Photometry of RR Lyrae variables in the globular cluster NGC 6171.
Abstract
Photometry in U, B, and V is reported for twenty-one RR Lyrae variables in and near the metal-rich globular cluster NGC 6171. One of the variables is probably not a cluster member. The variations in light and color are discussed, and correlations between various parameters of these curves are found to be similar to those in the more metal-poor globular clusters M3 and co Cen. The period-amplitude relation of NGC 6171 is shifted slightly toward shorter periods from that of the Oosterhoff group I cluster M3. Detailed comparisons are made with the results of nonlinear pulsation calculations by Christy. These show that the principal physical difference between variables in clusters of different metal abundance is their mean luminosity, which increases with decreasing metal abundance. The theory is successful in reproducing many of the observed characteristics of the variables and has therefore been used to derive the following physical quantities for the variables in NGC 6171: 0.84 < M,, < 1.10 mag, 0.40 < 0.51 , 0.33 < V < 043 with values near those given in italics being thought to be most lausible. Similar values for the mass and helium content V are derived for M3 and o Cen. It is pro able that a spread in mass of 20 percent occurs among the variables in NGC 6171.
- Publication:
-
The Astrophysical Journal Supplement Series
- Pub Date:
- November 1970
- DOI:
- 10.1086/190223
- Bibcode:
- 1970ApJS...22..249D