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The Red Supergiant Content of M31

Massey, Philip and Evans, Kate Anne (2016) The Red Supergiant Content of M31. Astrophysical Journal, 826 (2). Art. No. 224. ISSN 0004-637X.

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We investigate the red supergiant (RSG) population of M31, obtaining the radial velocities of 255 stars. These data substantiate membership of our photometrically selected sample, demonstrating that Galactic foreground stars and extragalactic RSGs can be distinguished on the basis of B − V, V − R two-color diagrams. In addition, we use these spectra to measure effective temperatures and assign spectral types, deriving physical properties for 192 RSGs. Comparison with the solar metallicity Geneva evolutionary tracks indicates astonishingly good agreement. The most luminous RSGs in M31 are likely evolved from 25–30 M_⊙ stars, while the vast majority evolved from stars with initial masses of 20 M_⊙ or less. There is an interesting bifurcation in the distribution of RSGs with effective temperatures that increases with higher luminosities, with one sequence consisting of early K-type supergiants, and with the other consisting of M-type supergiants that become later (cooler) with increasing luminosities. This separation is only partially reflected in the evolutionary tracks, although that might be due to the mis-match in metallicities between the solar Geneva models and the higher-than-solar metallicity of M31. As the luminosities increase the median spectral type also increases; i.e., the higher mass RSGs spend more time at cooler temperatures than do those of lower luminosities, a result which is new to this study. Finally we discuss what would be needed observationally to successfully build a luminosity function that could be used to constrain the mass-loss rates of RSGs as our Geneva colleagues have suggested.

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Additional Information:© 2016. The American Astronomical Society. Received 2016 April 16; revised 2016 May 24; accepted 2016 May 25; published 2016 August 2. We are grateful to the Steward Observatory Time Allocation Committee for their generous allocation of observing time on the MMT, and to Perry Berlind, Mike Calkins, and Marc Lacasse for their excellent support of Hectospec. P.M. would particularly like to thank Calkins for organizing and graciously hosting a very pleasant Thanksgiving dinner for all of the Mt Hopkins observers during the November observing run. Nelson Caldwell managed the difficult task of queue scheduling our program. Collaborator Kathryn Neugent participated in these observations and encouraged devoting the "spare" Hectospec fibers to this additional project; she was also kind enough to make useful comments on a draft of the manuscript, as did Cyril Georgy, Georges Meynet, and Sylvia Esktröm. An anonymous referee provided constructive comments. Emily Levesque and Joe Llama provided useful help with some of the coding for fitting the MARCS models. 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 (NSF). K.A.E.'s work was supported through the NSF's Research Experiences for Undergraduates program through Northern Arizona University and Lowell Observatory (AST-1461200), and P.M. was partially supported by the NSF through AST-1008020 and by Lowell Observatory. Facility: MMT (Hectospec) - MMT at Fred Lawrence Whipple Observatory. Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution. This paper uses data products produced by the OIR Telescope Data Center, supported by the Smithsonian Astrophysical Observatory.
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Lowell ObservatoryUNSPECIFIED
Subject Keywords:galaxies: individual (M31) ; galaxies: stellar content; Local Group; stars: massive; supergiants
Issue or Number:2
Record Number:CaltechAUTHORS:20160802-112855264
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Official Citation:Philip Massey and Kate Anne Evans 2016 ApJ 826 224
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69389
Deposited By: Ruth Sustaita
Deposited On:03 Aug 2016 17:02
Last Modified:03 Oct 2019 10:21

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