ... Class 0 and Class I protostars are thought to correspond to the earliest stages of stellar evolution. Still heavily embedded, they are efficiently accreting their surrounding envelopes (André et al., 1993), and power energetic outflows. ... The references are: (1) André et al. ...

Monthly Notices of the Royal Astronomical Society

Although chemical models predict that the deuterium fractionation in N 2 H + is a good evolutiona... more Although chemical models predict that the deuterium fractionation in N 2 H + is a good evolutionary tracer in the star formation process, the fractionation of nitrogen is still a poorly understood process. Recent models have questioned the similar evolutionary trend expected for the two fractionation mechanisms in N 2 H + , based on a classical scenario in which ionneutral reactions occurring in cold gas should have caused an enhancement of the abundance of N 2 D + , 15 NNH + , and N 15 NH +. In the framework of the ASAI IRAM-30m large program, we have investigated the fractionation of deuterium and 15 N in N 2 H + in the best known representatives of the different evolutionary stages of the Sun-like star formation process. The goal is to ultimately confirm (or deny) the classical 'ion-neutral reactions' scenario that predicts a similar trend for D and 15 N fractionation. We do not find any evolutionary trend of the 14 N/ 15 N ratio from both the 15 NNH + and N 15 NH + isotopologues. Therefore, our findings confirm that, during the formation of a Sun-like star, the core evolution is irrelevant in the fractionation of 15 N. The independence of the 14 N/ 15 N ratio with time, found also in high-mass star-forming cores, indicates that the enrichment in 15 N revealed in comets and protoplanetary discs is unlikely to happen at core scales. Nevertheless, we have firmly confirmed the evolutionary trend expected for the H/D ratio, with the N 2 H + /N 2 D + ratio decreasing before the pre-stellar core phase, and increasing monotonically during the protostellar phase. We have also confirmed clearly that the two fractionation mechanisms are not related.

Monthly Notices of the Royal Astronomical Society

Monthly notices of the Royal Astronomical Society, Jan 14, 2018

Evidence is mounting that the small bodies of our Solar System, such as comets and asteroids, hav... more Evidence is mounting that the small bodies of our Solar System, such as comets and asteroids, have at least partially inherited their chemical composition from the first phases of the Solar System formation. It then appears that the molecular complexity of these small bodies is most likely related to the earliest stages of star formation. It is therefore important to characterize and to understand how the chemical evolution changes with solar-type protostellar evolution. We present here the Large Program "Astrochemical Surveys At IRAM" (ASAI). Its goal is to carry out unbiased millimeter line surveys between 80 and 272 GHz of a sample of ten template sources, which fully cover the first stages of the formation process of solar-type stars, from prestellar cores to the late protostellar phase. In this article, we present an overview of the surveys and results obtained from the analysis of the 3 mm band observations. The number of detected main isotopic species barely varies ...