11277(  1) - 03/30/07 11:24  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11277

Version: 1    Check-in Time: 30-Mar-2007 15:24:18       STScI Edit Number: 0

Title
RR Lyrae Variables in Local Group Galaxies
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Type             Cycle     Parallel Pointing Tolerance
AR               16        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Ata Sarajedini                University of Florida

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Abstract

We propose to reduce and analyze WFPC2 images of 5 Local Group galaxies in order to
identify and characterize their RR Lyrae variables. These galaxies, which include
NGC 147, IC 10, LGS 3, Tucana, and Andromeda V, have no published variability
studies using HST imaging.The presence of RR Lyrae variables would suggest that an
old (Age >~ 10 Gyr) stellar population is present in these galaxies. In additon,
because the minimum-light color of ab-type RR Lyraes is a constant irrespective of
metallicity or period, these stars can be used to study the extinction properties of
each galaxy. Furthermore, the period of ab-type RR Lyraes is directly related to
their metal abundance so that we can also study the metallicity distribution
function of each galaxy. Lastly, it is well known that RR Lyraes are excellent
distance indicators allowing us to measure the distance of each galaxy.
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