The RR Lyrae Variable Stars in the Globular Cluster M15

Abstract

view Abstract Citations (71) References (63) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The RR Lyrae Variable Stars in the Globular Cluster M15 Silbermann, N. A. ; Smith, Horace A. Abstract New CCD photometry is presented for RR Lyrae variable stars in the globular cluster M15. This photometry, mainly in V and R, with some additional B and I, is used to construct lightcurves of 44 RR Lyraes and one Cepheid in M15. One new low-amplitude RR Lyrae star was discovered. The observable parameters of the light curves are used, in conjunction with theoretical photometric indices, to obtain effective temperatures and bolometric magnitudes for the RR Lyrae stars. We confirm that the regions occupied by RRab and RRcd variables in M15 have little or no overlap in effective temperature. Photometry for variable and nonvariable horizontal branch stars in Ml5 is used to establish the high and low temperature boundaries of the instability strip. There is evidence that the blue edge of the M15 RR Lyrae instability strip becomes cooler at higher luminosities. Employing Cox's value of the mass of RRd stars, 0.75 Msun, and the pulsation equation, the absolute magnitude of the RR Lyrae stars in M15 is estimated to be <MV>= +0.36±0.12 mag. However, this result depends upon the adopted mass, bolometric correction, and color-temperature relation, which remain significantly uncertain. The implications of the absolute magnitude determination for the ages of the globular clusters are discussed. Publication: The Astronomical Journal Pub Date: August 1995 DOI: 10.1086/117555 Bibcode: 1995AJ....110..704S Keywords: STARS: VARIABLES: RR LYRAE; GLOBULAR CLUSTERS: INDIVIDUAL: M15 full text sources ADS | data products SIMBAD (82) CDS (1) Related Materials (1) Erratum: 1996AJ....111..567S