11254(  1) - 03/30/07 11:09  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11254

Version: 1    Check-in Time: 30-Mar-2007 15:09:39       STScI Edit Number: 0

Title
Analysis of Red Giant Oscillations from a 27 Day ACS/WFC  Time-Series on NGC 6397
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Type             Cycle     Parallel Pointing Tolerance
AR               16        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Ronald L. Gilliland           Space Telescope Science Institute
   CoI: Dr. Dennis Stello                 University of Sydney                          N

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Abstract

Observations of solar-like oscillations have started to provide excellent results
with firm detections in recent years for dwarfs, subgiants and red giant stars --
all with radial velocities. We are now poised to further exploit these recent
successes with more systematic exploration of oscillations in stars across the
color-magnitude diagram (CMD). Giants are of particular interest as allowing tests
of stellar structure and evolution in this complicated time in a stars life, while
presenting observational signals of much larger amplitude than for dwarfs. Study of
stellar oscillations requires unusual combinations of long time coverage to obtain
the requisite frequency resolution, and precision to detect the fraction of a mmag
amplitude modes to be studied here. Time coverage of one week is a lower limit for
study of modes which in the giants will have periods of 0.25-3 days, while intensive
observations over multiple weeks would be ideal. We will show excellent success at
detecting oscillations in giants (all of which are strongly saturated in these data)
from a 7 day observation program (GO 9750) conducted for extrasolar planet detection
in the galactic bulge. This proposal is for analysis of giants serendipitously
observed as part of GO-10424 a 126 orbit program with ACS/WFC on NGC 6397 to probe
the bottom of the white dwarf cooling sequence. These ~400 exposures over 27 days
for NGC 6397 will allow asteroseismic results on ~40 giants, including mode lifetime
estimates not possible at only 7 days.
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