arXiv subjects

G. De Marchi

Publications and source records attributed to G. De Marchi.

21 records · Page 2Linked to original sources

arXiv2000

The mass function of NGC288

We present NICMOS NIC3 observations of the Galactic globular cluster NGC 288, taken South - East at 2.4 times the cluster's half-light radius in the J and H bands. We have detected the cluster main sequence down to J~25 and H~24. The corresponding luminosity function covers the range 3<M_H<9 and peaks at M_H~6.8. The theoretical tracks of Baraffe et al. (1997) at [Fe/H]=-1.3 give a mass function which is best fitted by a log-normal distribution with characteristic mass m_c=0.42 Msolar and a standard deviation sigma=0.35. This result is fully consistent with the global mass function derived by Paresce & De Marchi (2000) for a sample of 12 globular clusters with very different dynamical histories, thus confirming that near the cluster's half-light radius the mass function appears ``undistorted'' by evaporation or tidal interactions with the Galaxy and should then reflect the initial mass function.

astro-ph↗

arXiv1998

The mass function of M4 from near IR and optical HST observations

Deep images of the galactic globular cluster M4 taken at various locations with the NIC3 and the WFPC2 cameras on HST were used to derive detailed local optical and near IR luminosity functions. White dwarfs have been detected for the first time on a color sequence at constant luminosity in the F110W band. Transformation of the observed luminosity functions into mass functions via the most up to date theoretical mass luminosity relations currently available results in best fit local mass functions, that consist of a power-law with single exponent x = -0.8 for the inner regions and a two-segment power-law which rises with x = 1 down to M_{814}=8.5 and then drops all the way to the detection limit with x = -0.3 for the outer regions.

astro-ph↗

arXiv1998

The Resolved Stellar Population of the Post-Starburst Galaxy NGC 1569

We present WFPC2-HST photometry (in the F439W and F555W bands) of the resolved stars in NGC 1569. The derived color-magnitude diagram (CMD) contains 2800 objects down to the 26th mag, and is complete down to the 23rd. Adopting the literature distance modulus and reddening, the CMD samples stars more massive than 4 Mo, corresponding to a look-back time of 0.15 Gyr approximately. The data are compared to synthetic CMDs to derive the recent star formation history in NGC 1569. It is found that the observed field has experienced a global burst of star formation (SF) lasting at least 0.1 Gyr, and ended a few Myr ago. During the burst, the SF rate was approximately constant, and, if quiescent periods occurred, they lasted less than 10 Myr. The level of the SF rate was very high: 0.5 Mo/yr for a Salpeter IMF, in stars with mass ranging from 0.1 to 120 Mo. When scaled for the surveyed area, the SF rate is approximately 100 times larger than found in the most active dwarf irregulars in the Local Group. The data are consistent with a Salpeter IMF, or slightly steeper exponents. We discuss the implications of our results in the general context of the evolution of dwarf galaxies.

astro-ph↗