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- ID:
- ivo://CDS.VizieR/J/A+AS/122/471
- Title:
- Variables in Omega Cen Fields 5139D-F
- Short Name:
- J/A+AS/122/471
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Tables 1-30 contain V band light curves for 30 variables reported in the paper. Tables 31-33 and 34-36 contain VI photometry presented in Figs. 8 and 9, respectively.
- ID:
- ivo://CDS.VizieR/J/AJ/110/2166
- Title:
- Variables in Sextans dSph galaxy
- Short Name:
- J/AJ/110/2166
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a survey for variable stars in the Sextans dwarf spheroidal (dSph) galaxy based on the analysis of 113 B and 48 V CCD images of four fields covering a total area of 18'x18'. We have identified 44 variables: 36 RR Lyr star, 6 anomalous Cepheids, one long-period red variable, all probable members of Sextans, and one foreground contact binary. We have used the pulsating stars to derive a true distance modulus of 19.67+/-0.15 for Sextans (or D=86+/-6kpc), where the error is primarily due to uncertainties in the luminosity-metallicity relation for RR Lyr stars. Based on our new data we conclude that [Fe/H]_Sex=-1.6+/-0.2, somewhat higher than the value from Suntzeff et al. (1993ApJ...418..208S) obtained from the analysis of fiber spectroscopy of the near-IR Calcium triplet. We present a new deep color-magnitude diagram for Sextans which reveals the presence of anomalous Cepheids in the galaxy. This young population may represent as much as 25% of the total stellar content of Sextans. We find a surprisingly strong correlation between the frequency of anomalous Cepheids in dSph galaxies and galaxian luminosity and speculate on the possible origin of this strange effect. The RR Lyr stars in Sextans do not exhibit the Oosterhoff dichotomy observed in globular clusters and in the Galactic halo field.
- ID:
- ivo://CDS.VizieR/J/AJ/110/1141
- Title:
- Variables in the Sagittarius dSph
- Short Name:
- J/AJ/110/1141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present time-series CCD photometry of a field in the newly discovered dwarf spheroidal galaxy in Sagittarius (hereafter Sgr), and of a nearby control field. These data, which consist of VI images obtained during the 1994 OGLE season, were used to identify and study variable stars in both fields. We discovered ten variable stars in the Sgr field, nine of which have light curves and periods consistent with RR Lyr stars or anomalous Cepheids. The control field contains four short-period contact eclipsing binaries, but no pulsating variables. The variables in the Sgr field include a bright RR Lyr star that is almost certainly located in front of Sgr in the galactic bulge, a short-period contact binary located near or within Sgr, and a short-period pulsating star that may either be a foreground halo RR Lyr star or an anomalous Cepheid within Sgr. The seven remaining variables in the Sgr field are RR Lyr stars with very similar mean apparent magnitudes; we conclude that they are members of Sgr. We estimate the total number of RR Lyr stars in Sgr to be 1930+/-730 if M(V,Sgr)=-13, or 310+/-120 if M(V,Sgr)=-11. The frequency of pulsating variables in Sgr is consistent with earlier conclusions that the galaxy consists of a predominant old (age>~10Gyr) population.
- ID:
- ivo://CDS.VizieR/J/A+A/463/589
- Title:
- Variables stars in NGC 362
- Short Name:
- J/A+A/463/589
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 362 is a bright southern globular cluster in the foreground of the Small Magellanic Cloud (SMC), for which no extensive variability survey has ever been done. Finding regularly pulsating RR Lyrae stars in the cluster can lead to improved metallicity and distance estimates of the system, while other types of variable objects may be used to confirm the results. Time-series CCD photometric observations have been obtained. Light curves have been derived with both profile fitting photometry and image subtraction. We developed a simple method to convert flux phase curves to magnitudes, which allows the use of empirical light curve shape vs. physical parameters calibrations. Periods and light curve parameters of the detected variable stars have been determined with Fourier analysis, phase dispersion minimization and string-length minimization. Using the RR Lyrae metallicity and luminosity calibrations, we have determined the relative iron abundances and absolute magnitudes of the stars. The color-magnitude diagram has been fitted with Yale-Yonsei isochrones to determine reddening and distance independently. For five RR Lyrae stars we obtained radial velocity measurements from optical spectra. We found 45 RR Lyr stars, of which the majority are new discoveries. While most of them are cluster members, as shown by their radial velocities and positions in the color-magnitude diagram, we also see a few stars in the galactic field and in the outskirts of the SMC. About half of the RR Lyraes exhibit light curve changes (Blazhko effect). The RR Lyrae-based metallicity of the cluster is [Fe/H]=-1.16+/-0.25, the mean absolute magnitude of the RR Lyrae stars is M_V=0.82+/-0.04mag implying a distance of 7.9+/-0.6kpc. The mean period of RRab stars is 0.585+/-0.081days. These properties place NGC 362 among the Oosterhoff type I globular clusters. The isochrone fit implies a slightly larger distance of 9.2+/-0.5kpc and an age of 11+/-1Gyr. We also found 11 eclipsing binaries, 14 pulsating stars of other types, including classical Cepheids in the SMC and 15 variable stars with no firm classification. NGC 362 hosts a large number of RR Lyrae stars, which makes the cluster a potentially important test object for studying the Blazhko effect in a chemically homogeneous environment.
- ID:
- ivo://CDS.VizieR/J/A+A/367/759
- Title:
- Variable stars in IC 1613
- Short Name:
- J/A+A/367/759
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nearby galaxies IC 1613 and NGC 6822 were observed over four years to detect short period Cepheids and to obtain good light curves for Fourier decomposition. The program was carried out with a relatively small telescope, the Dutch 0.9m at ESO-La Silla, and the observations were performed without filter (white light), or Wh-band. In this paper we present the results of the observations of Fields C and D in IC 1613 (3.8'x3.8' each). The analysis of the light curves of 3297 stars in the two fields has allowed the detection of 92 variable stars. A total of 34 Population I Cepheids have been found, while only 7 of these objects were previously known in these fields. Most of the stars have short periods and some of them are first overtone mode pulsators. Among the other variable stars there are one eclipsing binary and five W Vir candidates. A nova event was observed in Field D.
- ID:
- ivo://CDS.VizieR/J/MNRAS/406/329
- Title:
- Variable stars in M54
- Short Name:
- J/MNRAS/406/329
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new B, V and I CCD time-series photometry for 177 variable stars in a 13x13arcmin^2^ field centred on the globular cluster M54 using the European Southern Observatory (ESO)-Danish 1.54-m telescope in La Silla, 94 of which are newly identified variables. The total sample is composed of two anomalous Cepheids, 144 RR Lyrae stars (108 RR0 and 36 RR1), three SX Phoenicis, seven eclipsing binaries (five W UMa and two Algol binaries), three variables of uncertain classification and 18 long-period variables. Ephemerides are provided for all the observed short-period variables. The positional accuracy is better than 0.2".
- ID:
- ivo://CDS.VizieR/J/ApJ/449/164
- Title:
- Variable Stars in MC Clusters. II
- Short Name:
- J/ApJ/449/164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a study aimed at identifying variable stars in the rich LMC cluster NGC 1850. V and I band CCD imaging spanning more than 5 years in a 10'x10' field surrounding the cluster has allowed us to identify more than 30 variable stars, including seven classical Cepheids, one anomalous Cepheid, two RR Lyrae variables, 19 long-period variables (LPVs), one blue eclipsing binary, one possible pair of eclipsing giants, and several peculiar variables. The only likely cluster member is a Cepheid. Isochrone fitting to the cluster CMD yields an age of 80 Myr if an LMC distance modulus of 18.5 is adopted. A comparison of pulsation and evolution masses for the Cepheids still yields a ratio of evolution to pulsation mass of ~1.2 for evolution models computed with core overshoot parameter Lambda = 0.5, where Lambda = 2d_ov/H_p, d_ov is the distance that convection overshoots beyond the Schwarzschild boundary and H_p is the pressure scale height. An overshoot parameter Lambda ~ 1.0 would be required to bring the evolution and pulsation masses into agreement. One of the Cepheids in the field is a bump Cepheid. A calculation of the bump mass yields a value in reasonable agreement with the pulsation mass. We show that detailed modelling of individual bump Cepheids is capable of providing very tight constraints on the LMC distance modulus. The Cepheid period-luminosity-color relation compared to the theoretical relation yields a LMC distance modulus of 18.60. Finally, arguments are presented which suggest that the LPVs are a mixture of fundamental mode pulsators and small-amplitude overtone pulsators.
- ID:
- ivo://CDS.VizieR/J/other/RMxAA/54.15
- Title:
- Variable stars in NGC 6934
- Short Name:
- J/other/RMxAA/54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report an analysis of new V and I CCD time-series photometry of the globular cluster NGC 6934. Through the Fourier decomposition of the RR Lyrae light curves, the mean values of [Fe/H] and the distance of the cluster were estimated, we found; [Fe/H]_UVES_=-1.48+/-0.14 and d=16.03+/-0.42kpc, and [Fe/H]_UVES_=-1.43+/-0.11 and d=15.91+/-0.39kpc, from the calibrations of RRab and RRc stars respectively. Independent distance estimations from SX Phe and SR stars are also discussed. Individual absolute magnitudes, radii and masses are also reported for RR Lyrae stars. We found 12 new variables: 4 RRab, 3 SX Phe, 2 W Virginis (CW) and 3 semi-regular (SR). The inter-mode or "either-or" region in the instability strip is shared by the RRab and RRc stars. This characteristic, observed only in some OoI clusters and never seen in an OoII, is discussed in terms of mass distribution in the ZAHB.
- 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.
