arXiv subjects

S. R. Zaggia

Publications and source records attributed to S. R. Zaggia.

4 recordsLinked to original sources

arXiv2000

Use of DPOSS data to study globular cluster halos: an application to M 92

We exploited the large areal coverage offered by the DPOSS to analyze the outermost regions of the galactic globular cluster M 92. Two independent photometric reduction programs (SKICAT and DAOPHOT) were used to construct a color-magnitude diagram and a surface density profile for this cluster, based on J- and F-band DPOSS plates. A strong similarity has been found in the performance of the two programs in the low--crowded outermost cluster regions. After removing the background contribution, we obtained the cluster outer surface density profile down to a surface brightness magnitude of mu_V ~ 31 mag/sq.arcsec and matched it with the inner profile of Trager et al. 1995. The profile shapes match very well: since our data are uncalibrated, the shift in magnitude between the profiles has been also used to calibrate our profile. The analysis shows that the cluster has an extra tidal halo extending out to ~ 30 arcmin from the cluster center at a 3 sigma level over the background noise. This halo is revealed to be almost circular.

astro-ph↗

arXiv1997

The Luminosity and Mass Function of the Globular Cluster NGC1261

I-band CCD images of two large regions of the Galactic globular cluster NGC 1261 have been used to construct stellar luminosity functions (LF) for 14000 stars in three annuli from 1.4' from the cluster center to the tidal radius. The LFs extend to M_I~8 and tend to steepen from the inner to the outer annulus, in agreement with the predictions of the multimass King-Michie model that we have calculated for this cluster. The LFs have been transformed into mass functions. Once corrected for mass segregation the global mass function of NGC 1261 has a slope x_0=0.8+/-0.5

astro-ph↗

arXiv1997

Pal 1: Another Young Galactic Halo Globular Cluster?

Deep V and I CCD images of the loosely populated Galactic globular cluster Pal 1 and the surrounding field have been obtained with the INT. A color magnitude diagram down to V(lim) ~ 24, and a luminosity function complete down to V(lim) ~ 23.25 have been constructed. Adopting a reddening E(V-I)=0.20+/-0.04 and comparing the CMD of Pal 1 with 47 Tucanae, we obtain a distance modulus (m-M)o=15.25+/-0.25, indicating that Pal 1 is located 3.7+/-0.4 kpc above the Galactic disc and 17.3+/-1.6 kpc from the Galactic center. Comparison with 47 Tuc and M71 shows that Pal 1 must be significantly younger. The best fitting isochrones (Bertelli et al, 1994) give an age between 6.3 and 8 Gyrs, which would make Pal 1 the youngest Galactic globular cluster so far identified, casting some doubt on the real nature of this object. The luminosity function shows some evidence for mass segregation, consistent with the very short relaxation time. The global mass function can be fitted with a power law of slope x=-1.4+/-0.7. This mass function is anomalously flat, suggesting either a strong dynamical evolution or an initial mass function significantly different from most of the other halo globular clusters. A discussion on the possible nature of Pal 1 is presented.

astro-ph↗

arXiv1994

Major axis kinematics of 15 early-type galaxies in the Fornax cluster

Major axis rotation curves and velocity dispersions profiles, extending out to about one effective radius, are presented for 15 ellipticals and S0's out of the photometric sample of Fornax cluster galaxies studied by Caon \etal\ (1994). A brief description of the spectroscopic and photometric characteristics of each galaxy is provided, together with a comparison with previous studies. Six of the nine E's are possibly misclassified S0's or ellipticals harboring a disk-like component. Two galaxies (NGC~1399 and 1404) show a hint of counter-rotation. Evidence is given that the \bright\ and the \ordinary\ families of early-type galaxies, first introduced by Capaccioli \etal\ (1992), look distinct also in term of the anisotropy parameter $(\Vm/σ)^*$.

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