The Oosterhoff period groups and the age of globular clusters. II. Properties of RR Lyrae stars in six clusters: the P-L-A relation.
Abstract
Data for RR Lyrae stars in six clusters are used to test the conclusion of Paper I that, at every temperature, period shifts exist between variables in one cluster relative to those in another of a different Oosterhoff group. Variables in M3, M4, M15, NGC 6171, NGC 6891, and ωCen have the same shifts in the period-temperature as in the period-amplitude relations; no shifts occur in the temperature- amplitude relation.
The period residuals, Δ log P, determined for individual stars in M3 and in ω Cen, correlate with their observed apparent magnitudes; hence, the observed spread in LRR is real. Brighter variables than others in the same cluster have longer periods at fixed Te or A. The data are consistent with ΔMbol = 3Δ log P expected from P <ρ>1/2 = constant at fixed mass. Combining the period deviations at fixed amplitude with the observed magnitude variations leads to a period-luminosity- amplitude relation for equal metallicity ab RR Lyrae variables of the form Mbol = Mbol(M315.52) -3(log P+0.l29AB +0.088), where Mbol(M3l5.52) is the absolute magnitude of RR Lyrae stars in M3 that have Mbol = 15.52. The coefficient of the period-amplitude term will be -4.2 rather than -3 if mass is a function of metallicity as predicted by the models.- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 1981
- DOI:
- 10.1086/159140
- Bibcode:
- 1981ApJ...248..161S
- Keywords:
-
- Blue Stars;
- Giant Stars;
- Globular Clusters;
- Light Curve;
- Stellar Evolution;
- Stellar Oscillations;
- Variable Stars;
- Abundance;
- Line Spectra;
- Lyra Constellation;
- Stellar Magnitude;
- Stellar Mass;
- Stellar Models;
- Stellar Temperature;
- Astrophysics