- ID:
- ivo://CDS.VizieR/J/A+A/520/A46
- Title:
- Stroemgren photometry of 12 RR Lyrae stars
- Short Name:
- J/A+A/520/A46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- RR Lyrae stars have been observed to improve the insight into processes at work in their atmospheres. Simultaneous Stroemgren-photometry allows to obtain a rapid sequence of measurements in which photometric indices are unaffected by non-optimum observing conditions. The indices y, b-y, and c1 are used with an established calibration to derive Teff and to determine the gravity, logg_BJ_ from the Balmer jump, throughout the pulsation cycle. By employing the equations for stellar structure, additional parameters can be derived.
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- ID:
- ivo://CDS.VizieR/J/ApJS/209/5
- Title:
- Superflares of Kepler stars. I.
- Short Name:
- J/ApJS/209/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By extending our previous study by Maehara et al. (2012, Cat. J/other/Nat/485.478), we searched for superflares on G-type dwarfs (solar-type stars) using Kepler data for a longer period (500 days) than that (120 days) in our previous study. As a result, we found 1547 superflares on 279 G-type dwarfs, which is much more than the previous 365 superflares on 148 stars. Using these new data, we studied the statistical properties of the occurrence rate of superflares, and confirmed the previous results, i.e., the occurrence rate (dN/dE) of superflares versus flare energy (E) shows a power-law distribution with dN/dE{prop.to}E^-{alpha}^, where {alpha}~2. It is interesting that this distribution is roughly similar to that for solar flares. In the case of the Sun-like stars (with surface temperature 5600-6000K and slowly rotating with a period longer than 10 days), the occurrence rate of superflares with an energy of 10^34^-10^35^erg is once in 800-5000yr. We also studied long-term (500 days) stellar brightness variation of these superflare stars and found that in some G-type dwarfs the occurrence rate of superflares was extremely high, ~57 superflares in 500 days (i.e., once in 10 days). In the case of Sun-like stars, the most active stars show a frequency of one superflare (with 10^34^erg) in 100 days. There is evidence that these superflare stars have extremely large starspots with a size about 10 times larger than that of the largest sunspot. We argue that the physical origin of the extremely high occurrence rate of superflares in these stars may be attributed to the existence of extremely large starspots.
- ID:
- ivo://CDS.VizieR/J/A+A/506/519
- Title:
- Supervised classification of CoRoT variables
- Short Name:
- J/A+A/506/519
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we describe the pipeline for the fast supervised classification of light curves observed by the CoRoT exoplanet CCDs. We present the classification results obtained for the first four measured fields, which represent a one-year in-orbit operation. The basis of the adopted supervised classification methodology has been described in detail in a previous paper, as is its application to the OGLE database. Here, we present the modifications of the algorithms and of the training set, to optimize the performance when applied to the CoRoT data. Classification results are presented for the observed fields IRa01, SRc01, LRc01, and LRa01 of the CoRoT mission. Statistics on the number of variables and the number of objects per class are given and typical light curves of high-probability candidates are shown. We also report on new stellar variability types discovered in the CoRoT data. The full classification results are publicly available.
- ID:
- ivo://CDS.VizieR/J/A+A/475/1159
- Title:
- Supervised classification of variable stars
- Short Name:
- J/A+A/475/1159
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The fast classification of new variable stars is an important step in making them available for further research. Selection of science targets from large databases is much more efficient if they have been classified first. Defining the classes in terms of physical parameters is also important to get an unbiased statistical view on the variability mechanisms and the borders of instability strips. Our goal is twofold: provide an overview of the stellar variability classes that are presently known, in terms of some relevant stellar parameters; use the class descriptions obtained as the basis for an automated `supervised classification' of large databases. Such automated classification will compare and assign new objects to a set of pre-defined variability training classes. For every variability class, a literature search was performed to find as many well-known member stars as possible, or a considerable subset if too many were present. Next, we searched on-line and private databases for their light curves in the visible band and performed period analysis and harmonic fitting. The derived light curve parameters are used to describe the classes and define the training classifiers. We compared the performance of different classifiers in terms of percentage of correct identification, of confusion among classes and of computation time. We describe how well the classes can be separated using the proposed set of parameters and how future improvements can be made, based on new large databases such as the light curves to be assembled by the CoRoT and Kepler space missions. The derived classifiers' performances are so good in terms of success rate and computational speed that we will evaluate them in practice from the application of our methodology to a large subset of variable stars in the OGLE database and from comparison of the results with published OGLE variable star classifications based on human intervention. These results will be published in a subsequent paper.
- ID:
- ivo://CDS.VizieR/J/MNRAS/381/851
- Title:
- SuperWASP-North extrasolar planet candidates
- Short Name:
- J/MNRAS/381/851
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Wide Angle Search for Planets (WASP) photometrically surveys a large number of nearby stars to uncover candidate extrasolar planet systems by virtue of small-amplitude light curve dips on a <=5d time-scale typical of the 'Hot-Jupiters'. Observations with the SuperWASP-North instrument between 2004 April and September produced a rich photometric data set of some 1.3x10^9^ data points from 6.7 million stars. Our custom-built data acquisition and processing system produces ~0.02mag photometric precision at V=13. We present the transit candidates in the 03h-06h RA range. Out of 141895 light curves with sufficient sampling to provide adequate coverage, 2688 show statistically significant transit-like periodicities. Out of these, 44 pass a visual inspection of the light curve, of which 24 are removed through a set of cuts on the statistical significance of artefacts. All but four of the remaining 20 objects are removed when prior information at higher spatial resolution from existing catalogues is taken into account. Of the four candidates remaining, one is considered a good candidate for follow-up observations with three further second-priority targets. We provide detailed information on these candidates, as well as a selection of the false-positives and astrophysical false-alarms that were eliminated, and discuss briefly the impact of sampling on our results.
- ID:
- ivo://CDS.VizieR/J/A+A/535/A3
- Title:
- SuperWASP observations of pulsating Am stars
- Short Name:
- J/A+A/535/A3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have studied over 1600 Am stars at a photometric precision of 1mmag with SuperWASP photometric data. Contrary to previous belief, we find that around 200 Am stars are pulsating delta Sct and gamma Dor stars, with low amplitudes that have been missed in previous, less extensive studies. While the amplitudes are generally low, the presence of pulsation in Am stars places a strong constraint on atmospheric convection, and may require the pulsation to be laminar. While some pulsating Am stars have been previously found to be delta Sct stars, the vast majority of Am stars known to pulsate are presented in this paper. They will form the basis of future statistical studies of pulsation in the presence of atomic diffusion.
- ID:
- ivo://CDS.VizieR/J/A+A/467/785
- Title:
- SuperWASP/ROSAT periodic variable stars
- Short Name:
- J/A+A/467/785
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical lightcurves of 428 periodic variable stars coincident with ROSAT X-ray sources, detected using the first run of the SuperWASP photometric survey. Only 68 of these were previously recognised as periodic variables. A further 30 of these objects are previously known pre-main sequence stars, for which we detect a modulation period for the first time. Amongst the newly identified periodic variables, many appear to be close eclipsing binaries, their X-ray emission is presumably the result of RS CVn type behaviour. Others are probably BY Dra stars, pre-main sequence stars and other rapid rotators displaying enhanced coronal activity. A number of previously catalogued pulsating variables (RR Lyr stars and Cepheids) coincident with X-ray sources are also seen, but we show that these are likely to be misclassifications. We identify four objects which are probable low mass eclipsing binary stars, based on their very red colour and light curve morphology.
- ID:
- ivo://CDS.VizieR/J/A+A/605/A111
- Title:
- Surface rotation of Kepler red giant stars
- Short Name:
- J/A+A/605/A111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Kepler allows the measurement of starspot variability in a large sample of field red giants for the first time. With a new method that combines autocorrelation and wavelet decomposition, we measure 361 rotation periods from the full set of 17,377 oscillating red giants in our sample. This represents 2.08% of the stars, consistent with the fraction of spectroscopically detected rapidly rotating giants in the field. The remaining stars do not show enough variability to allow us to measure a reliable surface rotation period. Because the stars with detected rotation periods have measured oscillations, we can infer their global properties, e.g. mass and radius, and quantitatively evaluate the predictions of standard stellar evolution models as a function of mass. Consistent with results for cluster giants, when we consider only the 4881 intermediate-mass stars, M>2.0M_{sun}_from our full red giant sample, we do not find the enhanced rates of rapid rotation one would expect from angular momentum conservation. We therefore suggest that either enhanced angular momentum loss or radial differential rotation must be occurring in these stars. Finally, when we examine the 575 low-mass (M<1.1M_{sun}_) red clump stars in our sample, which we would have expected to exhibit slow (non-detectable) rotation, 15% of them actually have detectable rotation. This suggests a high rate of interactions and stellar mergers on the red giant branch.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A11
- Title:
- SWASP catalogue of RR Lyrae stars
- Short Name:
- J/A+A/607/A11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We set out to compile a catalogue of RRab pulsating variables in the SuperWASP archive and identify candidate Blazhko effect objects within this catalogue. We analysed their light curves and power spectra for correlations in their common characteristics to further our understanding of the phenomenon. Pulsation periods were found for each SWASP RRab object using phase dispersion minimisation techniques. Low frequency periodic signals detected in the CLEAN power spectra of RRab stars were matched with modulation sidebands and combined with pairs of sidebands to produce a list of candidate Blazhko periods. A novel technique was used in an attempt to identify Blazhko effect stars by comparing scatter at different parts of the folded light curve. Pulsation amplitudes were calculated based on phase folded light curves. The SuperWASP RRab catalogue consists of 4963 objects of which 3397 are previously unknown. We discovered 983 distinct candidates for Blazhko effect objects, 613 of these being previously unknown in the literature as RR Lyrae stars, and 894 are previously unknown to be Blazhko effect stars. Correlations were investigated between the scatter of points on the light curve, the periods and amplitudes of the objects' pulsations, and those of the Blazhko effect.
- ID:
- ivo://CDS.VizieR/J/AJ/150/129
- Title:
- Swift UVOT stars survey. II. RR Lyrae in M3 and M15
- Short Name:
- J/AJ/150/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results of a Near-UltraViolet (NUV) survey of RR Lyrae stars from the Ultraviolet Optical Telescope (UVOT) on board the Swift Gamma-ray Burst Mission. It is well-established that RR Lyrae stars have large amplitudes in the far- and near-ultraviolet. We have used UVOT's unique wide-field NUV imaging capability to perform the first systematic NUV survey of variable stars in the Galactic globular clusters M3 and M15. We identify 280 variable stars, comprised of 275 RR Lyrae, 2 anomalous Cepheids, 1 classical Cepheid, 1 SX Phoenicis star, and 1 possible long-period or irregular variable. Only two of these are new discoveries. We compare our results to previous investigations and find excellent agreement in the periods with significantly larger amplitudes in the NUV. We map out, for the first time, an NUV Bailey diagram from globular clusters, showing the usual loci for fundamental mode RRab and first overtone RRc pulsators. We show the unique sensitivity of NUV photometry to both the temperatures and the surface gravities of RR Lyrae stars. Finally, we show evidence of an NUV period-metallicity-luminosity relationship. Future investigations will further examine the dependence of NUV pulsation parameters on metallicity and Oosterhoff classification.
