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Aims. In this article we describe the search for white dwarfs (WDs) in the multi-band photometric data of the Capodimonte deep field survey.

Aims.Our goal is to recover the Galactic halo spatial density by means of field stars. To this aim, we have applied a new technique to the Capodimonte Deep Field (OACDF, Alcalá et al. 2004), as a pilot study in view of the VLT Survey Telescope (VST) stellar projects. Considering this unique chance to collect deep and wide-field photometry with the VST, our method may represent a useful tool towards definitive mapping of the Galactic halo.

Aims.This paper develops a method for obtaining the star formation histories of a mixed, resolved population through the use of color-magnitude diagrams (CMDs). The method provides insight into the local star formation rate, analyzing the observations of the Hipparcos satellite through a comparison with synthetic CMDs computed for different histories with an updated stellar evolution library.

This note presents theoretical color-magnitude diagrams (CMDs) and metallicity evolution for Galactic multipopulation models coupled to stellar evolution models for systems undergoing stripping and re-accretion of ambient material, called “open” systems in our recent studies (Valle et al. 2005, A&A, 435, 551). We show that the observables for such systems, in particular those related to the recovered star formation as a function of time, are ambiguous – systems with non-monotonic star formation rates can appear as either bursting systems or galaxies with a hiatus in the star formation.

We present deep, accurate, and homogeneous multiband optical (U, B, V, I) photometry of the Carina dwarf spheroidal galaxy, based on more than 4000 individual CCD images from three different ground-based telescopes. Special attention was given to the photometric calibration, and the precision for the B, V, and Ibands is generally better than 0.01 mag. We have performed detailed comparisons in the V, B- V, and V, B- Icolor-magnitude diagrams (CMDs) between Carina and three old, metal-poor Galactic globular clusters (GGCs, M53, M55, M79). We find that only the more metal-poor GCs (M55, [Fe/H] = -1.85; M53, [Fe/H] = -2.02 dex) provide a good match with the Carina giant branch. We have performed a similar comparison in the V, V- ICMD with three intermediate-age clusters (IACs) of the Small Magellanic Cloud (Kron 3, NGC 339, Lindsay 38). We find that the color extent of the subgiant branch (SGB) of the two more metal-rich IACs (Kron 3, [Fe/H] = -1.08; NGC339, [Fe/H] = -1.36 dex) is smaller than the range among Carina's intermediate-age stars. Moreover, the slope of the RGB of these two IACs is shallower than the slope of the Carina RGB. However, the ridge line of the more metal-poor IAC (Lindsay 38, [Fe/H] = -1.59 dex) agrees quite well with the Carina intermediate-age stars. These findings indicate that Carina's old stellar population is metal-poor and appears to have a limited spread in metallicity (?[Fe/H] = 0.2-0.3 dex). The Carina's intermediate-age stellar population can hardly be more metal-rich than Lindsay 38, and its spread in metallicity also appears modest. We also find that the synthetic CMD constructed assuming a metallicity spread of 0.5 dex for the intermediate-age stellar component predicts evolutionary features not supported by observations. In particular, red clump stars should attain colors that are redder than red giant stars, but this is not seen. These results are at odds with recent spectroscopic investigations suggesting that Carina stars cover a broad range in metallicity (?[Fe/H] ? 1-2 dex). We also present a new method to estimate the metallicity of complex stellar systems using the difference in color between the red clump and the middle of the RR Lyrae instability strip. The observed colors of Carina's evolved stars indicate a metallicity of [Fe/H] = -1.70 ± 0.19 dex, which agrees quite well with spectroscopic measurements.

Aims.We present an application of the Richardson-Lucy algorithm to the analysis of color?magnitude diagrams by converting the CMD into an image and using a restoring point spread function function (psf) derived from the known, often complex, sources of error.Methods.We show numerical experiments that demonstrate good recovery of the original image and establish convergence rates for ideal cases with single Gaussian uncertainties and poisson noise using a ?2 statistic. About 30?50 iterations suffice. As an application, we show the results for a particular case, the Hipparcos sample of the solar neighborhood where the uncertainties are mainly due to parallax which we model with a composite weighted Gaussian using the observed error distributions. The resulting psf has a slightly narrower core and broader wings than a single Gaussian. The reddening and photometric errors are considerably reduced by restricting the sample to within 80 pc and to MV ?3.5.Results.We find that the recovered ?image?, which has a narrower, better defined main sequence and a more clearly defined red giant clump, can be used as input to stellar evolution modeling of the star formation rate in the solar vicinity and, with more contributing uncertainties taken into account, for general Galactic and extragalactic structure and population studies.

We present J,H,Ksphotometry from the the Multi conjugate Adaptive optics Demonstrator (MAD), a visitor instrument at the VLT, of a resolved stellar population in a small crowded field in the bar of the Large Magellanic Cloud near the globular cluster NGC 1928. In a total exposure time of 6, 36 and 20 min, magnitude limits were achieved of J~ 20.5 mag, H~ 21 mag, and Ks~ 20.5 mag respectively, with S/N> 10. This does not reach the level of the oldest Main Sequence Turnoffs, however the resulting Colour–Magnitude Diagrams are the deepest and most accurate obtained so far in the infrared for the LMC bar. We combined our photometry with deep optical photometry from the Hubble Space Telescope/Advanced Camera for Surveys, which is a good match in spatial resolution. The comparison between synthetic and observed CMDs shows that the stellar population of the field we observed is consistent with the star formation history expected for the LMC bar, and that all combinations of IJHKsfilters can, with some care, produce the same results. We used the red clump magnitude in Ksto confirm the LMC distance modulus as, μ0= 18.50 ± 0.06r± 0.09smag. We also addressed a number of technical aspects related to performing accurate photometry with adaptive optics images in crowded stellar fields, which has implications for how we should design and use the Extremely Large Telescopes of the future for studies of this kind.

We present a detailed study of the dwarf galaxy VV124 (UGC4879), recently recognized as a remarkably isolated member of the Local Group. We have obtained deep (r≃ 26.5) wide-field (23′ × 23′) g,r photometry of individual stars with the LBC camera at the Large Binocular Telescope under sub-arcsec seeing conditions. The color–magnitude diagram suggests that the stellar content of the galaxy is dominated by an old, metal-poor population, with a significant metallicity spread. A very clean detection of the RGB tip allows us to derive an accurate distance of D= 1.3 ± 0.1 Mpc. Combining surface photometry with star counts, we are able to trace the surface brightness profile of VV124 out to  ~5′ ≃ 1.9 kpc radius (where μr≃ 30 mag/arcsec2), showing that it is much more extended than previously believed. Moreover, the surface density map reveals the presence of two symmetric flattened wings emanating from the central elongated spheroid and aligned with its major axis, resembling a stellar disk seen nearly edge-on. We also present H iobservations obtained with the Westerbork Synthesis Radio Telescope (WSRT), the first ever of this object. A total amount of  ≃ 106M⊙of H igas is detected in VV124. Compared to the total luminosity, this gives a value of MHI/LV= 0.11, which is particularly low for isolated Local Group dwarfs. The spatial distribution of the gas does not correlate with the observed stellar wings. The systemic velocity of the H iin the region superposed to the stellar main body of the galaxy is Vh=  −25 km s-1. The velocity field shows substructures typical of galaxies of this size but no sign of rotation. The H ispectra indicates the presence of a two-phase interstellar medium, again typical of many dwarf galaxies.