Andrew Tkachenko, Holher Lehmann, Barry Smalley, Jonas Debosscher, Conny Aerts
Ground-based spectroscopic follow-up observations of the pulsating stars
observed by the Kepler satellite mission are needed for their asteroseismic
modelling. We aim to derive the fundamental parameters for a sample of 26 Gamma
Doradus candidate stars observed by the Kepler satellite mission to accomplish
one of the required preconditions for their asteroseismic modelling and to
compare our results with the types of pulsators expected from the existing
light curve analysis. We use the spectrum synthesis method to derive the
fundamental parameters like Teff, logg, [M/H], and vsini from newly obtained
spectra and compute the spectral energy distribution from literature photometry
to get an independent measure of Teff. We find that most of the derived Teff
values agree with the values given in the Kepler Input Catalogue. According to
their positions in the HR-diagram three stars are expected Gamma Dor stars, ten
stars are expected Delta Sct stars, and seven stars are possibly Delta Sct
stars at the hot border of the instability strip. Four stars in our sample are
found to be spectroscopic binary candidates and four stars have very low
metallicity where two show about solar C abundance. Six of the 10 stars located
in the Delta Sct instability region of the HR-diagram show both Delta Sct and
Gamma Dor-type oscillations in their light curves implying that Gamma Dor-like
oscillations are much more common among the Delta Sct stars than predicted by
theory. Moreover, seven stars showing periods in the Delta Sct and the Delta
Sct-Gamma Dor range in their light curves are located in the HR-diagram left of
the blue edge of the theoretical Delta Sct instability strip. The consistency
of these findings with recent investigations based on high-quality Kepler data
implies the need for a revision of the theoretical Gamma Dor and Delta Sct
instability strips.
View original:
http://arxiv.org/abs/1202.1116
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