Pulsations in the atmosphere of the roAp star HD 24712 - II. Theoretical models

Hideyuki Saio, Tanya Ryabchikova, Mikhail Sachkov

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)

Abstract

We discuss pulsations of the rapidly oscillating Ap (roAp) star HD 24712 (HR 1217) based on non-adiabatic analyses taking into account the effect of dipole magnetic fields. We have found that all the pulsation modes appropriate for HD 24712 are damped, i.e. the κ-mechanism excitation in the hydrogen ionization layers is not strong enough to excite high-order p modes with periods consistent with observed ones, all of which are found to be above the acoustic cut-off frequencies of our models.The main (2.721 mHz) and the highest (2.806 mHz) frequencies are matched with modified l= 2 and 3 modes, respectively. The large frequency separation (≈68 μHz) is reproduced by models which lay within the error box of HD 24712 on the Hertzsprung-Russell diagram. The nearly equally spaced frequencies of HD 24712 indicate the small frequency separation to be as small as ≈0.5 μHz. However, the small separation derived from theoretical l= 1 and 2 modes is found to be larger than ∼3 μHz. The problem of equal spacing could be resolved by assuming that the spacings correspond to pairs of l= 2 and 0 modes; this is possible because magnetic fields significantly modify the frequencies of l= 0 modes. The amplitude distribution on the stellar surface is strongly affected by the magnetic field resulting in the predominant concentration at the polar regions. The modified amplitude distribution of a quasi-quadrapole mode predicts a rotational amplitude modulation consistent with the observed one.Amplitudes and phases of radial velocity variations for various spectral lines are converted to relations of amplitude/phase versus optical depth in the atmosphere. Oscillation phase delays gradually outward in the outermost layers indicating the presence of waves propagating outward. The phase changes steeply around log τ∼-3.5, which supports a T-τ relation having a small temperature inversion there.

Original languageEnglish
Pages (from-to)1729-1738
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Volume403
Issue number4
DOIs
Publication statusPublished - 2010 Apr
Externally publishedYes

Keywords

  • Stars: individual: HD 24712
  • Stars: magnetic fields
  • Stars: oscillations

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Fingerprint

Dive into the research topics of 'Pulsations in the atmosphere of the roAp star HD 24712 - II. Theoretical models'. Together they form a unique fingerprint.

Cite this