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Register a new userHigh-Amplitude gamma Doradus Variables
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According to most literature sources, the amplitude of the pulsational variability observed in gamma Doradus stars does not exceed 0.1 mag in Johnson V. We have analyzed fifteen high-amplitude gamma Doradus stars with photometric peak-to-peak amplitudes well beyond this limit, with the aim of unraveling the mechanisms behind the observed high amplitudes and investigating whether these objects are in any way physically distinct from their low-amplitude counterparts. We have calculated astrophysical parameters and investigated the location of the high-amplitude gamma Doradus stars and a control sample of fifteen low-amplitude objects in the log Teff versus log L diagram. Employing survey data and our own observations, we analyzed the photometric variability of our target stars using discrete Fourier transform. Correlations between the observed primary frequencies, amplitudes and other parameters like effective temperature and luminosity were investigated. The unusually high amplitudes of the high-amplitude gamma Doradus stars can be explained by the superposition of several base frequencies in interaction with their combination and overtone frequencies. Although the maximum amplitude of the primary frequencies does not exceed an amplitude of 0.1 mag, total light variability amplitudes of over 0.3 mag (V) can be attained in this way. Low- and high-amplitude gamma Doradus stars do not appear to be physically distinct in any other respect than their total variability amplitudes but merely represent two ends of the same, uniform group of variables.
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Our goal is to assess Gaias performance on the period recovery of short period (p < 2 hours) and small amplitude variability. To reach this goal first we collected the properties of variable stars that fit the requirements described above. Then we built a database of synthetic light-curves with short period and low amplitude variability with time sampling that follows the Gaia nominal scanning law and with noise level corresponding to the expected photometric precision of Gaia. Finally we performed period search on the synthetic light-curves to obtain period recovery statistics. This work extends our previous period recovery studies to short period variable stars which have non-stationary Fourier spectra.
We present a spectroscopic survey of known and candidate $gamma$,Doradus stars. The high-resolution, high signal-to-noise spectra of 52 objects were collected by five different spectrographs. The spectral classification, atmospheric parameters (teff, $log g$, $xi$), $vsin i$ and chemical composition of the stars were derived. The stellar spectral and luminosity classes were found between G0-A7 and IV-V, respectively. The initial values for teff and logg were determined from the photometric indices and spectral energy distribution. Those parameters were improved by the analysis of hydrogen lines. The final values of teff, logg and $xi$ were derived from the iron lines analysis. The teff values were found between 6000,K and 7900,K, while logg,values range from 3.8 to 4.5,dex. Chemical abundances and $vsin i$ values were derived by the spectrum synthesis method. The $vsin i$ values were found between 5 and 240,km,s$^{-1}$. The chemical abundance pattern of $gamma$,Doradus stars were compared with the pattern of non-pulsating stars. It turned out that there is no significant difference in abundance patterns between these two groups. Additionally, the relations between the atmospheric parameters and the pulsation quantities were checked. A strong correlation between the $vsin i$ and the pulsation periods of $gamma$,Doradus variables was obtained. The accurate positions of the analysed stars in the H-R diagram have been shown. Most of our objects are located inside or close to the blue edge of the theoretical instability strip of $gamma$,Doradus.
The hot $gamma$~Doradus stars have multiple low frequencies characteristic of $gamma$~Dor or SPB variables, but are located between the red edge of the SPB and the blue edge of the $gamma$~Dor instability strips where all low-frequency modes are stable in current models of these stars. Though $delta$~Sct stars also have low frequencies, there is no sign of high frequencies in hot $gamma$~Dor stars. We obtained spectra to refine the locations of some of these stars in the H-R diagram and conclude that these are, indeed, anomalous pulsating stars. The Maia variables have multiple high frequencies characteristic of $beta$~Cep and $delta$~Sct stars, but lie between the red edge of the $beta$~Cep and the blue edge of the $delta$~Sct instability strips. We compile a list of all Maia candidates and obtain spectra of two of these stars. Again, it seems likely that these are anomalous pulsating stars which are currently not understood.
$gamma$ Doradus is the prototype star for the eponymous class of pulsating stars that consists of late A-early F main-sequence stars oscillating in low-frequency gravito-inertial modes. Being among the brightest stars of its kind (V = 4.2), $gamma$ Dor benefits from a large set of observational data that has been recently completed by high-quality space photometry from the TESS mission. With these new data, we propose to study $gamma$ Dor as an example of possibilities offered by synergies between multi-technical ground and space-based observations. Here, we present the preliminary results of our investigations.
We present here preliminary results concerning 32 stars identified as main gamma Doradus candidates by the COROT Variable Classifier (CVC) among the 4 first fields of the exoplanet CCDs.
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