AAS 201st Meeting, January, 2003
Session 104. NOAO Survey Programs
Special, Wednesday, January 8, 2003, 2:00-3:30pm, 608-609

## [104.06] Initial Results from the Chandra Galactic Plane Survey

J. Grindlay, P. Zhao, J. Hong, D. Kim, S. Laycock, P. Edmonds, E. Schlegel (CfA), H. Cohn, P. Lugger, A. Rogel (Indiana Univ.)

We report initial results from the first 26 fields surveyed in the first two years of our ongoing deep galactic plane survey with Chandra. The Chandra Multiwavelength Plane (ChaMPlane) survey of the galactic plane will survey some ~100 ACIS fields over 5 years, selected for exposure at least ~20ksec, galactic latitude b \lesssim12deg, and minimum column density NH, with a primary goal to measure or constrain the poorly known accretion source content of the Galaxy. The most common such systems, cataclysmic variables, have space densities still uncertain by 1-2 orders of magnitude. Unambiguous optical identifications of ChaMPlane sources are being obtained for a significant fraction from deep R and H\alpha (and V,I) imaging with the MOSAIC cameras on the CTIO and KPNO 4m telescopes under the NOAO Long Term Surveys Program, and followup spectroscopy is being conducted with WIYN/HYDRA and Magellan/LDSS2. We find that most Chandra sources in the anti-center galactic plane are a mixture of background AGN and stellar coronal sources, with logN-logS source counts in fact consistent with AGN dominating this faint source sample. However, in the galactic bulge (l < 5-10deg), a significant excess of faint sources is seen: at x-ray flux values Fx(2-8 keV) ~1 x 10-14 erg-cm-2-s-1, the excess above the extragalactic source counts is at least a factor of 5. These (relatively) hard sources are unlikely to be normal stars, and instead an enhanced population of CVs and compact binaries in the galactic bulge is likely. Probable optical counterparts (to R ~ 24) and spectroscopic identifications (to R ~22) are presented for some sources in several example bulge fields (and see paper by Zhao et al) but are limited by reddening. We describe several models, and future tests with the ongoing survey (and its resulting optical and x-ray databases), to determine the nature of this new component of the galactic x-ray source population. The ChaMPlane x-ray and optical surveys are supported by NASA/Chandra grant AR2-3002A and NSF grant AST-0098683, respectively.