Abstract
The non-radially pulsating subdwarf B star PG 0014+067 has previously been presented as a classic case for asteroseismological study, having a moderately rich mode spectrum uncomplicated by severe rotational splitting. Notwithstanding the excellence of previous work, empirical evidence for mode identification is needed to test the modelling results. Consequently high-speed multicolour photometry was obtained over six nights in 2004 August using the high-speed multichannel photometer ULTRACAM on the 4.2-m William Herschel Telescope with a sampling interval of 5 s. To ameliorate the window function, additional single-channel photometry was obtained on five nights in the same time envelope using the 2-m Faulkes Telescope North with a sampling interval of 23 s. 19 individual frequencies have been identified in a combined `white light' data set. Amplitudes have been measured in filtered light (u', g' and r') for 13 of these. Three groups of closely spaced frequencies have spacings of 3, 13 and 2 muHz. Although on the cusp of the frequency resolution, there is evidence that the rotational period should be nearer to 4 d rather than the 1.35 d reported previously, if we assume that these close frequencies belong to a multiplet. It has not proved possible to identify modes unambiguously using the amplitude ratio method because of the errors on the amplitudes, but we do exclude that the two dominant modes have l= 3 or 4; they must be either l= 0, 1, 2.
Highlights
Since the discovery of non-radial pulsations in subdwarf B stars (Kilkenny et al 1997), much effort has been directed towards asteroseismological studies of their internal structure (e.g. Brassard et al 2001; Kilkenny et al 2002, 2003)
This paper describes results obtained from the William Herschel Telescope (WHT) and Faulkes Telescope North (FTN) data alone
We have reduced the FTN data with the pipeline described by Gänsicke et al (2004)
Summary
Since the discovery of non-radial pulsations in subdwarf B (sdB) stars (Kilkenny et al 1997), much effort has been directed towards asteroseismological studies of their internal structure (e.g. Brassard et al 2001; Kilkenny et al 2002, 2003). Since the discovery of non-radial pulsations in subdwarf B (sdB) stars (Kilkenny et al 1997), much effort has been directed towards asteroseismological studies of their internal structure The first study of PG 0014+067 (Brassard et al 2001) was seminal in demonstrating the power of asteroseismology in probing sdB star structure and evolution; the accuracy of the mass measurement and its agreement with canonical stellar evolution predictions have given impetus to the entire field. The apparently slow surface rotation of most sdB stars may mask a more rapidly rotating core (Sills & Pinsonneault 2000), which may give rise to differential splitting between the frequencies of modes of different radial order k (Kawaler & Hostler 2004, 2005). While the current data and the WET data are independent of one another, the results they demonstrate in common represent a mutual effort
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