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Paper: Time-Resolved High-Resolution Spectroscopy of the Bright sdBV Balloon 090100001
Volume: 392, Hot Subdwarf Stars and Related Objects
Page: 265
Authors: Telting, J.H.; Østensen, R.H.; Geier, S.; Heber, U.; Glowienka, L.; Nielsen, T.; Frandsen, S.
Abstract: In the autumn of 2006 we obtained in total about 1600 time-resolved high-resolution spectra with the aim to identify the main pulsation mode in Balloon 090100001 by studying the line-profile variations. Here we present the first results obtained from 842 spectra secured in August 2006.

We phase fold the spectra onto the known dominant period of 2.80746mHz, to study the abundances and line-broadening as a function of pulsation phase. The abundances do not stand out against those of other subdwarf B stars, hence we find no evidence to suggest that the richness of the frequency spectrum and/or the high pulsation amplitudes are related to abundance effects. The abundances do not change with pulsational phase.

The metal lines in Balloon 090100001 are much broader than for non-pulsating subdwarfs, and during the cycle of the main pulsation the line broadening varies with ∼ 2 km/s amplitude. Hence we find clear evidence for pulsational broadening of the lines.

We combined the information content of 56 narrow absorption lines through a cross-correlation technique, to create cross-correlation functions that for each individual pulsation phase approximate the average line-profile shape. The resulting profiles have sufficient signal-to-noise for a mode-identification analysis.

To fit the line profiles we consider all modes with ≤ 2 and associated |m|, and use a model of the 3D pulsational surface velocity field. The models with = 2 do not fit the profiles. The best fit is obtained from the model of a radial pulsation ( = 0).

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