arXiv subjects

Dante Minniti

Publications and source records attributed to Dante Minniti.

220 records · Page 13Linked to original sources

arXiv1997

Radial Velocities of Globular Clusters in the Giant Elliptical Galaxy NGC 1399

We report on the radial velocity measurements of 18 globular clusters and one dE galaxy in the field of the giant elliptical galaxy NGC 1399, the dominant galaxy of the Fornax cluster. We present also the radial velocity measurements of some candidates for young and super metal-rich globular clusters, which turn out to be foreground or background objects, viz. 28 stars and 7 galaxies. The bonafide globular clusters are selected, on the basis of their magnitudes and colors, to be metal-rich. For this cluster sample we measure a mean radial velocity of v_{rad} = 1353 +/- 79 km/s, and a velocity dispersion of 338 +/- 56 km/s. Using a few different mass estimators, this implies M/L values in the range 50-130 within a radius of 28 kpc, consistent with M/L rising with radius. Our velocity dispersion estimate is intermediate between the value computed from the integrated stellar light at smaller radii, and that computed at large radii from recent X-ray observations.

astro-ph↗

arXiv1996

Imaging With STIS: Astronomy at V = 30

In February, 1997, the second Space Shuttle servicing mission to the Hubble Observatory will install the Space Telescope Imaging Spectrograph (STIS). This new instrument will greatly enhance the spectroscopic capabilities of the Hubble Space Telescope by providing a longslit format and CCD detector technology. STIS can also be used as an imager, providing an alternative to the Wide Field Planetary Camera 2. The filter set of STIS is limited and does not contain standard bandpasses, but we show here that this does not preclude useful broad band photometry. In fact, the STIS photometric system may be preferable to that of WFPC2 for certain applications where a faint limiting magnitude and fine spatial resolution are overriding considerations. The two optical wide-band choices on STIS are a clear aperture and a longpass ($λ> 5500$Å) filter. We define an effective shortpass filter from the difference of these, making two-color photometry possible with STIS. We present preliminary transformations between the STIS system and Cousins BVRI bandpasses, showing that these transformations are very well-behaved over almost all temperatures, luminosities, and abundances for normal stars. In an 8-orbit cycle, STIS will be able to reach signal-to-noise of $\sim 5-10$ at V = 30.0 in its clear and longpass imaging modes, a significant increase in the power of HST to address a number of fundamental issues out of reach of current instrumentation capabilities on the ground or in space.

astro-ph↗

arXiv1996

Dwarf Galaxies Also Have Stellar Halos

We present evidence for the existence of an old stellar halo in the dwarf irregular galaxy WLM, an isolated member of the Local Group. The halo consists of population-II stars, with low metallicities and age $\geq 10^{10}$yr. The finding of a halo in a dwarf irregular galaxy argues for a generic mode of galaxy formation that requires a halo in the presence of a disk, regardless of galaxy size. This implies that formation mechanisms are similar along the spiral Hubble sequence, and favors the scenarios where the formation takes place during the original collapse and accretion of the protogalactic gas clouds. Halo formation also appears not necessarily to be related to the presence of a bulge or a nucleus, since WLM lacks both of these components.

astro-ph↗

arXiv1995

Field Stars and Clusters of the Galactic Bulge: Implications for Galaxy Formation

The results of a kinematic study of the Galactic bulge based on spectra of red giants in fields at projected distances of 1.4-1.8 kpc from the Galactic center are presented. There is a marked trend of kinematics with metallicity, in the sense that the more metal-poor population has higher velocity dispersion and lower rotation velocity than the metal-rich population. The K giants more metal--poor than [Fe/H] = -1 have halo-like kinematics, with no significant rotation and sigma = 120 km/s independent of Galactocentric distance. The velocity dispersion of the giants with [Fe/H] > -1 decreases with increasing Galactocentric distance, and this population is rotating with V = 0.9 km/s/degree. The present observations, together with the observed metallicity gradient imply bulge formation through dissipational collapse. In such a picture, low angular momentum gas lost from the formation of the halo was deposited in the bulge. The bulge would then be younger than the halo. Observations of the Galactic globular cluster system are consistent with this picture, if we associate the metal-rich globular clusters within 3 kpc of the Galactic center with the bulge rather than with the thick disk or halo. Data on the RR Lyr in Baade's window are also consistent with this picture if these stars are considered part of the inner halo rather than the bulge.

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