AAS 195th Meeting, January 2000
Session 75. Intrinsic Variable Stars
Display, Friday, January 14, 2000, 9:20am-6:30pm, Grand Hall

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[75.07] Variable Stars in the Globular Clusters 47 Tucanae and Terzan 5

P.D. Edmonds (HCO), R.L. Gilliland (STScI), C.D. Bailyn (Yale University), H.N. Cohn (Indian University), A.M. Cool (SFSU), A.S. Fruchter (STScI), J.E. Grindlay (HCO), P.M. Lugger (Indiana University)

We have made searches for variable stars in two metal-rich globular clusters, 47 Tucanae and Terzan 5. Using extensive CTIO observations in UBVI we have detected low amplitude, relatively short period variability among the red giants in 47 Tuc, probably caused by pulsations. This confirms the earlier detection of K giant variability in this cluster by Edmonds and Gilliland using HST observations. Although K giant variability has been studied in field stars, our CTIO work represents the first detailed study of such variability in a globular cluster. We discuss the period and amplitude distribution of these variable K giants, their positions in the color magnitude diagram and the implications of this variability for stellar astrophysics. We have also detected several other cluster variables including long-period variables, an eclipsing binary and a pulsating blue straggler, plus a number of SMC variables including two RR Lyrae variables. Our shorter Terzan 5 observations, using NICMOS, have detected a RR Lyrae variable in this highly reddened, solar metallicity cluster, adding to the class of long period RR Lyraes found in metal-rich clusters. No evidence has been found for variability from the low-mass X-ray binary and millisecond pulsar known in Terzan 5.

This work was partially supported by HST grant GO-7889.

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