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For refcode 1996ApJ...462..684T:
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Copyright by American Astronomical Society. Reproduced by permission
1996ApJ...462..684T THE RESOLVED STELLAR POPULATION OF LEO A ELINE TOLSTOY Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, and Kapteyn Astronomical Institute, Postbus 800, NL-9700 AV Groningen, The Netherlands Received 1995 April 24; accepted 1995 November 15 ABSTRACT New observations of the resolved stellar population of the extremely metal-poor Magellanic dwarf irregular galaxy Leo A in Thuan-Gunn r, g, i, and narrowband H{alpha} filters are presented. Using the recent Cepheid variable star distance determination to Leo A by Hoessel et al., we are able to create an accurate color-magnitude diagram (CMD). We have used the Bavesian inference method described by Tolstoy & Saha to calculate the likelihood of a Monte Carlo simulation of the stellar population of Leo A being a good match to the data within the well understood errors in the data. The magnitude limits on our data are sensitive enough to look back at ~1 Gyr of star formation history at the distance of Leo A. To explain the observed ratio of red to blue stars in the observed CMD, it is necessary to invoke either a steadily decreasing star formation rate toward the present time or gaps in the star formation history. We also compare the properties of the observed stellar population with the known spatial distribution of the H I gas and H II regions to support the conclusions from CMD modeling. We consider the possibility that currently there is a period of diminished star formation in Leo A, as evidenced by the lack of very young stars in the CMD and the faint H II regions. How the chaotic H I distribution, with no observable rotation, fits into our picture of the evolution of Leo A is as yet unclear. Subject headings: galaxies: individual: Leo A - galaxies: stellar content - Hertzsprung-Russell diagram - stars: formation
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