The sixth frequency of roAp star HR 1217

• Type: Article in International Scientific Journal
• Date: 2001

Authors

Cunha, MS (Author) FCUP

Journal

Title: Monthly Notices of the Royal Astronomical Society

Vol. 325

Pages: 373-378

ISSN: 0035-8711

Publisher: Oxford University Press

Indexing

ISI Web of Knowledge - 39 Citations

Scopus - 30 Citations

Other information

Authenticus ID: P-000-TXF

DOI: 10.1046/j.1365-8711.2001.04434.x

Abstract (EN): The frequency of the sixth mode observed in HR 1217 cannot currently be understood in the light of the asymptotic theory for high-frequency acoustic modes, valid for adiabatic pulsations in spherically symmetric stars. Deviations from spherical symmetry will change the frequency of the observed oscillations away from the frequencies predicted by the asymptotic theory. Among other things, the presence of a magnetic field in the star will introduce such deviations from spherical symmetry. In the present work we inspect the effect of the magnetic field on the oscillations of HR 1217. Although we model HR 1217 in a rather simplified manner, we believe, as argued in the text, that the essence of the conclusions would not be modified if a more sophisticated model were to be used instead. The results show that the frequency of the sixth mode observed in HR 1217 might be understood if the effect of the magnetic field on the frequencies of the oscillations is fully taken into account. Moreover, we interpret the sixth frequency as a mode of even degree, and explain the absence from the observations of an intermediate l = 1, m = 0 mode as the result of large energy losses associated with the coupling of the latter with Alfvenic waves, in the strongly magnetized outer layers of the star. Finally, we show how, in the light of this explanation, the frequency of the sixth mode might be used in order to put constraints on the parameters characterizing the star.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 6