The fundamental parameters of the roAp star HD 24712
A rapidly oscillator at the red edge of the instability strip⋆
Univ. Grenoble Alpes, IPAG,
2 CNRS, IPAG, 38000 Grenoble, France
3 Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
4 Institute for Astrophysics, Georg-August-University, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
5 Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Bd de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
6 CHARA Array, Mount Wilson Observatory, 91023 Mount Wilson CA, USA
Received: 8 December 2015
Accepted: 24 April 2016
Context. There is still a debate about the nature of the mechanism that causes the pulsation excitation of the rapidly oscillating Ap stars that oscillate above the highest theoretically acoustic frequency. HD 24712 is a good test case for such a study because it is bright, its parallax accurately determined, and its frequency spectrum is well known.
Aims. Visible long-baseline interferometry is a unique technique for measuring accurate angular diameters of targets as small as the brightest roAp stars, and thus estimating accurate radii by a method as independent as possible of atmosphere models.
Methods. We used the visible spectrograph VEGA at the CHARA long-baseline optical array to observe HD 24712, and we derived its limb-darkened diameter. We also estimated its bolometric flux from spectroscopic data in the literature and determined its radius, luminosity, and effective temperature.
Results. We determined a limb-darkened angular diameter of 0.335 ± 0.009 mas for HD 24712 and derived a radius of R = 1.772 ± 0.057 R⊙, a luminosity of L = 7.2 ± 1.8 L⊙, and an effective temperature of Teff = 7235 ± 280 K, which is in very close agreement with the values provided by the self-consistent stratified model developed for this star. We used these fundamental parameters to set HD 24712 in the Hertzsprung-Russell diagram. Its position is marginally consistent with the region where high radial order modes are predicted to be excited by the κ-mechanism.
Conclusions. We conclude that oscillations in this star are most likely not driven by the κ-mechanism.
Key words: stars: fundamental parameters / stars: individual: HD 24712 / techniques: high angular resolution / techniques: interferometric
© ESO, 2016