What do High Redshift Galaxy Clusters Look Like?

2009

We derive new calibrations that relate the mean J-Ks photometric colors of red giant branch (RGB) stars at MKs=-5.5 and -5.0 with cluster metallicity. The new calibrations are derived using a sample of intermediate age (1--8 Gyr) clusters in the Large and Small Magellanic Clouds, with the JHKs photometry taken from the SIRIUS photometric survey of the Magellanic Clouds. Cluster metallicities are literature data, obtained either from the high resolution or infrared calcium triplet spectroscopy of individual RGB stars. We find systematic differences between the RGB color vs. metallicity relations derived in this work and those determined by Valenti et al. (2004), the latter ones obtained for a sample of old Galactic globular clusters. In terms of age, this discrepancy corresponds to ˜ 5 Gyr and therefore can be attributed to the age difference between the two cluster samples used in the derivation of the corresponding RGB color vs. metallicity relations.

International Astronomical Union Colloquium, 1993

Among 67 early A-type stars at high galactic latitudes, selected to have both small m1and large c1Strömgren photometric indices, we find about one third to have quite normal dwarf or subgiant spectra at MK classification dispersion. Those stars with peculiarities included 10 newλBootis stars, though none of these appeared significantly evolved. We wonder whether some of the metal-weak dwarf stars in our set may be field horizontal-branch equivalents of the blue, downward-curving, low-luminosity end of the blue horizontal-branch stars.

1998

Dans cet article, nous proposons une approche qui combine les méthodes statistiques avancées et la flexibilité des approches interactives manuelles en clustering visuel. Nous présentons l'interface Semi-Supervised Visual Clustering (SSVC). Sa contribution principale est l'apprentissage d'une métrique de projection optimale pour la visualisation en coordonnées en étoiles ainsi que pour l'extension 3D que nous avons développée. La métrique de distance de projection est apprise à partir des retours de l'utilisateur soit en termes de similarité/dissimilarité entre les items, soit par l'annotation directe. L'interface SSVC permet, de plus, une utilisation hybride dans laquelle un ensemble de paramètres sont manuellement fixés par l'utilisateur tandis que les autres paramètres sont déterminés par un algorithme de distance optimale.

2001

The Astrophysical Journal, 1991

Publications of the Astronomical Society of Japan, 1981