---
author:
- Grzegorz Kopacki and Andrzej Pigulski
title: Variable stars in the globular cluster M79
---

Introduction, Observations and Results
======================================

In the last two decades we observed a rapid increase in the number of variable stars detected in Galactic globular clusters. The main reason for this was the invention of the image subtraction method (ISM, [@ala98]) and its application to CCD data obtained with small telescopes (e.g. [@kop09]). The ISM enables making a complete inventory of bright variable stars, such as RR Lyrae variables, because it works well in crowded stellar fields like the cluster core. However, there are still many globular clusters poorly searched for variable stars, especially pulsating stars of the RR Lyrae and SX Phoenicis types.

Here we present results of a variability analysis for the southern globular cluster M79 (NGC1904) of intermediate metallicity (\[Fe/H\]${}=-1.57$). The Catalogue of Variable Stars in Globular Clusters (CVSGC, [@cle01]) listed 13 objects in the field of this cluster including nine RR Lyrae stars, one semiregular variable and three stars suspected for variability.

We used two sets of observations. The first one consisted of 690 $V$-filter and 230 $I_{\rm C}$-filter CCD frames obtained during one-month observing run in Feb/Apr, 2008 using 40-inch telescope at SSO, Australia. The other one included 80 $V$-filter CCD frames acquired during one week of observation in Apr, 2008 using 40-inch telescope at SAAO, South Africa.

We have detected two new RR Lyrae stars, both of the RRc type. The mean period of RRab stars in M79 is equal to $\langle P\rangle_{\rm ab}=0.69$ d, and relative percentage of RRc stars amounts to $N_{\rm c}/(N_{\rm ab}+N_{\rm c})=44$ %. With these values we conclude that M79 belongs to the Oosterhoff’s II group of globular clusters.

We show that v7 is a W Virginis-type star. Moreover, three SX Phoenicis stars were found among cluster’s blue stragglers. One of them, n18, and RRc star v9 are multiperiodic pulsators. The period ratio for n18 indicates that this SX Phoenicis star is a double-mode radial pulsator. Positions and periods of all observed periodic stars are given in Table \[tab:1\]. Irregular light variations were also found in a dozen of red giants located at the tip of the cluster’s red giant branch.

[p[0.8cm]{}p[2cm]{}p[2cm]{}p[2cm]{}p[0.8cm]{}]{} Var& $\alpha_{2000}$ \[$^{\rm h}$ $^{\rm m}$ $^{\rm s}$\]& $\delta_{2000}$ \[$^\circ$ $^\prime$ $^{\prime\prime}$\]& P \[d\]& Type\
v3& 5 24 13.54& $-$24 32 29.1& 0.73602& RRab\
v4& 5 24 17.77& $-$24 32 16.2& 0.63339& RRab\
v5& 5 24 10.23& $-$24 31 03.6& 0.66894& RRab\
v6& 5 24 06.03& $-$24 29 32.9& 0.339065& RRc\
v7& 5 24 12.68& $-$24 31 41.9& 13.946& WVir\
v9& 5 24 12.58& $-$24 31 52.6& 0.37905& RRc\
& & & 0.36099&\
& & & 0.37049&\
v10& 5 24 12.13& $-$24 31 34.5& 0.72894& RRab\
v11& 5 24 11.93& $-$24 31 34.6& 0.8232& RRab\
v12& 5 24 11.35& $-$24 31 28.3& 0.32394& RRc\
v13& 5 24 10.59& $-$24 31 11.5& 0.68931& RRab\
n14& 5 23 23.74& $-$24 27 46.3& 0.309058& RRc\
n15& 5 24 07.77& $-$24 31 00.3& 0.323758& RRc\
n16& 5 24 09.97& $-$24 31 07.3& 0.038763& SXPhe\
n17& 5 24 14.15& $-$24 33 20.7& 0.044803& SXPhe\
n18& 5 24 10.86& $-$24 31 11.8& 0.050276& SXPhe\
& & & 0.039169&\

This work was supported by Polish Ministry of Science grant N203 014 31/2650.

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