Browsing by Subject "double main-sequence"
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Item The ACS Survey Of Galactic Globular Clusters. III. The Double Subgiant Branch Of NGC 1851(2008-01) Milone, A. P.; Bedin, L. R.; Piotto, G.; Anderson, J.; King, I. R.; Sarajedini, A.; Dotter, A.; Chaboyer, B.; Marin-Franch, A.; Majewski, S.; Aparicio, A.; Hempel, M.; Paust, N. E. Q.; Reid, I. N.; Rosenberg, A.; Siegel, M.; Siegel, M.Photometry with the Hubble Space Telescope Advanced Camera for Surveys (HSTACS) reveals that the subgiant branch (SGB) of the globular cluster NGC 1851 splits into two well-defined branches. If the split is due only to an age effect, the two SGBs would imply two star formation episodes separated by similar to 1 Gyr. We discuss other anomalies in NGC 1851 that could be interpreted in terms of a double stellar population. Finally, we compare the case of NGC 1851 with the other two globulars known to host multiple stellar populations, and show that all three clusters differ in several important respects.Item Very Large Telescope Kinematics for Omega Centauri: Further Support for A Central Black Hole(2010-08) Noyola, Eva; Gebhardt, Karl; Kissler-Patig, Markus; Lutzgendorf, Nora; Jalali, Behrang; de Zeeuw, P. T.; Baumgardt, Holger; Gebhardt, KarlThe Galactic globular cluster. Centauri is a prime candidate for hosting an intermediate- mass black hole. Recent measurements lead to contradictory conclusions on this issue. We use VLT- FLAMES to obtain new integrated spectra for the central region of. Centauri. We combine these data with existing measurements of the radial velocity dispersion profile taking into account a new derived center from kinematics and two different centers from the literature. The data support previous measurements performed for a smaller field of view and show a discrepancy with the results from a large proper motion data set. We see a rise in the radial velocity dispersion in the central region to 22.8 +/- 1.2 km s(-1), which provides a strong sign for a central black hole. Isotropic dynamical models for. Centauri imply black hole masses ranging from 3.0 x 10(4) to 5.2 x 10(4) M(circle dot) depending on the center. The best-fitted mass is (4.7 +/- 1.0) x 10(4) M(circle dot).