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

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•+7.5 −17.5 ) 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.Key words. asteroseismology -stars: oscillations -stars: variables: delta Scuti -stars: interiors -stars: fundamental parametersstars: rotation The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes,

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“…The large number of frequencies detected from space observations allow the application of statistical techniques to detect frequency patterns [3]. The large separations estimated from such studies are consistent with those predicted by recent self-consistent field (SCF) rotating models [4].…”

Non-adiabatic pulsations in ESTER models

“…In a recent paper, [7] derived an observational scaling relation between the large frequency separation and the mean density of several δ Scuti stars in eclipsing binary systems, in agreement with previous theoretical predictions [8]. Such large separations have also been used to create echelle diagrams [9,10]. However, no firm identification has been obtained for individual modes.…”

Frequency regularities of acoustic modes and multi-colour mode identification in rapidly rotating stars

“…These uniform spacings have also been modelled through asymptotic semi-analytical formulas (Pasek et al 2012). A&A 601, A130 (2017) In observed spectra, recurrent frequency spacings that may correspond to the large separation or half its value have been found in some stars (García Hernández et al 2009;García Hernández et al 2013;Paparó et al 2016). Moreover, García Hernández et al (2015) show that mean density estimates based on this type of spacings (obtained via a scaling relation similar to the one in Reese et al 2008, but based on SCF models) are compatible with independent mass and radii measurements obtained for δ Scuti stars in binary systems.…”