Time-series spectroscopy of the rapidly oscillating Ap star HR 3831 |
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Authors: | Ivan K Baldry Timothy R Bedding |
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Institution: | Chatterton Astronomy Department, School of Physics, University of Sydney, NSW 2006, Australia;Anglo-Australian Observatory, P.O. Box 296, Epping, NSW 1710, Australia |
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Abstract: | We present time-series spectroscopy of the rapidly oscillating Ap (roAp) star HR 3831. This star has a dominant pulsation period of 11.7 min and a rotation period of 2.85 d. We have analysed 1400 intermediate-resolution spectra of the wavelength region 6100–7100 Å obtained over one week, using techniques similar to those we applied to another roAp star, α Cir. We confirm that the H α velocity amplitude of HR 3831 is modulated with rotation phase. Such a modulation was predicted by the oblique pulsator model, and rules out the spotted pulsator model. However, further analysis of H α and other lines reveals rotational modulations that cannot easily be explained using the oblique pulsator model. In particular, the phase of the pulsation as measured by the width of the H α line varies with height in the line. The variation of the H α bisector shows a very similar pattern to that observed in α Cir, which we have previously attributed to a radial node in the stellar atmosphere. However, the striking similarities between the two stars, despite the much shorter period of α Cir (6.8 min), argues against this interpretation unless the structure of the atmosphere is somewhat different between the two stars. Alternatively, the bisector variation is a signature of the degree ? of the mode and not the overtone value n . High-resolution studies of the metal lines in roAp stars are needed to understand fully the form of the pulsation in the atmosphere. |
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Keywords: | techniques: spectroscopic stars: chemically peculiar stars: individual: HR 3831 stars: oscillations stars: variables: other |
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