Martha L. Hazen

RR Lyrae stars and color-magnitude diagram of the globular cluster NGC 6388

We present new V, B-V, and V, V-R color-magnitude diagrams for the bulge globular cluster NGC 6388. These diagrams indicate that NGC 6388 is a metal-rich globular cluster with color-magnitude morphology similar to that of 47 Tucanae. We have conducted a search for new variable stars close to NGC 6388, finding three new RR Lyrae stars. The membership of these and previously discovered RR Lyrae stars near NGC 6388 is discussed. There is reason for believing that some of these variables are nonmembers. Others, however, may belong to the cluster and may be similar to the RR Lyrae star V9 in 47 Tuc.

Variable stars within 25 arcmin of the LMC globular cluster NGC 2210

Based on a photometric analysis of 63 photographic plates taken between 1975 and 1985 with the CTIO 1.5 and 4 m telescopes, and new photoelectric and CCD photometry, pulsational characteristics are presented for 52 newly discovered field RR Lyrae variables within 0.5° of the LMC globular cluster NGC 2210. The surface density of the field RR Lyrae stars is 80 per square degree, which is as high as that found in Grahams NGC 1783 field, and higher than that found in several outer halo fields of the LMC. Eleven RR Lyrae stars located within the tidal radius of the cluster, and 33 non-RR Lyrae field variables are also discussed

The variable stars in the globular cluster NGC 6139

Photometry is presented for ten new variables within the tidal radius of NGC 6139 and for six new variables outside the tidal radius. Of the former, five have periods indicating they are probable RR Lyrae stars; these variables seem likely to be members of the cluster. An apparent visual distance modulus for NGC 6139 of 17.2 + or - 0.4 mag is derived. The RR Lyrae stars in the cluster show period shifts appropriate to a cluster of considerably low metallicity than has been observed for NGC 6139. 14 refs.

The variable stars in the globular cluster NGC 6642

Photometry is presented for sixteen new and two previously discovered variables within the tidal radius of NGC 6642, and for eight new and three previously known variables outside the tidal radius. Of the former, ten have well-determined periods, indicating that they are RR Lyrae stars, and an additional seven are also probable RR Lyraes; most of these seem likely to be members of the cluster. An apparent visual distance modulus for NGC 6642 of 15.6±0.4 mag is derived. This value is 0.8 mag larger than the previous estimates. The RRc stars in the cluster show period shifts appropriate to its metallicity; the RRab stars show shifts corresponding to a somewhat lower metallicity

The variable stars in the field of the globular cluster NGC 6544

A search for variable stars in the neighborhood of the galactic globular cluster NGC 6544 has located two variables within the tidal radius of the cluster and two outside. A star of large proper motion was also detected. One of the variables within the tidal radius is possibly an eclipsing binary; the other is a RR Lyrae type ab star that may be a cluster member. The two field variables are RR Lyrae type ab stars