The Flattening of Globular Clusters

In the three nearest luminous galaxies, the Milky Way System, the Andromeda Galaxy and NGC 5128 the brightest globular clusters are rounder than the faintest ones. On the other hand (contrary to some previous results) the flattening of individual LMC clusters is found to be independent of their luminosities. This suggests the possibility that the relationship between the flattening and luminosity of clusters might depend on host galaxy luminosity. No significant differences are found between the intrinsic flattening distributions of Galactic old halo, Galactic young halo and Galactic bulge/disk clusters. Such a dependence might perhaps have been expected if tidal forces (which are largest at small Galactocentric distances) removed angular momentum from globular clusters. The preliminary conclusion by Norris that clusters with blue horizontal branches are more flattened than red HB clusters is not confirmed by the larger data base that is now available. In other words there is no evidence for the puzzling claimed correlation between the flattening and the horizontal branch morphology of Galactic globular clusters.Comment: 20 pages text + tables; 5 postscript figures. Astronomical Journal, in pres

What are S0 (0) Galaxies?

Among early-type galaxies with almost circular isophotes E0 and E1 galaxies are, at 99.3% significance, more luminous than face-on objects classified as S0 (0) and S(0) (1). This result supports the view that rotation and "diskiness" are more important in the outer regions of faint-early type galaxies than they are for more luminous galaxies of very early morphological type.Comment: 7 pages. 0 figures. Astrophysical Jounral Letters in pres

Are the Luminosities of RR Lyrae Stars Affected by Second Parameter Effects?

There is a serious discrepancy between the distance to the LMC derived from the Cepheid Period-Luminosity relation and that obtained by using the Galactic calibration for the luminosity of RR Lyrae stars. It is suggested that this problem might be due to the fact that second parameter effects make it inappropriate to apply Galactic calibrations to RR Lyrae variables in the Magellanic Clouds, i.e. Mv(RR) could depend on both [Fe/H] and on one or more second parameters.Comment: 10 pages as uuencoded compressed Postscript. Also available at http://www.dao.nrc.ca/DAO/SCIENCE/science.htm

The Light Curve of S Andromedae

Historical observations of S And, in combination with the color versus rate-of-decline relationship for well-observed SN 1991bg-like supernovae, are used to estimate a rate of decline Delta m15 (B) = 2.21 and an intrinsic color at maximum [B(0) - V(0)]o = 1.32 for SN 1885A.Comment: 6 pages, no figures. To appear in the Astronomical Journal Feb 200

Globular Clusters in Dwarf Galaxies

Data are presently available on the luminosities and half-light radii of 101 globular clusters associated with low-luminosity parent galaxies. The luminosity distribution of globulars embedded in dwarf galaxies having $M_{v} > -16$ is found to differ dramatically from that for globular clusters surrounding giant host galaxies with $M_{v} < -16$. The luminosity distribution of globular clusters in giant galaxies peaks at $M_{v} \sim -7.5$, whereas that for dwarfs is found to increases monotonically down to the completeness limit of the cluster data at $M_{v} \sim -5.0$. Unexpectedly, the power law distribution of the luminosities of globular clusters hosted by dwarf galaxies is seen to be much flatter than the that of bright unevolved part of the luminosity distribution of globular clusters associated with giant galaxies. The specific frequency of globular clusters that are fainter than $M_{v} = -7.5$ is found to be particularly high in dwarf galaxies. The luminosity distribution of the LMC globular clusters is similar to that in giant galaxies, and differs from those of the globulars in dwarf galaxies. The present data appear to show no strong dependence of globular cluster luminosity on the morphological types of their parent galaxies. No attempt is made to explain the unexpected discovery that the luminosity distribution of globular clusters is critically dependent on parent galaxy luminosity (mass?), but insensitive to the morphological type of their host galaxy.Comment: Figure 6 replaced to be published in the Astronomical Journa