- ID:
- ivo://CDS.VizieR/J/ApJ/659/1241
- Title:
- Stellar variability in Galactic Center
- Short Name:
- J/ApJ/659/1241
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a diffraction-limited, photometric variability study of the central 5"x5" of the Galaxy conducted over the past 10-years using speckle imaging techniques on the W.M. Keck I 10 m telescope. Within our limiting magnitude of m_K_<16mag for images made from a single night of data, we find a minimum of 15K[2.2um]-band variable stars out of 131 monitored stars. The only periodic source in our sample is the previously identified variable IRS 16SW, for which we measure an orbital period of 19.448+/-0.002-days.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/139/321
- Title:
- Stellar variability towards Galactic Bulge
- Short Name:
- J/A+AS/139/321
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Table "stars.dat" contains the catalogue of variable stars discovered and/or observed for the 12 low-extinction fields towards the galactic bulge, with the IAG/USP Meridian Circle. The first column of the catalog indicates the star label, formed by a name that identifies the window (see Table 1) and a sequential number that indicates the position of the object in the corresponding database. The following columns display successively the mean right ascension, the mean declination, their standard deviations (in seconds and in arcseconds, respectively) (J2000); the mean magnitude observed (m_{Val}), the difference between the maximum and the minimum magnitude value observed, the number of observations, a estimative for the period, if possible, or a indication "NF" when the stars show periodic characteristics but we aren't able to found a period, or "NC" when the star can be aperiodic or have few observations. The next column have the tentative classification and the last are the remarks about the previous known variables. Finding charts will be available upon request from the authors.
- ID:
- ivo://CDS.VizieR/J/A+A/370/496
- Title:
- Stroemgren by photometry of AI Aurigae
- Short Name:
- J/A+A/370/496
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present eleven years of Stroemgren by-photometry of the red semiregular variable star AI Aurigae. Data were obtained with the 0.53m telescope of the Lowell Observatory between 1985 and 1996.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/407/1059
- Title:
- Stroemgren photometry of V2109 Cyg
- Short Name:
- J/A+A/407/1059
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of simultaneous uvby{beta} photometry carried out from 1999 to 2001 of the variable V2109 Cyg together with a spectroscopic analysis based on one high resolution spectrum obtained in 2000. From this study, the star is definitively classified as an evolved {delta} Sct-type variable with solar metal abundances. This conclusion is also supported by the detected multiperiodic pulsational behaviour and the observed variation of the m1 index over the pulsation cycle.
- ID:
- ivo://CDS.VizieR/J/A+A/291/121
- Title:
- Study of star V9 in 47 Tuc
- Short Name:
- J/A+A/291/121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an infrared K-band light curve and a radial velocity curve for the RR Lyrae star V9 in the metal rich globular cluster 47 Tucanae ([Fe/H]=-0.71). Combining these new data with the optical photometry presented in Carney et al. (1993PASP..105..294C), we perform a Baade-Wesselink analysis and derive a distance modulus of 47 Tuc of 13.23mag+/-0.17 and absolute mean magnitudes of <M_V_>=0.32mag and <M_K_>=-0.57mag for V9. We also present a well populated visual-infrared color-magnitude diagram of the cluster, reaching from the upper red giant branch to the subgiant branch.
- 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.
