Short Period Variables in Leo A

Details Short Period Variables in Leo A Short Period Variables in Leo A

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aas...19916004d&link_type=abstract

American Astronomical Society, 199th AAS Meeting, #160.04; Bulletin of the American Astronomical Society, Vol. 34, p.570

Astronomy and Astrophysics

Astronomy

Scientific paper

We present the results of a search for short-period variable stars in Leo A. We have found 92 candidate variables: 8 candidate RR Lyrae stars and 84 short-period Cepheids. From the RR Lyraes, we measure a distance modulus of (m-M)0 = 24.51 +/- 0.12, or 0.80 +/- 0.04 Mpc. This discovery of RR Lyraes confirms, for the first time, the presence of an ancient (> ~ 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 (> ~ 2 Gyr) stars surrounding Leo A, with a scale length roughly 50% larger than that of the dominant young population. The median absolute magnitude of our Cepheid sample is MV = -1.1, fainter than 95.5% of SMC and 98.9% 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, the characteristics of the Leo A Cepheids appear to be the natural extension of the classical Cepheid period-luminosity relations to low metallicity, rather than coming from 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 (BHeBs), which populate the instability strip at lower luminosities than do higher-metallicity BHeBs.

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