Showing papers by "Dominion Astrophysical Observatory published in 1988"

Intrinsic integrated UBVRI colors of Galactic globular clusters

Abstract: Published observational data on 50 Galactic globular clusters, including spectral classifications, homogenized colors, and color excesses, are compiled in extensive tables, graphs, and diagrams and analyzed to determine the intrinsic-color/integrated-spectral-type relationship in the UBVRI system. These relationships are found to exhibit significant slopes, although the RI colors do not contribute substantially to the intrinsic-color determination. The values of a(B-V) for the northern and southern Galactic hemispheres are found to be 0.068 + or - 0.006 and 0.039 + or - 0.003 mag, respectively.

The Twin-Nucleus Merging Galaxy Markarian 266 (NGC 5256)

Abstract: Optical imaging in continuum and line wavelengths, spatially resolved optical spectroscopy, and 21 cm radio imaging of Markarian 266 are presented. The galaxy has faint extended plumes of luminosity, which indicate that it is a recent merger. There are extended regions of blue luminosity suggestive of recent star formation, and remarkable structure in forbidden O III line emission. Spectroscopic data show the velocities and densities in the ionized gas. Radio observations taken with the VLA show that both nuclei are resolved radio sources, and that there is a third radio source between them which has no optical counterpart; 21-cm absorption is seen against the brighter optical nucleus, indicating possible infall. These results are discussed in terms of galaxy mergers, nuclear activation, and ionized gas. Mkn 266 has many similarities to Arp 220 and appears to be a somewhat lower-luminosity version of the IRAS ultraluminous galaxies.

The NGC 5128 cluster system.

Abstract: We review what has been learned about the globular clusters in NGC 5128 (Cen A). Two independent programs (our work at CTIO and Sharpies’ work at the AAT) have confirmed 87 objects as clusters in NGC 5128 from their velocities. We discuss the colors of the clusters, which are indicative of a wide range of metallicities, their velocities, and their origin as genuine globular clusters in this elliptical galaxy.

A Survey of Globular Cluster Velocity Dispersions

Abstract: We have used the Dominion Astrophysical Observatory radial velocity spectrometer on the 3.6m Canada-France-Hawaii telescope to obtain radial velocities, accurate to ∼0.8 km/s, for ∼20 stars in each of nine globular clusters. The stars are generally within three core radii of the cluster center. The cluster names and metallicities (the latter are averages of values in Zinn and West (1984), Pilachowski (1984), and Webbink (1985)) are given in Table I. This sample includes two clusters with cusps in their surface brightness profiles: NGC 6624 and 6681.

Globular Cluster Color-Magnitude Diagrams

Abstract: This review concentrates on new generalities emerging from this, the second “golden era” of B,V color-magnitude diagrams (CMDs), and remarks about future work in other photometric systems.

The search for high redshift quasars

Abstract: The techniques used for the detection of high redshift quasars are reviewed and compared. There is a gradual decline in the space density of quasars with redshift for z > 2. The space density for quasars with z > 3.4 is estimated to be ~0.2 deg-2 for R < 19.5 and the slope of the luminosity function appears to be nearly flat. Surveys of large areas, at least 100 square degrees, are required to obtain the necessary statistics to define the form of the density and luminosity functions at early epochs.

Globular Cluster Systems in Galaxies: Main Trends and Future Directions

Abstract: This was a really exciting conference! The main problem in summarizing it is that so many new and important results were presented, making it impossible to mention each one individually. In reviewing this conference I shall first discuss new results, then problem areas revealed by papers and during discussions and finally desiderata and trends for future work.

The Core of the M 87 Globular Cluster System

Abstract: We have observed the central distribution of globular clusters in M 87 The core radius of the cluster system is an order of magnitude larger than that of the underlying galaxy

Evidence for Mass Segregation in NGC 5466

Abstract: Forty-eight blue straggler stars have been discovered in NGC 5466, the only Galactic globular cluster known to contain an anomalous Cepheid of the sort found in dwarf galaxies The stars were identified in color-magnitude diagrams constructed from photometry of deep photographic plates taken with the Canada-France-Hawaii 36 m telescope (calibrated with new UBV photoelectric photometry), and from point spread function photometry of CCD frames taken with the Palomar 5 m telescope The stars typically have magnitudes ∼ 19 m 1 and colors ∼ 0 m 2 Forty-two of the 48 stars are situated inside of R=25 arcmin (see Fig1), the projected radius containing half the cluster luminosity, and only six stars are found between 25 and 9 arcmin A one-sided, two-sample Kolmogorov-Smirnov test (using the CCD data) establishes at the 98% significance level that the blue stragglers are more centrally concentrated than the subgiant stars of the same magnitude By fitting multi-component King models to the projected radial distributions (Fig2), the mean mass of the blue stragglers is shown to be ∼15 to two times larger than the masses of the stars that contributed the light from which the core and tidal radii were derived (ie M(Blue Str)=13±03 M⊙) Because the central relaxation time for NGC 5466 is much less than the cluster age, the different radial distributions are attributed to mass segregation A similar mass segregation is also observed in the globular cluster NGC 5053, where Nemec and Cohen (1986, in preparation) have recently identified ∼30 blue stragglers The low stellar aensity and small escape velocity of NGC 5466 make a recent epoch of star formation (during which the blue stragglers might have formed as massive single stars) seem unlikely Instead, the blue stragglers probably are either close binary systems that have transferred mass, or are coalesced stars The very low frequency of stellar collisions expected in the center of NGC 5466 suggests that the blue stragglers are primordial binary systems The simultaneous presence in NGC 5466 of the blue stragglers and the anomalous Cepheid V19, and their relative numbers, supports the hypothesis that there is an evolutionary connection between the two types of stars By fitting theoretical isochrones to the photographic c-m diagram, NGC 5466 is estimated to have an age of 18±3 Gyr

Globular Clusters in Different Types of Spiral Galaxies

Abstract: Studies of globular clusters in spiral galaxies are still available for only a few galaxies with a limited range of galactic types. We have identified (or set upper limits on) the cluster systems in several edge-on spirals ranging from the early-type spiral NGC 7814 to the late type NGC 5907. We discuss the properties of the cluster systems and their relationship to the properties of the parent galaxies.

New Main-Sequence Luminosity Functions for Globular Clusters

Abstract: We report new results from a program which is aimed at obtaining deep CCD photometry for a sample of relatively nearby globular clusters having a wide range of metallicities. The CCD cameras on the CFHT 3.6 m, CTIO 4 m and KPNO 4 m telescopes have been used over the past 4 years to obtain deep exposures in regions of a number of clusters. In order to avoid the severest crowding, all of our observations have been obtained at distances of greater than ∼ 5 core radii from the cluster centers. The images have been analysed by using the DAOPHOT point-spread-function fitting routines.