Summaries are presented of the photoelectric measurements of stellar Ca II H and K line intensity made at Mount Wilson Observatory during the years 1966-1983. These results are derived from 65,263 individual observations of 1296 stars. For each star, for each observing season, the maximum, minimum, mean, and variation of the instrumental H and K index "S" are given, as well as a measurement of the accuracy of observation. A total of 3110 seasonal summaries are reported.

Photoelectric UBV observations of 1782 stars are used to explore properties of the HK objective-prism survey conducted by Beers, Preston, and Shectman with the Curtis-Schmidt telescope of the Cerro Tololo Inter-American Observatory. We construct an intrinsic (U - B)0 versus (B - V)0 relation for blue horizontal branch stars and use it to derive estimates of E(B - V) color excesses in 50 survey fields. Comparison of these with the reddening maps of Burstein and Heiles indicates good agreement except in low-latitude fields toward the Galactic bulge. We describe qualitative features of the stellar content of the HK survey by use of unreddened two-color diagrams and indicate how the photometric data may prove useful in several applications. Finally, we use a halo density model to estimate the variation of completeness with apparent magnitude, B, in our catalog of field horizontal branch star candidates.

From analysis of a large sample of field blue horizontal-branch stars we find that the mean unreddened color, w, in the color window -0.02 < (B-V)0 < + 0.18 increases outward in the Galaxy by approximately 0.025 on 2 kpc < R < 12 kpc. On the basis of several tests of the sample, we conclude that this result is due neither to errors in reddening estimates nor to contamination of the sample by stars of the young disk or by the population described by Lance (1988b).

Spectroscopy is reported for 769 hot stars selected from the HK objective-prism/interference-filter survey of Beers et al. [AJ, 90, 2089 (1985)]. This sample spans a wide range of objective-prism classifications, from stars with extremely blue continuous spectra to stars with broad Balmer H-epsilon typical of AB- or A-type stars. Many of the stars included were originally classified as candidate metal-deficient stars. All of these stars exhibit medium-resolution spectra consistent with temperatures hotter than the main-sequence turnoff of metal-poor halo stars, or are composites of late-type and early type stars. Previously published broadband UBV photometry is available for 193 stars in this sample, and is used to confirm or refine the stellar classifications obtained from the medium-resolution spectroscopy. When available, photometric information is used to obtain estimates of the surface temperature for degenerates and O- and B-type subdwarfs based on previously derived calibrations. Several extremely hot (T(eff) > 50 000 K) He-rich sdO stars are identified. Four stars exhibit very narrow Balmer profiles typical of supergiant B-type stars or post-AGB objects. The apparent magnitudes of these stars (14 less-than-or-equal-to V less-than-or-equal-to 15) require that they must be less luminous than normal supergiants if they are members of the Galaxy. The great majority of stars in our sample (551) are clearly recognized as field horizontal-branch (FHB) or mid- to late-type A stars on the basis of their Balmer line profiles. We lack the necessary intermediate-band photometry required to unambiguously distinguish between these stars on the basis of surface gravity alone. However, the location of the subset of these stars with available broadband photometry in the (U - B)0 vs (B - V)0 two-color diagram (which is affected by both metal abundance and surface gravity) suggests that our sample contains a mixture of FHB and A stars with a wide range of abundances. The A stars exhibit rotation and line-of-sight dispersion consistent with membership in the galactic thick disk. The FHB stars (as well as the several hundred FHB/A stars which we are presently unable to uniquely assign to either FHB or A classifications) exhibit kinematic properties which suggest a transition from thick disk to halo.

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.