BGSU Variable Stars in Globular Clusters

Goals:

To detect and photometer variable stars in Galactic globular clusters, and thereby improve the census of such stars. In most cases, we aim to provide time-series photometry in multiple passbands, determine periods of variation, and provide phased light curves of each variable, along with mean photometric properties and characterization of variability class. Scientific topics of interest include:

• Statistical population studies (e.g., number of stars per unit luminosity of host cluster) to shed light on formation mechanisms.
• Determine mean magnitudes in BVRIK passbands for calibrating absolute magnitude (luminosity) once SIM parallaxes become available.
• Determine mean and minimum-light colors (e.g., B-V, V-I, V-K) to improve interstellar reddening measurements.
• CCD-based light curves of long period (Mira-like) variables at the AGB (and RGB?) tip.

Useful links:

• Christine Clement's Catalogue of Variable Stars in Globular Clusters (extended Sawyer-Hogg catalogue)
• Bill Harris's Catalogue of Parameters of Milky Way Globular Clusters (and web-interface tool)
• DAOPHOT point-spread funcition photometry programs by Peter Stetson: 1987 daophot // 1994 allframe // 2000 standard*s
• ISIS image-subtraction variable star detection by Christophe Alard
• 2MASS all-sky JHKs photometric survey (query all-sky point source catalog)
• RR Lyrae links: David Darling // John Martin // Katrien Kolenberg

Published Papers:

• Baker, J.M., Layden, A.C., Welch, D.L., & Webb, T.M.A., 2007, AJ, 133, 139-146, Variable Stars in Metal-Rich Globular Clusters. III. NGC 6539 [plots, data files, and a FITS image of the cluster with corresponding coordinates; tar.gz, 11.4 Mb].
• Layden, A.C., Bowes, B.T., Welch, D.L., & Webb, T.M.A., 2003, AJ, 126, 255, Variable Stars in Metal-Rich Globular Clusters: II. NGC 6316 [data files and a FITS image of the cluster with corresponding coordinates; tar.gz, 4 Mb].
• Layden, A.C. & Sarajedini, A. 2003, AJ, 125, 208-223, Photometry of the Globular Cluster NGC 3201 and its Variable Stars, [file containing data files, FITS image with corresponding corrdinates, and an individual light curve for each RRL (eps); tar.gz, 2.7 Mb]
• Layden, .C. & Sarajedini, Ata 2000, AJ, 119, 1760, Photometry of the Globular Cluster M54 and the Sagittarius Dwaft Galaxy: the Age-Metallicity Relation
• Layden, A.C., Ritter, L.A., Welch, D.L., & Webb, T.M.A. 1999, AJ, 117, 1313, The Variable Stars and Blue Horizontal Branch of the Metal-Rich Globular Cluster NGC 6441, [gzipped fits image, TABLE 1, TABLE 6].

Talks and Conference Proceedings:

• Katie Guldenschuh, Variable Stars Toward the Globular Cluster NGC 6496, at 2004 Variable Star Meeting (BGSU)
• Gregorsok, J.D., Layden, A.C., Welch, D.L., & Webb, T.M.A., 2004, American Astronomical Society Meeting 203, #52.04, Variable Stars in the Globular Cluster NGC 6637 (M69)
• Guldenschuh, K.A., Layden, A.C., Welch, D.L., & Webb, T.M.A., 2004, American Astronomical Society Meeting 203, #52.05, Variable Stars in the Globular Cluster NGC 6496
• Layden, A.C., Cool, A., von Hippel, T., & Sarajedini, A. RR Lyrae Stars in the Globular NGC 3201: Light Curves, Reddening, and Distance, Leuven, Belgium, July 2001 (postscript, 39 kb)
• Layden, A.C., Bowes, B.T., Ritter, L.A., Welch, D.L., & Webb, T.M.A., A Photometric Survey for Variable Stars in Twelve Metal Rich Globular Clusters, IAU Symposium 176, Budapest, August 1999
• Layden, A.C., Bowes, B.T., Welch, D.L., & Webb, T.M.A., Variable Stars Towards the Metal-Rich Globular Cluster NGC 6316, AAS, January 1999

Andy Layden, updated 2007 Feb 20