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Register a new userStudy of rotational splittings in $delta$~Scuti stars using pattern finding techniques
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Added by
Alejandro Ram\\'on-Ballesta
Publication date
2021
fields
Physics
and research's language is
English
Authors
A. Ramon-Ballesta
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Detecting and understanding rotation in stellar interiors is nowadays one of the unsolved problems in stellar physics. Asteroseismology has been able to provide insights on rotation for the Sun, solar-like stars, and compact objects like white dwarfs. However, this is still very difficult for intermediate-mass stars. These stars are moderate-to-rapid rotators. Rotation splits and shifts the oscillation modes, which makes the oscillation spectrum more complex and harder to interpret. Here we study the oscillation patterns of a sample of benchmark $delta$~Sct stars belonging to eclipsing binary systems with the objective to find the frequency spacing related to the rotational splitting ($delta r$). For this task, we combine three techniques: the Fourier transform, the autocorrelation function, and the histogram of frequency differences. The last two showed a similar behaviour. For most of the stars, it was necessary to determine the large separation ($Delta u$) prior to spot $delta r$. This is the first time we may clearly state that one of the periodicities present in the p~modes oscillation spectra of $delta$~Sct stars corresponds to the rotational splitting. This is true independently of the stellar rotation rate. These promising results pave the way to find a robust methodology to determine rotational splittings from the oscillation spectra of $delta$~Sct stars and, thus, understanding the rotational profile of intermediate-mass pulsating stars.
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We present statistical characteristics of 1,578 {delta} Scuti stars including nearby field stars and cluster member stars within the Milky Way. We obtained 46% of these stars (718 stars) from the works done by Rodr{i}guez and collected the remaining 54% stars (860 stars) from other literatures. We updated the entries with the latest information of sky coordinate, color, rotational velocity, spectral type, period, amplitude and binarity. The majority of our sample are well characterized in terms of typical period range (0.02-0.25 days), pulsation amplitudes (<0.5 mag) and spectral types (A-F type). Given this list of {delta} Scuti stars, we examined relations between their physical properties (i.e., periods, amplitudes, spectral types and rotational velocities) for field stars and cluster members, and confirmed that the correlations of properties are not significantly different from those reported in the Rodr{i}guezs works. All the {delta} Scuti stars are cross-matched with several X-ray and UV catalogs, resulting in 27 X-ray and 41 UV-only counterparts. These counterparts are interesting targets for further study because of their rarity and uniqueness in showing {delta} Scuti-type variability and X-ray/UV emission at the same time. The compiled catalog can be accessed through the web interface http://stardb.yonsei.ac.kr/DeltaScuti
Inspired by the so appealing example of red giants, where going from a handful of stars to thousands revealed the structure of the eigenspectrum, we inspected a large homogeneous set of around 1860 {delta} Scuti stars observed with CoRoT. This unique data set reveals a common regular pattern which appears to be in agreement with island modes featured by theoretical non-perturbative treatments of fast rotation. The comparison of these data with models and linear stability calculations suggests that spectra can be fruitfully characterized to first order by a few parameters which might play the role of seismic indices for {delta} Scuti stars, as {Delta u} and { u_{max}} do for red giants. The existence of this pattern offers an observational support for guiding further theoretical works on fast rotation. It also provides a framework for further investigation of the observational material collected by CoRoT and Kepler. Finally, it sketches out the perspective of using {delta} Scuti stars pulsations for ensemble asteroseismology.
In this work, we have gone one step further from the study presented in the first CoRoT symposium. Our analysis consists on constructing a model database covering the entire uncertainty box of the $delta$ Sct star HD174966, derived from the usual observables ($mathrm{T}_{mathrm{eff}}$, $log g$ and [Fe/H]), and constraining the models representative of the star. To do that, we use the value of the periodicity (related to $Delta u_{ell}$) found in its CoRoT pulsating spectrum.
Eclipsing binaries with a $delta$ Sct component are powerful tools to derive the fundamental parameters and probe the internal structure of stars. In this study, spectral analysis of 6 primary $delta$ Sct components in eclipsing binaries has been performed. Values of $T_{rm eff}$, $v sin i$, and metallicity for the stars have been derived from medium-resolution spectroscopy. Additionally, a revised list of $delta$ Sct stars in eclipsing binaries is presented. In this list, we have only given the $delta$ Sct stars in eclipsing binaries to show the effects of the secondary components and tidal-locking on the pulsations of primary $delta$ Sct components. The stellar pulsation, atmospheric and fundamental parameters (e.g., mass, radius) of 92 $delta$ Sct stars in eclipsing binaries have been gathered. Comparison of the properties of single and eclipsing binary member $delta$ Sct stars has been made. We find that single $delta$ Sct stars pulsate in longer periods and with higher amplitudes than the primary $delta$ Sct components in eclipsing binaries. The $v sin i$ of $delta$ Sct components is found to be significantly lower than that of single $delta$ Sct stars. Relationships between the pulsation periods, amplitudes, and stellar parameters in our list have been examined. Significant correlations between the pulsation periods and the orbital periods, $T_{rm eff}$, $log g$, radius, mass ratio, $v sin i$, and the filling factor have been found.
We present a seismic study of $delta$ Scuti based on a mode identification from multicoulor photometry. The dominant frequency can be associated only with a radial mode and the second frequency is, most probably, a dipole mode. The other six frequencies have more ambiguous identifications. The photometric mode identification provided also some constraints on the atmospheric metallicity [m/H]$approx$+0.5 and microturbulent velocity $xi_tapprox 4~kms$. For models reproducing the dominant frequency, we show that only the fundamental mode is possible and the first overtone is excluded. However, the location of $delta$ Scuti near the terminal age main sequence requires the consideration of three stages of stellar evolution. For the star to be on the main sequence, it is necessary to include overshooting from the convective core with a parameter of at least $alpha_{rm ov}=0.25$ at the metallicity greater than $Z=0.019$. It turned out that the value of the relative amplitude of the bolometric flux variations (the nonadiabatic parameter $f$) is mainly determined by the position of the star in the HR diagram, i.e., by its effective temperature and luminosity, whereas the effect of the evolutionary stage is minor. On the other hand, the convective efficiency in the subphotospheric layers has a dominant effect on the value of the parameter $f$. %in the $delta$ Sct star models. Comparing the theoretical and empirical values of $f$ for the radial dominant mode, we obtain constraints on the mixing length parameter $alpha_{rm MLT}$ which is less than about 1.0, independently of the adopted opacity data and chemical mixture. This value of $alpha_{rm MLT}$ is substantially smaller than for a calibrated solar model indicating rather low to moderately efficient convection in the envelope of $delta$ Scuti.
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