RR Lyrae variables in the globular cluster M3 (NGC5272). I. BVI CCD photometry

New BVI CCD photometry is presented for 60 RR Lyrae variables in the globular cluster M3. Light curves have been constructed and ephemerides have been (re)-derived for all of them. Four stars (i.e. V29, V136, V155 and V209), although recognized as variables, had no previous period determinations. Also, the period derived for V129 is significantly different from the one published by Sawyer-Hogg (1973). Light curve parameters, i.e. mean magnitudes, amplitudes and rise-times, have been derived. The discussion of these results in the framework of the stellar evolution and pulsation theories will be presented in a forthcoming paper.Comment: 19 pages, latex, uses mn.sty, 12 encapsulated figures, to be published in MNRAS, text and figures also available at http://www.bo.astro.it/bap/BAPhome.html or via anonymous ftp at ftp://boas3.bo.astro.it/bap/files (bap98-12-textfig.ps

The extended structure of the remote cluster B514 in M31. Detection of extra-tidal stars

We present a study of the density profile of the remote M31 globular cluster B514, obtained from HST/ACS observations. Coupling the analysis of the distribution of the integrated light with star counts we can reliably follow the profile of the cluster out to r~35", corresponding to ~130pc. The profile is well fitted, out to ~15 core radii, by a King Model having C=1.65. With an estimated core radius r_c=0.38", this corresponds to a tidal radius of r_t~17" (~65pc). We find that both the light and the star counts profiles show a departure from the best fit King model for r>~8" - as a surface brightness excess at large radii, and the star counts profile shows a clear break in correspondence of the estimated tidal radius. Both features are interpreted as the signature of the presence of extratidal stars around the cluster. We also show that B514 has a half-light radius significantly larger than ordinary globular clusters of the same luminosity. In the M_V vs. log r_h plane, B514 lies in a region inhabited by peculiar clusters, like Omega Cen, G1, NGC2419 and others, as well as by the nuclei of dwarf elliptical galaxies.Comment: 9 pages, 6 figures. Accepted for publication in Astronomy & Astrophysic

Correlations of Globular Cluster Properties: Their Interpretations and Uses

Correlations among the independently measured physical properties of globular clusters (GCs) can provide powerful tests for theoretical models and new insights into their dynamics, formation, and evolution. We review briefly some of the previous work, and present preliminary results from a comparative study of GC correlations in the Local Group galaxies. The results so far indicate that these diverse GC systems follow the same fundamental correlations, suggesting a commonality of formative and evolutionary processes which produce them.Comment: An invited review, to appear in "New Horizons in Globular Cluster Astronomy", eds. G. Piotto, G. Meylan, S.G. Djorgovski, and M. Riello, ASPCS, in press (2003). Latex file, 8 pages, 5 eps figures, style files include

A Population of Massive Globular Clusters in NGC 5128

We present velocity dispersion measurements of 14 globular clusters in NGC 5128 (Centarus A) obtained with the MIKE echelle spectrograph on the 6.5m Magellan Clay telescope. These clusters are among the most luminous globular clusters in NGC 5128 and have velocity dispersions comparable to the most massive clusters known in the Local Group, ranging from 10 - 30 km/s. We describe in detail our cross-correlation measurements, as well as simulations to quantify the uncertainties. These 14 globular clusters are the brightest NGC 5128 globular clusters with surface photometry and structural parameters measured from the Hubble Space Telescope. We have used these measurements to derive masses and mass-to-light ratios for all of these clusters and establish that the fundamental plane relations for globular clusters extend to an order of magnitude higher mass than in the Local Group. The mean mass-to-light ratio for the NGC 5128 clusters is ~3+/-1, higher than measurements for all but the most massive Local Group clusters. These massive clusters begin to bridge the mass gap between the most massive star clusters and the lowest-mass galaxies. We find that the properties of NGC 5128 globular clusters overlap quite well with the central properties of nucleated dwarf galaxies and ultracompact dwarf galaxies. As six of these clusters also show evidence for extratidal light, we hypothesize that at least some of these massive clusters are the nuclei of tidally stripped dwarfs.Comment: ApJ Accepted, 15 pages, 9 figures, uses emulateapj.st

Deep HST-WFPC2 photometry of NGC 288. II. The Main Sequence Luminosity Function

The Main Sequence Luminosity Function (LF) of the Galactic globular cluster NGC 288 has been obtained using deep WFPC2 photometry. We have employed a new method to correct for completeness and fully account for bin-to-bin migration due to blending and/or observational scatter. The effect of the presence of binary systems in the final LF is quantified and is found to be negligible. There is a strong indication of the mass segregation of unevolved single stars and clear signs of a depletion of low mass stars in NGC 288 with respect to other clusters. The results are in good agreement with the prediction of theoretical models of the dynamical evolution of NGC 288 that take into account the extreme orbital properties of this cluster.Comment: 16 pages, 6 .ps figures. Low resolution version of fig. 1; full resolution figure soon available at http://www.bo.astro.it/bap/BAPhome.html l. Latex. emulateapj5.sty macro included. Accepted for publication by The Astronomical Journa

Photometry of the Globular Cluster NGC 5466: Red Giants and Blue Stragglers

We present wide-field BVI photometry for about 11,500 stars in the low-metallicity cluster NGC 5466. We have detected the red giant branch bump for the first time, although it is at least 0.2 mag fainter than expected relative to the turnoff. The number of red giants (relative to main sequence turnoff stars) is in excellent agreement with stellar models from the Yonsei-Yale and Teramo groups, and slightly high compared to Victoria-Regina models. This adds to evidence that an abnormally large ratio of red giant to main-sequence stars is not correlated with cluster metallicity. We discuss theoretical predictions from different research groups and find that the inclusion or exclusion of helium diffusion and strong limit Coulomb interactions may be partly responsible. We also examine indicators of dynamical history: the mass function exponent and the blue straggler frequency. NGC 5466 has a very shallow mass function, consistent with large mass loss and recently-discovered tidal tails. The blue straggler sample is significantly more centrally concentrated than the HB or RGB stars. We see no evidence of an upturn in the blue straggler frequency at large distances from the center. Dynamical friction timescales indicate that the stragglers should be more concentrated if the cluster's present density structure has existed for most of its history. NGC 5466 also has an unusually low central density compared to clusters of similar luminosity. In spite of this, the specific frequency of blue stragglers that puts it right on the frequency -- cluster M_V relation observed for other clusters.Comment: 51 pages, 21 figures, 1 electronic table, accepted to Ap

A New Version of Reimers' law of Mass Loss Based on a Physical Approach

We present a new semi-empirical relation for the mass loss of cool stellar winds, which so far has frequently been described by "Reimers' law". Originally, this relation was based solely on dimensional scaling arguments without any physical interpretation. In our approach, the wind is assumed to result from the spill-over of the extended chromosphere, possibly associated with the action of waves, especially Alfven waves, which are used as guidance in the derivation of the new formula. We obtain a relation akin to the original Reimers law, but which includes two new factors. They reflect how the chromospheric height depends on gravity and how the mechanical energy flux depends, mainly, on effective temperature. The new relation is tested and sensitively calibrated by modelling the blue end of the Horizontal Branch of globular clusters. The most significant difference from mass loss rates predicted by the Reimers relation is an increase by up to a factor of 3 for luminous late-type (super-)giants, in good agreement with observations.Comment: 12 pages, 4 figures, accepted by ApJ Letter