- ID:
- ivo://CDS.VizieR/J/A+A/635/A43
- Title:
- Stellar rotation periods from K2 Campaigns 0-18
- Short Name:
- J/A+A/635/A43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Rotation period measurements of stars observed with the Kepler mission have revealed a lack of stars at intermediate rotation periods, accompanied by a decrease of photometric variability. Whether this so-called dearth region is a peculiarity of stars in the Kepler field, or reflects a general manifestation of stellar magnetic activity, is still under debate. The K2 mission has the potential to unravel this mystery by measuring stellar rotation and photometric variability along different fields in the sky. Our goal is to measure stellar rotation periods and photometric variabilities for tens of thousands of K2 stars, located in different fields along the ecliptic plane, to shed light on the relation between stellar rotation and photometric variability. We use Lomb-Scargle periodograms, auto-correlation and wavelet functions to determine consistent rotation periods. Stellar brightness variability is assessed by computing the variability range, R_var_, from the light curve. We further apply Gaussian mixture models to search for bimodality in the rotation period distribution. Combining measurements from all K2 campaigns, we detect rotation periods in 29860 stars. The reliability of these periods was estimated from stars observed more than once. We find that 75-90% of the stars show period deviation smaller than 20% between different campaigns, depending on the peak height threshold in the periodograms. For effective temperatures below 6000K, the variability range shows a local minimum at different periods, consistent with an isochrone age of ~750Myr. Additionally, the rotation period distribution shows evidence for bimodality, although the dearth region in the K2 data is less pronounced compared to the Kepler field. The period at the dip of the bimodal distribution shows good agreement with the period at the local variability minimum. We conclude that the rotation period bimodality is present in different fields of the sky, and is hence a general manifestation of stellar magnetic activity. The reduced variability in the dearth region is interpreted as a cancelation between dark spots and bright faculae. Our results strongly advocate that the role of faculae has been underestimated so far, suggesting a more complex dependence of the brightness variability on the rotation period.
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- ID:
- ivo://CDS.VizieR/J/PASP/114/656
- Title:
- Stellar variability in field stars
- Short Name:
- J/PASP/114/656
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a 5 night wide-field time-series photometric survey that detects variable field stars. We find that the fraction of stars whose light curves show variations depends on color and magnitude, reaching 17% for the brightest stars in this survey (V~4) for which the photometric precision is best. The fraction of stars found to be variable is relatively high at colors bluer than the Sun and relatively low at colors similar to the Sun and increases again for stars redder than the Sun. We present light curves for a sample of the pulsating and eclipsing variables. Most of the stars identified as pulsating variables have low amplitudes ({Delta}V=0.01-0.05), relatively blue colors, and multiple periods. There are 13 stars we identify as either SX Phoenicis or {delta} Scuti stars. These classes represent a significant contribution to the total number of blue variables found in this survey. Another 17 stars are identified as eclipsing variables, which have a wide range in color, magnitude, and amplitude. Two variable giants are observed, and both show night-to-night ~1% variations. We present data for 222 variables in total, most of which are not classified. Implications of surveys for stellar variability and interferometry are briefly discussed. On 2000 March 16-20 UT we observed a time series of images in V and one or two images each in UBRI toward two 59'x59' fields using the NOAO Mosaic Camera at the Kitt Peak 0.9 m telescope.
- 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.
- 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.
