An in-depth study of HD 174966 with CoRoT photometry and HARPS spectroscopy

Large separation as a new observable for δ Scuti stars ^{⋆,⋆⋆,⋆⋆⋆}

¹ Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
e-mail: agh@astro.up.pt
² Instituto de Astrofísica de Andalucía (CSIC), CP3004, Granada, Spain
³ Departamento de Astrofísica, Centro de Astrobiología (INTA-CSIC), PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁴ LESIA, Observatoire de Paris, CNRS UMR 8109, Université Pierre et Marie Curie, Université Denis Diderot, 5 place J. Janssen, 92195 Meudon, France
⁵ INAF-Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
⁶ Instituto de Astrofísica de Canarias, 38200, La Laguna, Tenerife, Spain
⁷ Departamento de Astrofísica, Universidad de La Laguna, 38205, La Laguna, Tenerife, Spain
⁸ Spanish Virtual Observatory, 28691 Villanueva de la Cañada, Madrid, Spain
⁹ Université de Toulouse, UPS-OMP, IRAP, Tarbes, France
¹⁰ CNRS, IRAP, 57 avenue d’Azereix, 65000 Tarbes, France
¹¹ Institut d’Astrophysique Spatiale, CNRS/Université Paris XI UMR 8617, 91405 Orsay, France

Received: 19 August 2012
Accepted: 5 July 2013

Abstract

Aims. The aim of this work was to use a multi-approach technique to derive the most accurate values possible of the physical parameters of the δ Sct star HD 174966, which was observed with the CoRoT satellite. In addition, we searched for a periodic pattern in the frequency spectra with the goal of using it to determine the mean density of the star.

Methods. First, we extracted the frequency content from the CoRoT light curve. Then, we derived the physical parameters of HD 174966 and carried a mode identification out from the spectroscopic and photometric observations. We used this information to look for the models fulfilling all the conditions and discussed the inaccuracies of the method because of the rotation effects. In a final step, we searched for patterns in the frequency set using a Fourier transform, discussed its origin, and studied the possibility of using the periodicity to obtain information about the physical parameters of the star.

Results. A total of 185 peaks were obtained from the Fourier analysis of the CoRoT light curve, all of which were reliable pulsating frequencies. From the spectroscopic observations, 18 oscillation modes were detected and identified, and the inclination angle (62.5°_-17.5^+7.5) and the rotational velocity of the star (142 km s^-1) were estimated. From the multi-colour photometric observations, only three frequencies were detected that correspond to the main ones in the CoRoT light curve. We looked for periodicities within the 185 frequencies and found a quasiperiodic pattern Δν ~ 64 μHz. Using the inclination angle, the rotational velocity, and an Echelle diagram (showing a double comb outside the asymptotic regime), we concluded that the periodicity corresponds to a large separation structure. The quasiperiodic pattern allowed us to discriminate models from a grid. As a result, the value of the mean density is achieved with a 6% uncertainty. So, the Δν pattern could be used as a new observable for A-F type stars.