We present a comprehensive database of kinematic, photometric and positional information for 352 objects in the field of M87 (NGC 4486), the central giant elliptical galaxy in the Virgo cluster; the ...majority of the objects are globular clusters associated with that galaxy. New kinematic information comes from multi-slit observations with the Multi-Object Spectrograph (MOS) of the Canada-France-Hawaii Telescope, an investigation which has added 96 new velocities to and confirmed many of the earlier values in a pre-existing dataset of 256 velocities published elsewhere. The photometry, consisting of magnitudes and colors in the Washington T1, C-T1 system, is based on CCD observations made at CTIO and KPNO. The composite database represents the largest compilation of pure Population II dynamical tracers yet identified in any external galaxy; moreover, it extends to larger spatial scales than have earlier investigations. The inclusion of photometric information allows independent study of the distinct red and blue sub-populations of the bimodal GCS of M87. In a companion paper (Cote et al. 2001), we use this dataset to analyse the present dynamical state of the M87 globular cluster system, and consider the question of its interaction and formation history.
We present Washington system C,T_1 CMDs of 13 star clusters and their surrounding fields which lie in the outer parts of the LMC disk. Ages are determined by means of the magnitude difference between ...the giant branch clump and the turnoff, while metallicities are derived from the location of the giant and subgiant branches as compared to fiducial star clusters. We find that in most cases the stellar population of each star cluster is quite similar to that of the field where it is embedded. Three particular fields present remarkable properties: (i) The so far unique cluster ESO121-SC03 at ~9 Gyr has a surrounding field which shares the same properties. (ii) The field surrounding the far eastern intermediate age cluster OHSC37 is noteworthy in the sense that we do not detect any evidence of LMC stars. (iii) The fields of SL388 and SL509 present CMDs with a secondary clump ~0.45 mag fainter than the dominant intermediate age clump, suggesting a stellar population component located behind the LMC disk at a distance comparable to that of the SMC. The mean metallicity derived for the intermediate age outer disk clusters is <Fe/H>=-0.7 and for their surrounding fields <Fe/H>=-0.6. These values are significantly lower than found by Olszewski et al. (1991, AJ, 101, 515) for a sample of clusters of similar age, but are in good agreement with several recent studies. A few clusters stand out in the age--metallicity relation in the sense that they are intermediate age clusters at relatively low metallicity (Fe/H~-1).
We report the first results of a color-magnitude diagram survey of 25 candidate old LMC clusters. For almost all of the sample, it was possible to reach the turnoff region, and in many clusters we ...have several magnitudes of the main sequence. Age estimates based on the magnitude difference \(\delta T_1\) between the giant branch clump and the turnoff revealed that no new old clusters were found. The candidates turned out to be of intermediate age (1-3 Gyr) We show that the apparently old ages as inferred from integrated UBV colors can be explained by a combination of stochastic effects produced by bright stars and by photometric errors for faint clusters lying in crowded fields. The relatively metal poor candidates from the CaII triplet spectroscopy also turned out to be of intermediate age. This, combined with the fact that they lie far out in the disk, yields interesting constraints regarding the formation and evolution of the LMC disk. We also study the age distribution of intermediate age and old clusters This homogeneous set of accurate relative ages allows us to make an improved study of the history of cluster formation/destruction for ages \(>1\)Gyr. We confirm previous indications that there was apparently no cluster formation in the LMC during the period from 3-8 Gyr ago, and that there was a pronounced epoch of cluster formation beginning 3 Gyrs ago that peaked at about 1.5 Gyrs ago. Our results suggest that there are few, if any, genuine old clusters in the LMC left to be found.
We present HST WFPC2 imaging of the nearby low-surface-brightness dwarf spheroidal galaxy ESO 410-G005, which has been resolved into stars for the first time. The resulting color-magnitude diagram ...for about 2500 stars shows a red giant branch branch with a tip at I=(22.4+-0.15), which yields a distance of D=(1.9+-0.2) Mpc. ESO 410-G005 is found to be metal-poor with a mean metallicity of (-1.8+-0.4) dex estimated from its red giant branch. Upper asymptotic giant branch stars appear to be present near the center of the galaxy, indicative of a substantial, centrally concentrated intermediate-age population, unless these objects are artifacts of crowding. Previous studies did not detect ESO 410-G005 in H alpha or in HI. ESO 410-G005 is a probable member of the Sculptor group. Its linear separation from the nearest spiral, NGC 55, is 230 kpc on the sky. The deprojected separation ranges from 340 to 615 kpc depending on the assumed distance of NGC 55. ESO 410 G005 appears to be a relatively isolated dSph within the Sculptor group. Its absolute magnitude, Mv = (-12.1+-0.2) mag, its central surface brightness, mu_V = (22.7+-0.1) mag/arcsec^2, and its mean metallicity, Fe/H = (-1.8+-0.4) dex, follow the trend observed for dwarf galaxies in the Local Group. (abridged)
Focusing on the essential Baudisch, Patrick; DeCarlo, Doug; Duchowski, Andrew T. ...
Communications of the ACM,
03/2003, Letnik:
46, Številka:
3
Magazine Article
Attentive displays address the need for rendering power and computer display resolution. The five examples presented here illustrate a common goal with very different approaches to achieving it.
Focusing on the essential Baudisch, Patrick; DeCarlo, Doug; Duchowski, Andrew T ...
Communications of the ACM,
03/2003, Letnik:
46, Številka:
3
Magazine Article
Attentive displays address the need for rendering power and computer display resolution. The five examples presented here illustrate a common goal with very different approaches to achieving it.
