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1521. Variable stars in NGC 6819 field
ID:
ivo://CDS.VizieR/J/MNRAS/358/795
Title:
Variable stars in NGC 6819 field
Short Name:
J/MNRAS/358/795
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report on the discovery of 141 further variable stars found in the field of the open cluster NGC 6819. The stars were identified from time-series photometric data obtained on the Isaac Newton Telescope, La Palma, during two observing runs covering the 19 nights between 1999 June 22-30 and 1999 July 22-31. The variables found include 53 eclipsing binaries, of which eight stars appear to be RS CVns, in addition to 70 stars showing spot activity, 13 showing long-period variability and five variables of other types.
1522. Variable stars in NGC 7039 field
ID:
ivo://CDS.VizieR/J/PASP/123/671
Title:
Variable stars in NGC 7039 field
Short Name:
J/PASP/123/671
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report variable stars identified in the field of the Galactic open cluster, NGC 7039. In the fall/winter of 2009, imaging photometry has been acquired, mainly in the R band, for eight open clusters using the 81 cm Tenagra telescope in Arizona. We present the results for our first target, NGC 7039. We have found 42 new variable stars and six suspected variable stars.
1523. Variable stars in NGC 2257. I.
ID:
ivo://CDS.VizieR/J/AJ/138/1310
Title:
Variable stars in NGC 2257. I.
Short Name:
J/AJ/138/1310
Date:
21 Oct 2021
Publisher:
CDS
Description:
The variable stars in the Large Magellanic Cloud star cluster NGC 2257 are reinvestigated using photometry (to ~20th mag) of over 400 new B, V CCD images taken with the CTIO 0.9m telescope on 14 nights in 2007 December and 2008 January. New period searches have been made using two independent algorithms (CLEAN, Period04); the resultant periods of most of the stars are consistent with the pulsation periods derived previously, and where there are discrepancies these have been resolved. For the B and V light curves, accurate Fourier coefficients and parameters are given. Six new variable stars have been discovered (V45-50), including a bright candidate long-period variable star showing secondary oscillations (V45) and two anomalously bright RRc stars (V48 and V50), which are shown to be brightened and reddened by nearby red giant stars. Also discovered among the previously known variable stars are three double-mode RR Lyrae stars (V8, V16, and V34) and several Blazhko variables. Archival Hubble Space Telescope images and the photometry by Johnson et al. (Cat. J/ApJ/527/199) have been used to define better the properties of the most crowded variable stars. The total number of cluster variable stars now stands at forty-seven: 23 RRab stars, four of which show Blazhko amplitude variations; 20 RRc stars, one showing clear Blazhko variations and another showing possible Blazhko variations; the three RRd stars, all having the dominant period ~0.36 day and period ratios P1/P0 ~0.7450; and an LPV star located near the tip of the red giant branch. A comparison of the RRd stars with those in other environments shows them to be most similar to those in IC4499.
1524. Variable stars in NGC 5024 (M53)
ID:
ivo://CDS.VizieR/J/MNRAS/416/2265
Title:
Variable stars in NGC 5024 (M53)
Short Name:
J/MNRAS/416/2265
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report CCD V and I time series photometry of the globular cluster NGC 5024 (M53). The technique of difference image analysis has been used which enables photometric precisions better than 10mmag for stars brighter than V~18.5mag even in the crowded central regions of the cluster. The high photometric precision has resulted in the discovery of two new RR1 stars and 13 SX Phe stars. A detailed identification chart is given for all the variable stars in the field of our images of the cluster. Periodicities were calculated for all RR Lyrae and SX Phe stars and a critical comparison is made with previous determinations.
1525. Variable stars in NGC 5024 (M53)
ID:
ivo://CDS.VizieR/J/MNRAS/424/2722
Title:
Variable stars in NGC 5024 (M53)
Short Name:
J/MNRAS/424/2722
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have performed a careful investigation of the 74 candidate variable stars presented by Safonova & Stalin (2011AJ....142..179S) . For this purpose we used our data base of imaging and light curves from Arellano Ferro et al. (J/MNRAS/416/2265 and J/MNRAS/420/1333). We find that two candidates are known variable stars, eight candidates were discovered first by Arellano Ferro et al. (J/MNRAS/416/2265), but would not have been known to Safonova & Stalin (2011AJ....142..179S) at the time of their paper submission, while four candidates are new variables. Three of the new variables are SX Phe type and one is a semiregular (SR) type red giant variable. We also tentatively confirm the presence of true variability in two other candidates, and we are unable to investigate another four candidates because they are not in our data base. However, we find that the remaining 54 candidate variable stars are spurious detections where systematic trends in the light curves have been mistaken for true variability. We believe that the erroneous detections are caused by the adoption of a very low detection threshold used to identify these candidates.
1526. Variable stars in original CTI-I survey
ID:
ivo://CDS.VizieR/J/AJ/133/2883
Title:
Variable stars in original CTI-I survey
Short Name:
J/AJ/133/2883
Date:
21 Oct 2021
Publisher:
CDS
Description:
The existing CCD/Transit Instrument (CTI-I) survey database was searched for variable stars with 12<V<18.5. This magnitude range corresponds to the saturation limit and the practical faint limit of the original survey (1987-1992). The CTI-I imaged a strip of the sky with a narrow spread of declination over all right ascensions. The resulting survey area covers a large range of both Galactic latitude and longitude, and includes approximately 50deg^2^. Numerous challenges created by the automated photometry pipeline and associated solutions to these problems implemented during the variable suspect selection process are described. The final list contains 1807 stars. Details and the photometry of each are provided to facilitate selection for follow-up observations and subsequent analysis. Known variable stars listed in the General Catalog of Variable Stars are identified, and follow-up observations at the US Air Force Academy Observatory of selected brighter suspects (V<15) previously not identified as variable are also described.
1527. Variable stars in Pegasus field
ID:
ivo://CDS.VizieR/J/MNRAS/362/117
Title:
Variable stars in Pegasus field
Short Name:
J/MNRAS/362/117
Date:
21 Oct 2021
Publisher:
CDS
Description:
Recent wide field photometric surveys, which target a specific field for long durations, are ideal for studying both long- and short-period stellar variability. Here, we report on 75 variable stars detected during the observations of a field in Pegasus using the Wide Angle Search for Planets Prototype (WASP0) instrument, 73 of which are new discoveries. The variables detected include 16 {delta} Scuti stars, 34 eclipsing binaries, 3 BY Draconis stars and 4 RR Lyraes. We estimate that the fraction of stars in the field brighter than V~13.5 exhibiting variable behaviour with an amplitude greater than 0.6% rms is ~0.4%. These results are compared with other wide field stellar variability surveys, and implications for detecting transits due to extra-solar planets are discussed.
1528. Variable stars in Sculptor dSph
ID:
ivo://CDS.VizieR/J/MNRAS/462/4349
Title:
Variable stars in Sculptor dSph
Short Name:
J/MNRAS/462/4349
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the identification of 634 variable stars in the Milky Way dwarf spheroidal (dSph) satellite Sculptor based on archival ground-based optical observations spanning ~24yr and covering ~2.5deg^2^. We employed the same methodologies as the 'Homogeneous Photometry' series published by Stetson. In particular, we have identified and characterized one of the largest (536) RR Lyrae samples so far in a Milky Way dSph satellite. We have also detected four Anomalous Cepheids, 23 SX Phoenicis stars, five eclipsing binaries, three field variable stars, three peculiar variable stars located above the horizontal branch - near to the locus of BL Herculis - that we are unable to classify properly. Additionally, we identify 37 long period variables plus 23 probable variable stars, for which the current data do not allow us to determine the period. We report positions and finding charts for all the variable stars, and basic properties (period, amplitude, mean magnitude) and light curves for 574 of them. We discuss the properties of the RR Lyrae stars in the Bailey diagram, which supports the coexistence of subpopulations with different chemical compositions. We estimate the mean mass of Anomalous Cepheids (~1.5M_{sun}_) and SX Phoenicis stars (~1M_{sun}_). We discuss in detail the nature of the former. The connections between the properties of the different families of variable stars are discussed in the context of the star formation history of the Sculptor dSph galaxy.
1529. Variable stars in Southern polar region
ID:
ivo://CDS.VizieR/J/PASP/131/H4201
Title:
Variable stars in Southern polar region
Short Name:
J/PASP/131/H4201
Date:
21 Oct 2021
Publisher:
CDS
Description:
The regions around the celestial poles offer the ability to find and characterize long-term variables from ground-based observatories. We used multi-year Evryscope data to search for high-amplitude (~=5% or greater) variable objects among 160000 bright stars (m_v_<14.5) near the South Celestial Pole. We developed a machine-learning-based spectral classifier to identify eclipse and transit candidates with M-dwarf or K-dwarf host stars, and potential low-mass secondary stars or gas-giant planets. The large amplitude transit signals from low-mass companions of smaller dwarf host stars lessens the photometric precision and systematics removal requirements necessary for detection, and increases the discoveries from long-term observations with modest light-curve precision among the faintest stars in the survey. The Evryscope is a robotic telescope array that observes the Southern sky continuously at 2-minute cadence, searching for stellar variability, transients, transits around exotic stars and other observationally challenging astrophysical variables. The multi-year photometric stability is better than 1% for bright stars in uncrowded regions, with a 3{sigma} limiting magnitude of g=16 in dark time. In this study, covering all stars 9<m_v_<14.5, in declinations -75{deg} to -90{deg}, and searching for high-amplitude variability, we recover 346 known variables and discover 303 new variables, including 168 eclipsing binaries. We characterize the discoveries and provide the amplitudes, periods, and variability type. A 1.7R_J_ planet candidate with a late K-dwarf primary was found and the transit signal was verified with the PROMPT telescope network. Further follow-up revealed this object to be a likely grazing eclipsing binary system with nearly identical primary and secondary K5 stars. Radial-velocity measurements from the Goodman Spectrograph on the 4.1 meter SOAR telescope of the likely lowest-mass targets reveal that six of the eclipsing binary discoveries are low-mass (0.06-0.37M_{sun}_) secondaries with K-dwarf primaries, strong candidates for precision mass-radius measurements.
1530. Variable stars in the field of Andromeda XXV. III.
ID:
ivo://CDS.VizieR/J/ApJ/829/26
Title:
Variable stars in the field of Andromeda XXV. III.
Short Name:
J/ApJ/829/26
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present B and V time series photometry of Andromeda XXV, the third galaxy in our program on the Andromeda's satellites, which we have imaged with the Large Binocular Cameras of the Large Binocular Telescope. The field of Andromeda XXV is found to contain 62 variable stars, for which we present light curves and characteristics of the light variation (period, amplitudes, variability type, mean magnitudes, etc.). The sample includes 57 RR Lyrae variables (46 fundamental-mode-RRab, and 11 first-overtone-RRc, pulsators), 3 anomalous Cepheids, 1 eclipsing binary system, and 1 unclassified variable. The average period of the RRab stars (<Pab>=0.60 {sigma}=0.04d) and the period-amplitude diagram place Andromeda XXV in the class of the Oosterhoff-Intermediate objects. From the average luminosity of the RR Lyrae stars we derive for the galaxy a distance modulus of (m-M)_0_=24.63+/-0.17mag. The color-magnitude diagram reveals the presence in Andromeda XXV of a single, metal-poor ([Fe/H]=-1.8dex) stellar population as old as ~10-12Gyr, traced by a conspicuous red giant branch and the large population of RR Lyrae stars. We discovered a spherically shaped high density of stars near the galaxy center. This structure appears to be at a distance consistent with Andromeda XXV and we suggest it could either be a star cluster or the nucleus of Andromeda XXV. We provide a summary and compare the number and characteristics of the pulsating stars in the M31 satellites analyzed so far for variability.