Browsing by Author "Smith, Horace A."
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- ItemErratum: "Variable Stars in the Unusual, Metal-Rich Globular Cluster NGC 6388" [Astron. J. 124, 949 (2002)](2003) Pritzl, Barton J.; Smith, Horace A.; Catelan, Márcio; Sweigart, Allen V.In Tables 4 and 5, we inadvertently listed Modified Heliocentric Julian Dates instead of ordinary Heliocentric Julian Dates as indicated in the table headings. To make the listed dates match the table headings, 0.5 should be added to the listed dates. Corrected tables with ordinary Heliocentric Julian Dates are given below. We thank Christine Clement, who noticed this error and brought it to our attention....
- ItemNew Variable Stars in CMa Globular Cluster Candidates(2011) Amigo, Pía; Catelan, Márcio; Stetson, Peter B.; Smith, Horace A.; Cacciari, Carla; Zoccali, ManuelaWe present the preliminary results of an image-subtraction analysis of the Galactic globular cluster M79 (NGC 1904), as well as a new investigation of the variable star population in NGC 1851. Both M79 and NGC 1851 have been previously associated with the Canis Major overdensity, which has been suggested to have an extragalactic origin. We found 6 new RR Lyrae in M79, and also recovered 3 previously known RR Lyrae. The average period of the 5 ab-type RR Lyrae is 0.68 d, corresponding to an Oosterhoff II classification -- which is unusual, though not unprecedented, for systems of extragalactic origin. We also report on the discovery of at least 4 previously unknown variables in NGC 1851....
- ItemPhysical parameters for RR Lyrae stars in the sdss filter system(2013) Catelan, Márcio; Torrealba, Gabriel I.; Cáceres, Claudio; Smith, Horace A.; De Lee, Nathan; Fitzgerald, MichaelWe present a calibration of the metallicity and physical parameters (temperature, luminosity, gravity, mass, radius) for RR Lyrae stars using the ugriz sdss photometric system. Our work is based on calculations of synthetic horizontal branches (HBs), fully taking into account evolutionary effects for a wide range in metallicities and HB morphologies. We provide analytical fits that are able to provide all quantities mentioned with very high (internal) precision, based solely on mean sdss magnitudes and colors....
- ItemRR Lyrae in the LMC: Insights Into the Oosterhoff Phenomenon(2013) Kuehn, Charles A; Smith, Horace A.; Catelan, Marcio; Jeon, Young-Beom; Nemec, James M.; Walker, Alistair R.; Kunder, Andrea; Dame, Kyra; Pritzl, Barton J.; De Lee, Nathan; Borissova, JuraAlthough more than eight decades have passed since P. Th. Oosterhoff drew attention to differences in the properties of RR Lyrae variables in globular clusters, the origin and significance of the Oosterhoff groups remain unclear. Nonetheless, the accumulation of extensive new observations of RR Lyrae stars in globular clusters of the Milky Way and Local Group galaxies allows a fresh look at the phenomenon. Insights come not only from surveys of variables within the original Oosterhoff groups I and II but also from recent observations of the Oosterhoff-intermediate systems found especially in smaller Local Group galaxies. We will compare properties of RR Lyrae in several systems to investigate what they reveal about system-to-system differences of transition temperature between fundamental-mode and first overtone pulsators and of horizontal branch luminosity. Both transition temperature and horizontal branch luminosity have at various times been credited as playing roles in the creation of the Oosterhoff dichotomy....
- ItemRR Lyrae Period-Amplitude Diagrams: From Bailey to Today(2011) Smith, Horace A.; Catelan, Marcio; Kuehn, CharlesMore than a century ago, Solon Bailey's pioneering investigations of the variable stars in globular clusters allowed the first period-amplitude diagrams to be constructed for their RR Lyrae stars. These diagrams differ from cluster to cluster, and there has been debate as to whether these differences are correlated mainly with [Fe/H] or with Oosterhoff type. It is clear now that a cluster's Oosterhoff type plays an important role in determining its period-amplitude relation, although the Oosterhoff dichotomy itself is correlated with metallicity. Not all clusters follow the usual patterns, however. The globular clusters NGC 6388 and NGC 6441 have period-amplitude diagrams similar to those of metal-poor Oosterhoff type II globular clusters, but they themselves are comparatively metal-rich. The period-amplitude diagrams of Oosterhoff-intermediate systems are discussed....
- ItemRR Lyrae Variables in Stellar Systems(2009) Smith, Horace A.; Catelan, Marcio; Clementini, GisellaThe pioneering studies of RR Lyrae stars in globular clusters by Oosterhoff and by Sawyer Hogg in the 1930s and 1940s called attention to interesting systematic differences among RR Lyrae populations in different systems. When such studies were extended to the dwarf spheroidal companions of the Milky Way in the 1960s, it was found that the average properties of their RR Lyrae stars were often different from those that had previously been observed in globular clusters. Observations of RR Lyrae stars have now extended to the Andromeda Galaxy and other Local Group systems, with still greater variety being apparent. Our understanding of the reasons for these differences among the RR Lyrae populations in different systems is by no means complete, but properties of RR Lyrae stars within these different systems are tied to differing horizontal branch morphologies and also shed light upon scenarios for the formation of the Galaxy....
- ItemThe Oosterhoff Dichotomy in the Milky Way and Other Local Group Galaxies(2010) Smith, Horace A.; Catelan, Marcio; Clementini, G.; Kuehn, C.; Pritzl, B.; Beers, T.; De Lee, N.; Kinemuchi, K.; Greco, C.; Ripepi, V.; Marconi, M.; Musella, I.; Moretti, M. I.; Dall'Ora, M.; Contreras, R.; Zorotovic, M.In 1939, P. Th. Oosterhoff investigated the properties of RR Lyrae stars in five of the globular clusters of the Milky Way. He discovered that these clusters divided into two groups, now known as Oosterhoff groups I and II, on the basis of the properties of their RR Lyrae stars. Subsequent studies of RR Lyrae variables in additional globular clusters found that most Milky Way globular clusters that contain significant numbers of RR Lyrae stars fall into one or another of the two Oosterhoff groups. Moreover, globular clusters of Oosterhoff group I tend to be more metal-rich than those of Oosterhoff group II. However, the dwarf galaxies surrounding the Milky Way, and their globular clusters, do not exhibit the Oosterhoff dichotomy. Moreover, the bulge globular clusters NGC 6388 and NGC 6441 cannot be easily assigned to one of the traditional Oosterhoff groups. We will discuss the implications of the Oosterhoff dichotomy and the Oosterhoff gap for stellar evolution and for the formation and evolution of the Galactic halo. This work has been supported in part by the National Science Foundation....
- ItemVariable Stars in Metal-Rich Globular Clusters: NGC 6304 and NGC 6569(2002) Pritzl, Barton J.; Smith, Horace A.; Catelan, Marcio; Sweigart, Allen V.It has recently become evident that the RR Lyrae in metal-rich globular clusters ([Fe/H]> -1.0) have properties different from those of metal-rich RR Lyrae found in the field. In particular, they have longer periods than field RR Lyrae of similar metallicities, implying that the cluster RR Lyrae are more luminous than their field counterparts. Because RR Lyrae stars are major Population II standard candles, this finding has consequences for the ages of globular clusters and the galactic and extragalactic distance scales. We propose observations with the YALO telescope to obtain B,V CCD photometry of the RR Lyrae in the metal-rich globular clusters NGC 6304 and NGC 6569. These data will be used to obtain accurate periods and light curves for the RR Lyrae and will be compared to those in other systems to determine their relative luminosities. Direct comparisons will also be made to the other metal-rich globular clusters known to contain RR Lyrae.