M22: A [Fe/H] Abundance Range Revealed

Intermediate resolution spectra at the Ca II triplet have been obtained for 55 candidate red giants in the field of the globular cluster M22 with the VLT/FORS instrument. Spectra were also obtained for a number of red giants in standard globular clusters to provide a calibration of the observed line strengths with overall abundance [Fe/H]. For the 41 M22 member stars that lie within the V-V_HB bounds of the calibration, we find an abundance distribution that is substantially broader than that expected from the observed errors alone. We argue that this broad distribution cannot be the result of differential reddening. Instead we conclude that, as has long been suspected, M22 is similar to omega Cen in having an intrinsic dispersion in heavy element abundance. The observed M22 abundance distribution rises sharply to a peak at [Fe/H] = -1.9 with a broad tail to higher abundances: the highest abundance star in our sample has [Fe/H] = -1.45 dex. If the unusual properties of omega Cen have their origin in a scenario in which the cluster is the remnant nucleus of a disrupted dwarf galaxy, then such a scenario likely applies also to M22.Comment: 29 pages, 9 figures, accepted for publication in the Astrophysical Journa

CN Bimodality at Low Metallicity: The Globular Cluster M53

We present low resolution UV-blue spectroscopic observations of red giant stars in the globular cluster M53 ([Fe/H]=-1.84), obtained to study primordial abundance variations and deep mixing via the CN and CH absorption bands. The metallicity of M53 makes it an attractive target: a bimodal distribution of 3883 angstrom CN bandstrength is common in moderate- and high-metallicity globular clusters ([Fe/H] > -1.6) but unusual in those of lower metallicity ([Fe/H] < -2.0). We find that M53 is an intermediate case, and has a broad but not strongly bimodal distribution of CN bandstrength, with CN and CH bandstrengths anticorrelated in the less-evolved stars. Like many other globular clusters, M53 also exhibits a general decline in CH bandstrength and [C/Fe] abundance with rising luminosity on the red giant branch.Comment: 8 pages including 11 figures and 1 table, accepted by PAS

The distance of M33 and the stellar population in its outskirts

We present deep V,I photometry of two $9.4' x 9.4' field in the outer regions of the M33 galaxy. We obtain a robust detection of the luminosity of the Red Giant Branch Tip (I{TRGB}=20.72 +- 0.08) from which we derived a new estimate of the distance modulus of M33, (m-M)_0=24.64 +- 0.15, corresponding to a distance D=847 +- 60 Kpc. By comparison of the color and magnitude of the observed Red Giant Branch stars with ridge lines of template globular clusters we obtained the photometric metallicity distribution of the considered fields in three different metallicity scales. The derived metallicity distributions are very similar over a range of distances from the galactic center 10' <= R <= 33', and are characterized by a well defined peak at [M/H] ~ -0.7 ([Fe/H] ~ -1.0, in the Zinn & West scale) and a weak metal-poor tail reaching [M/H] ~ -2.0. Our observations demonstrate that Red Giant Branch and Asymptotic Giant Branch stars have a radial distribution that is much more extended than the young MS stars associated with the star-forming disc.Comment: 10 pages,10 figures,accepted for publication in Astronomy & Astrophysic

Local Surface Density of the Galactic Disk from a 3-D Stellar Velocity Sample

We have re-estimated the surface density of the Galactic disk in the solar neighborhood within $\pm$ 0.4 kpc of the Sun using parallaxes and proper motions of a kinematically and spatially unbiased sample of 1476 old bright red giant stars from the Hipparcos catalog with measured radial velocities from Barbier-Brossat & Figon (2000). We determine the vertical distribution of the red giants as well as the vertical velocity dispersion of the sample, (14.4 $\pm$ 0.26 km/sec), and combine these to derive the surface density of gravitating matter in the Galactic disk as a function of the galactic coordinate $z$. The surface density of the disk increases from 10.5 $\pm$ 0.5 $M_{\odot}$ / pc$^2$ within $\pm$ 50 pc to 42 $\pm$ 6 $M_{\odot}$ / pc$^2$ within $\pm$ 350 pc. The estimated volume density of the galactic disk within $\pm$ 50 pc is about 0.1 $M_{\odot}$ / pc$^3$ which is close to the volume density estimates of the observed baryonic matter in the solar neighborhood.Comment: 24 pages, 15 figures, AJ in pres

The distance to the Sgr dwarf spheroidal galaxy from the Red Giant Branch Tip

We derived the distance to the central region of the Sagittarius dwarf spheroidal galaxy from the Red Giant Branch Tip. The obtained distance modulus is $(m-M)_0=17.10\pm0.15$, corresponding to a heliocentric distance $D=26.30\pm1.8$ Kpc. This estimate is in good agreement with the distance obtained from RR Lyrae stars of the globular cluster M~54, located in the core of the Sgr galaxy, once the most accurate estimate of the cluster metallicity and the most recent calibration of the $M_V(RRLy) vs.[Fe/H]$ relation are adopted.Comment: 6 pages, 5 figure, Accepted for publication in MNRA

The distance to the Leo I dwarf spheroidal galaxy from the Red Giant Branch Tip

We present V and I photometry of a 9.4 arcmin X 9.4 arcmin field centered on the dwarf spheroidal galaxy Leo I. The I magnitude of the tip of the Red Giant Branch is robustly estimated from two different datasets (I^{TRGB}=17.97 +0.05/-0.03). From this estimate, adopting [M/H]=-1.2 from the comparison of RGB stars with Galactic templates, we obtain a distance modulus (m-M)_0=22.02 +/- 0.13, corresponding to a distance D=254 +16/-19 Kpc.Comment: 6 pages, 5 figures, Fig. 1 and 2 provided in low resolution version. Latex. Accepted for publication by MNRA