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Time-resolved high-resolution spectroscopy
of the pulsating
sdB star QQ Vir (PG1325+101)
John Telting et al., Shanghai, July 2009
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Introduction: How feasible is a high-spectral-resolution
line-profile
analysis for subdwarfs?
We need high S/N spectra.
Problem 2a: Pulsating subdwarfs are
faint: low S/N spectra
Problem 2b: Subdwarf p-modes
have short periods: short exposures ⇒ low S/N
Solutions:
Phase-fold the spectra onto a known pulsation period to
obtain fewer spectra but with higher S/N. Per phase bin one needs a
sufficient number of spectra for the other pulsation frequences to
average out.
Combine the information of many lines in the spectrum to
increase the S/N of the line profile. For instance, using the
cross-correlation function as an approximation of the average line
profile of a spectrum (Woolf et al. 2002).
Avoid lines that have large intrinsic broadening
(Hydrogen, Helium), and avoid blends if possible. This to enhance the
contrast of pulsational line-profile variability with respect to
intrinsic line broadening.