Hostname: page-component-77c89778f8-rkxrd Total loading time: 0 Render date: 2024-07-19T08:50:07.242Z Has data issue: false hasContentIssue false

Color-Luminosity Relations for the Resolved Hot Stellar Populations in the Centers of M31 and M32

Published online by Cambridge University Press:  25 May 2016

Thomas M. Brown
Affiliation:
Laboratory for Astronomy & Solar Physics, Code 681, NASA/GSFC, Greenbelt, MD, USA 20771
Henry C. Ferguson
Affiliation:
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, USA 21218
S. A. Stanford
Affiliation:
Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA, USA 94550
Jean-Michel Deharveng
Affiliation:
Laboratoire d'Astronomic Spatiale du CNRS, Traverse du Siphon, BP 8, F-13376 Marseille Cedex 12, France

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

We present Faint Object Camera (FOC) ultraviolet images of the central 14 x 14″ of Messier 31 and Messier 32. The hot stellar population detected in the composite UV spectra of these galaxies is partially resolved into stars, and we measure their colors and apparent magnitudes. We detect 433 stars in M31 and 138 stars in M32, down to limits of mF275W = 25.5 mag and mF175W = 24.5 mag. We investigate the luminosity functions of the sources, their spatial distribution, their color-magnitude diagrams, and their total integrated far-UV flux. Although M32 has a weaker UV upturn than M31, the luminosity functions and color-magnitude diagrams of M31 and M32 are surprisingly similar, and are inconsistent with a majority contribution from any of the following: post-AGB stars more massive than 0.56 M, main sequence stars, or blue stragglers. The luminosity functions and color-magnitude diagrams are consistent with a dominant population of stars evolving from the extreme horizontal branch (EHB) along tracks of mass 0.47–0.53 M. These stars are well below the detection limits of our images while on the zero-age EHB, but become detectable while in the more luminous (but shorter) post-HB phases. Our observations require that only a very small fraction of the main sequence population (2% in M31 and 0.5% in M32) in these two galaxies evolve though the EHB and post-EHB phases, with the remainder rapidly evolving through bright post-AGB evolution with few resolved stars expected in the small field of view covered by the FOC.

Type
Part 2: The Database
Copyright
Copyright © Astronomical Society of the Pacific 1999 

References

Bertola, F., Capaccioli, M., Oke, J.B. 1982, ApJ, 254, 494 Google Scholar
Bertola, F., et al. 1995, ApJ, 438, 694 Google Scholar
Bressan, A., Chiosi, C., Fagotto, F. 1994, ApJS, 94, 63 Google Scholar
Brown, T.M., et al. 1997, ApJ, 482, 685 Google Scholar
Burstein, D., et al. 1988, ApJ, 328, 400 Google Scholar
Dorman, B., Rood, R.T., O'Connell, R.W. 1993, ApJ, 419, 596 Google Scholar
Ferguson, H.C., et al. 1991, ApJ, 382, L69 Google Scholar
Greggio, L., Renzini, A. 1990, ApJ, 364, 35 Google Scholar
Horch, E., Demarque, P., Pinsonneault, M. 1992, ApJ, 388, L53 Google Scholar
King, I.R., et al. 1992, ApJ, 397, L35 Google Scholar
King, I.R., Stanford, S.A., Crane, P. 1995, AJ, 109, 164 CrossRefGoogle Scholar
Lauer, T.R., et al. 1993, AJ, 106, 1436 Google Scholar
Vassiliadis, E., Wood, P.R. 1994, ApJS, 92, 125 CrossRefGoogle Scholar