We report on spectroscopic observations for 1044 stars, located primarily in the southern Galactic hemisphere, chosen from a list of candidate metal-deficient stars discovered in the HK objective-prism survey. Metal abundances for the program stars, on the [Fe/H] scale, are obtained from a previously published calibration of the variation in the equivalent width of the Ca II K absorption line (lambda-3933 angstrom) as a function of broadband (B-V)0 color. Broadband UBV photometry is available for roughly one-third of the present sample. For the majority of stars without available photometry (primarily stars with an inferred [Fe/H] > -2.0), we obtain estimated dereddened (B-V)0 colors from an empirical calibration of the variation of Balmer line equivalent width with broadband color. Radial velocities, with accuracies on the order of 10 km s-1, are obtained for all our program stars. Distance estimates, accurate to 10%-15%, are reported for the subsample of program stars with available photometry. Less accurate distances are obtained for the remaining stars by a calibration of apparent magnitude with crude brightness estimates from the original survey plates. The sample reported here includes 734 stars with [Fe/H] less-than-or-equal-to -1.0, 446 stars with [Fe/H] less-than-or-equal-to -2.0, 70 stars with [Fe/H] less-than-or-equal-to -3.0, and at least three stars with [Fe/H] less-than-or-equal-to -4.0. Due to uncertainties in the calibration of our metal-abundance determinations for late-type stars, the actual number of stars with [Fe/H] less-than-or-equal-to -4.0 in the present sample may be on the order of 5-10. Fifty stars in our sample exhibit anomalously strong G bands, characteristic of the subgiant CH stars discussed by Bond. Among the most metal-deficient objects (as inferred from their Ca II K equivalent widths), we identify six stars with moderate to strong CN bands. The present program stars form the basis for addressing a wide range of questions concerning the formation and evolution of the Galactic halo population, and, by inference, the nature of the first generations of star formation in the universe. The number of extremely metal-poor stars ([Fe/H] less-than-or-equal-to -2.0) reported in the present sample is roughly quadruple the sample size of nonkinematically selected stars of similar metal abundance reported by previous workers, and is on the order of the total previous samples of stars in this abundance regime when all sources are included. The number of stars with [Fe/H] less-than-or-equal-to -3.0 in the present sample is seven times the number of previously identified stars with spectroscopically determined abundances which are this low. We emphasize, however, that the present sample only represents on the order of 10% of the number of such extreme objects that remain to be discovered upon completion of the follow-up spectroscopy and photometry of metal-deficient candidates identified in our ongoing objective-prism survey.

We report the discovery of the first candidate microlensing event to be discovered in the direction of the Galactic Bulge. The peak brightness of the candidate event occurred on June 15, 1993. The event had time scale (R0/V, R0 - the Einstein radius, V - the transverse velocity of the lens) equal to 23.8 +/- 0.9 day and amplification A = 2.4 +/- 0. 1. The lensed star is at the tum-off point in the Galactic Bulge. The lensing object is likely to be a disk M-dwarf of about 0.3 M..

We describe an ongoing survey to search for dark matter via lensing events of stars in the Galactic Bulge. The principal properties of the survey are described, and some preliminary results are shown for newly-discovered variables. We discuss some of the projects related to the study of the Galactic Bulge that can be addressed using these data, and describe the future plans for the survey over the coming few years.

From analysis of a photometrically selected sample of 175 metal-poor field stars with main sequence gravities (hereafter BMPs) and UBV colors blueward of the most metal-poor globular cluster main-sequence turnoffs, 0.15<(B - V)0<0.35, and properties of the candidate lists of the HK objective prism survey, we calculate the space density and a suitably defined specific frequency of BMPs within approximately 2 kpc of the Sun. We consider two cases. If we adopt the luminosities and color distribution of globular cluster blue stragglers (hereafter BS) for BMPs, the BMP space density is approximately 350 kpc-3, from which we obtain a specific frequency S(BMP)-8, a value 9 times larger than that of BSs in globular clusters. From this result, we conclude that cluster-type BSs are but a minor component of the field BMPs and that the remainder must be of a different nature. If we adopt luminosities of metal-poor models halfway between the Zero Age Main Sequence and the phase of core hydrogen exhaustion, we obtain a space density of 450 (+300,-150) kpc-3 and a specific frequency S(BMP) = 10(+5,-3). From a subsample of 107 BMPs with available radial velocities we derive a galactic rotation of 128 km s-1 and an isotropic velocity dispersion of sigma(rphitheta) approximately 90 km s-1 values intermediate between those of halo and thick-disk populations. From analysis of a larger sample of stars on 0. 15<(B - V)0<0.35 binned by a crude line-blanketing parameter, we find that our results are insensitive to adopted BMP selection criteria: none of these subsamples of A- and early F-type stars above the galactic plane possess disk kinematics. The region of the UBV two-color diagram occupied by BMPs could be populated by metal-deficient, main-sequence gravity stars with ages substantially younger than those of the metal-poor halo. Because we cannot imagine how or where the observed local population of BMPs could have been produced within our galaxy during the past 3 to 10 Gyr, we suggest that BMPs are the bluest members of metal-poor intermediate-age main sequences accreted, probably, from dwarf spheroidal satellites of the Milky Way during the past 10 Gyr. We discuss observational consequences of this suggestion.

The analysis of the first three years of the OGLE data revealed 12 microlensing events of the Galactic bulge stars, with the characteristic time scales in the range 8.6 < t(0) < 80 days, where t(0) = R(E)/V. A complete sample of nine events gave the optical depth to gravitational microlensing larger than (3.3 +/- 1.2) x 10(-6), in excess of current theoretical estimates, indicating a much higher efficiency for microlensing by either bulge or disk lenses. The lenses are likely to be ordinary stars in the Galactic bar, which has its long axis elongated towards us. At this time we have no evidence that the OGLE events are related to dark matter. The OGLE color magnitude diagrams reveal the presence of the Galactic bar and a low density inner disk region similar to 4 kpc in radius. A catalogue of a few thousand variable stars is in preparation.

The color temperature and Balmer jump inferred from UBV and Stromgren photometric indices, the low gravity and low metallicity derived from spectrum analysis, and weakness of all CH molecular lines combine to suggest that HD 195636 is in an evolutionary state near the transition between the horizontal branch and asymptotic giant branch. The projected equatorial rotational velocity of PID 195636 is V-e sin i=25 km/s, a value at least 2.5 times greater than that expected if known blue horizontal branch axial rotators in globular clusters conserve envelope angular momentum during horizontal branch evolution. Constancy of the radial velocity on time scales of 3, 10, and 90 days indicates that the axial rotation is not due to co-rotation in a short-period binary. Therefore, it seems most plausible that transfer of angular momentum from core to envelope occurred during HB evolution. The Balmer line profiles are peculiar. H alpha is abnormally shallow, as if the core were filled by emission, and higher members of the Balmer series are significantly broader than those of HD 200564, a slightly cooler giant star of similar metallicity. The space velocity of HD 195636 calculated for an assumed RHB/AGB luminosity, M-V=-0.5, is 470 km/s retrograde, a high but not extraordinary value. (C) 1997 American Astronomical Society.

CS 22966-043 is an ultra-short-period pulsating star with high velocity (RV = -266 km s(-1)) discovered during the course of a search for spectroscopic binaries among blue metal-poor field stars, in progress since 1992. With respect to period (0.0374 days), mean color ((B-V) = 0.24), and metal abundance ([Fe/H] approximate to -2.4), it closely resembles the SX Phoenicis stars found among the blue stragglers in NGC 5053. CS 22966-043 also is the primary of a spectroscopic binary with (probable) period of 430 days. Light-travel time across the projected orbit, as large as 0.0037 days, must be added to the times of observation to combine data obtained in different years with minimal phase dispersion. If CS 22966-043 is, indeed, a blue straggler formed by binary interaction as is now generally believed, then it seems most probable that the interaction was one of mass transfer from the present-day secondary during its post-main-sequence evolution rather than merger of a close binary. The latter option would require that this rare field star was, in addition, a member of a primordial triple system.