Suchergebnisse

Aims. We aim to reveal the physical properties and chemical composition of the cores in the California molecular cloud (CMC), so as to better understand the initial conditions of star formation. Methods. We made a high-resolution column density map (18.2′′) with Herschel data, and extracted a complete sample of the cores in the CMC with the fellwalker algorithm. We performed new single-pointing observations of molecular lines near 90 GHz with the IRAM 30m telescope along the main filament of the CMC. In addition, we also performed a numerical modeling of chemical evolution for the cores under the physical conditions. Results. We extracted 300 cores, of which 33 are protostellar and 267 are starless cores. About 51% (137 of 267) of the starless cores are prestellar cores. Three cores have the potential to evolve into high-mass stars. The prestellar core mass function (CMF) can be well fit by a log-normal form. The high-mass end of the prestellar CMF shows a power-law form with an index α = -0.9 ± 0.1 that is shallower than that of the Galactic field stellar mass function. Combining the mass transformation efficiency (ϵ) from the prestellar core to the star of 15 ± 1% and the core formation efficiency (CFE) of 5.5%, we suggest an overall star formation efficiency of about 1% in the CMC. In the single-pointing observations with the IRAM 30m telescope, we find that 6 cores show blue-skewed profile, while 4 cores show red-skewed profile. [HCO + ]/[HNC] and [HCO + ]/[N 2 H + ] in protostellar cores are higher than those in prestellar cores; this can be used as chemical clocks. The best-fit chemical age of the cores with line observations is ~5 × 10 4 yr. © ESO 2018. ; Chinese Government Scholarship: 201804910583 ; 2017YFA0402600, 2017YFA0402702 ; Russian Science Foundation, RSF: 18-12-00351 ; Deutsche Forschungsgemeinschaft, DFG: WA3628-1/1 ; National Basic Research Program of China (973 Program): 2015CB857101 ; National Natural Science Foundation of China, NSFC: 11763002, U1431111, 11721303, 11703040, 11703074 ; Acknowledgements. We acknowledge valuable comments from the referee. We thank Charles J. Lada for useful discussion on the manuscript. We thank A. Men'shchikov, D. S. Berry, and S. Bardeau for their technical support with Getsources, Starlink and Gildas, respectively. This work is supported by National Key R&D Program of China (No. 2017YFA0402600; 2017YFA0402702), National Key Basic Research Program of China (973 Program) (No. 2015CB857101), National Natural Science foundation of China (No. 11703040; 11703074; 11721303; 11763002; U1431111), and Chinese Government Scholarship (No. 201804910583). D.A.S. acknowledges support from the Heidelberg Institute of Theoretical Studies for the project "Chemical kinetics models and visualization tools: Bridging biology and astronomy". A.I.V. acknowledges support by the Russian Science Foundation (No. 18-12-00351). K.W. acknowledges support by the German Research Foundation (grant WA3628-1/1).

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)".