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16711. Variable Stars in the Galactic Center
ID:
ivo://CDS.VizieR/J/MNRAS/470/3427
Title:
Variable Stars in the Galactic Center
Short Name:
J/MNRAS/470/3427
Date:
21 Oct 2021
Publisher:
CDS
Description:
We used four-year baseline HST/WFC3 IR observations of the Galactic Centre in the F153M band (1.53 micron) to identify variable stars in the central ~2.3'x2.3' field. We classified 3845 long-term (periods from months to years) and 76 short-term (periods of a few days or less) variables among a total sample of 33070 stars. For 36 of the latter ones, we also derived their periods (<3 days). Our catalog not only confirms bright long period variables and massive eclipsing binaries identified in previous works, but also contains many newly recognized dim variable stars. For example, we found delta Scuti and RR Lyrae stars towards the Galactic Centre for the first time, as well as one BL Her star (period < 1.3d). We cross-correlated our catalog with previous spectroscopic studies and found that 319 variables have well-defined stellar types, such as Wolf-Rayet, OB main sequence, supergiants and asymptotic giant branch stars. We used colours and magnitudes to infer the probable variable types for those stars without accurately measured periods or spectroscopic information. We conclude that the majority of unclassified variables could potentially be eclipsing/ellipsoidal binaries and Type II Cepheids. Our source catalog will be valuable for future studies aimed at constraining the distance, star formation history and massive binary fraction of the Milky Way nuclear star cluster.
16712. Variable stars in the Galactic center
ID:
ivo://CDS.VizieR/J/ApJ/523/248
Title:
Variable stars in the Galactic center
Short Name:
J/ApJ/523/248
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report results of a time series analysis of high-resolution K-band imaging, photometry, and polarimetry of stars in the Galactic center cluster covering 7 consecutive years. In our statistical sample with m_K_<13, about half of the stars show indication of variability consistent with most of them being long-period variable, asymptotic giant branch stars. Some long-period variables already proposed in the literature are confirmed. They are identified with asymptotic giant branch stars. For the first time we show that the bright He I source IRS 16SW is a short-period variable with a period of ~9.72 days. It is most likely an eclipsing binary with a lower mass limit of >=100M_{sun}_. This confirms previous modeling of characteristics of the near-infrared spectra, which also indicated that IRS 16SW is a massive, young hot star. We also present the results of a polarization survey covering the central parsec of the Galaxy. Stars whose polarization vectors differ from the overall polarization, which is parallel to the Galactic plane, are mostly situated in the "minispiral", a region of high thermal flux density at centimeter radio wavelengths. Some of these sources appear extended in the high-resolution images and have featureless red spectra. We interpret these objects as young stars that may have just recently been formed and are still embedded in a dust shell.
16713. Variable stars in the globular cluster DDO 216-A1
ID:
ivo://CDS.VizieR/J/ApJ/837/54
Title:
Variable stars in the globular cluster DDO 216-A1
Short Name:
J/ApJ/837/54
Date:
21 Oct 2021
Publisher:
CDS
Description:
We confirm that the object DDO 216-A1 is a substantial globular cluster at the center of Local Group galaxy DDO 216 (the Pegasus dwarf irregular), using Hubble Space Telescope ACS imaging. By fitting isochrones, we find the cluster metallicity [M/H]=-1.6+/-0.2, for reddening E(B-V)=0.16+/-0.02; the best-fit age is 12.3+/-0.8Gyr. There are ~30 RR Lyrae variables in the cluster; the magnitude of the fundamental mode pulsators gives a distance modulus of 24.77+/-0.08 --identical to the host galaxy. The ratio of overtone to fundamental mode variables and their mean periods make DDO 216-A1 an Oosterhoff Type I cluster. We find a central surface brightness of 20.85+/-0.17 F814W mag/arcsec^2^, a half-light radius of 3.1" (13.4pc), and an absolute magnitude M814=-7.90+/-0.16 (M/M_{sun}_~10^5^). King models fit to the cluster give the core radius and concentration index, r_c_=2.1"+/-0.9" and c=1.24+/-0.39. The cluster is an "extended" cluster somewhat typical of some dwarf galaxies and the outer halo of the Milky Way. The cluster is projected <~30pc south of the center of DDO 216, unusually central compared to most dwarf galaxy globular clusters. Analytical models of dynamical friction and tidal destruction suggest that it probably formed at a larger distance, up to ~1kpc, and migrated inward. DDO 216 has an unexceptional specific cluster frequency, S_N_=10. DDO 216 is the lowest-luminosity Local Group galaxy to host a 10^5^M_{sun}_ globular cluster and the only transition-type (dSph/dIrr) galaxy in the Local Group with a globular cluster.
16714. Variable stars in the globular cluster M92
ID:
ivo://CDS.VizieR/J/other/PZ/16.213
Title:
Variable stars in the globular cluster M92
Short Name:
J/other/PZ/16.21
Date:
21 Oct 2021
Publisher:
CDS
Description:
10 RR Lyr-type variables in M92 are studied. Data obtained from observations carried out by the author (1961-1965) and those of the past years were used. Periods of brightness variations, diagrams O-C, mean curves, period-amplitude and period-asymmetry relations were determined. Variations of the periods of studied variables were discovered; 3 of them do not possess Blazko effect. A distance of 10.5kpc to M92 was obtained according to the media,n magnitude of the studied stars.
16715. Variable Stars in the Large Magellanic Clouds
ID:
ivo://CDS.VizieR/II/247
Title:
Variable Stars in the Large Magellanic Clouds
Short Name:
II/247
Date:
21 Oct 2021
Publisher:
CDS
Description:
The MACHO Project is a collaboration between scientists at the Mt. Stromlo & Siding Spring Observatories, the Center for Particle Astrophysics at the Santa Barbara, San Diego, & Berkeley campuses of the University of California, and the Lawrence Livermore National Laboratory. The primary aim of the project is a search for dark matter in the halo of the Milky Way in the form of objects like brown dwarfs or planets also named MACHOs, for MAssive Compact Halo Objects. The signature of these MACHOs is the occasional amplification of the light from extragalactic stars by the gravitational lens effect. The amplification can be large, but events are extremely rare: it is necessary to monitor photometrically several million stars for a period of years in order to obtain a useful detection rate. The MACHO project is described by Alcock et al. (1992, in "Robotic Telescopes in the 1990s", A.V. Fillippenko Ed., ASP Conf. Series 34, p.193). A dedicated 1.27-m telescope at Mount Stromlo, Australia is used to obtain observations of the LMC year-round, using a camera imaging a field of view of 0.5 square degrees at prime focus. Photometric observations of the LMC fields are obtained in two bandpasses simultaneously, using a dichroic beamsplitter to direct the blue (440-590nm) and red (590-780nm) light onto 2x2 mosaics of 2048x2048 Loral CCDs; the 15um pixels map to 0.63arcsec on the sky. The photometric reduction methods are detailed in Alcock et al. (1996ApJ...461...84A).
16716. Variable stars in the M16-M17 field
ID:
ivo://CDS.VizieR/II/320
Title:
Variable stars in the M16-M17 field
Short Name:
II/320
Date:
21 Oct 2021
Publisher:
CDS
Description:
The original work was published as a paper book by the Perugia University in 1999. Before that, only the variable stars list (coordinates, classifications, periods, epochs, magnitude ranges) was published (P. Maffei, 1975IBVS..985....1M) The photographic material was discontinuously collected with the two Schmidt telescopes of the Asiago Observatory and with the Schmidt telescope of the Catania Astrophysical Observatory in the years 1961 to 1991. 103a-O without or with filter GG13 and hypersensitized with NH3 or pre-flashed I-N+RG5 were used. Date, JD, exposure time, emulsion/filter combination and the observer for each plate are listed in Table 1 and Table 2. The variable search was carried out with the blink microscope plate comparator of the Asiago Observatory. Details about the history and the reduction of the observational material are given in the "main.htm" file; the digitization was made by Alessandro Nesci.
16717. Variable Stars in the Sculptor dwarf galaxy
ID:
ivo://CDS.VizieR/J/A+AS/112/407
Title:
Variable Stars in the Sculptor dwarf galaxy
Short Name:
J/A+AS/112/407
Date:
21 Oct 2021
Publisher:
CDS
Description:
The central area of the Sculptor dwarf galaxy was surveyed for variable stars as a side-program of the OGLE project. Light curves in the V band were obtained for 226 RR Lyr stars and for 3 anomalous cepheids. The data on RR Lyr variables in four nearby dwarf galaxies are summarized and discussed briefly.
16718. Variable stars in the SMCNOD
ID:
ivo://CDS.VizieR/J/MNRAS/480/669
Title:
Variable stars in the SMCNOD
Short Name:
J/MNRAS/480/669
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of a recently discovered stellar overdensity near the northern edge of the Small Magellanic Cloud (SMCNOD). We exploited variable stars from the fourth release of the Optical Gravitational Lensing Experiment. We used mainly pulsating variable stars and investigated their potential association with the SMCNOD using their spatial distribution and distances. We found four rather spatially concentrated anomalous Cepheids and eight evenly dispersed RR Lyrae stars to be most likely members of this overdensity. The anomalous Cepheids inside the SMCNOD trace possible intermediate-age population with ages ranging between 2 and 4.5Gyr. The age distribution of anomalous Cepheids seems to be in a good agreement with the age distribution of anomalous Cepheids in the SMC. Using empirical relations for RR Lyrae stars, we determined the median metallicity for a possible old population in the SMCNOD to be [Fe/H]_SMCNOD_=-1.71+/-0.21dex, which is in agreement with median metallicity of the old SMC population. The density profile for anomalous Cepheids shows a small anomaly at the position of the SMCNOD, on the other hand, RR Lyrae variables show no such deviation. The probability of finding the observed number of variable stars at the location of the SMCNOD by chance is very low for anomalous Cepheids (0.7 per cent) but high for RR Lyrae stars (13.0 per cent). Based on its variable stars content, we thus confirm the presence of a modest overdensity in intermediate-age stars in the SMCNOD and conclude that it probably has its origin in the SMC rather than to be the remnant of an accreted dwarf galaxy.
16719. Variable stars in 47 Tuc fields 104A-E
ID:
ivo://CDS.VizieR/J/A+AS/128/19
Title:
Variable stars in 47 Tuc fields 104A-E
Short Name:
J/A+AS/128/19
Date:
21 Oct 2021
Publisher:
CDS
Description:
CCD photometry for 42 variables from the field of 47 Tuc = NGC 104 is presented. VI photometry for a large set of stars from the surveyed fields is also given.
16720. Variable stars in VVV globulars. II.
ID:
ivo://CDS.VizieR/J/A+A/651/A47
Title:
Variable stars in VVV globulars. II.
Short Name:
J/A+A/651/A47
Date:
22 Feb 2022
Publisher:
CDS
Description:
The Galactic globular clusters (GGCs) located in the inner regions of the Milky Way suffer from high extinction that makes their observation challenging. High densities of field stars in their surroundings complicate their study even more. The VISTA Variables in the Via Lactea (VVV) survey provides a way to explore these GGCs in the near-infrared where extinction effects are highly diminished. We conduct a search for variable stars in several inner GGCs, taking advantage of the unique multi-epoch, wide-field, near-infrared photometry provided by the VVV survey. We are especially interested in detecting classical pulsators that will help us constrain the physical parameters of these GGCs. In this paper, the second of a series, we focus on NGC 6656 (M 22), NGC 6626 (M 28), NGC 6569, and NGC 6441; these four massive GGCs have known variable sources, but quite different metallicities. We also revisit 2MASS-GC 02 and Terzan 10, the two GGCs studied in the first paper of this series. We present an improved method and a new parameter that efficiently identify variable candidates in the GGCs. We also use the proper motions of those detected variable candidates and their positions in the sky and in the color-magnitude diagrams to assign membership to the GGCs. We identify and parametrize in the near-infrared numerous variable sources in the studied GGCs, cataloging tens of previously undetected variable stars. We recover many known classical pulsators in these clusters, including the vast majority of their fundamental mode RR Lyrae. We use these pulsators to obtain distances and extinctions toward these objects. Recalibrated period-luminosity-metallicity relations for the RR Lyrae bring the distances to these GGCs to a closer agreement with those reported by Gaia, except for NGC 6441, which is an uncommon Oosterhoff III GGC. Recovered proper motions for these GGCs also agree with those reported by Gaia, except for 2MASS-GC 02, the most reddened GGC in our sample, where the VVV near-infrared measurements provide a more accurate determination of its proper motions.

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