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Register a new userFrequency analysis of Delta Scuti stars towards the Galactic bulge
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We have performed a frequency analysis of 10,092 Delta Scuti-type stars detected in the fourth phase of the Optical Gravitational Lensing Experiment (OGLE) towards the Galactic bulge, which is the most numerous homogeneous sample of Delta Scuti stars observed so far. The main goal was to search for stars pulsating in at least two radial modes simultaneously. We have found 3083 candidates for such stars, which is the largest set obtained to date. Among them, 2655 stars pulsate in two radial modes, 414 stars pulsate in three radial modes, and 14 stars pulsate in four radial modes at the same time. We report the identification of 221 Delta Scuti stars pulsating in the fundamental mode, first overtone, and third overtone simultaneously. We show the most populated Petersen and Bailey diagrams and discuss statistical properties of the identified frequencies based on this numerous sample. Additionally, we present theoretical predictions of period ratios for Delta Scuti stars pulsating in overtones from the fourth to the seventh.
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We present a collection of 10 111 genuine delta Sct-type pulsating variable stars detected in the OGLE-IV Galactic bulge fields. In this sample, 9835 variables are new discoveries. For most of the stars photometric data cover the whole decade 2010-2019. We illustrate a huge variety of light curve shapes of delta Sct variables. Long-term observations have allowed us to spot objects with evident period, amplitude, and mean brightness variations. Our analysis indicates that about 28% of the stars are single-mode pulsators. Fourteen delta Sct stars show additional eclipsing or ellipsoidal binary modulation. We report significant attenuation or even disappearance of the pulsation signal in six sources. The whole set of variables is a mix of objects representing various Milky Ways populations, with the majority of stars from the Galactic bulge. There are also representatives of the Sagittarius Dwarf Spheroidal Galaxy. Some of the newly detected variables could be SX Phe-type stars residing in globular clusters. The collection, including full V- and I-band time-series data, is available to the astronomical community from the OGLE On-line Data Archive.
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
The current knowledge of the abundance pattern in delta Scuti stars is based on the analysis of just a few field stars. We aim to determine the general chemical properties of the atmospheres of delta Scuti stars based on a statistically relevant sample of stars and will investigate whether the abundance pattern is close to solar, an assumption generally made for pulsation models. We have analysed high-resolution, high signal-to-noise ratio spectra of seven field delta Scuti stars. We derived the fundamental parameters and the photospheric abundances and compared them to a similar sample of cluster delta Scuti stars. With the use of a t-test we demonstrated that there is no difference between the two samples, which allows us to merge them, resulting in a sample of fifteen delta Scuti stars. We did not find any substantial difference between the abundance pattern of our sample of delta Scuti stars and a sample of normal early A- and late F-type stars. One field star in our sample, HD 124953, is most likely a pulsating Am star.
Based on the medium-high resolution (R~ 20,000), modest signal-to-noise ratio (S/N > 70) FLAMES-GIRAFFE spectra, we investigated the copper abundances of 129 red giant branch stars in the Galactic bulge with [Fe/H] from -1.14 to 0.46 dex. The copper abundances are derived from both local thermodynamic equilibrium (LTE) and nonlocal thermodynamic equilibrium (NLTE) with the spectral synthesis method. We find that the NLTE effects for Cu I lines show a clear dependence on metallicity, and they gradually increase with decreasing [Fe/H] for our sample stars. Our results indicate that the NLTE effects of copper are important not only for metal-poor stars but also for supersolar metal-rich ones and the LTE results underestimate the Cu abundances. We note that the [Cu/Fe] trend of the bulge stars is similar to that of the Galactic disk stars spanning the metallicity range of -1.14 < [Fe/H] < 0.0 dex and the [Cu/Fe] ratios increase with increasing metallicity when [Fe/H] is from~-1.2 to~-0.5 dex, favoring a secondary (metallicity-dependent) production of Cu.
A sequence search method was developed to search regular frequency spacing in delta Scuti stars by visual inspection and algorithmic search. We searched for sequences of quasi-equally spaced frequencies, containing at least four members per sequence, in 90 delta Scuti stars observed by CoRoT. We found an unexpectedly large number of independent series of regular frequency spacing in 77 delta Scuti stars (from 1 to 8 sequences) in the non-asymptotic regime. We introduce the sequence search method presenting the sequences and echelle diagram of CoRoT 102675756 and the structure of the algorithmic search. Four sequences (echelle ridges) were found in the 5-21 d^{-1} region, where the pairs of the sequences are shifted (between 0.5-0.59 d^{-1}) by twice the value of the estimated rotational splitting frequency (0.269 d^{-1}). The general conclusions for the whole sample are also presented in this paper. The statistics of the spacings derived by the sequence search method, by FT and that of the shifts are also compared. In many stars, more than one almost equally valid spacing appeared. The model frequencies of FG Vir and their rotationally split components were used to reveal a possible explanation that one spacing is the large separation, while the other is a sum of the large separation and the rotational frequency. In CoRoT 102675756, the two spacings (2.249 and 1.977 d^{-1}) agree better with the sum of a possible 1.710 d^{-1} large separation and two or one times, respectively, the value of the rotational frequency.
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