THE LOCAL-DENSITY OF HALO GIANTS

A new estimate of the local density of halo giants-36 +/- 7 with M(V) < 0.5 per kpc3-is presented. This number is derived from an objective-prism survey for nearby metal-weak stars, and so is free from many of the assumptions needed to derive the local halo density in the traditional way, from high proper motion surveys. This number agrees well with estimates of the local density of halo horizontal-branch stars, but is approximately a factor of 2 smaller than the density derived by Bahcall & Casertano [ApJ, 308, 347 (1986)]. This may be due to the inclusion of some thick disk stars in their proper-motion selected sample. The halo density derived from giants can be expressed as a disk-to-halo ratio of 850 : 1 (+/- 35%). Using these results, a simple model is built to predict numbers of halo giants in specified directions in the Galaxy. It is shown that it performs much better than the Bahcall-Soniera model, in the specific case of halo giants. Finally, the surface brightness due to the halo at the solar radius is calculated to be 27.7 V magnitudes per arcsec2, if the Galaxy was viewed from the outside, edge-on, thus raising the possibility of detecting light from halo field stars in other galaxies similar to our own.