NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-05-26 T08:01:32 PDT
Help | Comment | NED Home

For refcode 1998AJ....116.1244T:
Retrieve 1 NED object in this reference.
Please click here for ADS abstract

NED Abstract

Copyright by American Astronomical Society. Reproduced by permission
1998AJ....116.1244T WIDE FIELD PLANETARY CAMERA 2 OBSERVATIONS OF LEO A: A PREDOMINANTLY YOUNG GALAXY WITHIN THE LOCAL GROUP ELINE TOLSTOY Space Telescope-European Coordinating Facility, Karl-Schwarzschild Strasse 2, D-85748 Garching bei Munchen, Germany J. S. GALLAGHER, A. A. COLE, AND J. G. HOESSEL Department of Astronomy, University of Wisconsin at Madison, 475 North Charter Street, Madison, WI 53706 A. SAHA National Optical Astronomy Observatories, 950 North Cherry Avenue, Tucson, AZ 85726-6732 R. C. DOHM-PALMER AND E. D. SKILLMAN School of Physics and Astronomy, University of Minnesota, 116 Church Street, Minneapolis, MN 55455 AND MARIO MATEO AND D. HURLEY-KELLER Department of Astronomy, University of Michigan, 821 Dennison Building, Ann Arbor, MI 48109-1090 Received 1998 April 14; revised 1998 May 18 ABSTRACT The unprecedented detail of the Wide Field Planetary Camera 2 (WFPC2) color-magnitude diagrams (CMDs) of the resolved stellar population of Leo A presented here allows us to determine a new distance and an accurate star formation history for this extremely metal-poor Local Group dwarf irregular galaxy. From the position of the red clump, the helium-burning blue loops, and the tip of the red giant branch, we obtain a distance modulus, m - M = 24.2 +/- 0.2, or 690 +/- 60 kpc, which places Leo A firmly within the Local Group. Our interpretation of these features in the WFPC2 CMDs at this new distance based upon extremely low-metallicity (Z = 0.0004) theoretical stellar evolution models suggests that this galaxy is predominantly young, i.e., less than 2 Gyr old. A major episode of star formation 900-1500 Gyr ago can explain the red clump luminosity and also fits in with our interpretation of the number of anomalous Cepheid variable stars seen in this galaxy. We cannot rule out the presence of an older, underlying globular cluster age stellar population with these data. However, using the currently available stellar evolution models, it would appear that such an older population is limited to no more than 10% of the total star formation to have occurred in this galaxy. Leo A provides a nearby laboratory for studying young metal-poor stars and investigations of metal-poor galaxy evolution, such as is supposed to occur for larger systems at intermediate and high redshifts. Key words: galaxies: irregular-Local Group-color-magnitude diagrams- galaxies: stellar content-stars: distances
Retrieve 1 NED object in this reference.
Please click here for ADS abstract

Back to NED Home