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Session 82 - Globular Clusters.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center

[82.11] The Globular Clusters Project -- First Results from ASCA

A. P. Smale, K. Mukai (USRA, NASA/GSFC), J. H. Swank (NASA/GSFC), D. J. Christian (UCB/CEA), A. N. Parmar (ESTEC)

We describe a long-term, multi-satellite study of the spectral and temporal behavior of the luminous globular cluster X-ray sources, utilizing the unique capabilities of ASCA, XTE, and SAX. The ASCA medium-resolution spectra will enable us to search for low-energy line emission and edge features, and make direct measurements of the elemental abundances of the sources to compare with the cluster abundances. With XTE we will study the fast temporal behavior of these sources -- low/high frequency noise, msec lags, pulsar searches etc -- in many cases for the first time. With the wide spectral range of XTE and SAX we can look for the low-energy black-body components and high-energy power-law tails which have been reported from some cluster sources, hunt for orbital periods where not known, and perform detailed burst analyses. Our sample includes all the GC sources brighter than \sim10^36 erg s^-1 with known distances and [Fe/H] values; these sources span the range from the most metal-rich cluster known (Terzan 1; 1.7 Solar) to one of the most metal-poor (NGC 7078; <0.01 Solar). To date we have been awarded a total of 460 ksec of ASCA and XTE time, and a SAX proposal is pending.

We present here the first results from the ASCA observation of X2127+119 (M15/NGC 7078). X2127+119 was observed for \sim 26 hrs beginning 1995 May 16/01:00 UT, covering 1.5 cycles of the 17.1-hr binary period. The source luminosity was L_x=3.8\times10^36 erg s^-1 (1--10 keV; 9.7 kpc). The data provide good coverage of the 5-hr eclipse, during which we find that the measured column density rises by 30%. No significant changes in N_H or other parameters are found at other phases; in particular, our initial analysis does not show the large N_H increase at \phi\sim0.6 reported from previous observations.

The results of fitting more complex (variable abundance) models will be presented at the meeting. We will also show early results from the ASCA observations of X1746-371 (NGC 6441) and X1850-086 (NGC 6712), performed in 1995 Sept and Oct respectively.

Program listing for Wednesday