- 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.
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Search Results
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/MNRAS/478/5091
- Title:
- Variable young stars photometry
- Short Name:
- J/MNRAS/478/5091
- Date:
- 10 Dec 2021 13:53:12
- Publisher:
- CDS
- Description:
- Variability in young stellar objects (YSOs) is one of their primary characteristics. Long-term, multifilter, high-cadence monitoring of large YSO samples is the key to understand the partly unusual light curves that many of these objects show. Here we introduce and present the first results of the HOYS-CAPS citizen science project that aims to perform such monitoring for nearby (d<1kpc) and young (age<10Myr) clusters and star-forming regions, visible from the northern hemisphere, with small telescopes. We have identified and characterized 466 variable (413 confirmed young) stars in eight young, nearby clusters. All sources vary by at least 0.2mag in V, have been observed at least 15 times in V, R, and I in the same night over a period of about 2 yr, and have a Stetson index of larger than 1. This is one of the largest samples of variable YSOs observed over such a time span and cadence in multiple filters. About two-thirds of our sample are classical T-Tauri stars, while the rest are objects with depleted or transition discs. Objects characterized as bursters show by far the highest variability. Dippers and objects whose variability is dominated by occultations from normal interstellar dust or dust with larger grains (or opaque material) have smaller amplitudes. We have established a hierarchical clustering algorithm based on the light-curve properties that allows the identification of the YSOs with the most unusual behaviour and to group sources with similar properties. We discuss in detail the light curves of the unusual objects V2492 Cyg, V350 Cep, and 2MASS J21383981+5708470.
- ID:
- ivo://CDS.VizieR/J/ApJ/707/89
- Title:
- Variation of mid-IR extinction
- Short Name:
- J/ApJ/707/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on the data obtained from the Spitzer/Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIPMSE) Legacy Program and the Two Micron All Sky Survey (2MASS) project, we derive the extinction in the four IRAC bands, [3.6], [4.5], [5.8], and [8.0]um, relative to the 2MASS Ks band (at 2.16um) for 131 GLIPMSE fields along the Galactic plane within |l|<=65{deg}, using red giants and red clump giants as tracers. As a whole, the mean extinction in the IRAC bands (normalized to the 2MASS Ks band), A_[3.6]_/A_Ks_~0.63+/-0.01, A_[4.5]_/A_Ks_~0.57+/-0.03, A_[5.8]/A_Ks_~0.49+/-0.03, A_[8.0]_/A_Ks_~0.55+/-0.03, exhibits little variation with wavelength (i.e., the extinction is somewhat flat or gray). As far as individual sightline is concerned, however, the wavelength dependence of the mid-infrared interstellar extinction A_{lambda}_/A_Ks_ varies from one sightline to another, suggesting that there may not exist a "universal" IR extinction law.
- ID:
- ivo://CDS.VizieR/J/ApJ/846/115
- Title:
- V-band photometry and RVs of V482 Persei system
- Short Name:
- J/ApJ/846/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report spectroscopic and differential photometric observations of the A-type system V482 Per, which reveal it to be a rare hierarchical quadruple system containing two eclipsing binaries. One binary has the previously known orbital period of 2.4 days and a circular orbit, and the other a period of 6 days, a slightly eccentric orbit (e=0.11), and shallow eclipses only 2.3% deep. The two binaries revolve around their common center of mass in a highly elongated orbit (e=0.85) with a period of 16.67yr. Radial velocities are measured for all components from our quadruple-lined spectra and are combined with the light curves and measurements of times of minimum light for the 2.4 day binary to solve for the elements of the inner and outer orbits simultaneously. The line-of-sight inclination angles of the three orbits are similar, suggesting they may be close to coplanar. The available observations appear to indicate that the 6 day binary experiences significant retrograde apsidal motion in the amount of about 60 deg per century. We derive absolute masses for the four stars good to better than 1.5%, along with radii with formal errors of 1.1% and 3.5% for the 2.4 day binary and ~9% for the 6 day binary. A comparison of these and other physical properties with current stellar evolution models gives excellent agreement for a metallicity of [Fe/H]=-0.15 and an age of 360Myr.
- ID:
- ivo://CDS.VizieR/J/A+A/445/617
- Title:
- V823 Cas BV(RI)c differential photometry
- Short Name:
- J/A+A/445/617
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using extended multicolour CCD photometry of the triple-mode radial pulsator V823 Cas we studied the properties of the coupling frequencies invoked by nonlinear processes. Our results support that a resonance connection affects the mode coupling behaviour. The P1/P0 period ratio of V823 Cas has an "out of range" value if compared with the period ratios of the known double mode pulsators, while the P2/P1 period ratio is normal. The periods and period ratios cannot be consistently interpreted without conflict with pulsation and/or evolution models. We describe this failure with the suggestion that at present, the periods of V823 Cas are in a transient, resonance affected state, thus do not reflect the true parameters of the object. The anomalous period change behaviour of the fundamental and second overtone modes supports this idea. We have also raised the possibility that a f0+f2=2f1 resonance may act in triple mode pulsators.
- ID:
- ivo://CDS.VizieR/J/AJ/120/1548
- Title:
- V523 Cas UBVR_C_I_C_ photometry
- Short Name:
- J/AJ/120/1548
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The cool, overcontact, close binary, V523 Cassiopeiae was observed with the 1 m reflector at the US Naval Observatory, Flagstaff Station. The photometry was very good, with a precision on the order of a few millimagnitudes, but not numerous enough for complete light-curve analyses (e.g., differential corrections). A conventional published synthesis has been found acceptable as a fiducial model, and most of the observational weight has been used to develop a spot model for the stars and to support the validity of theoretical limb-darkening coefficients. Both photospheres and chromospheres contribute to the model. This result indicates that multifilter measures of this and similarly cool binaries are necessary for fuller descriptions of stellar activity cycles. A number of newly determined times of minimum light solidify the published rate of period variability.
- ID:
- ivo://CDS.VizieR/J/other/RAA/17.20
- Title:
- V977 Cep and V982 Cep long-term photometry
- Short Name:
- J/other/RAA/17.2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Long-term BVRI photometric light curves of the pre-main sequence stars V977 Cep and V982 Cep during the period from 2000 October to 2016 August are presented. The stars are located in the vicinity of the reflection nebula NGC 7129. Our photometric data show that both stars exhibit strong photometric variability in all optical passbands, which is typical for Classical T Tauri stars. Using our observational data we analyze the reasons for the observed brightness variations. In the case of V977 Cep we identify previously unknown periodicity in its light curve.
- ID:
- ivo://CDS.VizieR/J/other/RAA/14.1264
- Title:
- V350 Cep UBVRI long-term photometry
- Short Name:
- J/other/RAA/14.1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Results from UBVRI optical photometric observations of the pre-main sequence star V350 Cep during the period 2004-2014 are presented. The star was discovered in 1977 due to its remarkable increase in brightness by more than 5mag (R). In previous studies, V350 Cep is considered to be a potential FUor or EXor eruptive variable. Our data suggest that during the period of observations the star keeps its maximum brightness with low amplitude photometric variations. Our conclusion is that V350 Cep is probably an intermediate object between FUors and EXors, similar to V1647 Ori.
