Suchergebnisse

Context. AB Aur is a Herbig Ae star that hosts a prototypical transition disk. The disk shows a plethora of features connected with planet formation mechanisms, such as spiral arms, dust cavities, and dust traps. Understanding the physical and chemical characteristics of these features is crucial to advancing our knowledge of the planet formation processes. Aims. We aim to characterize the gaseous disk around the Herbig Ae star AB Aur. A complete spectroscopic study was performed using NOEMA to determine the physical and chemical conditions with high spatial resolution. Methods. We present new NOrthern Extended Millimeter Array (NOEMA) interferometric observations of the continuum and (CO)-C-12, (CO)-C-13, (CO)-O-18, H2CO, and SO lines obtained at high resolution. We used the integrated intensity maps and stacked spectra to derive reliable estimates of the disk temperature. By combining our (CO)-C-13 and (CO)-O-18 observations, we computed the gas-to-dust ratio along the disk. We also derived column density maps for the different species and used them to compute abundance maps. The results of our observations were compared with a set of Nautilus astrochemical models to obtain insight into the disk properties. Results. We detected continuum emission in a ring that extends from 0.6 '' to similar to 2.0 '', peaking at 0.97 '' and with a strong azimuthal asymmetry. The molecules observed show different spatial distributions, and the peaks of the distributions are not correlated with the binding energy. Using H2CO and SO lines, we derived a mean disk temperature of 39 K. We derived a gas-to-dust ratio that ranges from 10 to 40 along the disk. Abundance with respect to (CO)-C-13 for SO (similar to 2 x 10(-4)) is almost one order of magnitude greater than the value derived for H2CO (1.6 x 10(-5)). The comparison with Nautilus models favors a disk with a low gas-to-dust ratio (40) and prominent sulfur depletion. Conclusions. From a very complete spectroscopic study of the prototypical disk around AB Aur, we derived, for the first time, the gas temperature and the gas-to-dust ratio along the disk, providing information that is essential to constraining hydrodynamical simulations. Moreover, we explored the gas chemistry and, in particular, the sulfur depletion. The derived sulfur depletion is dependent on the assumed C/O ratio. Our data are better explained with C/O similar to 0.7 and S/H = 8 x 10(-8). © ESO 2020 ; P.R.M. and A.F. thank the Spanish MINECO for funding support from AYA2016-75066-C2-1/2-P, AYA2017-85111P. S.P.T.M. acknowledges to the European Union's Horizon 2020 research and innovation program for funding support given under agreement No 639450 (PROMISE). M.O. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the AYA2017-84390-C2-1-R grant (cofunded by FEDER) and through the Center of Excellence Severo Ochoa award for the Instituto de Astrofisica de Andalucia (SEV/2017/0709). ; Peer reviewed

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

21 pags., 16 figs., 7 tabs., 2 apps. ; Context. Sulphur is one of the most abundant elements in the Universe. Surprisingly, sulphuretted molecules are not as abundant as expected in the interstellar medium and the identity of the main sulphur reservoir is still an open question. Aims. Our goal is to investigate the H2S chemistry in dark clouds, as this stable molecule is a potential sulphur reservoir. Methods. Using millimeter observations of CS, SO, H2S, and their isotopologues, we determine the physical conditions and H2S abundances along the cores TMC 1-C, TMC 1-CP, and Barnard 1b. The gas-grain model NAUTILUS is used to model the sulphur chemistry and explore the impact of photo-desorption and chemical desorption on the H2S abundance. Results. Our modeling shows that chemical desorption is the main source of gas-phase H2S in dark cores. The measured H2S abundance can only be fitted if we assume that the chemical desorption rate decreases by more than a factor of 10 when nH > 2 × 104. This change in the desorption rate is consistent with the formation of thick H2O and CO ice mantles on grain surfaces. The observed SO and H2S abundances are in good agreement with our predictions adopting an undepleted value of the sulphur abundance. However, the CS abundance is overestimated by a factor of 5-10. Along the three cores, atomic S is predicted to be the main sulphur reservoir. Conclusions. The gaseous H2S abundance is well reproduced, assuming undepleted sulphur abundance and chemical desorption as the main source of H2S. The behavior of the observed H2S abundance suggests a changing desorption efficiency, which would probe the snowline in these cold cores. Our model, however, highly overestimates the observed gas-phase CS abundance. Given the uncertainty in the sulphur chemistry, we can only conclude that our data are consistent with a cosmic elemental S abundance with an uncertainty of a factor of 10. ; We thank the Spanish MINECO for funding support from AYA2016-75066-C2-1/2-P, AYA2017-85111P, and ERC under ERC-2013-SyG, G. A. 610256 NANOCOSMOS. JM acknowledges the support of ERC-2015-STG No. 679852 RADFEEDBACK. S.P.T.M. acknowledge to the European Union's Horizon 2020 research and innovation program for funding support given under grant agreement No 639459 (PROMISE).

26 pags., 7 figs., 2 tabs., 2 apps. ; GEMS is an IRAM 30 m Large Program whose aim is determining the elemental depletions and the ionization fraction in a set of prototypical star-forming regions. This paper presents the first results from the prototypical dark cloud Taurus molecular cloud (TMC) 1. Extensive millimeter observations have been carried out with the IRAM 30 m telescope (3 and 2 mm) and the 40 m Yebes telescope (1.3 cm and 7 mm) to determine the fractional abundances of CO, HCO, HCN, CS, SO, HCS, and N H in three cuts which intersect the dense filament at the well-known positions TMC 1-CP, TMC 1-NH3, and TMC 1-C, covering a visual extinction range from A ~ 3 to ~20 mag. Two phases with differentiated chemistry can be distinguished: (i) the translucent envelope with molecular hydrogen densities of 1-5 × 10 cm; and (ii) the dense phase, located at A > 10 mag, with molecular hydrogen densities >10 cm. Observations and modeling show that the gas phase abundances of C and O progressively decrease along the C/C/CO transition zone (A~ 3 mag) where C/H ~ 8 × 10 and C/O ~ 0.8-1, until the beginning of the dense phase at A ~ 10 mag. This is consistent with the grain temperatures being below the CO evaporation temperature in this region. In the case of sulfur, a strong depletion should occur before the translucent phase where we estimate an S/ H ~ (0.4-2.2) × 10, an abundance ~7-40 times lower than the solar value. A second strong depletion must be present during the formation of the thick icy mantles to achieve the values of S/H measured in the dense cold cores (S H ~ 8 × 10) . Based on our chemical modeling, we constrain the value of ζ to ~(0.5-1.8) × 10 s in the translucent cloud. ; We thank the Spanish MINECO for funding support from AYA2016-75066-C2-1/2-P, and the ERC under ERC-2013-SyG, G. A. 610256 NANOCOSMOS. JM acknowledges the support of ERC-2015-STG No. 679852 RADFEEDBACK. SPTM acknowledges to the European Union's Horizon 2020 research and innovation program for funding support given under grant agreement No 639459 (PROMISE). RMD acknowledges support provided by an award from the Simons Foundation (SCOL#321183, KO). GMC acknowedges funding support fromAYA2017-85322-R. MT acknowledges partial support from project AYA2016-79006-P." ; Peer Reviewed

Aims. The Seeds Of Life In Space IRAM/NOEMA large program aims at studying a set of crucial complex organic molecules in a sample of sources with a well-known physical structure that covers the various phases of solar-type star formation. One representative object of the transition from the prestellar core to the protostar phases has been observed toward the very low luminosity object (VeLLO) L1521F. This type of source is important to study to link prestellar cores and Class 0 sources and also to constrain the chemical evolution during the process of star formation. Methods. Two frequency windows (81.6-82.6 GHz and 96.65-97.65 GHz) were used to observe the emission from several complex organics toward the L1521F VeLLO. These setups cover transitions of ketene (H2CCO), propyne (CH3CCH), formamide (NH2CHO), methoxy (CH3O), methanol (CH3OH), dimethyl ether (CH3OCH3), and methyl formate (HCOOCH3). Results. Only two transitions of methanol (A+, E2) have been detected in the narrow window centered at 96.7 GHz (with an upper limit on E1) in a very compact emission blob (∼7″ corresponding to ∼1000 au) toward the northeast of the L1521F protostar. The CS 2-1 transition is also detected within theWideX bandwidth. Consistently with what has been found in prestellar cores, the methanol emission appears ∼1000 au away from the dust peak. The location of the methanol blob coincides with one of the filaments that have previously been reported in the literature. The excitation temperature of the gas inferred from methanol is (10 ± 2) K, while the H2 gas density (estimated from the detected CS 2-1 emission and previous CS 5-4 ALMA observations) is a factor >25 higher than the density in the surrounding environment (n(H2) ≥ 107 cm-3). Conclusions. Based on its compactness, low excitation temperature, and high gas density, we suggest that the methanol emission detected with NOEMA is (i) either a cold and dense shock-induced blob that formed recently (≤ a few hundred years) by infalling gas or (ii) a cold and dense fragment that may just have been formed as a result of the intense gas dynamics within the L1521F VeLLO system. © 2020 C. Favre et al. ; Russian Science Foundation, RSF: 18–12–00351 ; Australian Education International, Australian Government, AEI: MDM-2017-0737 ; Agence Nationale de la Recherche, ANR: ANR-15-IDEX-02 ; European Research Council, ERC ; Horizon 2020 Framework Programme, H2020: 741002 ; Ministerio de Economía y Competitividad, MINECO: AYA2016-79006-P ; European Regional Development Fund, FEDER: ESP2017-86582-C4-1-R ; Acknowledgements. We thank our referee, Dr. Kazuki Tokuda, (i) for his fruitful comments that have improved the quality of our paper and (ii) for sharing his continuum emission map. This work is supported by 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 Univ. Grenoble-Alpes. C.F., C.V. and C.C. acknowledge the funding from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme, for the Project The Dawn of Organic Chemistry (DOC), grant agreement No 741002. I.J.-S. has received partial support from the Spanish FEDER (project number ESP2017-86582-C4-1-R), and State Research Agency (AEI) through project number MDM-2017-0737 Unidad de Excelencia María de Maeztu–Centro de Astrobiología (INTA-CSIC). A.P. acknowledges the financial support of the Russian Science Foundation project 18–12–00351. A.C.-T acknowledges support from MINECO project AYA2016-79006-P.

Aims. The Seeds Of Life In Space IRAM/NOEMA large program aims at studying a set of crucial complex organic molecules in a sample of sources with a well-known physical structure that covers the various phases of solar-type star formation. One representative object of the transition from the prestellar core to the protostar phases has been observed toward the very low luminosity object (VeLLO) L1521F. This type of source is important to study to link prestellar cores and Class 0 sources and also to constrain the chemical evolution during the process of star formation. Methods. Two frequency windows (81.6-82.6 GHz and 96.65-97.65 GHz) were used to observe the emission from several complex organics toward the L1521F VeLLO. These setups cover transitions of ketene (HCCO), propyne (CHCCH), formamide (NHCHO), methoxy (CHO), methanol (CHOH), dimethyl ether (CHOCH), and methyl formate (HCOOCH). Results. Only two transitions of methanol (A, E) have been detected in the narrow window centered at 96.7 GHz (with an upper limit on E) in a very compact emission blob (∼7″ corresponding to ∼1000 au) toward the northeast of the L1521F protostar. The CS 2-1 transition is also detected within theWideX bandwidth. Consistently with what has been found in prestellar cores, the methanol emission appears ∼1000 au away from the dust peak. The location of the methanol blob coincides with one of the filaments that have previously been reported in the literature. The excitation temperature of the gas inferred from methanol is (10 ± 2) K, while the H gas density (estimated from the detected CS 2-1 emission and previous CS 5-4 ALMA observations) is a factor >25 higher than the density in the surrounding environment (n(H) ≥ 10 cm). Conclusions. Based on its compactness, low excitation temperature, and high gas density, we suggest that the methanol emission detected with NOEMA is (i) either a cold and dense shock-induced blob that formed recently (≤ a few hundred years) by infalling gas or (ii) a cold and dense fragment that may just have been formed as a result of the intense gas dynamics within the L1521F VeLLO system. ; With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

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.