Variable Stars In Globular Clusters Research Articles

Variable stars in globular clusters: Specifics of the catalog compilation

Variable stars in globular clusters: Specifics of the catalog compilation

AN AO-ASSISTED VARIABILITY STUDY OF FOUR GLOBULAR CLUSTERS*

ABSTRACT The image-subtraction technique applied to study variable stars in globular clusters represented a leap in the number of new detections, with the drawback that many of these new light curves could not be transformed to magnitudes due to severe crowding. In this paper, we present observations of four Galactic globular clusters, M 2 (NGC 7089), M 10 (NGC 6254), M 80 (NGC 6093), and NGC 1261, taken with the ground-layer adaptive optics module at the SOAR Telescope, SAM. We show that the higher image quality provided by SAM allows for the calibration of the light curves of the great majority of the variables near the cores of these clusters as well as the detection of new variables, even in clusters where image-subtraction searches were already conducted. We report the discovery of 15 new variables in M 2 (12 RR Lyrae stars and 3 SX Phe stars), 12 new variables in M 10 (11 SX Phe and 1 long-period variable), and 1 new W UMa-type variable in NGC 1261. No new detections are found in M 80, but previous uncertain detections are confirmed and the corresponding light curves are calibrated into magnitudes. Additionally, based on the number of detected variables and new Hubble Space Telescope/UVIS photometry, we revisit a previous suggestion that M 80 may be the globular cluster with the richest population of blue stragglers in our Galaxy.

A Catalog of Accurate Equatorial Coordinates for Variable Stars in Globular Clusters

ABSTRACTWe have compiled a catalog of equatorial coordinates for 3398 variable stars in those 103 globular clusters that, according to the most recent update of the Catalogue of Variable Stars in Globular Clusters (CVSGC) available in 2008 June (essentially that of 2002, with some more recent additions), had known variable stars. Our catalog is in the electronic attachment to this article. We found that 216 stars are also contained in the General Catalogue of Variable Stars (GCVS) or in the New Catalogue of Suspected Variable Stars (with Supplement); most of these identifications were not previously recognized. We also detected a number of previously unknown cross-identifications among stars of the CVSGC. Our results allow us to initiate compilation of name lists in order to add to the GCVS those stars from the CVSGC that satisfy GCVS naming criteria.

Variable Star Status of Two Stars: V204 and I-I-39 in M3

The star I-I-42 (=vZ1390), a cluster member in M3, located near the red edge of the instability strip of the horizontal branch, was discovered by Roberts and Sandage as a low amplitude variable, it was designated as V204 in the catalogue of variable stars in globular clusters, but its coordinates given in all versions of this catalogue are wrong since 1955. We argue that V204 is indeed a low amplitude HB variable star, located near to the red edge of the instability strip, with a period of 0.74785(d) and an amplitude of about 0.04 mag in V. We also find that the red cluster member star I-I-39 is a low amplitude variable with a period of 1.16(d) and amplitude of about 0.03 mag in V which might be pulsating at the second overtone.

Variable stars in the globular cluster M 92

Results of a search for variable stars in the central region of the Oosterhoff II type globular cluster M 92 are presented. Out of the 28 variable and suspected variable stars listed in the Catalogue of Variable Stars in Globular Clusters (Clement [CITE]) only two were not observed. Surprisingly, almost half of the observed suspected variables did not show any evidence of variability. Only one out of the 11 candidate RR Lyrae variables of Kadla et al. ([CITE]) appeared to be variable. Moreover, variable v7, until now classified as an RR Lyrae star with a period of about 0.515 d, turned out to be of the BL Herculis type, with the period approximately twice that long. In addition, six new variables were found in the very core of the cluster: four of the RR Lyrae and the remaining two of the SX Phoenicis type. RRc variable v11 shows changes in the light curve shape. Due to the aliasing problems, however, we can state only that this star is biperiodic. There is a possibility that v11 belongs to the new group of recently discovered double-period RRc variables pulsating in non-radial mode. Altogether, light curves were obtained for 20 variable stars. The total number of known RR Lyrae stars in M 92 equals now 17, 11 of type RRab and the remaining 6, RRc. The mean period of RRab variables amounts to d, while the average period for RRc variables is equal to d. Mean V magnitudes, mean colours, and ranges of variations were derived for 12 RR Lyrae stars and the BL Herculis variable. Period-shift analysis for M 92 and M 2 resulted in finding that despite significant difference in metal abundance between these two clusters ([Fe/H] = -2.24 for M 92 and -1.62 for M 2), there is no firm evidence for a shift in period.

HELEN SAWYER HOGG (1905-1993)

ABSTRACT With Helen Sawyer Hogg's death in January 1993, the astronomical community lost a most distinguished scientist as well as a visionary role model for female astronomers, and Canada lost a gifted educator of both students and the public. For over 60 years she was a leading authority on variable stars in globular clusters, publishing in excess of 200 papers; an International Astornomical Union Colloquim was held in her honor of her life work in August 1972. Her contributions were recognized by many national and international awards throughout her career, including Fellow of the Royal Society of Canada in 1946 (first woman in Physical Sciences) and Companion of the Order of Canada in 1976. Helen Hogg shared her infectious enthusiasm for astronomy with her many dear friends around the world, including family, colleagues, former and present studnets, and her devoted public (for 30 years this busy bowman wrote a weekly column "With the Stars" in the Toronto Star_).

Problems of variable stars in globular clusters

Problems of variable stars in globular clusters

General Properties of the Two Groups of Globular Clusters and Their Variable Stars

The dependences of the numbers of variable stars in globular clusters on the chemical composition are studied. For given metallicity the numbers of RR Lyrae stars reduced to some definite total number of stars in the cluster are different for the two groups of globular clusters introduced by Mironov.

Some Problems in the Study of Variable Stars in Globular Clusters

Three quarters of a century separates us from the beginning of systematic observations of variable stars in globular clusters. During the last 45 yr the name of Mrs Prof. Dr H. B. Sawyer Hogg has always been in the astronomical literature. Her activity is closely connected with investigations of variable stars in globular clusters.The complex dependences between the presence of variable stars of different types and the properties of the globular clusters were discovered long ago. For instance, the RR Lyr variables do not occur in clusters of high metallicity. Red variables on the contrary do not occur in clusters of very low metallicity. The presence and peculiarities of variable stars have been used for the classification of globular clusters (van Agt and Oosterhoff, 1959; Castellani et al., 1970).

The Helium Abundance in the Envelopes of the Bluest RR Lyrae Stars in Globular Clusters and Dependence of Globular Cluster Variable Star Properties on Chemical Composition

AbstractThe helium abundance Y in the envelopes of RR Lyrae stars in globular clusters has been estimated. The values of Y range from 0.07 to 0.59. The properties of variable stars in globular clusters of two types distinguished by a type of dependence of the horizontal branch form on the chemical composition are compared. The clusters of type I are shown to be on the average poorer in RR Lyrae stars than those of type II. The RR Lyrae stars in type I clusters are on the average brighter by 0.1 mag. It is found that as Y increases, the cluster richness in W Virginis variables decreases.

THE PERIOD-LUMINOSITY RELATION OF THE CEPHEIDS

Around the turn of the century two investigations were started at the Harvard Observatory that had a far-reaching influence on the further development of astronomy: Henrietta S. Leavitt's investigation of the variable stars in the two Magellanic Clouds and Solon I. Bailey's investigation of the variable stars in globular clusters. The Magellanic Clouds turned out to be veritable mines of cepheids with periods longer than one day. In contrast, the overwhelming majority of the variables in globular clusters were cepheids with periods shorter than one day ; they were so characteristic of globular clusters that Bailey proposed for them the name cluster -type variables. Further investigations of these variables led to two very remarkable results. The most striking was Miss Leavitt's discovery that the brightness of the cepheids in the Magellanic Clouds is a function of the period of the lightvariation (the observed brightness increases with the period). Since there was every reason to believe that the objects in each Cloud are at practically the same distance from us, the observed period-brightness relation clearly implied a period-luminosity relation for the cepheids with periods longer than one day. Once established, this period-luminosity relation obviously would provide a simple and very powerful tool for determining the distance of any cepheid of known apparent brightness and period.

Wholesale Commodity Prices in the United States, 1700-1861. Arthur Harrison Cole

Previous articleNext article No AccessBook ReviewsWholesale Commodity Prices in the United States, 1700-1861. Arthur Harrison Cole Chester W. WrightChester W. Wright Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Journal of Political Economy Volume 49, Number 6Dec., 1941 Article DOIhttps://doi.org/10.1086/255800 Views: 1Total views on this site Citations: 1Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:B. V. Kukarkin Some Problems in the Study of Variable Stars in Globular Clusters, International Astronomical Union Colloquium 21 (Apr 2016): 8–20.https://doi.org/10.1017/S0252921100033261