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Date and Time of the Query: 2019-05-20 T00:32:35 PDT
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For refcode 2002AJ....123.3154D:
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2002AJ....123.3154D VARIABLE STARS IN LEO A: RR LYRAE STARS, SHORT-PERIOD CEPHEIDS, AND IMPLICATIONS FOR STELLAR CONTENT ANDREW E. DOLPHIN, A. SAHA, AND JENNIFER CLAVER Kitt Peak National Observatory, National Optical Astronomy Observatory, P.O. Box 26372, Tucson, AZ 85726; dolphin@noao.edu, saha@noao.edu, jclaver@noao.edu EVAN D. SKILLMAN Department of Astronomy, University of Minnesota, 116 Church Street, SE, Minneapolis, MN 55455; skillman@astro.umn.edu A. A. COLE Department of Physics and Astronomy, 538 LGRT, University of Massachusetts, Amherst, MA 01003: cole@condor.astro.umass.edu J. S. GALLAGHER Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706; jsg@astro.wisc.edu ELINE TOLSTOY Kapteyn Astronomical Institute, University of Groningen, Postbus 800, NL-9700 AV Groningen, Netherlands; etolstoy@astro.rug.nl AND R. C. DOHM-PALMER AND MARIO MATEO Department of Astronomy, 821 Dennison Building, University of Michigan, Ann Arbor, MI 48109-1090; rdpalmer@astro.lsa.umich.edu, mateo@astro.lsa.umich.edu Received 2001 November 5; accepted 2002 February 19 ABSTRACT We present the results of a search for short-period variable stars in Leo A. We have found 92 candidate variables, including eight candidate RR Lyrae stars. From the RR Lyrae stars, we measure a distance modulus of (m - M)_0_ = 24.51 +/- 0.12, or 0.80 +/- 0.04 Mpc. This discovery of RR Lyrae stars confirms for the first time the presence of an ancient (older than ~11 Gyr) population in Leo A, accounting for at least 0.1% of the galaxy's V luminosity. We have also discovered a halo of old (more than ~2 Gyr) stars surrounding Leo A, with a scale length roughly 50% larger than that of the dominant young population. We also report the discovery of a large population of Cepheids in Leo A. The median absolute magnitude of our Cepheid sample is M_V_ = -1.1, fainter than 96% of SMC and 99% of LMC Cepheids. Their periods are also unusual, with three Cepheids that are deduced to be pulsating in the fundamental mode having periods of under 1 day. Upon examination, these characteristics of the Leo A Cepheid population appear to be a natural extension of the classical Cepheid period-luminosity relations to low metallicity, rather than being indicative of a large population of "anomalous" Cepheids. We demonstrate that the periods and luminosities are consistent with the expected values of low-metallicity blue helium-burning stars (BHeB's), which populate the instability strip at lower luminosities than do higher metallicity BHeB's. Key words: Cepheids - galaxies: individual (Leo A) - Local Group
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