- 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.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/790/48
- Title:
- Variable stars in M31 & M33. II. LBVs
- Short Name:
- J/ApJ/790/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An increasing number of non-terminal eruptions are being found in the numerous surveys for optical transients. Very little is known about these giant eruptions, their progenitors and their evolutionary state. A greatly improved census of the likely progenitor class, including the most luminous evolved stars, the luminous blue variables (LBVs), and the warm and cool hypergiants is now needed for a complete picture of the final pre-supernova stages of very massive stars. We have begun a survey of the evolved and unstable luminous star populations in several nearby resolved galaxies. In this second paper on M31 and M33, we review the spectral characteristics, spectral energy distributions, circumstellar ejecta, and evidence for mass loss for 82 luminous and variable stars. We show that many of these stars have warm circumstellar dust including several of the Fe II emission line stars, but conclude that the confirmed LBVs in M31 and M33 do not. The confirmed LBVs have relatively low wind speeds even in their hot, quiescent or visual minimum state compared to the B-type supergiants and Of/WN stars which they spectroscopically resemble. The nature of the Fe II emission line stars and their relation to the LBV state remains uncertain, but some have properties in common with the warm hypergiants and the sgB[e] stars. Several individual stars are discussed in detail. We identify three possible candidate LBVs and three additional post-red supergiant candidates. We suggest that M33-013406.63 (UIT301,B416) is not an LBV/S Dor variable, but is a very luminous late O-type supergiant and one of the most luminous stars or pair of stars in M33.
- 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/MNRAS/487/3505
- Title:
- Variable stars in NGC 2244
- Short Name:
- J/MNRAS/487/3505
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of the UBVIc variability search for variable stars in the young open cluster NGC 2244. In total, we found 245 variable stars. Most of them, are pre-main sequence variables with irregular variations typical for classical T Tauri stars (CTTSs). We found also 23 periodic variables, probably weak-lined T Tauri stars (WTTSs). We detected also four candidates for {delta} Scuti stars and 7 eclipsing binaries. Based on the mid-infrared Spitzer and WISE photometry and near infrared JHKS 2MASS photometry, we classified 104 young stellar sources among our variables: 1 Class I object, 1 Class I/flat spectrum object, 4 flat spectrum objects, 91 Class II objects, and 7 transition disc objects. This classification, together with r'i'H{alpha} IPHAS photometry and JHK UKIDSS photometry, were used for identification of pre-main sequence stars among irregular and periodic variables. In this way, 97 CTTS candidates (96 irregular and one periodic variable), 68 WTTS candidates (54 irregular and 14 periodic variables), and 6 Herbig Ae/Be stars were found. For 223 variable stars we calculated membership probability based on proper motions from Gaia DR2 catalogue. Majority of them, 143 stars, are cluster members with probability greater than 70 per cent. For only 36 variable stars the membership probability is smaller than 20 per cent.
- 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/129/2856
- Title:
- Variable stars in NGC 6791
- Short Name:
- J/AJ/129/2856
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have undertaken a long-term project, Planets in Stellar Clusters Extensive Search (PISCES), to search for transiting planets in open clusters. In this paper we present the results for NGC 6791, a very old, populous, metal-rich cluster. We have monitored the cluster for over 300hr, spread over 84 nights. We have not detected any good transiting planet candidates. Given the photometric precision and temporal coverage of our observations and the current best estimates for the frequency and radii of short-period planets, the expected number of detectable transiting planets in our sample is 1.5. We have discovered 14 new variable stars in the cluster, most of which are eclipsing binaries, and present high-precision light curves spanning 2 years for these new variables and also the previously known variables.
- 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/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.
