Kepler observations of Am stars★

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 06/2011; 414(1):792 - 800. DOI: 10.1111/j.1365-2966.2011.18454.x


We present an analysis of high-resolution spectra for two pulsating Am stars in the Kepler field. The stellar parameters derived in this way are important because parameters derived from narrow-band photometry may be affected by the strong metal lines in these stars. We analyse the Kepler time series of ten known Am stars and find that six of them clearly show δ Scuti pulsations. The other four appear to be non-pulsating. We derive fundamental parameters for all known pulsating Am stars from ground-based observations and also for the Kepler Am stars to investigate the location of the instability strip for pulsating Am stars. We find that there is not much difference between the Am-star instability strip and the δ Scuti instability strip. We find that the observed location of pulsating Am stars in the HR diagram does not agree with the location predicted from diffusion calculations.


Available from: L. A. Balona
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    ABSTRACT: The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-F type stars. We propose three main groups to describe the observed variety in pulsating A-F type stars: gamma Dor, delta Sct, and hybrid stars. We assign 63% of our sample to one of the three groups, and identify the remaining part as rotationally modulated/active stars, binaries, stars of different spectral type, or stars that show no clear periodic variability. 23% of the stars (171 stars) are hybrid stars, which is a much larger fraction than what has been observed before. We characterize for the first time a large number of A-F type stars (475 stars) in terms of number of detected frequencies, frequency range, and typical pulsation amplitudes. The majority of hybrid stars show frequencies with all kinds of periodicities within the gamma Dor and delta Sct range, also between 5 and 10 c/d, which is a challenge for the current models. We find indications for the existence of delta Sct and gamma Dor stars beyond the edges of the current observational instability strips. The hybrid stars occupy the entire region within the delta Sct and gamma Dor instability strips, and beyond. Non-variable stars seem to exist within the instability strips. The location of gamma Dor and delta Sct classes in the (Teff,logg)-diagram has been extended. We investigate two newly constructed variables 'efficiency' and 'energy' as a means to explore the relation between gamma Dor and delta Sct stars. Our results suggest a revision of the current observational instability strips, and imply an investigation of other pulsation mechanisms to supplement the kappa mechanism and convective blocking effect to drive hybrid pulsations.
    Astronomy and Astrophysics 07/2011; 534. DOI:10.1051/0004-6361/201117368 · 4.38 Impact Factor
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    ABSTRACT: We have studied over 1600 Am stars at a photometric precision of 1 mmag with SuperWASP photometric data. Contrary to previous belief, we find that around 200 Am stars are pulsating delta Sct and gamma Dor stars, with low amplitudes that have been missed in previous, less extensive studies. While the amplitudes are generally low, the presence of pulsation in Am stars places a strong constraint on atmospheric convection, and may require the pulsation to be laminar. While some pulsating Am stars have been previously found to be delta Sct stars, the vast majority of Am stars known to pulsate are presented in this paper. They will form the basis of future statistical studies of pulsation in the presence of atomic diffusion.
    Astronomy and Astrophysics 07/2011; 535. DOI:10.1051/0004-6361/201117230 · 4.38 Impact Factor
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    ABSTRACT: We present the analysis of the time series observations of CoRoT 102699796 obtained by the Convection, Rotation and planetary Transits (CoRoT) satellite that show the presence of five independent oscillation frequencies in the range 3.6–5 c d−1. Using spectra acquired with FLAMES@VLT, we derive the following stellar parameters: spectral type F1V, Teff= 7000 ± 200 K, log (g) = 3.8 ± 0.4, [M/H]=−1.1 ± 0.2, v sin i= 50 ± 5 km s−1, L/L⊙= 21+21− 11. Thus, for the first time we report the existence of a metal-poor, intermediate-mass pre-main-sequence (PMS) pulsating star. Ground-based and satellite data are used to derive the spectral energy distribution (SED) of CoRoT 102699796 extending from the optical to mid-infrared wavelengths. The SED shows a significant IR excess at wavelengths greater than ∼5 μm. We conclude that CoRoT 102699796 is a young Herbig Ae (F1Ve) star with a transitional disc likely associated with the H ii region [FT96]213.1-2.2. The pulsation frequencies have been interpreted in the light of the non-radial pulsation theory, using the losc code in conjunction with static and rotational evolutionary tracks. A minimization algorithm was used to find the best-fitting model with M= 1.84 M⊙, Teff= 6900 K which imply an isochronal age of t∼ 2.5 Myr. This result is based on the interpretation of the detected frequencies as g modes of low–moderate n-value. To our knowledge, this is the first time that such modes are identified in a intermediate-mass PMS pulsating star. Since CoRoT 102699796 lies in the region of the Hertzsprung–Russell (HR) diagram where the δ Sct and γ Dor instability strips intersect, we argue that the observed pulsation characteristics are intermediate between these classes of variables, i.e. CoRoT 102699796 is likely the first PMS hybrid γ Dor–δ Sct pulsator ever studied.
    Monthly Notices of the Royal Astronomical Society 09/2011; 416(2):1535-1545. DOI:10.1111/j.1365-2966.2011.19165.x · 5.11 Impact Factor
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