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Register a new userMOST discovers a multimode delta Scuti star in a triple system: HD 61199
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A field star, HD 61199 (V ~ 8), simultaneously observed with Procyon by the MOST (Microvariability & Oscillations of STars) satellite in continuous runs of 34, 17, and 34 days in 2004, 2005, and 2007, was found to pulsate in 11 frequencies in the delta Scuti range with amplitudes from 1.7 down to 0.09 mmag. The photometry also showed variations with a period of about four days. To investigate the nature of the longer period, 45 days of time-resolved spectroscopy was obtained at the Thueringer Landessternwarte Tautenburg in 2004. The radial velocity measurements indicate that HD 61199 is a triple system. A delta Scuti pulsator with a rich eigenspectrum in a multiple system is promising for asteroseismology. Our objectives were to identify which of the stars in the system is the delta Scuti variable and to obtain the orbital elements of the system and the fundamental parameters of the individual components, which are constrained by the pulsation frequencies of the delta Scuti star. Classical Fourier techniques and least-squares multi-sinusoidal fits were applied to the MOST photometry to identify the pulsation frequencies. The groundbased spectroscopy was analysed with least-squares-deconvolution (LSD) techniques, and the orbital elements derived with the KOREL and ORBITX routines. Asteroseismic models were also generated. The photometric and spectroscopic data are compatible with a triple system consisting of a close binary with an orbital period of 3.57 days and a delta Scuti companion (HD 61199,A) as the most luminous component. The delta Scuti star is a rapid rotator with about vsin i = 130 km/s and an upper mass limit of about 2.1 Msun. For the close binary components, we find they are of nearly equal mass, with lower mass limits of about 0.7 Msun.
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MOST observations and model analysis of the Herbig Ae star HD 34282 (V1366 Ori) reveal {delta}-Scuti pulsations. 22 frequencies are observed, 10 of which confirm those previously identified by Amado et al. (2006), and 12 of which are newly discovered in this work. We show that the weighted-average frequency in each group fits the radial p-mode frequencies of viable models. We argue that the observed pulsation spectrum extends just to the edge to the acoustic cut-off frequency and show that this also is consistent with our best-fitting models.
The star HD 51844 was observed in CoRoT LRa02 as a Seismo target which turned out to be an SB2 system. The 117 days long light curve revealed delta Scuti pulsation in the range of 6 to 15 d^{-1} where four frequencies have amplitudes larger than 1.4 mmag and a rich frequency spectrum with amplitudes lower than 0.6 mmag. Additionally, the light curve exhibits a brightening event recurring every 33.5 days with a maximum of 3 mmag and a duration of about 5 days. Thus, this star can be considered as a heartbeat candidate. The radial velocities from spectroscopy confirmed an eccentric binary system with nearly identical masses and physical parameters. The brightening event of the light curve coincides with the maximum radial velocity separation showing that the brightening is in fact caused by tidal distortion and/or reflected light. One component displays large line profile variations, while the other does not show significant variation. The frequency analysis revealed a quintuplet structure of the four highest-amplitude frequencies, which is due to the orbital motion of the pulsating star.
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.
We present an analysis of new Johnson and Stromgren photometric and medium-resolution spectroscopic observations of the delta Scuti type variable star V784 Cassiopeae. The data were obtained in three consecutive years between 1999 and 2001. The period analysis of the light curve resulted in the detection of four frequencies ranging from 9.15 c/d to 15.90 c/d, while there is a suggestion for more, unresolved frequency components, too. The mean Stromgren indices and Hipparcos parallax were combined to calculate the following physical parameters: <T_eff>=7100+-100 K, log g=3.8+-0.1, M_bol=1.50+-0.15 mag. The position of the star in the HR diagram was used to derive evolutionary mass and age yielding to a consistent picture of an evolved delta Scuti star with a mixture of radial plus non-radial modes.
In this paper, we analyze the light variations of KIC 10975348 using photometric data delivered from $Kepler$ mission. This star is exceptionally faint ($K_{p}$ = 18.6 mag), compared to most well-studied $delta$ Scuti stars. The Fourier analysis of the short cadence data (i.e. Q14, Q15 and Q16, spanning 220 days) reveals the variations are dominated by the strongest mode with frequency F0 = 10.231899 $rm{d^{-1}}$, which is compatible with that obtained from $RATS-Kepler$. The other two independent modes with F1 (= 13.4988 $rm{d^{-1}}$) and F2 (= 19.0002 $rm{d^{-1}}$) are newly detected and have amplitudes two orders of magnitude smaller than F0. We note that, for the first time, this star is identified to be a high-amplitude $delta$ Sct (HADS) star with amplitude of about 0.7 mag, and the lower ratio of F0/F1 = 0.758 suggests it might be a metal-rich variable star. The frequency F2 may be a third overtone mode, suggesting this target might be a new radial triple-mode HADS star. We perform $O - C$ analysis using 1018 newly determined times of maximum light and derive an ephemeris formula: $T_{max}$ = 2456170.241912(0)+0.097734(1) $times$ $E$. The $O - C$ diagram shows that the pulsation period of KIC 10975348 seems to show no obvious change, which is in contrast to that of the majority of HADS stars. The possible cause of that may be due to the current short time span of observations. To verify its possible period variations, regular observation from space with a longer time span in future is needed.
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