Radial Variations in the Color-Magnitude Diagram of NGC 6712

Previous abstract Next abstract

Session 58 -- The Galaxy
Display presentation, Thursday, 2, 1994, 9:20-6:30

[58.11] Radial Variations in the Color-Magnitude Diagram of NGC 6712

D.H.Martins (U. of Alaska)

A new analysis of photographic data for the globular cluster NGC 6712 is presented. The data set consists of three pairs of matched B and V plates obtained at CTIO with the 4-meter telescope and RC camera several years ago as part of another project. The plates were scanned using a 2048x2048 pixel array with pixel size 0.328 arcsec, centered near the cluster central star specified by Cudworth (AJ 96, 105, 1988). All scans were transformed into intensity using on-plate calibration spots through the IRAF DTOI routine. Photometric analysis was done using the ALLSTAR code within DAOPHOT. A total of about 10,000 stars were measured in B and V on the deepest plate (60, 30, and 15 minute exposures were used) pair. Once all the data had been transformed to the BV system, several techniques were employed to: a) examine the quality of the transforms to V and B-V; b) collate the observations by matching stars between plate pairs by position and V observations; c) average data for matched stars; d) construct color-magnitude diagrams (CMD) for different radial distances from the cluster center using x,y positions of stars in the scan array relative to the cluster center. These results and techniques will be summarized, using the complete data set, with several CMD's displayed. Of particular note is a concentration of horizontal branch stars near the cluster center. This work was supported by the NOAO and a grant from the University of Alaska, Anchorage.

Thursday program listing