[en] Observational data on the spatial distribution of galaxies in rich clusters are summarized, with a focus on the evidence for the existence of subclusters or clumps and the implications of such structures for the measurement of intrinsic properties such as M/L, velocity dispersion, luminosity function, and density profile. Consideration is given to X-ray double clusters, optically identified multiple-component clusters, simulations of cluster formation and evolution, dynamical models of double clusters, and the dynamical consequences of ignoring substructure. Techniques for taking subclusters into account when estimating local density or kinematic parameters are described; the integration of spatial and velocity information is outlined; and the use of D and cD galaxies as probes of cluster morphology is discussed. 45 references

[en] Observational data on a selected sample of 134 low-metal-abundance stars (approximate Fe/H = -2.0 or less) in the Galactic halo are presented in diagrams and briefly characterized, summarizing the preliminary report of Beers et al. (1985). The metal-poor population is found to be of spectral types F0-G5 and to comprise both stars near the halo main-sequence turnoff and stars on the red horizontal, giant, and asymptotic giant branches. The metallicity distribution is shown to remain constant down to the lowest measured Fe/H. 5 references

[en] Literature values for the equivalent width of the interstellar absorption line of Ca II K (3933 A) are used to constrain a simple empirical model for the strength of this line as a function of distance from the galactic plane. The best-fit model has an integrated Ca II K equivalent width in the direction perpendicular to the galactic plane of approximately 200 mA and a scale height of approximately 1100 pc. Such a model is useful for estimating (and correcting for) the contribution of the interstellar Ca II K feature to the total observed Ca II K line strength in the spectra of metal-deficient stars in the galactic halo. 23 refs

[en] We have measured 13 new redshifts for members in A98, a galaxy cluster with two large enhancements in X-ray surface brightness and galaxy number density. From the 24 known redshifts, we determine line-of-sight velocity dispersions of the individual subclusters. We find the line-of-sight velocity difference to be 539 +- 361 km s^-1. We describe a new method for determining the gravitational scale length for the condensation from the distribution of pairwise separations of the members. Stable mass estimates are obtained by application of the virial theorem. The M/L_B for the subclusters are 593 (A98N) and 432 (A98S), comparable with other rich clusters

[en] The novel estimators proposed for the kinematical properties of clusters of galaxies are both resistant in the presence of outliers and robust for a broad range of non-Gaussian underlying populations. Extensive simulations for a number of common situations realizable in small-to-large samples of cluster radial velocities allow the identification of minimum variance estimators. Also explored is the estimation of confidence intervals, using the jacknife and bootstrap resampling techniques. These methods are compared to simple formulas based on sample estimates of central location and scale. Estimators of confidence intervals on scale require resampling. 61 refs

[en] Rich galaxy clusters containing multiple condensations are common. This subclustering affects many cluster properties and provides insight into cluster evolution. Optical contour maps of the four clusters are presented and briefly discussed. (Auth.)

[en] We present a surface density contour map of the Cancer Cluster derived from galaxy counts in the Zwicky catalog. The contour map shows that the galaxy distribution is clumpy. When this spatial distribution is combined with nearly complete velocity information, the clumps stand out more clearly; there are significant differences in the mean velocities of the clumps which exceed their internal velocity dispersions. The Cancer cluster is not a proper ''cluster'' but is a collection of discrete groups, each with a velocity dispersion sigma_r roughly-equal300 km s^-₁, separating from one another with the cosmological flow. The mass-to-light ratio for galaxies in the main concentration is M/L_Bsub T/roughly-equal320 M_sunL_sun (H⁰ = 100 km s^-₁ Mpc^-₁)

[en] X-ray and optical observations of the cluster of galaxies Abell 744 are presented. The X-ray flux (assuming H(0) = 100 km/s per Mpc) is about 9 x 10 to the 42nd erg/s. The X-ray source is extended, but shows no other structure. Photographic photometry (in Kron-Cousins R), calibrated by deep CCD frames, is presented for all galaxies brighter than 19th magnitude within 0.75 Mpc of the cluster center. The luminosity function is normal, and the isopleths show little evidence of substructure near the cluster center. The cluster has a dominant central galaxy, which is classified as a normal brightest-cluster elliptical on the basis of its luminosity profile. New redshifts were obtained for 26 galaxies in the vicinity of the cluster center; 20 appear to be cluster members. The spatial distribution of redshifts is peculiar; the dispersion within the 150 kpc core radius is much greater than outside. Abell 744 is similar to the nearby cluster Abell 1060. 31 references

[en] Coordinates and brightness estimates are presented for 4408 candidate field horizontal-branch stars selected using an objective-prism, interference-filter survey technique. The candidates lie primarily in the southern Galactic hemisphere, and are distributed in color over the range B-V from -0.2 to 0.40. Previous spectroscopic observation of a subset of these candidates indicates that roughly 85 percent of the catalog objects are bona fide members of the field blue horizontal branch. The remaining candidates include, in order of frequency, stars with main-sequence gravity which are likely to be a mix of metal-deficient turnoff stars and field blue stragglers, metallic line (Am) stars, A stars of near-solar metallicity, and high-luminosity or binary stars. 16 references

[en] A method for estimating the stellar metal abundances is proposed which compares measures of the equivalent width of a single feature in moderate resolution (1 A) optical spectra of stars, the Ca II K line at 3933 A, with models of the predicted line strength as a function of the broadband B-V color and Fe/H. The approach is capable of providing estimates of stellar metallicity over the range -4.5 to -1.0 with a scatter of about 0.15 dex for dwarfs and giants in the color range 0.33-0.85. For cooler stars, with B-V in the range 0.85-1.1, the scatter may be as large as 0.19 dex. The calibration of the Ca II K index with Fe/H is discussed, and average radial velocities and abundances are presented for several galactic globular clusters. 88 refs