AAS 201st Meeting, January, 2003
Session 7. Globular Clusters and Their Contents
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[7.14] Blue Straggler Stars in the Globular Clusters 47 Tuc, M 3, and NGC 6752: HST STIS Spectroscopy

J. F. Sepinsky (Univ. of Delaware), R. A. Saffer (Villanova Univ.), M. M. Shara, D. Zurek (Dept. of Astrophysics, American Museum of Natural History)

Using the Hubble Space Telescope: Space Telescope Imaging Spectrograph, we were able to obtain over 65 spectra of globular cluster Blue Straggler Stars (BSS) in only 21 images. By placing the spectrograph slit over crowded fields of stars in the globular clusters (GCs) 47 Tucanae, M 3, and NGC 6752, we were able to average over 3 BSS per exposure, while also obtaining spectra of between 30 and 60 other GC members in each field. BSS are thought to be too massive for their GCs, and, indeed, a BSS has recently been shown (Shara et al. 1997, ApJ, 489, L59) to be a star whose mass is nearly twice the turnoff mass of 47 Tuc.

For each of the 21 fields observed, spectra were taken with the G430L and G430M gratings. The lower resolution G430L grating will be used to determine the masses of the stars in question, while the higher resolution G430M grating will be used to get accurate values of vsin i. Each image was processed using the iraf/calstis pipeline in two ways. First, the standard processing was used, but there were a number of hot pixels which the weekly dark correction did not remove. Since we have spectra covering a very large portion of our CCD, it was important to re-process these images with the dark frames updated by the daily dark exposures. This second set of reductions removed a large number of hot pixels, but left others which the earlier reduction removed. Thus, we extracted the spectra from the end product of each procedure, and compared the two to determine the best data. We present here a sample of that data, showing some BSS and typical background stars from each cluster, along with some representative steps from the data reduction procedure.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.