arXiv subjects

Emmanuel Caux

Publications and source records attributed to Emmanuel Caux.

At least 19 recordsLinked to original sources

arXiv2024

Multiple chemical tracers finally unveil the intricate NGC\,1333 IRAS\,4A outflow system. FAUST XVI

The exploration of outflows in protobinary systems presents a challenging yet crucial endeavour, offering valuable insights into the dynamic interplay between protostars and their evolution. In this study, we examine the morphology and dynamics of jets and outflows within the IRAS\,4A protobinary system. This analysis is based on ALMA observations of SiO(5--4), H$_2$CO(3$_{0,3}$--2$_{0,3}$), and HDCO(4$_{1,4}$--3$_{1,3}$) with a spatial resolution of $\sim$150\,au. Leveraging an astrochemical approach involving the use of diverse tracers beyond traditional ones has enabled the identification of novel features and a comprehensive understanding of the broader outflow dynamics. Our analysis reveals the presence of two jets in the redshifted emission, emanating from IRAS\,4A1 and IRAS\,4A2, respectively. Furthermore, we identify four distinct outflows in the region for the first time, with each protostar, 4A1 and 4A2, contributing to two of them. We characterise the morphology and orientation of each outflow, challenging previous suggestions of bends in their trajectories. The outflow cavities of IRAS\,4A1 exhibit extensions of 10$''$ and 13$''$ with position angles (PA) of 0$^{\circ}$ and -12$^{\circ}$, respectively, while those of IRAS\,4A2 are more extended, spanning 18$''$ and 25$''$ with PAs of 29$^{\circ}$ and 26$^{\circ}$. We propose that the misalignment of the cavities is due to a jet precession in each protostar, a notion supported by the observation that the more extended cavities of the same source exhibit lower velocities, indicating they may stem from older ejection events.

astro-ph.GA↗

arXiv2022

FAUST III. Misaligned rotations of the envelope, outflow, and disks in the multiple protostellar system of VLA 1623$-$2417

We report a study of the low-mass Class-0 multiple system VLA 1623AB in the Ophiuchus star-forming region, using H$^{13}$CO$^+$ ($J=3-2$), CS ($J=5-4$), and CCH ($N=3-2$) lines as part of the ALMA Large Program FAUST. The analysis of the velocity fields revealed the rotation motion in the envelope and the velocity gradients in the outflows (about 2000 au down to 50 au). We further investigated the rotation of the circum-binary VLA 1623A disk as well as the VLA 1623B disk. We found that the minor axis of the circum-binary disk of VLA 1623A is misaligned by about 12 degrees with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circum-binary disk is parallel to the large-scale magnetic field according to previous dust polarization observations, suggesting that the misalignment may be caused by the different directions of the envelope rotation and the magnetic field. If the velocity gradient of the outflow is caused by rotation, the outflow has a constant angular momentum and the launching radius is estimated to be $5-16$ au, although it cannot be ruled out that the velocity gradient is driven by entrainments of the two high-velocity outflows. Furthermore, we detected for the first time a velocity gradient associated with rotation toward the VLA 16293B disk. The velocity gradient is opposite to the one from the large-scale envelope, outflow, and circum-binary disk. The origin of its opposite gradient is also discussed.

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arXiv2021

FAUST II. Discovery of a Secondary Outflow in IRAS 15398-3359: Variability in Outflow Direction during the Earliest Stage of Star Formation?

We have observed the very low-mass Class 0 protostar IRAS 15398-3359 at scales ranging from 50 au to 1800 au, as part of the ALMA Large Program FAUST. We uncover a linear feature, visible in H2CO, SO, and C18O line emission, which extends from the source along a direction almost perpendicular to the known active outflow. Molecular line emission from H2CO, SO, SiO, and CH3OH further reveals an arc-like structure connected to the outer end of the linear feature and separated from the protostar, IRAS 15398-3359, by 1200 au. The arc-like structure is blue-shifted with respect to the systemic velocity. A velocity gradient of 1.2 km/s over 1200 au along the linear feature seen in the H2CO emission connects the protostar and the arc-like structure kinematically. SO, SiO, and CH3OH are known to trace shocks, and we interpret the arc-like structure as a relic shock region produced by an outflow previously launched by IRAS 15398-3359. The velocity gradient along the linear structure can be explained as relic outflow motion. The origins of the newly observed arc-like structure and extended linear feature are discussed in relation to turbulent motions within the protostellar core and episodic accretion events during the earliest stage of protostellar evolution.

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arXiv2019

Sulfur-Bearing Species Tracing the Disk/Envelope System in the Class I Protostellar Source Elias 29

We have observed the Class I protostellar source Elias 29 with Atacama Large Millimeter/submillimeter Array (ALMA). We have detected CS, SO, $^{34}$SO, SO$_2$, and SiO line emissions in a compact component concentrated near the protostar and a ridge component separated from the protostar by 4\arcsec\ ($\sim 500$ au). The former component is found to be abundant in SO and SO$_2$ but deficient in CS. The abundance ratio SO/CS is as high as $3^{+13}_{-2} \times 10^2$ at the protostar, which is even higher than that in the outflow-shocked region of L1157 B1. However, organic molecules (HCOOCH$_3$, CH$_3$OCH$_3$, CCH, and c-C$_3$H$_2$) are deficient in Elias 29. We attribute the deficiency in organic molecules and richness in SO and SO$_2$ to the evolved nature of the source or the relatively high dust temperature (\protect\raisebox{-0.7ex}{$\:\stackrel{\textstyle >}{\sim}\:$} 20 K) in the parent cloud of Elias 29. The SO and SO$_2$ emissions trace rotation around the protostar. Assuming a highly inclined configuration ($i \geq 65$\degr; 0\degr\ for a face-on configuration) and Keplerian motion for simplicity, the protostellar mass is estimated to be (0.8 -- 1.0) \Msun. The $^{34}$SO and SO$_2$ emissions are asymmetric in their spectra; the blue-shifted components are weaker than the red-shifted ones. Although this may be attributed to the asymmetric molecular distribution, other possibilities are also discussed.

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arXiv2019

On the nature of the compact sources in IRAS 16293-2422 seen in at centimeter to sub-millimeter wavelengths

We present multi-epoch continuum observations of the Class 0 protostellar system IRAS 16293-2422 taken with the Very Large Array (VLA) at multiple wavelengths between 7 mm and 15 cm (41 GHz down to 2 GHz), as well as single-epoch Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations covering the range from 0.4 to 1.3 mm (700 GHz down to 230 GHz). The new VLA observations confirm that source A2 is a protostar driving episodic mass ejections, and reveal the complex relative motion between A2 and A1. The spectrum of component B can be described by a single power law ($S_ν\propto ν^{2.28}$) over the entire range from 3 to 700 GHz (10 cm down to 0.4 mm), suggesting that the emission is entirely dominated by dust even at $λ$ = 10 cm. Finally, the size of source B appears to increase with frequency up to 41 GHz, remaining roughly constant (at $0''.39$ $\equiv$ 55 AU) at higher frequencies. We interpret this as evidence that source B is a dusty structure of finite size that becomes increasingly optically thick at higher frequencies until, in the millimeter regime, the source becomes entirely optically thick. The lack of excess free-free emission at long wavelengths, combined with the absence of high-velocity molecular emission indicates that source B does not drive a powerful outflow, and might indicate that source B is at a particularly early stage of its evolution.

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arXiv2018

Modelling the abundance structure of isocyanic acid (HNCO) toward the low-mass solar type protostar IRAS 16293-2422

Isocyanic acid (HNCO), the most stable of the simplest molecules containing the four main elements essential for organic chemistry, has been observed in several astrophysical environments such as molecular clouds, star-forming regions, external galaxies and comets. In this work, we model HNCO spectral line profiles toward the low-mass solar type protostar IRAS 16293$-2$422 observed with the ALMA interferometer, the IRAM, JCMT and APEX single-dish radio telescopes, and the HIFI instrument on board the Herschel Space Observatory. In star-forming environments, the HNCO emission is not always in Local Thermodynamical Equilibrium (LTE). A non-LTE radiative transfer approach is necessary to properly interpret the line profiles, and accurate collisional rate coefficients are needed. Here, we used the RADEX package with a completely new set of collisional quenching rates between HNCO and both ortho-H$_2$ and para-H$_2$ obtained from quantum chemical calculations yielding a novel potential energy surface in the rigid rotor approximation. We find that the lines profiles toward IRAS 16293$-$2422 are very well reproduced if we assume that the HNCO emission arises from a compact, dense and hot physical component associated with the hot corino, a warm component associated with the internal part of the protostellar envelope, and a cold and more extended component associated with the outer envelope. The derived HNCO abundances from our model agree well with those computed with the Nautilus chemical code.

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arXiv2018

Detection of HOCO+ in the protostar IRAS 16293-2422

The protonated form of CO2, HOCO+, is assumed to be an indirect tracer of CO2 in the millimeter/submillimeter regime since CO2 lacks a permanent dipole moment. Here, we report the detection of two rotational emission lines (4 0,4-3 0,3) and (5 0,5-4 0,4) of HOCO+ in IRAS 16293-2422. For our observations, we have used EMIR heterodyne 3 mm receiver of the IRAM 30m telescope. The observed abundance of HOCO+ is compared with the simulations using the 3-phase NAUTILUS chemical model. Implications of the measured abundances of HOCO+ to study the chemistry of CO2 ices using JWST-MIRI and NIRSpec are discussed as well.

astro-ph.GA↗

arXiv2018

Seeds of Life in Space (SOLIS). III. Zooming into the methanol peak of the pre-stellar core L1544

Towards the pre-stellar core L1544, the methanol (CH$_3$OH) emission forms an asymmetric ring around the core centre, where CH$_3$OH is mostly in solid form, with a clear peak 4000~au to the north-east of the dust continuum peak. As part of the NOEMA Large Project SOLIS (Seeds of Life in Space), the CH$_3$OH peak has been spatially resolved to study its kinematics and physical structure and to investigate the cause behind the local enhancement. We find that methanol emission is distributed in a ridge parallel to the main axis of the dense core. The centroid velocity increases by about 0.2~km~s$^{-1}$ and the velocity dispersion increases from subsonic to transonic towards the central zone of the core, where the velocity field also shows complex structure. This could be indication of gentle accretion of material onto the core or interaction of two filaments, producing a slow shock. We measure the rotational temperature and show that methanol is in local thermodynamic equilibrium (LTE) only close to the dust peak, where it is significantly depleted. The CH$_3$OH column density, $N_{tot}({\rm CH_3OH})$, profile has been derived with non-LTE radiative transfer modelling and compared with chemical models of a static core. The measured $N_{tot}({\rm CH_3OH})$ profile is consistent with model predictions, but the total column densities are one order of magnitude lower than those predicted by models, suggesting that the efficiency of reactive desorption or atomic hydrogen tunnelling adopted in the model may be overestimated; or that an evolutionary model is needed to better reproduce methanol abundance.

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arXiv2017

Vertical Structure of the Transition Zone from Infalling Rotating Envelope to Disk in the Class 0 Protostar, IRAS04368+2557

We have resolved for the first time the radial and vertical structure of the almost edge-on envelope/disk system of the low-mass Class 0 protostar L1527. For that, we have used ALMA observations with a spatial resolution of 0.25$^{\prime\prime}$$\times$0.13$^{\prime\prime}$ and 0.37$^{\prime\prime}$$\times$0.23$^{\prime\prime}$ at 0.8 mm and 1.2 mm, respectively. The L1527 dust continuum emission has a deconvolved size of 78 au $\times$ 21 au, and shows a flared disk-like structure. A thin infalling-rotating envelope is seen in the CCH emission outward of about 150 au, and its thickness is increased by a factor of 2 inward of it. This radius lies between the centrifugal radius (200 au) and the centrifugal barrier of the infalling-rotating envelope (100 au). The gas stagnates in front of the centrifugal barrier and moves toward vertical directions. SO emission is concentrated around and inside the centrifugal barrier. The rotation speed of the SO emitting gas is found to be decelerated around the centrifugal barrier. A part of the angular momentum could be extracted by the gas which moves away from the mid-plane around the centrifugal barrier. If this is the case, the centrifugal barrier would be related to the launching mechanism of low velocity outflows, such as disk winds.

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arXiv2017

L483: Warm Carbon-Chain Chemistry Source Harboring Hot Corino Activity

The Class 0 protostar, L483, has been observed in various molecular lines in the 1.2 mm band at a sub-arcsecond resolution with ALMA. An infalling-rotating envelope is traced by the CS line, while a very compact component with a broad velocity width is observed for the CS, SO, HNCO, NH$_2$CHO, and HCOOCH$_3$ lines. Although this source is regarded as the warm carbon-chain chemistry (WCCC) candidate source at a 1000 au scale, complex organic molecules characteristic of hot corinos such as NH$_2$CHO and HCOOCH$_3$ are detected in the vicinity of the protostar. Thus, both hot corino chemistry and WCCC are seen in L483. Although such a mixed chemical character source has been recognized as an intermediate source in previous single-dish observations, we here report the first spatially-resolved detection. A kinematic structure of the infalling-rotating envelope is roughly explained by a simple ballistic model with the protostellar mass of 0.1--0.2 $M_\odot$ and the radius of the centrifugal barrier (a half of the centrifugal radius) of 30--200 au, assuming the inclination angle of 80\degr\ (0\degr\ for a face-on). The broad line emission observed in the above molecules most likely comes from the disk component inside the centrifugal barrier. Thus, a drastic chemical change is seen around the centrifugal barrier.

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arXiv2016

Discovery of a Hot Corino in the Bok Globule B335

We report the first evidence of a hot corino in a Bok globule. This is based on the ALMA observations in the 1.2 mm band toward the low-mass Class 0 protostar IRAS 19347+0727 in B335. Saturated complex organic molecules (COMs), CH$_3$CHO, HCOOCH$_3$, and NH$_2$CHO, are detected in a compact region within a few 10 au around the protostar. Additionally, CH$_3$OCH$_3$, C$_2$H$_5$OH, C$_2$H$_5$CN, and CH$_3$COCH$_3$ are tentatively detected. Carbon-chain related molecules, CCH and c-C$_3$H$_2$, are also found in this source, whose distributions are extended over a few 100 au scale. On the other hand, sulfur-bearing molecules CS, SO, and SO$_2$, have both compact and extended components. Fractional abundances of the COMs relative to H$_2$ are found to be comparable to those in known hot-corino sources. Though the COMs lines are as broad as 5-8 km s$^{-1}$, they do not show obvious rotation motion in the present observation. Thus, the COMs mainly exist in a structure whose distribution is much smaller than the synthesized beam (0."58 x 0."52).

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arXiv2016

Subarcsecond Analysis of Infalling-Rotating Envelope around the Class I Protostar IRAS 04365+2535

Sub-arcsecond images of the rotational line emission of CS and SO have been obtained toward the Class I protostar IRAS 04365$+$2535 in TMC-1A with ALMA. A compact component around the protostar is clearly detected in the CS and SO emission. The velocity structure of the compact component of CS reveals infalling-rotating motion conserving the angular momentum. It is well explained by a ballistic model of an infalling-rotating envelope with the radius of the centrifugal barrier (a half of the centrifugal radius) of 50 AU, although the distribution of the infalling gas is asymmetric around the protostar. The distribution of SO is mostly concentrated around the radius of the centrifugal barrier of the simple model. Thus a drastic change in chemical composition of the gas infalling onto the protostar is found to occur at a 50 AU scale probably due to accretion shocks, demonstrating that the infalling material is significantly processed before being delivered into the disk.

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arXiv2016

Detection of CH3SH in protostar IRAS 16293-2422

The nature of the main sulphur reservoir in star forming regions is a long standing mystery. The observed abundance of sulphur-bearing species in dense clouds is only about 0.1 per cent of the same quantity in diffuse clouds. Therefore, the main sulphur species in star forming regions of the interstellar medium are still unknown. IRAS 16293-2422 is one of the regions where production of S-bearing species is favourable due to its conditions which allows the evaporation of ice mantles. We carried out observations in the 3 mm band towards the solar type protostar IRAS 16293-2422 with the IRAM 30m telescope. We observed a single frequency setup with the EMIR heterodyne 3 mm receiver with an Lower Inner (LI) tuning frequency of 89.98 GHz. Several lines of the complex sulphur species CH3SH were detected. Observed abundances are compared with simulations using the NAUTILUS gas-grain chemical model. Modelling results suggest that CH3SH has the constant abundance of 4e-9 (compared to H2) for radii lower than 200 AU and is mostly formed on the surfaces. Detection of CH3SH indicates that there may be several new families of S-bearing molecules (which could form starting from CH3SH) which have not been detected or looked for yet.

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arXiv2015

Abundance Anomaly of the $^{13}$C Isotopic Species of c-C$_3$H$_2$ in the Low-Mass Star Formation Region L1527

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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arXiv2014

Water deuterium fractionation in the high-mass star-forming region G34.26+0.15 based on Herschel/HIFI data

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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arXiv2012

Herschel CHESS discovery of the fossil cloud that gave birth to the Trapezium and Orion KL

As part of the Herschel Guaranteed Time Key Programme CHESS, we present the discovery of a diffuse gas component in the foreground of the intermediate-mass protostar OMC-2 FIR 4, located in the Orion A region. Making use of the full HIFI spectrum of OMC-2 FIR 4 obtained in CHESS, we detected several ground-state lines from OH+, H2O+, HF, and CH+, all of them seen in absorption against the dust continuum emission of the protostar's envelope. The lines peak at a velocity of 9 km/s, which is blue-shifted by 2 km/s with respect to the systemic velocity of OMC-2 FIR 4 (V = 11.4 km/s). We derived column densities for each species, as well as an upper limit to the column density of the undetected H3O+. In order to model and characterise the foreground cloud, we used the Meudon PDR code to run a homogeneous grid of models that spans a reasonable range of densities, visual extinctions, cosmic ray ionisation rates and far-ultraviolet (FUV) radiation fields. The results of our modelling indicate that the foreground cloud is composed of predominantly neutral diffuse gas (n(H) = 100 cm-3) and is heavily irradiated by an external source of FUV that most likely arises from the nearby Trapezium OB association. The cloud is 6 pc thick and bears many similarities with the so-called C+ interface between Orion-KL and the Trapezium cluster, 2 pc south of OMC-2 FIR 4. We conclude that the foreground cloud we detected is an extension of the C+ interface seen in the direction of Orion KL, and interpret it to be the remains of the parental cloud of OMC-1, which extends from OMC-1 up to OMC-2.

astro-ph.GA↗

arXiv2012

PlotXY: a high quality plotting system for the Herschel Interactive Processing Environment (HIPE), and the astronomical community

The Herschel Interactive Processing Environment (HIPE) was developed by the European Space Agency (ESA) in collaboration with NASA and the Herschel Instrument Control Centres to provide the astronomical community a complete environment to process and analyze the data gathered by the Herschel Space Observatory. One of the most important components of HIPE is the plotting system (named PlotXY) that we present here. With PlotXY it is possible to produce easily high quality publication ready 2D plots. It provides a long list of features, with fully configurable components, and interactive zooming. The entire code of HIPE is written in Java and is open source released under the GNU Lesser General Public License version 3. A new version of PlotXY is being developed to be independent from the HIPE code base; it is available to the software development community for the inclusion in other projects at the URL http://code.google.com/p/jplot2d/.

cs.GR↗

arXiv2012

A study of deuterated water in the low-mass protostar IRAS16293-2422

The HDO/H2O ratio is a powerful diagnostic to understand the evolution of water from the first stages of star formation to the formation of planets and comets. Our aim is to determine precisely the abundance distribution of HDO towards the low-mass protostar IRAS16293-2422 and learn more about the water formation mechanisms by determining the HDO/H2O abundance ratio. A spectral survey of the source IRAS16293-2422 was carried out in the framework of the CHESS Herschel Key program with the HIFI instrument, allowing the detection of numerous HDO lines. Other transitions have been observed previously with ground-based telescopes. The spherical Monte Carlo radiative transfer code RATRAN was used to reproduce the observed line profiles of HDO by assuming an abundance jump. To determine the H2O abundance throughout the envelope, a similar study was made of the H2-18O observed lines, as the H2O main isotope lines are contaminated by the outflows. We derive an inner HDO abundance of 1.7e-7 and an outer HDO abundance of 8e-11. To reproduce the HDO absorption lines, it is necessary to add an absorbing layer in front of the envelope. It may correspond to a water-rich layer created by the photodesorption of the ices at the edges of the molecular cloud. The HDO/H2O ratio is ~1.4-5.8% in the hot corino whereas it is ~0.2-2.2% in the outer envelope. It is estimated at ~4.8% in the added absorbing layer. Although it is clearly higher than the cosmic D/H abundance, the HDO/H2O ratio remains lower than the D/H ratio derived for other deuterated molecules observed in the same source. The similarity of the ratios derived in the hot corino and in the added absorbing layer suggests that water formed before the gravitational collapse of the protostar, contrary to formaldehyde and methanol, which formed later once the CO molecules had depleted on the grains.

astro-ph.GA↗