Article

# P-modes in rapidly rotating stars: Looking for regular patterns in synthetic asymptotic spectra

(Impact Factor: 0.92). 12/2010; 331(9-10). DOI: 10.1002/asna.201011455
Source: arXiv

ABSTRACT

According to a recent ray-based asymptotic theory, the high-frequency p-mode spectrum of rapidly rotating stars is a superposition of frequency subsets associated with dynamically independent regions of the ray-dynamics phase space. At high rotation rates corresponding to typical $\delta$ Scuti stars, two frequency subsets are expected to be visible : a regular frequency subset described by a Tassoul like formula and an irregular frequency subset with specific statistical properties. In this paper, we investigate whether the regular patterns can be detected in the resulting spectrum. We compute the autocorrelation function of synthetic spectra where the frequencies follow the asymptotic theory, the relative amplitudes are simply given by the modes' disk-averaging factors, and the frequency resolution is that of a CoRoT long run. Our first results are that (i) the detection of regular patterns strongly depends on the ratio of regular over irregular modes, (ii) low inclination angle configurations are more favorable than near equator-on configurations, (iii) in the absence of differential rotation, the $2 \Omega$ rotational splitting between $m=1$ and $m=-1$ modes is an easy feature to detect. Comment: 4 pages, 4 figures, proceedings of the HELAS-IV International Conference, accepted for publication in Astronomische Nachrichten

0 Followers
·
• Source
##### Article: Oscillations in rapidly rotating stars
[Hide abstract]
ABSTRACT: Spurred by the spectroscopic and interferometric observations of rapidly rotating stars and the highly accurate pulsation data coming from asteroseismology space missions, theoreticians have spent many years developing models for such stars and studying their oscillations. This has led to the discovery of new phenomena and new types of pulsation modes. In what follows, a review is given of the different methods used to model the effects of rotation on stellar pulsations, as well as a description of these effects on inertial, gravito-inertial, r and acoustic modes (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Astronomische Nachrichten 12/2010; 331(9‐10):1038 - 1043. DOI:10.1002/asna.201011452 · 0.92 Impact Factor
• Source
##### Article: Regular frequency patterns in the classical delta Scuti star HD 144277 observed by the MOST satellite
[Hide abstract]
ABSTRACT: We present high-precision time-series photometry of the classical delta Scuti star HD 144277 obtained with the MOST (Microvariability and Oscillations of STars) satellite in two consecutive years. The observed regular frequency patterns are investigated asteroseismologically. HD 144277 is a hot A-type star that is located on the blue border of the classical instability strip. While we mostly observe low radial order modes in classical delta Scuti stars, HD 144277 presents a different case. Its high observed frequencies, i.e., between 59.9c/d (693.9 microHz) and 71.1c/d (822.8microHz), suggest higher radial orders. We examine the progression of the regular frequency spacings from the low radial order to the asymptotic frequency region. Frequency analysis was performed using Period04 and SigSpec. The results from the MOST observing runs in 2009 and 2010 were compared to each other. The resulting frequencies were submitted to asteroseismic analysis. HD 144277 was discovered to be a delta Scuti star using the time-series photometry observed by the MOST satellite. Twelve independent pulsation frequencies lying in four distinct groups were identified. Two additional frequencies were found to be combination frequencies. The typical spacing of 3.6c/d corresponds to the spacing between subsequent radial and dipole modes, therefore the spacing between radial modes is twice this value, 7.2c/d. Based on the assumption of slow rotation, we find evidence that the two radial modes are the sixth and seventh overtones, and the frequency with the highest amplitude can be identified as a dipole mode. The models required to fit the observed instability range need slightly less metallicity and a moderate enhancement of the helium abundance compared to the standard chemical composition. Our asteroseismic models suggest that HD 144277 is a delta Scuti star close to the ZAMS with a mass of 1.66 solar masses.
Astronomy and Astrophysics 09/2011; 533. DOI:10.1051/0004-6361/201117272 · 4.38 Impact Factor
• Source
##### Article: Pulsation spectrum of delta Scuti stars: the binary HD 50870 as seen with CoRoT and HARPS
[Hide abstract]
ABSTRACT: Aims. We present the results obtained with the CoRoT satellite for HD 50870, a δ Sct star which was observed for 114.4 d. The aim of these observations was to evaluate the results obtained for HD 50844, the first δ Sct star monitored with CoRoT, on a longer time baseline. Methods. The 307,570 CoRoT datapoints were analysed with different techniques. The photometric observations were complemented over 15 nights of high-resolution spectroscopy with HARPS on a baseline of 25 d. These spectra were analysed to study the line profile variations and to derive the stellar physical parameters. Some uvby photometric observations were also obtained to better characterize the pulsation modes. Results. HD 50870 proved to be a low-amplitude, long-period spectroscopic binary system seen almost pole-on (i ≃ 21 o). The brighter component, which also has the higher rotational velocity (v sin i = 37.5 km s −1), is a δ Sct-type variable with a full light amplitude variation of about 0.04 mag. There is a dominant axisymmetric mode (17.16 d −1). Moreover, there are two groups of frequencies (about 19) in the intervals 6-9 and 13-18 d −1 , with amplitudes ranging from a few mmag to 0.3 mmag. After the detection of about 250 terms (corresponding to an amplitude of about 0.045 mmag) a flat plateau appears in the power spectrum in the low-frequency region up to about 35 d −1 . We were able to detect this plateau only thanks to the short cadence sampling of the CoRoT measurements (32 s). The density distribution vs. frequency of the detected frequencies seems rule out the possibility that this plateau is the result of a process with a continuum power spectrum. The spacings of the strongest modes suggest a quasi-periodic pattern. We failed to find a satisfactory seismic model that simultaneously matches the frequency range, the position in the HR diagram, and the quasi-periodic pattern interpreted as a large separation. Nineteen modes were detected spectroscopically from the line profile variations and associated to the photometric ones. Tentative ℓ, m values have been attributed to the modes detected spectroscopically. Prograde as well as retrograde modes are present with ℓ values up to 9. There are no traces of variability induced by solar-like oscillations.
Astronomy and Astrophysics 04/2012; 542(0004-6361). DOI:10.1051/0004-6361/201118682 · 4.38 Impact Factor