Gorlova, Nadya ; Lobel, Alex ; J Burgasser, Adam ; H Rieke, George ; Ilyin, Ilya ; R Stauffer, John

published in The Astrophysical Journal, 651 issue 2 (2006)

Abstract: The Astrophysical Journal The American Astronomical Society, find out more The Institute of Physics, find out more On the CO Near-Infrared Band and the Line-splitting Phenomenon in the Yellow Hypergiant ρ Cassiopeiae Nadya Gorlova1, Alex Lobel2, Adam J. Burgasser3, George H. Rieke1, Ilya Ilyin4, and John R. Stauffer5 © 2006. The American Astronomical Society. All rights reserved. Printed in U.S.A. The Astrophysical Journal, Volume 651, Number 2 Citation Nadya Gorlova et al 2006 ApJ 651 1130 DownloadArticle PDF View article References Download PDF 1025 Total downloads 2424 total citations on Dimensions. Turn on MathJax Get permission to re-use this article Share this article Share this content via email Share on Facebook (opens new window) Share on Twitter (opens new window) Share on Mendeley (opens new window) Hide article information Author affiliations 1 Steward Observatory, University of Arizona, 933 North Cherry Avenue, Room N204, Tucson, AZ 85721-0065 2 Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium 3 Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Building 37, Cambridge, MA 02139 4 Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany 5 Spitzer Science Center, California Institute of Technology, MS 314-6, Pasadena, CA 91125 Dates Received 2005 October 4 Accepted 2006 July 7 DOI https://doi.org/10.1086/507590 Journal RSS Create or edit your corridor alerts What are corridors? This link opens in a new tab. Create citation alert Abstract We report on multiepoch optical and near-infrared spectroscopy around the first-overtone rovibrational band of CO in the pulsating yellow hypergiant ρ Cas, one of the most massive stars in the Galaxy and a candidate SN II progenitor. We argue that the double cores of the CO absorption lines, which have previously been attributed to separate circumstellar shells expelled during its recurrent outbursts, result in fact from a superposition of a wide absorption line and a narrow central emission line. The CO line doubling returns over subsequent pulsation cycles, where the superposed line emission assumes its largest intensity near phases of maximum light. We find that the morphology and behavior of the CO band closely resemble the remarkable "line-splitting phenomenon" also observed in optical low-excitation atomic lines. Based on radiative transport calculations, we present a simplified model of the near-infrared CO emission emerging from cooler atmospheric layers in the immediate vicinity of the photosphere. We speculate that the kinetic temperature minimum in our model results from a periodic pulsation-driven shock wave. We further discuss a number of alternative explanations for the origin of the ubiquitous emission-line spectrum, possibly due to a quasi-chromosphere or a steady shock wave at the interface of a fast expanding wind and the interstellar medium. We present a number of interesting spectroscopic similarities between ρ Cas and other types of cool variable supergiants, such as the RV Tau and R CrB stars. We further propose a possibly common mechanism for the enigmatic outburst behavior of these luminous pulsating cool stars.

DOI: 10.1086/507590
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