Globular Clusters in the Magellanic Clouds.I:BV CCD-Photometry for 11 Clusters

We present BV CCD-data for 11 intermediate-age LMC clusters; the main conclusions are: 1. in the (V_to, V_cl,m) and (V-to, (V_to-V_cl,m)) planes the models yield a good overall description of the data; 2. with the current sample, it is impossible to firmly choose between "classical" and "overshooting" models; 3. the separation in colour between the MS band and the Red He-burning Clump is smaller than predicted by theoretical tracks; 4. the existence of the so-called "RGB phase-transition (Renzini and Buzzoni 1986) seems to be confirmed.Comment: 62 pages, 37 figures and tables 6 to 16 available on request, uuencoded compressed postscript file with tables 1-5 and 17-18 included, BAP 08-1994-020-OA

Theoretical Uncertainties in Red Giant Branch Evolution: The Red Giant Branch Bump

A Monte Carlo simulation exploring uncertainties in standard stellar evolution theory on the red giant branch of metal-poor globular clusters has been conducted. Confidence limits are derived on the absolute V-band magnitude of the bump in the red giant branch luminosity function (M_v,b) and the excess number of stars in thebump, R_b. The analysis takes into account uncertainties in the primordial helium abundance, abundance of alpha-capture elements, radiative and conductive opacities, nuclear reaction rates, neutrino energy losses, the treatments of diffusion and convection, the surface boundary conditions, and color transformations. The uncertainty in theoretical values for the red giant bump magnitude varies with metallicity between +0.13/-0.12 mag at [Fe/H] = -2.4 and +0.23/-0.21 mag at [Fe/H] = -1.0$. The dominant sources of uncertainty are the abundance of the alpha-capture elements, the mixing length, and the low-temperature opacities. The theoretical values of M_v,b are in good agreement with observations. The uncertainty in the theoretical value of R_b is +/-0.01 at all metallicities studied. The dominant sources of uncertainty are the abundance of the alpha-capture elements, the mixing length, and the high-temperature opacities. The median value of R_b varies from 0.44 at [Fe/H] = -2.4$ to 0.50 at [Fe/H] = -1.0. These theoretical values for R_b are in agreement with observations.Comment: 30 pages, 6 figures. To appear in Ap

The Accretion of Lyman Alplha Clouds onto Gas-Rech Protogalaxies; A Scenario for the Formation of Globular Star Clusters

A satisfactory theory for the formation of globular star clusters (GCs) has long been elusive, perhaps because their true progenitors had not yet been guessed. In this paper I propose a causal relationship between the strongly decreasing densities of Lyman alpha (LyA) clouds at high redshift and the formation of GCs - namely that GCs were created by the accretion of LyA clouds onto protogalaxies. I describe a scenario which involves an inherently stable and orderly cycling of compression and cooling in the central cores of clouds during the extended period of dissipation in the outer regins of gas-rich proto galaxies, culminating in a burst of efficient star formation. I demonstrate that the comoving density of GCs is comparable to that of LyA clouds at high redshift, that the energetic requirements for compression to core GC densities can be met, and that the time-scale for cooling is within obvious limits imposed by dynamical stability. This dissipative process requires there to be a large column of dissipated gas about the attractor in order to form GCs. In addition, the energy requirements for compression requires attractor masses greater than that capable of sustaining circular velocities of ~40 km/s. If this scenario is supported by numerical simulations, then by implication, the GCs were formed at modest redshifts of z~1-3. This knowledge could help to break the degeneracy between lookback time and redshift. The model is consistent with a picture of hierarchical galaxy growth over time scales of many billions of years.Comment: 7 pages. Accepted, 10 June 1999 Astrophysical Journa

Monoclonal gammopathy associated with multiple myeloma and visceral leishmaniasis in the dog: A comparison of two cases

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The Age Dependent Luminosities of the Red Giant Branch Bump, Asymptotic Giant Branch Bump, and Horizontal Branch Red Clump

Color-magnitude diagrams of globular clusters often exhibit a prominent horizontal branch (HB) and may also show features such as the red giant branch (RGB) bump and the asymptotic giant branch (AGB) bump. Stellar evolution theory predicts that the luminosities of these features will depend on the metallicity and age of the cluster. We calculate theoretical lines of 2 to 12 Gyr constant age RGB-bumps and AGB-bumps in the V(HB-Bump)--[Fe/H] diagram, which shows the brightness difference between the bump and the HB as a function of metallicity. In order to test the predictions, we identify giant branch bumps in new Hubble Space Telescope color-magnitude diagrams for 8 SMC clusters. First, we conclude that the SMC cluster bumps are RGB-bumps. The data for clusters younger than ~6 Gyr are in fair agreement the relative age dependent luminosities of the HB and RGB-bump. The V(HB-Bump)--[Fe/H] data for clusters older then ~6 Gyr demonstrate a less satisfactory agreement with our calculations. We conclude that ~6 Gyr is a lower bound to the age of clusters for which the Galactic globular cluster, age independent V(HB-Bump)--[Fe/H] calibration is valid. Application of the V(HB-bump)--[Fe/H] diagram to stellar population studies is discussed.Comment: Accepted for publication in the Astrophysical Journal, 30 pages, Latex aaspp4.sty, including 7 postscript figure

The Second-Parameter Effect in Metal-Rich Globular Clusters

Recent Hubble Space Telescope observations have found that the horizontal branches (HB's) in the metal-rich globular clusters NGC 6388 and NGC 6441 slope upward with decreasing B-V. Such a slope is not predicted by canonical HB models and cannot be produced by either a greater cluster age or enhanced mass loss along the red-giant branch (RGB). The peculiar HB morphology in these clusters may provide an important clue for understanding the second-parameter effect. We have carried out extensive evolutionary calculations and numerical simulations in order to explore three non-canonical scenarios for explaining the sloped HB's in NGC 6388 and NGC 6441: i) A high cluster helium abundance scenario, where the HB evolution is characterized by long blue loops; ii) A rotation scenario, where internal rotation during the RGB phase increases the HB core mass; iii) A helium-mixing scenario, where deep mixing on the RGB enhances the envelope helium abundance. All three of these scenarios predict sloped HB's with anomalously bright RR Lyrae variables. We compare this prediction with the properties of the two known RR Lyrae variables in NGC 6388. Other possible observational tests are suggested.Comment: 12 pages, including three embedded figures. ApJ (Letters), in pres

Variable Stars in the Unusual, Metal-Rich Globular Cluster NGC 6388

We have undertaken a search for variable stars in the metal-rich globular cluster NGC 6388 using time-series BV photometry. Twenty-eight new variables were found in this survey, increasing the total number of variables found near NGC 6388 to ~57. A significant number of the variables are RR Lyrae (~14), most of which are probable cluster members. The periods of the fundamental mode RR Lyrae are shown to be unusually long compared to metal-rich field stars. The existence of these long period RRab stars suggests that the horizontal branch of NGC 6388 is unusually bright. This implies that the metallicity-luminosity relationship for RR Lyrae stars is not universal if the RR Lyrae in NGC 6388 are indeed metal-rich. We consider the alternative possibility that the stars in NGC 6388 may span a range in [Fe/H]. Four candidate Population II Cepheids were also found. If they are members of the cluster, NGC 6388 would be the most metal-rich globular cluster to contain Population II Cepheids. The mean V magnitude of the RR Lyrae is found to be 16.85+/-0.05 resulting in a distance of 9.0 to 10.3 kpc, for a range of assumed values of for RR Lyrae. We determine the reddening of the cluster to be E(B-V)=0.40+/-0.03 mag, with differential reddening across the face of the cluster. We discuss the difficulty in determining the Oosterhoff classification of NGC 6388 and NGC 6441 due to the unusual nature of their RR Lyrae, and address evolutionary constraints on a recent suggestion that they are of Oosterhoff type II.Comment: 35 pages, 16 figures, emulateapj5/apjfonts style. Astronomical Journal, in press. We recommend the interested reader to download instead the preprint with full-resolution figures, which can be found at http://www.noao.edu/noao/staff/pritzl/clusters.htm

R705H mutation of MYH9 is associated with MYH9-related disease and not only with non-syndromic deafness DFNA17

MYH9-related disease (MYH9-RD) is a rare autosomal dominant disease caused by mutation of MYH9, the gene encoding for the heavy chain of non-muscle myosin IIA (NMMHC-IIA). MYH9-RD patients have macrothrombocytopenia and granulocyte inclusions (pathognomonic sign of the disease) containing wild-type and mutant NMMHC-IIA. During life they might develop sensorineural hearing loss, cataract, glomerulonephritis, and elevation of liver enzymes. One of the MYH9 mutations, p.R705H, was previously reported to be associated with DFNA17, an autosomal dominant non-syndromic sensorineural hearing loss without any other features associated. We identified the same mutation in two unrelated families, whose four affected individuals had not only hearing impairment but also thrombocytopenia, giant platelets, leukocyte inclusions, as well as mild to moderate elevation of some liver enzymes. Our data suggest that DFNA17 should not be a separate genetic entity but part of the wide phenotypic spectrum of MYH9-RD characterized by congenital hematological manifestations and variable penetrance and expressivity of the extra-hematological features

The Luminosity Function of M3

We present a high precision, large sample luminosity function (LF) for the Galactic globular cluster M3. With a combination of ground based and Hubble Space Telescope data we cover the entire radial extent of the cluster. The observed LF is well fit by canonical standard stellar models from the red giant branch (RGB) tip to below the main sequence turnoff point. Specifically, neither the RGB LF-bump nor subgiant branch LF indicate any breakdown in the standard models. On the main sequence we find evidence for a flat initial mass function and for mass segregation due to the dynamical evolution of the cluster.Comment: 18 pages, 13 figures. ApJ, in pres