The periods and the light curves of 12 variable stars of the globular cluster M92 have been studied analyzing 176 plates obtained with the 60 cm reflector of Bologna Observatory from 1964 to 1966. Combining the results of the present observations with Hachenberg's (1925, 1933, 1934) and Nassau's (1936), the periods were improved and the O-C diagrams for 9 variables were traced. A parabola well represents the residuals of the variables No. 3, 8 and 11. Variable 9 is likely not strictly periodic.
110 plates of the globular cluster M68, taken during 1951 to 1953 with the 24-inch reflector of the station of Lojano, have been the subject of a photometric investigation.
20 CCD images of the globular cluster M68, taken during 14th - 17th April 1989 with the 1.5m Danish telescope in La Silla, have been the subject of a photometric investigation.
We present the results of the application of the Image Subtraction Method (ISM) to the CCD observations of the central region of globular cluster M53. We have obtained good quality light curves of the 23 previously known RR Lyrae stars in this cluster. We have also confirmed the variability of ten RR Lyrae candidates discovered by Kravtsov. Moreover, we have found four new variables of this type in the core of the cluster. Altogether, the light curves have been obtained for 37 RR Lyrae stars. We also report the discovery of variations in six cluster bright giants.
The second parameter (the first being metallicity) defining the distribution of stars on the horizontal branch (HB) of globular clusters (GCs) has long been one of the major open issues in our understanding of the evolution of normal stars. Large photometric and spectroscopic databases are now available: they include large and homogeneous sets of colour-magnitude diagrams, cluster ages, and homogeneous data about chemical compositions from our FLAMES survey. We use these databases to re-examine this issue. Methods. We use the photometric data to derive median and extreme (i.e., the values including 90% of the distribution) colours and magnitudes of stars along the HB for about a hundred GCs. We transform these into median and extreme masses of stars on the HB, using the models developed by the Pisa group, and taking into account evolutionary effects. We compare these masses with those expected at the tip of the red giant branch (RGB) to derive the total mass lost by the stars.
We present the first part of the first large and homogeneous CCD color-magnitude diagram (CMD) data base, comprising 52 nearby Galactic globular clusters (GGC) imaged in the V and I bands using only two telescopes (one for each hemisphere). The observed clusters represent 75% of the known Galactic globulars with (m-M)V<=16.15mag, cover most of the globular cluster metallicity range (-2.2<=[Fe/H]<=-0.4), and span Galactocentric distances from ~1.2 to ~18.5kpc. In this paper, the CMDs for the 39 GGCs observed in the southern hemisphere are presented. The remaining 13 northern hemisphere clusters of the catalog are presented in a companion paper. For four clusters (NGC 4833, NGC 5986, NGC 6543, and NGC 6638) we present for the first time a CMD from CCD data. The typical CMD span from the 22^nd^ V magnitude to the tip of the red giant branch. Based on a large number of standard stars, the absolute photometric calibration is reliable to the ~0.02mag level in both filters. This catalog, because of its homogeneity, is expected to represent a useful data base for the measurement of the main absolute and relative parameters characterizing the CMD of GGCs.
In this paper we present the second and final part of a large and photometrically homogeneous CCD color-magnitude diagram (CMD) data base, comprising 52 nearby Galactic globular clusters (GGC) imaged in the V and I bands. The catalog has been collected using only two telescopes (one for each hemisphere).
The rest-frame near-IR spectra of intermediate age (1-2Gyr) stellar populations are dominated by carbon based absorption features offering a wealth of information. Yet, spectral libraries that include the near-IR wavelength range do not sample a sufficiently broad range of ages and metallicities to allow for accurate calibration of stellar population models and thus the interpretation of the observations. In this paper we investigate the integrated J- and H-band spectra of six intermediate age and old globular clusters in the Large Magellanic Cloud (LMC).
The Chandra/ACIS-I detectors observed NGC 5139 in imaging mode for two continuous periods (2000 January 24 02:15-09:46 and January 25 04:33-17:24 TT) for a total exposure of ~68.6ks. We combined the two observations and analyzed them as one. We searched for point sources using CELLDETECT, using only the 0.1-2.5keV energy range, excluding regions less than 16 pixels from the detector edges and keeping only sources with signal-to-noise ratio (S/N)>5.0. We find 40 X-ray point sources over the four ACIS-I chips and chip S2 of ACIS-S, which are numbered in order of decreasing S/N in Table 1.
We have used new wide-field imaging with the Magellan IMACS camera to search for globular cluster (GC) candidates around NGC 5128, the nearest giant E galaxy. The imaging data are in the B and R broadband filters and cover a 1.55 deg^2^ field centered on the galaxy, corresponding to an area about 90*90kpc^2^ at the distance of NGC 5128. All the fields were taken under exceptionally high-quality seeing conditions (FWHM=0.4-0.5" in R). Using this material we are able, for the first time in the literature, to construct a homogeneous list of GC candidates covering a wide span of the NGC 5128 halo and unusually free of field contaminants (foreground stars and faint background galaxies). Selecting the measured objects by color, magnitude, ellipticity, and profile size gives us a final catalog of 833 new high-quality GC candidates brighter than R=21 (0.8mag fainter than the standard GC luminosity function turnover point). The measured positions have better than 0.2" precision in both coordinates.
