Complexité chimique des protoétoiles de masse intermédiaire : une étude de Cep E-mm

Intermediate-mass stars (2 M⊙ ≤ M ≤ 10 M⊙) are among the dominant sources of FUV interstellar field in the Galaxy. They regulate the phases of interstellar medium and the whole process of galactic star formation. While solar-type and massive protostars have been and continue to be the subject of many studies, the formation of intermediate stars has been relatively little studied. Their physical structure, chemical composition and molecular richness are still a subject to explore.The aim of my thesis is to obtain a detailed census, as complete as possible ,of the physical and chemical structure of an isolated intermediate-mass protostar: Cep E-mm (100 L⊙).I have completed a spectral survey of the molecular emission in the (sub)millimetre bands between 72 and 350 GHz with IRAM 30m telescope. The sensitivity of the observations made it possible to identify the presence of numerous complex organic molecules (COMs) in the protostar envelope, but also several unusual molecular species in the protostellar jet. Additionally, further observations with the IRAM 30m telescope made it possible to map the molecular emission at large scale (20’’ to 11’’; 15000 to 8000 AU). In parallel, interferometric maps of the molecular emission between 86 – 90 GHz and 216 – 220 GHz were obtained with NOEMA, the IRAM interferometer, at 1.4’’ (1000 AU) of angular resolution. These observations allowed me to obtain the distribution of molecular emission within the source, from large scales in the outer parts of the extended envelope, to the small scales in the hot corino region. The single-dish and interferometric observations were reduced and analysed in a meticulous manner. More precisely, I identified and separated the molecular emission contribution from the different physical regions as observed with the IRAM 30m telescope. I have identified and characterized fours physical components that differ in their spectroscopic properties and excitation conditions: the extended envelope, the hot corino, the bipolar outflow and the high-velocity jet. Finally, the anisotropy of the brightness distribution from the outflow system cannot be modelled by the “classical” Gaussian approach. I have developed specific tools to estimate, in a semi-analytical manner, the coupling between the telescope lobe and the source.Les étoiles de masse intermédiaire (2M⊙ ≤ M ≤ 10M⊙) sont parmi les sources dominantes du champ interstellaire FUV dans la Galaxie. Elles régulent les phases du milieu interstellaire et l’ensemble des processus de formation stellaire galactique. Alors que les protoétoiles de type solaire et massives ont été et continuent à faire l’objet de nombreuses études, la formation des étoiles intermédiaires a été relativement peu étudiée. Leur structure physique, composition chimique et leur richesse moléculaire sont un domaine à explorer.L’objectif de ma thèse est d’obtenir un recensement détaillé et aussi complète que possible des propriétés physico-chimiques d’une protoétoile isolée de masse intermédiaire. Notre choix s’est porté sur Cep E-mm (100 L⊙).J’ai pour cela complété un relevé spectral de l’émission moléculaire dans les bandes (sub)millimétriques entre 72 et 350 GHz avec le télescope de 30m de l’IRAM. La sensibilité des observations a permis d’identifier la présence de nombreuses molécules complexes organiques (COMs) dans l’enveloppe de la protoétoile, mais aussi, plusieurs espèces moléculaires inhabituelles dans le jet généré par la protoétoile. Des observations complémentaires avec le télescope de 30m ont permis de cartographier l’émission moléculaire à grande échelle (20’’ à 11’’ ; 15000 à 8000 UA). En parallèle, des cartes interférométriques de l’émission moléculaire entre 86 – 90 GHz et 216 – 220 GHz ont été obtenues avec l’interféromètre de l’IRAM (NOEMA) à 1.4’’ (1000 UA) de résolution angulaire. Ces observations m’ont permis d’obtenir une première description de la distribution de l’émission moléculaire au sein de l’enveloppe, des grandes échelles, dans les parties extérieures de l’enveloppe étendue, aux petites échelles dans la région d’un hot corino. Les études présentées ici ont suivi un travail méticuleux de réduction et d’analyse des données, single-dish et interférométriques. Plus précisément, j’ai identifié et séparé les contributions à l’émission détectée dans le lobe du télescope de 30m de l’IRAM des différentes régions physiques du cœur protostellaire. De ce fait, j’ai identifié et caractérisé quatre composantes physiques qui diffèrent par leurs propriétés spectroscopiques et leurs conditions d’excitation : l’enveloppe étendue, le hot corino, le flot bipolaire basse vitesse et le jet à haute vitesse. Enfin, l’anisotropie de la distribution de brillance du flot et du jet bipolaire ne peut pas être modélisée par l’approche ‘’classique’’ d’une source gaussienne. J’ai développé des outils spécifiques semi-analytiques pour calculer de manière approchée, et plus raisonnable, le couplage entre le lobe du télescope et la source

Chemical complexity of intermediate mass protostars : a study of Cep E-mm

Les étoiles de masse intermédiaire (2M⊙ ≤ M ≤ 10M⊙) sont parmi les sources dominantes du champ interstellaire FUV dans la Galaxie. Elles régulent les phases du milieu interstellaire et l’ensemble des processus de formation stellaire galactique. Alors que les protoétoiles de type solaire et massives ont été et continuent à faire l’objet de nombreuses études, la formation des étoiles intermédiaires a été relativement peu étudiée. Leur structure physique, composition chimique et leur richesse moléculaire sont un domaine à explorer.L’objectif de ma thèse est d’obtenir un recensement détaillé et aussi complète que possible des propriétés physico-chimiques d’une protoétoile isolée de masse intermédiaire. Notre choix s’est porté sur Cep E-mm (100 L⊙).J’ai pour cela complété un relevé spectral de l’émission moléculaire dans les bandes (sub)millimétriques entre 72 et 350 GHz avec le télescope de 30m de l’IRAM. La sensibilité des observations a permis d’identifier la présence de nombreuses molécules complexes organiques (COMs) dans l’enveloppe de la protoétoile, mais aussi, plusieurs espèces moléculaires inhabituelles dans le jet généré par la protoétoile. Des observations complémentaires avec le télescope de 30m ont permis de cartographier l’émission moléculaire à grande échelle (20’’ à 11’’ ; 15000 à 8000 UA). En parallèle, des cartes interférométriques de l’émission moléculaire entre 86 – 90 GHz et 216 – 220 GHz ont été obtenues avec l’interféromètre de l’IRAM (NOEMA) à 1.4’’ (1000 UA) de résolution angulaire. Ces observations m’ont permis d’obtenir une première description de la distribution de l’émission moléculaire au sein de l’enveloppe, des grandes échelles, dans les parties extérieures de l’enveloppe étendue, aux petites échelles dans la région d’un hot corino. Les études présentées ici ont suivi un travail méticuleux de réduction et d’analyse des données, single-dish et interférométriques. Plus précisément, j’ai identifié et séparé les contributions à l’émission détectée dans le lobe du télescope de 30m de l’IRAM des différentes régions physiques du cœur protostellaire. De ce fait, j’ai identifié et caractérisé quatre composantes physiques qui diffèrent par leurs propriétés spectroscopiques et leurs conditions d’excitation : l’enveloppe étendue, le hot corino, le flot bipolaire basse vitesse et le jet à haute vitesse. Enfin, l’anisotropie de la distribution de brillance du flot et du jet bipolaire ne peut pas être modélisée par l’approche ‘’classique’’ d’une source gaussienne. J’ai développé des outils spécifiques semi-analytiques pour calculer de manière approchée, et plus raisonnable, le couplage entre le lobe du télescope et la source.Intermediate-mass stars (2 M⊙ ≤ M ≤ 10 M⊙) are among the dominant sources of FUV interstellar field in the Galaxy. They regulate the phases of interstellar medium and the whole process of galactic star formation. While solar-type and massive protostars have been and continue to be the subject of many studies, the formation of intermediate stars has been relatively little studied. Their physical structure, chemical composition and molecular richness are still a subject to explore.The aim of my thesis is to obtain a detailed census, as complete as possible ,of the physical and chemical structure of an isolated intermediate-mass protostar: Cep E-mm (100 L⊙).I have completed a spectral survey of the molecular emission in the (sub)millimetre bands between 72 and 350 GHz with IRAM 30m telescope. The sensitivity of the observations made it possible to identify the presence of numerous complex organic molecules (COMs) in the protostar envelope, but also several unusual molecular species in the protostellar jet. Additionally, further observations with the IRAM 30m telescope made it possible to map the molecular emission at large scale (20’’ to 11’’; 15000 to 8000 AU). In parallel, interferometric maps of the molecular emission between 86 – 90 GHz and 216 – 220 GHz were obtained with NOEMA, the IRAM interferometer, at 1.4’’ (1000 AU) of angular resolution. These observations allowed me to obtain the distribution of molecular emission within the source, from large scales in the outer parts of the extended envelope, to the small scales in the hot corino region. The single-dish and interferometric observations were reduced and analysed in a meticulous manner. More precisely, I identified and separated the molecular emission contribution from the different physical regions as observed with the IRAM 30m telescope. I have identified and characterized fours physical components that differ in their spectroscopic properties and excitation conditions: the extended envelope, the hot corino, the bipolar outflow and the high-velocity jet. Finally, the anisotropy of the brightness distribution from the outflow system cannot be modelled by the “classical” Gaussian approach. I have developed specific tools to estimate, in a semi-analytical manner, the coupling between the telescope lobe and the source

Seeds of Life in Space (SOLIS). III. Zooming Into the Methanol Peak of the Prestellar Core L1544

International audienceToward the prestellar core L1544, the methanol (CH3OH) emission forms an asymmetric ring around the core center, where CH3OH is mostly in solid form, with a clear peak at 4000 au to the northeast of the dust continuum peak. As part of the NOEMA Large Project SOLIS (Seeds of Life in Space), the CH3OH 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 toward the central zone of the core, where the velocity field also shows complex structure. This could be an indication of gentle accretion of material onto the core or the 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 CH3OH column density, N-tot(CH3OH), profile has been derived with non-LTE radiative transfer modeling and compared with chemical models of a static core. The measured N (tot)(CH3OH) 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 tunneling adopted in the model may be overestimated; or that an evolutionary model is needed to better reproduce methanol abundance

Seeds of Life in Space (SOLIS) VI. Chemical evolution of sulfuretted species along the outflows driven by the low-mass protostellar binary NGC1333-IRAS4A

International audienceContext. Low-mass protostars drive powerful molecular outflows that can be observed with millimetre and submillimetre telescopes. Various sulfuretted species are known to be bright in shocks and could be used to infer the physical and chemical conditions throughout the observed outflows. Aims. The evolution of sulfur chemistry is studied along the outflows driven by the NGC1333-IRAS4A protobinary system located in the Perseus cloud to constrain the physical and chemical processes at work in shocks. Methods. We observed various transitions from OCS, CS, SO, and SO2 towards NGC1333-IRAS4A in the 1.3, 2, and 3mm bands using the IRAM NOrthern Extended Millimeter Array and we interpreted the observations through the use of the Paris-Durham shock model. Results. The targeted species clearly show different spatial emission along the two outflows driven by IRAS4A. OCS is brighter on small and large scales along the south outflow driven by IRAS4A1, whereas SO2 is detected rather along the outflow driven by IRAS4A2 that is extended along the north east-south west direction. SO is detected at extremely high radial velocity up to +25 km s 1 relative to the source velocity, clearly allowing us to distinguish the two outflows on small scales. Column density ratio maps estimated from a rotational diagram analysis allowed us to confirm a clear gradient of the OCS/SO2 column density ratio between the IRAS4A1 and IRAS4A2 outflows. Analysis assuming non Local Thermodynamic Equilibrium of four SO2 transitions towards several SiO emission peaks suggests that the observed gas should be associated with densities higher than 105 cm 3 and relatively warm (T > 100 K) temperatures in most cases. Conclusions. The observed chemical differentiation between the two outflows of the IRAS4A system could be explained by a different chemical history. The outflow driven by IRAS4A1 is likely younger and more enriched in species initially formed in interstellar ices, such as OCS, and recently sputtered into the shock gas. In contrast, the longer and likely older outflow triggered by IRAS4A2 is more enriched in species that have a gas phase origin, such as SO2

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

International audienceWe have observed the very low-mass Class 0 protostar IRAS 15398-3359 at scales ranging from 50 to 1800 au, as part of the Atacama Large Millimeter/Submillimeter Array Large Program FAUST. We uncover a linear feature, visible in H2CO, SO, and C18O line emission, which extends from the source in 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 blueshifted with respect to the systemic velocity. A velocity gradient of 1.2 km s-1 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

Misaligned Rotations of the Envelope, Outflow, and Disks in the Multiple Protostellar System of VLA 1623-2417: FAUST. III

International audienceWe report a study of the low-mass Class 0 multiple system VLA 1623AB in the Ophiuchus star-forming region, using H13CO+ (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 circumbinary VLA 1623A disk, as well as the VLA 1623B disk. We found that the minor axis of the circumbinary disk of VLA 1623A is misaligned by about 12° with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circumbinary 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 circumbinary disk. The origin of its opposite gradient is also discussed

Chemical and Physical Characterization of the Isolated Protostellar Source CB68: FAUST IV

International audienceAbstract The chemical diversity of low-mass protostellar sources has so far been recognized, and environmental effects are invoked as its origin. In this context, observations of isolated protostellar sources without the influence of nearby objects are of particular importance. Here, we report the chemical and physical structures of the low-mass Class 0 protostellar source IRAS 16544−1604 in the Bok globule CB 68, based on 1.3 mm Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of ∼70 au that were conducted as part of the large program FAUST. Three interstellar saturated complex organic molecules (iCOMs), CH3OH, HCOOCH3, and CH3OCH3, are detected toward the protostar. The rotation temperature and the emitting region size for CH3OH are derived to be 131 ± 11 K and ∼10 au, respectively. The detection of iCOMs in close proximity to the protostar indicates that CB 68 harbors a hot corino. The kinematic structure of the C18O, CH3OH, and OCS lines is explained by an infalling–rotating envelope model, and the protostellar mass and the radius of the centrifugal barrier are estimated to be 0.08–0.30 M ⊙ and &lt;30 au, respectively. The small radius of the centrifugal barrier seems to be related to the small emitting region of iCOMs. In addition, we detect emission lines of c-C3H2 and CCH associated with the protostar, revealing a warm carbon-chain chemistry on a 1000 au scale. We therefore find that the chemical structure of CB 68 is described by a hybrid chemistry. The molecular abundances are discussed in comparison with those in other hot corino sources and reported chemical models.</jats:p