A comprehensive asteroseismic modelling of the high-amplitude δ Scuti star RV Arietis

Michel

et al. 2013

A&A

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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,

Section: Mode Identification From Strömgren Photometrymentioning

confidence: 59%

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

Hernández

Michel

et al. 2013

A&A

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“…In particular, the authors found that loci in the amplitude ratio-phase difference diagrams (Garrido 2000) become both aspect and m-dependent. In Casas et al (2006), it was found that mode contamination is significant for radial modes in δ Scuti stars. Therefore, mode contamination should be then taken into account for the correct identification using amplitude ratio-phase difference diagnostic diagrams.…”

Section: Mode Contaminationmentioning

confidence: 99%

The role of rotation on Petersen diagrams

Suárez

Garrido

2007

A&A

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Aims. In the present work, the effect of near-degeneracy on rotational Petersen diagrams (RPD) is analysed. Methods. Seismic models are computed considering rotation effects on both equilibrium models and adiabatic oscillation frequencies (including second-order near-degeneracy effects). Contamination of coupled modes and coupling strength on the first radial modes are studied in detail. Results. Analysis of relative intrinsic amplitudes of near-degenerate modes reveals that the identity of the fundamental radial mode and its coupled quadrupole pair are almost unaltered once near-degeneracy effects are considered. However, for the first overtone, a mixed radial/quadrupole identity is always predicted. The effect of near-degeneracy on the oscillation frequencies becomes critical for rotational velocities larger than 15-20 km s −1 , for which large wriggles in the evolution of the period ratios are obtained (up 10 −2 ). Such wriggles imply uncertainties, in terms of metallicity determinations using RPD, reaching up to 0.50 dex, which can be critical for Pop. I HADS (High Amplitude δ Scuti stars). In terms of mass determinations, uncertainties reaching up to 0.5 M are predicted. The location of such wriggles is found to be independent of metallicity and rotational velocity, and governed mainly by the avoidedcrossing phenomenon. Conclusions. Near-degeneracy affects significantly the Π 1/0 (Ω) period ratios even for relatively low rotational velocities, and that can be critical when accurate determinations of mass and metallicity are required. Nevertheless, analysis of near-degeneracy effects provides some clues for the identification of the fundamental radial mode, the first overtone, and their corresponding quadrupole coupled pairs. This can be especially useful when additional information on mode identification and/or metallicity is available, for example from multicolour photometry and/or spectroscopy, not only for accurate diagnostics on metallicity and mass, but also because it is possible to constrain, to some extent, the rotational velocity of the star (and thereby its inclination angle).

“…Using these tools, we performed a massive numerical study of HR 8799 in an attempt to constrain physical and theoretical parameters. In this work, we will follow the same scheme as that used for the study of RV Arietis, 29 Cygnis and 9 Aurigae (Casas et al 2006, 2009; Moya et al 2006).…”

Section: Introductionmentioning

confidence: 99%

The planetary system host HR 8799: on its λ Bootis nature

Monthly Notices of the Royal Astronomical Society

Amado

Barrado

et al. 2010

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HR 8799 is a λ Bootis, γ Doradus star hosting a planetary system and a debris disc with two rings. This makes this system a very interesting target for asteroseismic studies. This work is devoted to the determination of the internal metallicity of this star, linked with its λ Bootis nature (i.e. solar surface abundances of light elements and subsolar surface abundances of heavy elements), taking advantage of its γ Doradus pulsations. This is the most accurate way of obtaining this information, and this is the first time that such a study is performed for a planetary‐system‐host star. We have used the equilibrium code cesam and the non‐adiabatic pulsational code graco. We have applied the frequency ratio method (FRM) and the time‐dependent convection theory to estimate the mode identification, the Brunt–Vaïsälä frequency integral and the mode instability, making the selection of the models possible. When the non‐seismological constraints (i.e. HR 8799's position in the Hertzsprung–Russell diagram) are used, the solar abundance models are discarded. This result contradicts one of the main hypotheses for explaining the λ Bootis nature, namely the accretion/diffusion of gas by a star with solar abundance. Therefore, according to this result, a revision of this hypothesis is needed. The inclusion of accurate internal chemical mixing processes seems to be necessary to explain the peculiar abundances observed in the surface of stars with internal subsolar metallicities. The use of the asteroseismological constraints, like those provided by the FRM or the instability analysis, provides a very accurate determination of the physical characteristics of HR 8799. However, the dependence of the results on the inclination angle i still remains. The determination of this angle, more accurate multicolour photometric observations and high‐resolution spectroscopy can definitively fix the mass and metallicity of this star.