NGC 5011C: an overlooked dwarf galaxy in the Centaurus A group

(abridged) We report the discovery of a previously unnoticed member of the Centaurus A Group, NGC 5011C. While the galaxy is a well known stellar system listed with a NGC number its true identity remained hidden because of coordinate confusion and wrong redshifts in the literature. NGC 5011C attracted our attention since, at a putative distance of 45.3 Mpc, it would be a peculiar object having a very low surface brightness typical of a dwarf galaxy, and at the same time having the size of an early-type spiral or S0 galaxy. To confirm or reject this peculiarity, our immediate objective was to have the first reliable measurement of its recession velocity. The observations were carried out with EFOSC2 at the 3.6m ESO telescope. We found that NGC 5011C has indeed a low redshift of v_sun=647+/-96 km/sec and thus is a nearby dwarf galaxy rather than a member of the distant Centaurus cluster as believed for the past 23 years. Rough distance estimates based on photometric parameters also favor this scenario. As a byproduct of our study we update the redshift for NGC 5011B at v_sun=3227+/-50 km/sec. Applying population synthesis techniques, we find that NGC 5011B has a luminosity-weighted age of 4+/-1 Gyr and a solar metallicity, and that the luminosity-weighted age and metallicity of NGC 5011C are 0.9+/-0.1 Gyr and 1/5 solar. Finally we estimate a stellar mass of NGC 5011C comparable to that of dwarf spheroidal galaxies in the Local Group.Comment: 13 pages, 6 figures, accepted by the Astronomical Journa

Photometric catalog of nearby globular clusters (I)

We present the first part of the first large and homogeneous CCD color-magnitude diagram (CMD) data base, comprising 52 nearby Galactic globular clusters (GGC) imaged in the V and I bands using only two telescopes (one for each hemisphere). The observed clusters represent 75% of the known Galactic globulars with (m-M)v<=16.15 mag, cover most of the globular cluster metallicity range (-2.2 <= [Fe/H] <= -0.4), and span Galactocentric distances from ~1.2 to ~18.5 kpc. In this paper, the CMDs for the 39 GGCs observed in the southern hemisphere are presented. The remaining 13 northern hemisphere clusters of the catalog are presented in a companion paper. For four clusters (NGC 4833, NGC 5986, NGC 6543, and NGC 6638) we present for the first time a CMD from CCD data. The typical CMD spans from the 22nd V magnitude to the tip of the red giant branch. Based on a large number of standard stars, the absolute photometric calibration is reliable to the ~0.02 mag level in both filters. This catalog, because of its homogeneity, is expected to represent a useful data base for the measurement of the main absolute and relative parameters characterizing the CMD of GGCs.Comment: 34 pages, 108 figures, Astronomy & Astrophysics Supplement Series, in press. Full resolution figures can be obtained from the authors upon reques

Chemical composition of the stellar cluster Gaia1: No surprise behind Sirius

Indexación: Web of Science; Scopus.We observed six He-clump stars of the intermediate-Age stellar cluster Gaia1 with the MIKE/Magellan spectrograph. A possible extra-galactic origin of this cluster, recently discovered thanks to the first data release of the ESA Gaia mission, has been suggested, based on its orbital parameters. Abundances for Fe, α, proton-And neutron-capture elements have been obtained. We find no evidence of intrinsic abundance spreads. The iron abundance is solar ([FeI/H] = + 0.00 ± 0.01; σ = 0.03 dex). All the other abundance ratios are generally solar-scaled, similar to the Galactic thin disk and open cluster stars of similar metallicity. The chemical composition of Gaia1 does not support an extra-galactic origin for this stellar cluster, which can be considered as a standard Galactic open cluster.https://www.aanda.org/articles/aa/abs/2017/07/aa31009-17/aa31009-17.htm

Morphological transformation of NGC 205?

NGC 205 is a dwarf elliptical galaxy which shows many features that are more typical of disk galaxies, and our recent study of the central stellar population has added another peculiarity. In the central regions, star formation has been on-going continuously for a few hundred Myr, until ca. 20 Myr ago, perhaps fed by gas funneled to the center in the course of morphological transformation. In this contribution we use a deep, wide-field image obtained at a scale of 2"/px to show that subtle structures can be detected in and near the body of the dwarf galaxy. The southern tidal tail can be mapped out to unprecedented distances from the center, and we suggest that the northern tail is partially hidden behind a very extended dust lane, or ring, belonging to M31. A spiral pattern emerges across the body of the galaxy, but it might be explained by another M31 dust filament.Comment: 2 pages, 1 figure, poster contributed to IAU Symposium 262, Stellar Populations -- Planning for the Next Decade, G. Bruzual & S. Charlot, ed

The relative ages of LMC old clusters, and the case of NGC 1841

Using archival HST/WFPC2 imaging of 7 LMC globular clusters, and following the methods outlined in our previous study, we have reached the tightest constrain so far on their age dispersion, which cannot be greater than ~ 0.5 Gyr. We also confirm earlier results that their average age is comparable to that of the metal-poor Galactic globulars. Evidence is also provided that NGC 1841 is younger than the rest of LMC globulars.Comment: 2 pages, 1 figure, requires newpasp.sty. To appear in "New Horizons in Globular Cluster Astronomy", Giampaolo Piotto, George Meylan, George Djorgovski and Marco Riello, ed

The red giant branches of Galactic globular clusters in the [(V-I)o,Mv] plane: metallicity indices and morphology

The purpose of this study is to carry out a thorough investigation of the changes in morphology of the red giant branch (RGB) of Galactic globular clusters (GGC) as a function of metallicity, in the V,I bands. To this aim, two key points are developed in the course of the analysis. (a) Using our photometric V,I database for Galactic globular clusters (the largest homogeneous data sample to date; Rosenberg et al. 1999) we measure a complete set of metallicity indices, based on the morphology and position of the red-giant branch. In particular, we provide here the first calibration of the S, DV_(1.1) and DV_(1.4) indices in the (V-I,V) plane. We show that our indices are internally consistent, and we calibrate each index in terms of metallicity, both on the Zinn & West (1984) and the Carretta & Gratton (1997) scales. Our new calibrations of the (V-I)o,g, DV_(1.2), (V-I)_(-3.0) and (V-I)_(-3.5) indices are consistent with existing relations. (b) Using a grid of selected RGB fiducial points, we define a function in the {(V-I)o,Mi,[Fe/H]} space which is able to reproduce the whole set of GGC giant branches in terms of a single parameter (the metallicity). As a first test, we show that the function is able to predict the correct trend of our observed indices with metallicity. The usage of this function will improve the current determinations of metallicity and distances within the Local Group, since it allows to easily map [(V-I)o,Mi] coordinates into {[Fe/H],Mi} ones. To this aim the ``synthetic'' RGB distribution is generated both for the currently used Lee et al. (1990) distance scale, and for the most recent results on the RR Lyr distance scale.Comment: 14 pages, 11 PS figures, accepted for publication in Astronomy & Astrophysics, main journa