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Register a new userAmplitude Ratios as Mode Characterizors in delta Scuti stars
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Seismology of delta Scuti stars holds great potentials for testing theories of stellar structure and evolution. The ratio of mode amplitudes in light and in equivalent width of spectral lines can be used for mode identification. However, the amplitude ratios (AR) predicted from theory are usually inconsistent with observations. We here present the first results from a campaign aimed at calibrating observationally the absolute values of the AR.
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We have carried out a photometric and spectroscopic survey of bright high-amplitude delta Scuti (HADS) stars. The aim was to detect binarity and multiperiodicity (or both) in order to explore the possibility of combining binary star astrophysics with stellar oscillations. Here we present the first results for ten, predominantly southern, HADS variables. We detected the orbital motion of RS Gru with a semi-amplitude of ~6.5 km/s and 11.5 days period. The companion is inferred to be a low-mass dwarf star in a close orbit around RS Gru. We found multiperiodicity in RY Lep both from photometric and radial velocity data and detected orbital motion in the radial velocities with hints of a possible period of 500--700 days. The data also revealed that the amplitude of the secondary frequency is variable on the time-scale of a few years, whereas the dominant mode is stable. Radial velocities of AD CMi revealed cycle-to-cycle variations which might be due to non-radial pulsations. We confirmed the multiperiodic nature of BQ Ind, while we obtained the first radial velocity curves of ZZ Mic and BE Lyn. The radial velocity curve and the O-C diagram of CY Aqr are consistent with the long-period binary hypothesis. We took new time series photometry on XX Cyg, DY Her and DY Peg, with which we updated their O-C diagrams.
We present our first results for a sample of southern high-amplitude delta Scuti stars (HADS), based on a spectrophotometric survey started in 2003. For CY Aqr and AD CMi, we found very stable light and radial velocity curves; we confirmed the double-mode nature of ZZ Mic, BQ Ind and RY Lep. Finally, we detected gamma-velocity changes in RS Gru and RY Lep
We report on a multi-site photometric campaign on the high-amplitude $delta$ Scuti star V2367 Cyg in order to determine the pulsation modes. We also used high-dispersion spectroscopy to estimate the stellar parameters and projected rotational velocity. Time series multicolour photometry was obtained during a 98-d interval from five different sites. These data were used together with model atmospheres and non-adiabatic pulsation models to identify the spherical harmonic degree of the three independent frequencies of highest amplitude as well as the first two harmonics of the dominant mode. This was accomplished by matching the observed relative light amplitudes and phases in different wavebands with those computed by the models. In general, our results support the assumed mode identifications in a previous analysis of Kepler data.
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.
Bi-site time-series photometric and high-resolution spectroscopic observations were made for the double-mode high-amplitude $delta$ Scuti star VX Hya. The fundamental frequency $f_{0}=4.4763 rm{c days^{-1}}$, the first overtone $f_{1}=5.7897 rm{c days^{-1}}$ and 23 harmonics and linear combinations of $f_{0}$ and $f_{1}$ are detected by pulsation analysis. From the spectroscopic data, we get $rm{[Fe/H] = -0.2pm0.1 dex}$. The period change rate of the fundamental mode is obtained by using the Fourier-phase diagram method, which gives the value of $(1/P_{0})(dP_{0}/dt)=(1.81pm0.09) times 10^{-7} rm{yr}^{-1}$. With these results from the observations, we perform theoretical explorations with the stellar evolution code MESA, and constrain the models by fitting $f_{0}$, $f_{1}$, and $(1/P_{0})(dP_{0}/dt)$ within $3sigma$ deviations. The results show that the period change of VX Hya could be ascribed to the evolutionary effect. The stellar parameters of VX Hya could be derived as: the mass $2.385pm0.025 M_{odot}$, the luminosity $log(L/L_{odot})=1.93pm0.02$ and the age $(4.43pm0.13)times 10^8$ years. VX Hya is found to locate at the post-main-sequence stage with a helium core and a hydrogen-burning shell on the H${-}$R diagram.
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