The RR Lyrae variables and Horizontal Branch of NGC6656 (M22)
Abstract
The first calibrated broadband UBVI time-series photometry is presented for the RR Lyrae variable stars in NGC6656 (M22), with observations spanning a range of twenty-two years. We have also redetermined the variability types and periods for the RR Lyrae stars identified previously by photographic observations, revising the number of fundamental-mode RR Lyrae variables (RR0) to 10 and the number of first-overtone variables (RR1) to 16. The mean periods of the RR0 and RR1 variables are <P>_{RR0}=0.66 \pm 0.02 d and <P>_{RR1}=0.33 \pm 0.01 d, respectively, supporting an Oosterhoff II classification for the cluster. The number ratio of RR1- to all RR-type variables is N_1/N_{RR}=0.61, also consistent with an Oosterhoff II designation. Both the RR Lyrae stars' minimum light colors and the blue edge of the RR Lyrae instability strip suggest E(B-V)=0.36 \pm 0.02 mag toward M22. Regarding the HB morphology of M22, we find (B-R)/(B+V+R)=+0.97 \pm 0.1 and at least one "gap" located in an unusual part of the blue HB, in the middle of the so-called hot HB stars.
Keywords
Cite
@article{arxiv.1308.6573,
title = {The RR Lyrae variables and Horizontal Branch of NGC6656 (M22)},
author = {Andrea Kunder and Peter B. Stetson and Santi Cassisi and Andrew Layden and Giuseppe Bono and Marcio Catelan and Alistair R. Walker and Leonardo Paredes Alvarez and James L. Clem and Noriyuki Matsunaga and Maurizio Salaris and Jae-Woo Lee and Brian C. Chaboyer},
journal= {arXiv preprint arXiv:1308.6573},
year = {2015}
}
Comments
accepted to AJ