Suchergebnisse

4 pags., 2 figs. ; We present VLA and PdBI subarcsecond images (∼0.15″-0.6″) of the radio continuum emission at 7 mm and of the SO2 J = 19 2, 18 → 183, 15 and J = 278, 20 → 287, 21 lines toward the Cep A HW2 region. The SO2 images reveal the presence of a hot core internally heated by an intermediate-mass protostar, and a circumstellar rotating disk around the HW2 radio jet of size 600 × 100 AU and mass ∼1 M⊙. Keplerian rotation for the disk velocity gradient of ∼5 km s-1 requires a 9 M ⊙ central star, which cannot explain the total luminosity observed in the region. This may indicate that the disk does not rotate with a Keplerian law due to the extreme youth of this object. Our high-sensitivity radio continuum image at 7 mm shows, in addition to the ionized jet, an extended emission to the west (and marginally to the south) of the HW2 jet, filling the southwest cavity of the HW2 disk. From the morphology and location of this free-free continuum emission at centimeter and millimeter wavelengths (spectral index ∼0.4-1.5), we propose that the disk is photoevaporating due to the UV radiation from the central star. All this indicates that the Cep A HW2 region harbors a cluster of massive stars. Disk accretion seems to be the most plausible way to form massive stars in moderate density/luminosity clusters. © 2007. The American Astronomical Society. All rights reserved. ; We also acknowledge the Spanish MEC for the support provided through projects number ESP2004-00665, AYA2003-02785-E, and "Comunidad de Madrid" government under PRICIT project S-0505/ ESP-0277 (ASTROCAM). ; Peer Reviewed

Observations of young stellar objects (YSOs) in centimeter bands can probe the continuum emission from growing dust grains, ionized winds, and magnetospheric activity that are intimately connected to the evolution of protoplanetary disks and the formation of planets. We carried out sensitive continuum observations toward the Ophiuchus A star-forming region, using the Karl G. Jansky Very Large Array (VLA) at 10 GHz over a field-of-view of 6′ and with a spatial resolution of θmaj ×θmin ∼ 0.′′4 × 0.′′2. We achieved a 5 μJy beam-1 rms noise level at the center of our mosaic field of view. Among the 18 sources we detected, 16 were YSOs (three Class 0, five Class I, six Class II, and two Class III) and two were extragalactic candidates. We find that thermal dust emission generally contributed less than 30% of the emission at 10 GHz. The radio emission is dominated by other types of emission, such as gyro-synchrotron radiation from active magnetospheres, free-free emission from thermal jets, free-free emission from the outflowing photoevaporated disk material, and synchrotron emission from accelerated cosmic-rays in jet or protostellar surface shocks. These different types of emission could not be clearly disentangled. Our non-detections for Class II/III disks suggest that extreme UV-driven photoevaporation is insufficient to explain disk dispersal, assuming that the contribution of UV photoevaporating stellar winds to radio flux does not evolve over time. The sensitivity of our data cannot exclude photoevaporation due to the role of X-ray photons as an efficient mechanism for disk dispersal. Deeper surveys using the Square Kilometre Array (SKA) will have the capacity to provide significant constraints to disk photoevaporation. © A. Coutens et al. ; H2020 Marie SkÅ odowska-Curie Actions, MSCA: 823823 ; Fondo Nacional de Desarrollo Científico, Tecnológico y de Innovación Tecnológica, FONDECYT: 11181068 ; Russian Science Foundation, RSF: 18-12-00351 ; Horizon 2020 Framework Programme, H2020 ; University of Leeds ; Natural Sciences and Engineering Research Council of Canada, NSERC ; CUP C52I13000140001 ; Consejo Nacional de Ciencia y Tecnología, Paraguay, El CONACYT ; Dirección General de Asuntos del Personal Académico, Universidad Nacional Autónoma de México, DGAPA, UNAM: IN112417 ; Comisión Nacional de Investigación Científica y Tecnológica, CONICYT: AFB-170002 ; Deutsche Forschungsgemeinschaft, DFG: SPP 1833, ERC-2013-ADG ; Deutsche Forschungsgemeinschaft, DFG ; Science and Technology Facilities Council, STFC: ST/R000549/1 ; Deutsche Forschungsgemeinschaft, DFG ; National Research Council Canada, NRC ; European Research Council, ERC: PALs 320620 ; Science and Technology Facilities Council, STFC: ST/L004801 ; of Life Science Working Group of the SKA. The authors thank Hsieh Tien-Hao for providing the results of the classification method presented in Hsieh & Lai (2013). The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities. A.C. postdoctoral grant is funded by the ERC Starting Grant 3DICE (grant agreement 336474). I.J.-S. acknowledges the financial support received from the STFC through an Ernest Rutherford Fellowship (proposal number ST/L004801). L.L. acknowledges the financial support of DGAPA, UNAM (project IN112417), and CONACyT, México. A.C.T. acknowledges the financial support of the European Research Council (ERC; project PALs 320620). D.J. is supported by the National Research Council Canada and by an NSERC Discovery Grant. L.M.P. acknowledges support from CONICYT project Basal AFB-170002 and from FONDECYT Iniciación project #11181068. A.P. acknowledges the support of the Russian Science Foundation project 18-12-00351. D.S. acknowledges support by the Deutsche Forschungsgemeinschaft through SPP 1833: Building a Habitable Earth (SE 1962/6-1). M.T. has been supported by the DISCSIM project, grant agreement 341137 funded by the European Research Council under ERC-2013-ADG. C.W. acknowledges support from the University of Leeds and the Science and Technology Facilities Council under grant number ST/R000549/1. This work was partly supported by the Italian Ministero dell'Istruzione, Università e Ricerca through the grant Progetti Premiali 2012 – iALMA (CUP C52I13000140001), by the Deutsche Forschungs-gemeinschaft (DFG, German Research Foundation) – Ref no. FOR 2634/1 TE 1024/1-1, and by the DFG cluster of excellence Origin and Structure of the Universe (www.universe-cluster.de). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 823823. This project has also been supported by the PRIN-INAF 2016 "The Cradle of Life - GENESIS-SKA (General Conditions in Early Planetary Systems for the rise of life with SKA)".

28 pags., 22 figs., 4 tabs. ; Gas phase Elemental abundances in Molecular CloudS (GEMS) is an IRAM 30 m Large Program designed to provide estimates of the S, C, N, and O depletions and gas ionization degree, X(e−), in a selected set of star-forming filaments of Taurus, Perseus, and Orion. Our immediate goal is to build up a complete and large database of molecular abundances that can serve as an observational basis for estimating X(e−) and the C, O, N, and S depletions through chemical modeling. We observed and derived the abundances of 14 species (13CO, C18O, HCO+, H13CO+, HC18O+, HCN, H13CN, HNC, HCS+, CS, SO, 34SO, H2S, and OCS) in 244 positions, covering the AV ~3 to ~100 mag, n(H2) ~ a few 103 to 106 cm−3, and Tk ~10 to ~30 K ranges in these clouds, and avoiding protostars, HII regions, and bipolar outflows. A statistical analysis is carried out in order to identify general trends between different species and with physical parameters. Relations between molecules reveal strong linear correlations which define three different families of species: (1) 13CO and C18O isotopologs; (2) H13CO+, HC18O+, H13 CN, and HNC; and (3) the S-bearing molecules. The abundances of the CO isotopologs increase with the gas kinetic temperature until TK ~ 15 K. For higher temperatures, the abundance remains constant with a scatter of a factor of ~3. The abundances of H13 CO+, HC18 O+, H13 CN, and HNC are well correlated with each other, and all of them decrease with molecular hydrogen density, following the law ∝ n(H2)−0.8 ± 0.2. The abundances of S-bearing species also decrease with molecular hydrogen density at a rate of (S-bearing/H)gas ∝ n(H2)−0.6 ± 0.1. The abundances of molecules belonging to groups 2 and 3 do not present any clear trend with gas temperature. At scales of molecular clouds, the C18O abundance is the quantity that better correlates with the cloud mass. We discuss the utility of the 13CO/C18O, HCO+/H13CO+, and H13 CO+/H13CN abundance ratios as chemical diagnostics of star formation in external galaxies. ; We thank the Spanish the Spanish Ministerio de Ciencia e Innovación for funding support through AYA2016-75066-C2-1/2-P and PID2019-106235GB-I00. SG-B acknowledges support through grants PGC2018-094671-B-I00 (MICIU/AEI/FEDER,UE) and PID2019-106027GAC44. JRG acknowledges support through grants AYA2017-85111-P and PID2019-106110GB-I00. I.J.-S. has received partial support from the Spanish FEDER (project number ESP2017-86582-C4-1-R) and the State Research Agency (AEI; project number PID2019-105552RB-C41). SPTM acknowledges to the European Union's Horizon 2020 research and innovation program for funding support given under grant agreement No 639459 (PROMISE). ; Peer reviewed

Context. 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 NGC 1333-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 NGC 1333-IRAS4A in the 1.3, 2, and 3 mm 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. © ESO 2020. ; V.T. is grateful to Sylvie Cabrit and Guillaume Pineau des Forêts for stimulating discussions on the chemistry in shocks. The authors acknowledge the CALYPSO consortium for the use of the CALYPSO dataset. This work is based on observations carried out with the IRAM PdBI/NOEMA Interferometer under project numbers V05B and V010 (PI: M.V. Persson), U003 (PI: V. Taquet), and L15AA (PI: C. Ceccarelli and P. Caselli). IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). V.T. acknowledges the financial support from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement n. 664931. This work was supported by (i) the PRIN-INAF 2016 "The Cradle of Life – GENESIS-SKA (General Conditions in Early Planetary Systems for the rise of life with SKA)", (ii) the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme, for the Project "The Dawn of Organic Chemistry" (DOC), grant agreement No 741002, and (iii) the European MARIE SKŁODOWSKA-CURIE ACTIONS under the European Union's Horizon 2020 research and innovation programme, for the Project "Astro-Chemistry Origins" (ACO), Grant No 811312. C.F. acknowledges support from the French National Research Agency in the framework of the Investissements d'Avenir program (ANR-15-IDEX-02), through the funding of the "Origin of Life" project of the Université Grenoble-Alpes.