- ID:
- ivo://CDS.VizieR/J/A+A/588/A128
- Title:
- Variable stars in globular clusters
- Short Name:
- J/A+A/588/A128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To obtain time-series photometry of the very crowded central regions of Galactic globular clusters. To obtain better angular resolution than has been previously achieved with conventional CCDs on ground-based telescopes. To complete, or improve, the census of the variable star population in those stellar systems. Images were taken using the Danish 1.54-m Telescope at the ESO observatory at La Silla in Chile. The telescope was equipped with an electron-multiplying CCD, and the short-exposure-time images obtained (ten images per second) were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). Photometry was performed via difference image analysis. Automatic detection of variable stars in the field was attempted. The light curves of 12541 stars in the cores of ten globular clusters were statistically analysed to automatically extract the variable stars. We obtained light curves for 31 previously known variable stars (3 long-period irregular, 2 semi-regular, 20 RR Lyrae, 1 SX Phoenicis, 3 cataclysmic variables, 1 W Ursae Majoris-type and 1 unclassified) and we discovered 30 new variables (16 long-period irregular, 7 semi-regular, 4 RR Lyrae, 1 SX Phoenicis and 2 unclassified).
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/556/A20
- Title:
- Variable stars in globular NGC7492
- Short Name:
- J/A+A/556/A20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a photometric V,R,I CCD time-series analysis with a baseline of about eight years of the outer-halo globular cluster NGC 7492 with the aim of searching for new variables and using these (and the previously known variables) to determine the physical parameters of interest for the cluster (e.g. metallicity, absolute magnitude of the horizontal branch, distance, etc.). We used difference image analysis to extract precise light curves in the relatively crowded star field, especially towards the densely populated central region. Several different approaches were used for variability detection that recover the known variables and lead to new discoveries. We determined the physical parameters of the only RR0 star using a light-curve Fourier decomposition analysis. We found one new long-period variable and two SX Phe stars in the blue straggler region. We also present one candidate SX Phe star that requires follow-up observations.
- 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/87/361
- Title:
- Variable stars in M92
- Short Name:
- J/ApJ/87/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distance modulus of M92 is determined from the bright stars and the mean magnitude of 12 cluster-type variables. From the former, m-M=14.93; and from the latter, m-M=14.94+/-0.01. Two variables not belonging to the cluster are indicated, as well as two other stars with range in variation of 0.25mag, which are marked as probable variables. From star counts, the ratio of the minor to the major axis is found to be 0.85, with a position angle of the major axis of 28{deg}. Sensitometer tracings give 14' for the diameter of the cluster.
- ID:
- ivo://CDS.VizieR/J/MNRAS/442/2381
- Title:
- Variable stars in M4 primary field
- Short Name:
- J/MNRAS/442/2381
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a photometric search for variable stars in the core of the Galactic globular cluster Messier 4 (M 4). The input data are a large and unprecedented set of deep Hubble Space Telescope WFC3 images (large programme GO-12911; 120 orbits allocated), primarily aimed at probing binaries with massive companions by detecting their astrometric wobbles. Though these data were not optimized to carry out a time-resolved photometric survey, their exquisite precision, spatial resolution and dynamic range enabled us to firmly detect 38 variable stars, of which 20 were previously unpublished. They include 19 cluster-member eclipsing binaries (confirming the large binary fraction of M 4), RR Lyrae and objects with known X-ray counterparts. We improved and revised the parameters of some among published variables.
- 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/AJ/142/107
- Title:
- Variable stars in NGC 1466
- Short Name:
- J/AJ/142/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the first in a series of papers studying the variable stars in Large Magellanic Cloud globular clusters. The primary goal of this series is to better understand how the RR Lyrae stars in Oosterhoff-intermediate systems compare to those in Oosterhoff I/II systems. In this paper, we present the results of our new time-series BV photometric study of NGC 1466. A total of 62 variables were identified in the cluster, of which 16 are new discoveries. The variables include 30 RRab stars, 11 RRc stars, 8 RRd stars, 1 candidate RR Lyrae, 2 long-period variables, 1 potential anomalous Cepheid, and 9 variables of undetermined classification. We present photometric parameters for these variables.
- ID:
- ivo://CDS.VizieR/J/AJ/139/357
- Title:
- Variable stars in NGC 5286
- Short Name:
- J/AJ/139/357
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for variable stars in the globular cluster (GC) NGC 5286, which has recently been suggested to be associated with the Canis Major dwarf spheroidal galaxy. Fifty-seven variable stars were detected, only 19 of which had previously been known. Among our detections one finds 52 RR Lyrae (22 RRc and 30 RRab), 4 long-period variables, and 1 type II Cepheid of the BL Herculis type. Periods are derived for all of the RR Lyrae as well as the Cepheid, and BV light curves are provided for all the variables.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A120
- Title:
- Variable stars in NGC 6715
- Short Name:
- J/A+A/592/A120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We show the benefits of using Electron-Multiplying CCDs and the shift-and-add technique as a tool to minimise the effects of the atmospheric turbulence such as blending between stars in crowded fields and to avoid saturated stars in the fields observed. We intend to complete, or improve, the census of the variable star population in globular cluster NGC 6715. Our aim is to obtain high-precision time-series photometry of the very crowded central region of this stellar system via the collection of better angular resolution images than has been previously achieved with conventional CCDs on ground-based telescopes. Observations were carried out using the Danish 1.54-m Telescope at the ESO La Silla observatory in Chile. The telescope is equipped with an Electron-Multiplying CCD that allowed to obtain short-exposure-time images (ten images per second) that were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). The high precision photometry was performed via difference image analysis employing the DanDIA pipeline. We attempted automatic detection of variable stars in the field. We statistically analysed the light curves of 1405 stars in the crowded central region of NGC 6715 to automatically identify the variable stars present in this cluster. We found light curves for 17 previously known variable stars near the edges of our reference image (16 RR Lyrae and 1 semi-regular) and we discovered 67 new variables (30 RR Lyrae, 21 long-period irregular, 3 semi-regular, 1 W Virginis, 1 eclipsing binary, and 11 unclassified).
- 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.
