The high accuracy and the homogeneity of Hipparcos data for bright stars have allowed us to quantify the degree of variability of Be stars. This degree has been found to be highly dependent on the temperature of the star. Rapid variability is the main feature of the 86% of early Be and less than 20% of late Be stars taking into account the limit of detection considered. In addition to Be stars reported in the Hipparcos catalogue (ESA 1997, Cat. <I/239>) as short-period variables, we have been able to enlarge the number of detections as well as to confirm periods previously determined. Be stars that show larger amplitude rapid variations are proposed as candidates for a search of multiperiodicity i.e. as non-radial pulsators. We have also searched for the presence of outbursts and fading events in the Hipparcos data. Outbursts have been frequently and preferentially detected in early Be stars with rather low to moderate v sini while fading events seem to be more conspicuous in stars with higher v sini. Mid-term and long-term variations have also been investigated. Several stars have shown some evidence of temporary quasi-periodic oscillations ranging between 10 and 200 days. Finally information concerning long-term variations is reported. Cycles shorter than or equal to the Hipparcos mission have mainly been detected in stars earlier than B6. Long-term time scales of late Be stars are confirmed to be longer by far.
Time-series photometry of the CoRoT field SRc02 was obtained by the Berlin Exoplanet Search Telescope II (BEST II) in 2009. The main aim was to conduct a ground-based follow-up of the CoRoT field in order to detect variable stars with better spatial resolution than what can be achieved with the CoRoT Space Telescope. A total of 1846 variable stars were detected, of which only 30 have been previously known. For nine eclipsing binaries the stellar parameters were determined by modeling their light curves.
The Berlin Exoplanet Search Telescope II (BEST II) is a ground-based, small aperture, wide-angle telescope used to search for stellar light variations in the southern hemisphere. We report the results of a monitoring campaign observing a field in the Puppis constellation in late 2011/early 2012. Light curves were obtained for 130472 stars, out of which we identify 2169 variables, including 1829 newly discovered, 26 previously known, and 314 suspected variable stars. We determine periods and variability class for two previously known, but only suspected to be, variable stars. For eight individual eclipsing binary stars, including the two previously known but unclassified binaries, the system parameters were derived at the epoch of the observation by modeling the light curves. Eventually, in a catalog for all variable stars, we present coordinates, magnitude, and elements of light variations, e.g., epoch, period, amplitude, type, and light curves. This catalog concludes the BEST/BEST II project.
The Berlin Exoplanet Search Telescope II (BEST II) is a small wide field-of-view photometric survey telescope system located at the Observatorio Cerro Armazones, Chile. The high duty cycle combined with excellent observing conditions and millimagnitude photometric precision makes this instrument suitable for ground based support observations for the CoRoT space mission. Photometric data of the CoRoT LRa02 target field collected between November 2008 and March 2009 were analysed for stellar variability. The presented results will help in the future analysis of the CoRoT data, particularly in additional science programs related to variable stars. BEST II observes selected CoRoT target fields ahead of the space mission. The photometric data acquired are searched for stellar variability, periodic variable stars are identified with time series analysis of the obtained stellar light curves. We obtained the light curves of 104335 stars in the CoRoT LRa02 field over 41 nights. Variability was detected in light curves of 3726 stars of which 350 showed a regular period. These stars are, with the exception of 5 previously known variable stars, new discoveries.
BEST-II periodic variables in CoRoT LRa02 field. II.
Short Name:
J/AJ/143/140
Date:
21 Oct 2021
Publisher:
CDS
Description:
The CoRoT (Convection, Rotation and planetary Transit) field LRa02 has been observed with the Berlin Exoplanet Search Telescope II (BEST II) during the southern summer 2007/2008. A first analysis of stellar variability led to the publication of 345 newly discovered variable stars. Now, a deeper analysis of this data set was used to optimize the variability search procedure. Several methods and parameters have been tested in order to improve the selection process compared to the widely used J index for variability ranking. This paper describes an empirical approach to treat systematic trends in photometric data based upon the analysis of variance statistics that can significantly decrease the rate of false detections. Finally, the process of reanalysis and method improvement has virtually doubled the number of variable stars compared to the first analysis by Kabath et al. (Paper I, 2009, Cat. J/A+A/506/569). A supplementary catalog of 272 previously unknown periodic variables plus 52 stars with suspected variability is presented. Improved ephemerides are given for 19 known variables in the field. In addition, the BEST II results are compared with CoRoT data and its automatic variability classification.
We report on observations of the COROT IR01 field with the Berlin Exoplanet Search Telescope (BEST). BEST is a small-aperture telescope with a wide field of view (FOV). It is dedicated to searching for variable stars within the target fields of the COROT space mission to aid in minimizing false-alarm rates, and identifying potential targets for additional science. COROT's observational program started in 2007 February, with the "initial run" field (IR01) observed for about 2 months. BEST observed this field for 12 nights spread over 3 months in winter 2006. From the total of 30,426 stars observed in the IR01 field, 3769 were marked as suspected variable stars, and 54 of these showed clear periodicity. From these, 19 periodic stars are within the part of the COROT FOV covered in our data set.
In this paper, we report on observations of the CoRoT LRa1 field with the Berlin Exoplanet Search Telescope (BEST). The current paper is part of a series of papers describing the results of our stellar variability survey. The BEST is a small aperture telescope with a wide field of view (FOV). It is dedicated to searching for stellar variability within the target fields of the CoRoT space mission to aid in minimizing false-alarm rates and identify potential targets for additional science. The LRa1 field is CoRoT's second long run field located in the galactic anticenter direction. We observed the LRa1 stellar field on 23 nights between November and March 2005/2006. From 6099 stars marked as variable, 39 were classified as periodic variable stars and 27 of them are within the CoRoT FOV. We also confirmed the variability for four stars listed in the General Catalogue of Variable Stars (GCVS).
We report on photometric observations of the CoRoT LRc2 field with the new robotic Berlin Exoplanet Search Telescope II (BEST II). The telescope system was installed and commissioned at the Observatorio Cerro Armazones, Chile, in 2007. BEST II is a small aperture telescope with a wide field of view dedicated to the characterization of the stellar variability primarily in CoRoT target fields with high stellar densities. The CoRoT stellar field LRc2 was observed with BEST II up to 20 nights in 2007 July and August. From the acquired data containing about 100,000 stars, 426 new periodic variable stars were identified and 90% of them are located within the CoRoT exoplanetary CCD segments and may be of further interest for CoRoT additional science programs.
The COROT space mission will monitor several target fields for up to 150 days to perform asteroseismology and to search for extrasolar planets by photometric transits. Variable stars in the target fields are important objects for additional scientific studies but can also disturb the search for planetary transits. A variability characterization of the target fields prior to COROT observations is therefore important for two reasons: to find interesting variable stars to monitor further and to make an analysis of the impact of the variable stars on detecting extrasolar planet transits with COROT. The Berlin Exoplanet Search Telescope (BEST) is a small wide-angle telescope dedicated to high-precision photometry. It has observed a 9deg^2^ field of view centered at (RA,DE)=(19:00:00.0+00:01:55.2) (J2000.0) over 98 nights to search for variable stars in the surroundings of the first long-run target field (LRc1) of the COROT space mission. In this data set we identified 92 periodic variable stars, 86 of which are new discoveries and 6 of which are known from the General Catalogue of Variable Stars (GCVS). For five of the GCVS stars, variability could not be confirmed. Forty-three of the 92 detected periodic variable stars are identified as eclipsing binaries. We have evaluated the completeness of our survey for eclipsing binaries by comparing it to the expected fraction of eclipsing binaries based on Hipparcos observations. From this evaluation we show that the BEST data set presented here has a completeness of 20%-30% for periods longer than 1 day and is complete relative to Hipparcos for short-period binaries.
