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1541. 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.
1542. 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.
1543. Variable stars of Draco dSph
ID:
ivo://CDS.VizieR/J/AJ/136/1921
Title:
Variable stars of Draco dSph
Short Name:
J/AJ/136/1921
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a CCD survey of variable stars in the Draco dwarf spheroidal galaxy. This survey, which has the largest areal coverage since the original variable star survey by Baade & Swope (1961AJ.....66..300B), includes photometry for 270 RR Lyrae (RRL) stars, 9 anomalous Cepheids (ACs), 2 eclipsing binaries, and 12 slow, irregular red variables, as well as 30 background QSOs. Twenty-six probable double-mode RRL stars were identified. Observed parameters, including mean V and I magnitudes, V amplitudes, and periods, have been derived.
1544. Variable stars photometry from Dome A
ID:
ivo://CDS.VizieR/J/AJ/142/155
Title:
Variable stars photometry from Dome A
Short Name:
J/AJ/142/155
Date:
21 Oct 2021
Publisher:
CDS
Description:
Dome A on the Antarctic plateau is likely one of the best observing sites on Earth thanks to the excellent atmospheric conditions present at the site during the long polar winter night. We present high-cadence time-series aperture photometry of 10000 stars with i<14.5mag located in a 23deg^2^ region centered on the south celestial pole. The photometry was obtained with one of the CSTAR telescopes during 128 days of the 2008 Antarctic winter. We used this photometric data set to derive site statistics for Dome A and to search for variable stars. Thanks to the nearly uninterrupted synoptic coverage, we found six times as many variables as previous surveys with similar magnitude limits. We detected 157 variable stars, of which 55% were unclassified, 27% were likely binaries, and 17% were likely pulsating stars. The latter category includes {delta} Scuti, {gamma} Doradus, and RR Lyrae variables. One variable may be a transiting exoplanet.
1545. Variable young stars photometry
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.
1546. Variations of O-B stars in Mercator observations
ID:
ivo://CDS.VizieR/J/A+A/463/243
Title:
Variations of O-B stars in Mercator observations
Short Name:
J/A+A/463/243
Date:
21 Oct 2021
Publisher:
CDS
Description:
We selected a large sample of O-B stars that were considered as (candidate) slowly pulsating B, beta Cep, and Maia stars after the analysis of their Hipparcos data. We analysed both the Hipparcos data and our new seven passband Geneva data collected for these stars during the first three years of scientific operations of the Mercator telescope. We performed a frequency analysis for 28 targets with more than 50 high-quality Mercator observations to improve their variability classification. We searched for frequencies by using two independent frequency analysis methods and we applied a 3.6 S/N-level criterion to locate the significant peaks in the periodograms. In total we detected 60 frequencies, among which 32 new ones. We classified 21 objects as pulsating variables (7 new confirmed pulsating stars, including 2 hybrid beta Cep/SPB stars), 6 as non-pulsating variables (binaries or spotted stars), and 1 as photometrically constant stars. For the 27 confirmed variable stars in our sample, we give the values and the corresponding standard errors of the accepted frequencies, the amplitudes, the phases, the constant terms, and the residual standard deviations as found in the seven filters of the Geneva photometric system and in the Hp filter of the Hipparcos photometric system by fitting the data with a superposition of sinusoidal models with reference epoch HJD=2450000.
1547. V-band differential photometry for V889 Her
ID:
ivo://CDS.VizieR/J/A+A/622/A170
Title:
V-band differential photometry for V889 Her
Short Name:
J/A+A/622/A170
Date:
21 Oct 2021
Publisher:
CDS
Description:
Starspots are important manifestations of stellar magnetic activity. By studying their behaviour in young solar analogues, we can unravel the properties of their magnetic cycles. This gives crucial information of the underlying dynamo process. Comparisons with the solar cycle enable us to infer knowledge about how the solar dynamo has evolved during the Sun's lifetime. Here we study the correlation between photometric brightness variations, spottedness and mean temperature in V889 Her, a young solar analogue. Our data covers 18 years of spectroscopic and 25 years of photometric observations. We use Doppler imaging to derive temperature maps from high-resolution spectra. We use the Continuous Period Search method to retrieve mean V-magnitudes from photometric data. Our Doppler imaging maps show a persistent polar spot structure varying in strength. This structure is centered slightly off the rotational pole. The mean temperature derived from the maps shows an overall decreasing trend, as does the photometric mean brightness, until it reaches its minimum around 2017. The filling factor of cool spots, however, shows only a weak tendency to anti-correlate with the decreasing mean brightness. We interpret V889 Her to have entered into a grand maximum in its activity. The clear relation between the mean temperature of the Doppler imaging surface maps and the mean magnitude supports the reliability of the Doppler images. The lack of correlation between the mean magnitude and the spottedness may indicate that bright features in the Doppler images are real.
1548. V-band light curve & RVs of the Cepheid V473Lyr
ID:
ivo://CDS.VizieR/J/AJ/159/121
Title:
V-band light curve & RVs of the Cepheid V473Lyr
Short Name:
J/AJ/159/121
Date:
21 Oct 2021
Publisher:
CDS
Description:
V473Lyr is a classical Cepheid that is unique in having substantial amplitude variations with a period of approximately 3.3yr, thought to be similar to the Blazhko variations in RR Lyrae stars. We obtained an X-ray Multi-Mirror Mission (XMM)-Newton observation of this star to follow up a previous detection in X-rays. Rather than the X-ray burst and rapid decline near maximum radius seen in {delta}Cephei itself, the X-ray flux in V473Lyr remained constant for a third of the pulsation cycle covered by the observation. Thus the X-rays are probably not produced by the changes around the pulsation cycle. The X-ray spectrum is soft (kT=0.6keV), with X-ray properties consistent with a young low-mass companion. Previously there was no evidence of a companion in radial velocities or in Gaia and Hipparcos proper motions. While this rules out companions that are very close or very distant, a binary companion at a separation between 30 and 300au is possible. This is an example of an X-ray observation revealing evidence of a low-mass companion, which is important in completing the mass ratio statistics of binary Cepheids. Furthermore, the detection of a young X-ray bright companion is a further indication that the Cepheid (primary) is a Population I star, even though its pulsation behavior differs from other classical Cepheids.
1549. V-band light curves of variables in M80
ID:
ivo://CDS.VizieR/J/AcA/63/91
Title:
V-band light curves of variables in M80
Short Name:
J/AcA/63/91
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results of a search for variable stars in the globular cluster M 80. Application of the image subtraction method to the ground-based times-series of CCD frames resulted in finding nine new RR Lyr stars, six of the RRc and three of the RRab type, and four SX Phe variables.
1550. V-band photometric follow-up of RR Lyrae from SEKBO
ID:
ivo://CDS.VizieR/J/ApJ/756/23
Title:
V-band photometric follow-up of RR Lyrae from SEKBO
Short Name:
J/ApJ/756/23
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the steepening of the power-law slope beyond the Galactocentric radius of R~45kpc in the RR Lyrae (RRL) space density distribution found by Keller et al. (2008, Cat. J/ApJ/678/851). They identified 2016 RRL candidates derived from the analysis of archival observations of the Southern Edgeworth-Kuiper Belt Object (SEKBO) survey. Our aim is to verify the completeness of RRLs and ultimately the space density distribution function given by Keller et al. We followed up on a subset of 137 candidates with a range of magnitudes (V~14-20) using the Faulkes Telescope (FT) database and confirmed 57 candidates as real RRLs. A cross-match between SEKBO RRL survey and Sloan Digital Sky Survey Data Release-7 (SDSS DR-7) revealed 272 RRL candidates in common. Applying the color selection criteria proposed by Ivezi\'c et al. (2005AJ....129.1096I) resulted in 193 likely RRLs. The completeness as a function of magnitude was calculated empirically from the combined set of SEKBO RRL candidates from current FT data, SDSS cross-matched data, and the Prior et al. catalog (2009, Cat. J/ApJ/691/306). This resulted in a spatial density distribution characterized by two power laws with a break radius R within a range between 45kpc and 50kpc, similar to the results of Keller et al. We find the power-law slopes for the inner halo as n_inner_=-2.78+/-0.02 and for the outer halo as n_outer_=-5.0+/-0.2.