Context. We present the third data release of the European Space Agency's Gaia mission, Gaia DR3.... more Context. We present the third data release of the European Space Agency's Gaia mission, Gaia DR3. This release includes a large variety of new data products, notably a much expanded radial velocity survey and a very extensive astrophysical characterisation of Gaia sources. Aims. We outline the content and the properties of Gaia DR3, providing an overview of the main improvements in the data processing in comparison with previous data releases (where applicable) and a brief discussion of the limitations of the data in this release. Methods. The Gaia DR3 catalogue is the outcome of the processing of raw data collected with the Gaia instruments during the first 34 months of the mission by the Gaia Data Processing and Analysis Consortium. Results. The Gaia DR3 catalogue contains the same source list, celestial positions, proper motions, parallaxes, and broad band photometry in the G, G BP , and G RP pass-bands already present in the Early Third Data Release, Gaia EDR3. Gaia DR3 introduces an impressive wealth of new data products. More than 33 million objects in the ranges G RVS < 14 and 3100 < T eff < 14500, have new determinations of their mean radial velocities based on data collected by Gaia. We provide G RVS magnitudes for most sources with radial velocities, and a line broadening parameter is listed for a subset of these. Mean Gaia spectra are made available to the community. The Gaia DR3 catalogue includes about 1 million mean spectra from the radial velocity spectrometer, and about 220 million low-resolution blue and red prism photometer BP/RP mean spectra. The results of the analysis of epoch photometry are provided for some 10 million sources across 24 variability types. Gaia DR3 includes astrophysical parameters and source class probabilities for about 470 million and 1500 million sources, respectively, including stars, galaxies, and quasars. Orbital elements and trend parameters are provided for some 800 000 astrometric, spectroscopic and eclipsing binaries. More than 150 000 Solar System objects, including new discoveries, with preliminary orbital solutions and individual epoch observations are part of this release. Reflectance spectra derived from the epoch BP/RP spectral data are published for about 60 000 asteroids. Finally, an additional data set is provided, namely the Gaia Andromeda Photometric Survey, consisting of the photometric time series for all sources located in a 5.5 degree radius field centred on the Andromeda galaxy. Conclusions. This data release represents a major advance with respect to Gaia DR2 and Gaia EDR3 because of the unprecedented quantity, quality, and variety of source astrophysical data. To date this is the largest collection of all-sky spectrophotometry, radial velocities, variables, and astrophysical parameters derived from both low-and high-resolution spectra and includes a spectrophotometric and dynamical survey of SSOs of the highest accuracy. The non-single star content surpasses the existing data by orders of magnitude. The quasar host and galaxy light profile collection is the first such survey that is all sky and space based. The astrophysical information provided in Gaia DR3 will unleash the full potential of Gaia's exquisite astrometric, photometric, and radial velocity surveys.
We present new empirical estimates of the ∆V bump HB parameter for 15 Galactic globular clusters ... more We present new empirical estimates of the ∆V bump HB parameter for 15 Galactic globular clusters (GGCs) using accurate and homogeneous ground-based optical data. Together with similar evaluations available in the literature, we ended
We present Ca−uvby Strömgren photometry of the Baade’s Window, including the Galactic globular c... more We present Ca−uvby Strömgren photometry of the Baade’s Window, including the Galactic globular cluster NGC 6522. We separate field and cluster stars by adopting color–color planes and proper motions. We then estimate the global metallicity of red-giants (RGs) in NGC 6522 by using a new theoretical metallicity calibration of the Strömgren index hk presented in (Calamida et al. 2011). We find that metallicities estimated by adopting the hk index and the Ca–y color are systematically more metal-rich than metallicities estimated with hk and the u–y, v–y and b–y colors. Current evidence indicate that the hk metallicity index is affected not only by the Ca abundance, but also by another source of opacity. 1 Introduction and data reduction The study of the Milky Way bulge is fundamental to understand the star formation history of the Galactic spheroid. The Milky Way bulge is indeed dominated by metal-rich old stars (t> 10 Gyr, Zoccali et al. 2003). Their metallicity distribution is ce...
We present deep multiband (F435W, F625W, and F658N) photometric data of the Globular Cluster ω Ce... more We present deep multiband (F435W, F625W, and F658N) photometric data of the Globular Cluster ω Cen collected with the Advanced Camera for Surveys on board of the Hubble Space Telescope. We identified in the (F435W-F625W, F435W) plane more than two thousand White Dwarf (WD) candidates using three out of nine available pointings. Such a large sample appears in agreement with predictions based on the ratio between WD and Horizontal Branch (HB) evolutionary lifetimes. We also detected ≈ 1600 WDs in the (F658N-F625W, F625W) plane, supporting the evidence that a large fraction of current cluster WDs are Hα bright.
We calculated new estimates of the ∆V HB parameter for 15 Galactic Globular Clusters (GGCs) using... more We calculated new estimates of the ∆V HB parameter for 15 Galactic Globular Clusters (GGCs) using accurate ground-based photometric data. We enlarged our sample with literature data and we obtained a sample of 62 GGCs covering a wide metallicity range (-2.16≤[M/H]≤-0.58 dex). To compare the data with the theory we used theoretical models from Pietrinferni et al. (2004, 2006) and two different metallicity scales. We found that the observed values are higher (∼0.4 mag) than the canonical predictions. Moreover, the discepancy increases in the Kraft & Ivans (2003, 2004) metallicity scale and it decreases in the Carretta & Gratton (1997) scale. We investigated also the impact of CNONa extreme mixture and higher He-enhanced abundance (Y = 0.30). The use of these models is not in the direction to explain the observed discrepancy.
We present three different optical and near-infrared (NIR) data sets for evolved stars in the Gal... more We present three different optical and near-infrared (NIR) data sets for evolved stars in the Galactic Globular Cluster ω Centauri . The comparison Based on observations made with the ESO Telescopes at the La Silla and Paranal Observatories, programme IDs: 63.L-0686, 64.N-0038, 68.D-0545 Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussels, Belgium Vrije Universiteit Brussel, OBSS/WE, Pleinlaan 2, B-1050 Brussels, Belgium; [email protected], [email protected] Nordic Optical Telescope, Apartado 474, E-38700 Santa Cruz de La Palma, Spain INAF-Osservatorio Astronomico di Roma, via Frascati 33, Monte Porzio Catone, Rome, Italy; [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected] Università di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Rome, Italy; [email protected], [email protected] Dipartimento di Fisica ”E. Fermi”, Univ. Pisa...
In this paper we investigate the hot end of the HB, presenting evolutionary constraints concernin... more In this paper we investigate the hot end of the HB, presenting evolutionary constraints concerning the CM diagram location and the gravity of hot HB stars. According to the adopted evolutionary scenario, we predict an upper limit for HB temperatures of about logTe = 4.45, remarkably cooler than previous estimates. We nd that such a theoretical prescription appears in good agreement with available observational data concerning both stellar temperatures and gravities. The problem of gaps in the HB distribution is nally discussed, suggesting that, at the least in the case of the cluster NGC 6752, evolutionary gaps, a bimodal distribution of CNO or stellar rotation should all play a negligible role.
The merger of two neutron stars is predicted to give rise to three major detectable phenomena: a ... more The merger of two neutron stars is predicted to give rise to three major detectable phenomena: a short burst of γ-rays, a gravitational-wave signal, and a transient optical-near-infrared source powered by the synthesis of large amounts of very heavy elements via rapid neutron capture (the r-process). Such transients, named 'macronovae' or 'kilonovae', are believed to be centres of production of rare elements such as gold and platinum. The most compelling evidence so far for a kilonova was a very faint near-infrared rebrightening in the afterglow of a short γ-ray burst at redshift z = 0.356, although findings indicating bluer events have been reported. Here we report the spectral identification and describe the physical properties of a bright kilonova associated with the gravitational-wave source GW170817 and γ-ray burst GRB 170817A associated with a galaxy at a distance of 40 megaparsecs from Earth. Using a series of spectra from ground-based observatories covering t...
This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past... more This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands.
We present accurate and deep multiband B,R,Hα data for the globular cluster ω Cen collected with ... more We present accurate and deep multiband B,R,Hα data for the globular cluster ω Cen collected with the Advanced Camera for Surveys on HST. The photometric catalogue includes more than one million stars. By adopting severe selection criteria we identified more than 600 bona fide White Dwarfs (WDs). Empirical evidence suggests that a small sample of WDs are Hα-bright. The comparison between WD isochrones and observations shows a reasonable agreement at fainter magnitudes and a mismatch at the brighter ones.
We present deep and accurate Near-Infrared (NIR) photometry of the Galactic Globular Cluster (GC)... more We present deep and accurate Near-Infrared (NIR) photometry of the Galactic Globular Cluster (GC) ω Cen. Data were collected using the Multi-Conjugate Adaptive Optics Demonstrator (MAD) on VLT (ESO). The unprecedented quality of the images provided the opportunity to perform accurate photometry in the central crowded regions. Preliminary results indicate that the spread in age among the different stellar populations in ω Cen is limited.
Monthly Notices of the Royal Astronomical Society, 2014
STREGA (STRucture and Evolution of the GAlaxy) is a guaranteed time survey being performed at the... more STREGA (STRucture and Evolution of the GAlaxy) is a guaranteed time survey being performed at the VST (the ESO Very Large Telescope Survey Telescope) to map about 150 square degrees in the Galactic halo, in order to constrain the mechanisms of galactic formation and evolution. The survey is built as a 5 yr project, organized in two parts: a core programme to explore the surrounding regions of selected stellar systems and a second complementary part to map the southern portion of the Fornax orbit and extend the observations of the core programme. The adopted stellar tracers are mainly variable stars (RR Lyraes and long-period variables) and main-sequence turn-off stars for which observations in the g, r, i bands are obtained. We present an overview of the survey and some preliminary results for three observing runs that have been completed. For the region centred on ω Cen (37 deg 2), covering about three tidal radii, we also discuss the detected stellar density radial profile and angular distribution, leading to the identification of extratidal cluster stars. We also conclude that the cluster tidal radius is about 1.2 deg, in agreement with values in the literature based on the Wilson model.
ABSTRACT We present an extensive spectroscopic investigation of evolved old- and intermediate-age... more ABSTRACT We present an extensive spectroscopic investigation of evolved old- and intermediate-age stellar tracers of the Carina dSph galaxy. We discuss the approach we devised to calibrate the two European Southern Observatory multi-object spectrographs (FLAMES, FORS2). Pros and cons of the two instruments are also mentioned. Finally, we present preliminary results concerning the radial velocity distribution of the entire star sample (˜ 1460 objects).
STREGA (STRucture and Evolution of the Galaxy) is an ongoing VLT Survey Telescope Guaranteed Time... more STREGA (STRucture and Evolution of the Galaxy) is an ongoing VLT Survey Telescope Guaranteed Time survey, covering an area of about 150 square degrees, aimed at investigating the mechanisms of formation and evolution of the Galactic Halo. The project is organised into two parts: a core programme to search for the signatures of interaction between selected stellar systems and the Galactic Halo and a complementary part focussed on the southern portion of the Fornax Stream. The basis is the use of variable stars (RR Lyrae and long period variables) and main sequence turn-off stars as tracers of stellar overdensities. Observations in g,r,i bands, with additional filters, u, Strömgren v and Hα for selected fields, will allow investigation of the properties of Halo white dwarfs and interacting binaries. We present an overview of the survey and some first results, in particular for the region centred on Omega Centauri
We present V,I deep CCD photometry for three fields of the dwarf galaxy in Sagittarius (Sgr), loc... more We present V,I deep CCD photometry for three fields of the dwarf galaxy in Sagittarius (Sgr), located at l=5.6 o , b=-14.1 o. One of the fields is centered on the globular cluster NGC 6715 (M54), which lies in one of the dense clumps of the Sgr galaxy. Comparing the CMD of Sgr with those of globular clusters which are believed to be kinematically associated with the dwarf galaxy (Da Costa & Armandroff 1995), we conclude that the stellar population of Sgr presents a spread in metallicity of-0.71≤[Fe/H]≤-1.58, and that the dominant population (10 Gyr old) is extremely similar to the star content of the associated globular cluster Terzan 7. The estimated distance to Sgr is d 24.55 Kpc.
We discuss how a wide field imager with very high spatial resolution on a relatively small telesc... more We discuss how a wide field imager with very high spatial resolution on a relatively small telescope-but located in an observing site with very good seeing-might constrain the fraction of binary stars in Galactic globular clusters. We also mention the role that the new data might play in investigating advanced evolutionary phases of lowmass stars. Moreover, we discuss the role that an Extremely Large Telescope might have on the longstanding problem of cosmic distances and stellar populations. In particular, we discuss the impact that the detection of Cepheids in galaxies at the distance of the Coma cluster and of RR Lyrae stars in galaxies at the distance of the Virgo cluster might have on the calibration of secondary distance indicators.
Context. We present the third data release of the European Space Agency's Gaia mission, Gaia DR3.... more Context. We present the third data release of the European Space Agency's Gaia mission, Gaia DR3. This release includes a large variety of new data products, notably a much expanded radial velocity survey and a very extensive astrophysical characterisation of Gaia sources. Aims. We outline the content and the properties of Gaia DR3, providing an overview of the main improvements in the data processing in comparison with previous data releases (where applicable) and a brief discussion of the limitations of the data in this release. Methods. The Gaia DR3 catalogue is the outcome of the processing of raw data collected with the Gaia instruments during the first 34 months of the mission by the Gaia Data Processing and Analysis Consortium. Results. The Gaia DR3 catalogue contains the same source list, celestial positions, proper motions, parallaxes, and broad band photometry in the G, G BP , and G RP pass-bands already present in the Early Third Data Release, Gaia EDR3. Gaia DR3 introduces an impressive wealth of new data products. More than 33 million objects in the ranges G RVS < 14 and 3100 < T eff < 14500, have new determinations of their mean radial velocities based on data collected by Gaia. We provide G RVS magnitudes for most sources with radial velocities, and a line broadening parameter is listed for a subset of these. Mean Gaia spectra are made available to the community. The Gaia DR3 catalogue includes about 1 million mean spectra from the radial velocity spectrometer, and about 220 million low-resolution blue and red prism photometer BP/RP mean spectra. The results of the analysis of epoch photometry are provided for some 10 million sources across 24 variability types. Gaia DR3 includes astrophysical parameters and source class probabilities for about 470 million and 1500 million sources, respectively, including stars, galaxies, and quasars. Orbital elements and trend parameters are provided for some 800 000 astrometric, spectroscopic and eclipsing binaries. More than 150 000 Solar System objects, including new discoveries, with preliminary orbital solutions and individual epoch observations are part of this release. Reflectance spectra derived from the epoch BP/RP spectral data are published for about 60 000 asteroids. Finally, an additional data set is provided, namely the Gaia Andromeda Photometric Survey, consisting of the photometric time series for all sources located in a 5.5 degree radius field centred on the Andromeda galaxy. Conclusions. This data release represents a major advance with respect to Gaia DR2 and Gaia EDR3 because of the unprecedented quantity, quality, and variety of source astrophysical data. To date this is the largest collection of all-sky spectrophotometry, radial velocities, variables, and astrophysical parameters derived from both low-and high-resolution spectra and includes a spectrophotometric and dynamical survey of SSOs of the highest accuracy. The non-single star content surpasses the existing data by orders of magnitude. The quasar host and galaxy light profile collection is the first such survey that is all sky and space based. The astrophysical information provided in Gaia DR3 will unleash the full potential of Gaia's exquisite astrometric, photometric, and radial velocity surveys.
We present new empirical estimates of the ∆V bump HB parameter for 15 Galactic globular clusters ... more We present new empirical estimates of the ∆V bump HB parameter for 15 Galactic globular clusters (GGCs) using accurate and homogeneous ground-based optical data. Together with similar evaluations available in the literature, we ended
We present Ca−uvby Strömgren photometry of the Baade’s Window, including the Galactic globular c... more We present Ca−uvby Strömgren photometry of the Baade’s Window, including the Galactic globular cluster NGC 6522. We separate field and cluster stars by adopting color–color planes and proper motions. We then estimate the global metallicity of red-giants (RGs) in NGC 6522 by using a new theoretical metallicity calibration of the Strömgren index hk presented in (Calamida et al. 2011). We find that metallicities estimated by adopting the hk index and the Ca–y color are systematically more metal-rich than metallicities estimated with hk and the u–y, v–y and b–y colors. Current evidence indicate that the hk metallicity index is affected not only by the Ca abundance, but also by another source of opacity. 1 Introduction and data reduction The study of the Milky Way bulge is fundamental to understand the star formation history of the Galactic spheroid. The Milky Way bulge is indeed dominated by metal-rich old stars (t> 10 Gyr, Zoccali et al. 2003). Their metallicity distribution is ce...
We present deep multiband (F435W, F625W, and F658N) photometric data of the Globular Cluster ω Ce... more We present deep multiband (F435W, F625W, and F658N) photometric data of the Globular Cluster ω Cen collected with the Advanced Camera for Surveys on board of the Hubble Space Telescope. We identified in the (F435W-F625W, F435W) plane more than two thousand White Dwarf (WD) candidates using three out of nine available pointings. Such a large sample appears in agreement with predictions based on the ratio between WD and Horizontal Branch (HB) evolutionary lifetimes. We also detected ≈ 1600 WDs in the (F658N-F625W, F625W) plane, supporting the evidence that a large fraction of current cluster WDs are Hα bright.
We calculated new estimates of the ∆V HB parameter for 15 Galactic Globular Clusters (GGCs) using... more We calculated new estimates of the ∆V HB parameter for 15 Galactic Globular Clusters (GGCs) using accurate ground-based photometric data. We enlarged our sample with literature data and we obtained a sample of 62 GGCs covering a wide metallicity range (-2.16≤[M/H]≤-0.58 dex). To compare the data with the theory we used theoretical models from Pietrinferni et al. (2004, 2006) and two different metallicity scales. We found that the observed values are higher (∼0.4 mag) than the canonical predictions. Moreover, the discepancy increases in the Kraft & Ivans (2003, 2004) metallicity scale and it decreases in the Carretta & Gratton (1997) scale. We investigated also the impact of CNONa extreme mixture and higher He-enhanced abundance (Y = 0.30). The use of these models is not in the direction to explain the observed discrepancy.
We present three different optical and near-infrared (NIR) data sets for evolved stars in the Gal... more We present three different optical and near-infrared (NIR) data sets for evolved stars in the Galactic Globular Cluster ω Centauri . The comparison Based on observations made with the ESO Telescopes at the La Silla and Paranal Observatories, programme IDs: 63.L-0686, 64.N-0038, 68.D-0545 Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussels, Belgium Vrije Universiteit Brussel, OBSS/WE, Pleinlaan 2, B-1050 Brussels, Belgium; [email protected], [email protected] Nordic Optical Telescope, Apartado 474, E-38700 Santa Cruz de La Palma, Spain INAF-Osservatorio Astronomico di Roma, via Frascati 33, Monte Porzio Catone, Rome, Italy; [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected] Università di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Rome, Italy; [email protected], [email protected] Dipartimento di Fisica ”E. Fermi”, Univ. Pisa...
In this paper we investigate the hot end of the HB, presenting evolutionary constraints concernin... more In this paper we investigate the hot end of the HB, presenting evolutionary constraints concerning the CM diagram location and the gravity of hot HB stars. According to the adopted evolutionary scenario, we predict an upper limit for HB temperatures of about logTe = 4.45, remarkably cooler than previous estimates. We nd that such a theoretical prescription appears in good agreement with available observational data concerning both stellar temperatures and gravities. The problem of gaps in the HB distribution is nally discussed, suggesting that, at the least in the case of the cluster NGC 6752, evolutionary gaps, a bimodal distribution of CNO or stellar rotation should all play a negligible role.
The merger of two neutron stars is predicted to give rise to three major detectable phenomena: a ... more The merger of two neutron stars is predicted to give rise to three major detectable phenomena: a short burst of γ-rays, a gravitational-wave signal, and a transient optical-near-infrared source powered by the synthesis of large amounts of very heavy elements via rapid neutron capture (the r-process). Such transients, named 'macronovae' or 'kilonovae', are believed to be centres of production of rare elements such as gold and platinum. The most compelling evidence so far for a kilonova was a very faint near-infrared rebrightening in the afterglow of a short γ-ray burst at redshift z = 0.356, although findings indicating bluer events have been reported. Here we report the spectral identification and describe the physical properties of a bright kilonova associated with the gravitational-wave source GW170817 and γ-ray burst GRB 170817A associated with a galaxy at a distance of 40 megaparsecs from Earth. Using a series of spectra from ground-based observatories covering t...
This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past... more This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands.
We present accurate and deep multiband B,R,Hα data for the globular cluster ω Cen collected with ... more We present accurate and deep multiband B,R,Hα data for the globular cluster ω Cen collected with the Advanced Camera for Surveys on HST. The photometric catalogue includes more than one million stars. By adopting severe selection criteria we identified more than 600 bona fide White Dwarfs (WDs). Empirical evidence suggests that a small sample of WDs are Hα-bright. The comparison between WD isochrones and observations shows a reasonable agreement at fainter magnitudes and a mismatch at the brighter ones.
We present deep and accurate Near-Infrared (NIR) photometry of the Galactic Globular Cluster (GC)... more We present deep and accurate Near-Infrared (NIR) photometry of the Galactic Globular Cluster (GC) ω Cen. Data were collected using the Multi-Conjugate Adaptive Optics Demonstrator (MAD) on VLT (ESO). The unprecedented quality of the images provided the opportunity to perform accurate photometry in the central crowded regions. Preliminary results indicate that the spread in age among the different stellar populations in ω Cen is limited.
Monthly Notices of the Royal Astronomical Society, 2014
STREGA (STRucture and Evolution of the GAlaxy) is a guaranteed time survey being performed at the... more STREGA (STRucture and Evolution of the GAlaxy) is a guaranteed time survey being performed at the VST (the ESO Very Large Telescope Survey Telescope) to map about 150 square degrees in the Galactic halo, in order to constrain the mechanisms of galactic formation and evolution. The survey is built as a 5 yr project, organized in two parts: a core programme to explore the surrounding regions of selected stellar systems and a second complementary part to map the southern portion of the Fornax orbit and extend the observations of the core programme. The adopted stellar tracers are mainly variable stars (RR Lyraes and long-period variables) and main-sequence turn-off stars for which observations in the g, r, i bands are obtained. We present an overview of the survey and some preliminary results for three observing runs that have been completed. For the region centred on ω Cen (37 deg 2), covering about three tidal radii, we also discuss the detected stellar density radial profile and angular distribution, leading to the identification of extratidal cluster stars. We also conclude that the cluster tidal radius is about 1.2 deg, in agreement with values in the literature based on the Wilson model.
ABSTRACT We present an extensive spectroscopic investigation of evolved old- and intermediate-age... more ABSTRACT We present an extensive spectroscopic investigation of evolved old- and intermediate-age stellar tracers of the Carina dSph galaxy. We discuss the approach we devised to calibrate the two European Southern Observatory multi-object spectrographs (FLAMES, FORS2). Pros and cons of the two instruments are also mentioned. Finally, we present preliminary results concerning the radial velocity distribution of the entire star sample (˜ 1460 objects).
STREGA (STRucture and Evolution of the Galaxy) is an ongoing VLT Survey Telescope Guaranteed Time... more STREGA (STRucture and Evolution of the Galaxy) is an ongoing VLT Survey Telescope Guaranteed Time survey, covering an area of about 150 square degrees, aimed at investigating the mechanisms of formation and evolution of the Galactic Halo. The project is organised into two parts: a core programme to search for the signatures of interaction between selected stellar systems and the Galactic Halo and a complementary part focussed on the southern portion of the Fornax Stream. The basis is the use of variable stars (RR Lyrae and long period variables) and main sequence turn-off stars as tracers of stellar overdensities. Observations in g,r,i bands, with additional filters, u, Strömgren v and Hα for selected fields, will allow investigation of the properties of Halo white dwarfs and interacting binaries. We present an overview of the survey and some first results, in particular for the region centred on Omega Centauri
We present V,I deep CCD photometry for three fields of the dwarf galaxy in Sagittarius (Sgr), loc... more We present V,I deep CCD photometry for three fields of the dwarf galaxy in Sagittarius (Sgr), located at l=5.6 o , b=-14.1 o. One of the fields is centered on the globular cluster NGC 6715 (M54), which lies in one of the dense clumps of the Sgr galaxy. Comparing the CMD of Sgr with those of globular clusters which are believed to be kinematically associated with the dwarf galaxy (Da Costa & Armandroff 1995), we conclude that the stellar population of Sgr presents a spread in metallicity of-0.71≤[Fe/H]≤-1.58, and that the dominant population (10 Gyr old) is extremely similar to the star content of the associated globular cluster Terzan 7. The estimated distance to Sgr is d 24.55 Kpc.
We discuss how a wide field imager with very high spatial resolution on a relatively small telesc... more We discuss how a wide field imager with very high spatial resolution on a relatively small telescope-but located in an observing site with very good seeing-might constrain the fraction of binary stars in Galactic globular clusters. We also mention the role that the new data might play in investigating advanced evolutionary phases of lowmass stars. Moreover, we discuss the role that an Extremely Large Telescope might have on the longstanding problem of cosmic distances and stellar populations. In particular, we discuss the impact that the detection of Cepheids in galaxies at the distance of the Coma cluster and of RR Lyrae stars in galaxies at the distance of the Virgo cluster might have on the calibration of secondary distance indicators.
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Papers by L. Pulone