Multifrequency high spectral resolution observations of HCN toward the circumstellar envelope of y Canum Venaticorum

Autor: John H. Lacy, Marcelino Agúndez, E. Montiel, Thomas K. Greathouse, M. Santander-García, José Pablo Fonfría, Matthew J. Richter, José Cernicharo, S. Massalkhi, Curtis DeWitt
Přispěvatelé: European Commission, National Aeronautics and Space Administration (US), Ministerio de Economía y Competitividad (España), Universities Space Research Association (US), University of Stuttgart, University of Hawaii, Centre National de la Recherche Scientifique (France), Max Planck Society, Instituto Geográfico Nacional (España), University of Massachusetts, National Science Foundation (US)
Rok vydání: 2021
Předmět:
Zdroj: Digital.CSIC. Repositorio Institucional del CSIC
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Popis: 24 pags., 11 figs., 2 tabs.
High spectral resolution observations toward the low mass-loss rate C-rich, J-type asymptotic giant branch (AGB) star Y CVn were carried out at 7.5, 13.1, and 14.0 μm with the Echelon-cross-echelle Spectrograph mounted on the Stratospheric Observatory for Infrared Astronomy and the Texas Echelon-cross-echelle Spectrograph on the Infrared Telescope Facility. Around 130 HCN and H13CN lines of bands ν2, 2ν2, 2ν2 - ν2, 3ν2 - 2ν2, 3ν2 - ν2, and 4ν2 - 2ν2 were identified involving lower levels with energies up to ? 3900 K. These lines were complemented with the pure rotational lines J = 1-0 and 3-2 of the vibrational states up to 2ν2 acquired with the Institut de Radioastronomie Millimétrique 30 m telescope, and with the continuum taken with Infrared Space Observatory. We analyzed the data in detail by means of a ro-vibrational diagram and with a code written to model the absorption and emission of the circumstellar envelope of an AGB star. The continuum is mostly produced by the star with a small contribution from dust grains comprising warm to hot SiC and cold amorphous carbon. The HCN abundance distribution seems to be anisotropic close to Y CVn and in the outer layers of its envelope. The ejected gas is accelerated up to the terminal velocity (? 8 km s-1) from the photosphere to ? 3R? , but there is evidence of higher velocities (? 9-10 km s-1) beyond this region. In the vicinity of the star, the line widths are as high as ? 10 km s-1, which implies a maximum turbulent velocity of 6 km s-1 or the existence of other physical mechanisms probably related to matter ejection that involve higher gas expansion velocities than expected. HCN is rotationally and vibrationally out of local thermodynamic equilibrium throughout the whole envelope. It is surprising that a difference of about 1500 K in the rotational temperature at the photosphere is needed to explain the observations at 7.5 and 13-14 μm. Our analysis finds a total HCN column density that ranges from ? 2.1 × 1018 to 3.5 × 1018 cm-2, an abundance with respect to H2 of 3.5 × 10-5 to 1.3 × 10-4, and a 12C/13C isotopic ratio of ? 2.5 throughout the whole envelope.
The research leading to these results has received funding support from the European Research Council under the European Union’s Seventh Framework Program (FP/2007-2013) / ERC Grant Agreement n. 610256 NANOCOSMOS. EJM acknowledges financial support for this work through award #06_0144 which was issued by USRA and provided by NASA. MJR and EXES observations are supported by NASA cooperative agreement 80NSSC19K1701. MSG thanks Spanish MCIN through grant AYA2016-78994-P. Based in part on observations made with the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA is jointly operated by the Universities Space Research Association, Inc. (USRA), under NASA contract NNA17BF53C, and the Deutsches SOFIA Institut (DSI) under DLR contract 50 OK 0901 to the University of Stuttgart. Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration. This work is based on observations carried out under project numbers 155-16 and 048-17 with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This publication makes use of data products from the Widefield Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration
Databáze: OpenAIRE
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