G. Clementini - Profile on Academia.edu (original) (raw)

Papers by G. Clementini

arXiv: Solar and Stellar Astrophysics, 2019

Stellar variability studies are now reaching a completely new level thanks to ESA's Gaia miss... more Stellar variability studies are now reaching a completely new level thanks to ESA's Gaia mission, which enables us to locate many variable stars in the Hertzsprung-Russell diagram and determine the various instability strips/bands. Furthermore, this mission also allows us to detect, characterise and classify many millions of new variable stars thanks to its very unique nearly simultaneous multi-epoch survey with different instruments (photometer, spectro-photometer, radial velocity spectrometer). An overview of what can be found in literature in terms of mostly data products by the Gaia consortium is given. This concerns the various catalogues of variable stars derived from the Gaia time series and also the location and motion of variable stars in the observational Hertzsprung-Russell diagram. In addition, we provide a list of a few thousands of variable white dwarf candidates derived from the DR2 published data, among them probably many hundreds of new pulsating white dwarfs. O...

Stellar Populations, 1995

We discuss typicalities and atypicalities in the stellar population of a Galactic globular cluster.

The Oosterhoff Dichotomy in the Milky Way and Other Local Group Galaxies

Bulletin of the …, 2010

The Oosterhoff Dichotomy in the Milky Way and Other Local Group Galaxies ... Horace A. Smith1, M.... more The Oosterhoff Dichotomy in the Milky Way and Other Local Group Galaxies ... Horace A. Smith1, M. Catelan2, G. Clementini3, C. Kuehn1, B. Pritzl4, TC Beers1, N. De Lee5, K. Kinemuchi5, C. Greco6, V. Ripepi7, M. Marconi7, I. Musella7,

Arxiv preprint arXiv: …, 2008

As first Paper of a series devoted to study the old stellar population in clusters and fields in ... more As first Paper of a series devoted to study the old stellar population in clusters and fields in the Small Magellanic Cloud, we present deep observations of NGC 121 in the F555W and F814W filters, obtained with the Advanced Camera for Surveys on the Hubble Space ...

Monthly Notices of the Royal Astronomical Society

This is an erratum to the paper Cepheid metallicity in the Leavitt law (C-metall) surv e y-I. HAR... more This is an erratum to the paper Cepheid metallicity in the Leavitt law (C-metall) surv e y-I. HARPS-N@TNG spectroscopy of 47 classical Cepheids and 1 BL Her variables, published in MNRAS, 2021, 508, 4047-4071. In the original version, during the preparation of the proofs, the header of the second page of table 3 was erroneously substituted with the header of the first page, while the numbers in the table were not affected. In this erratum we provide the entire Table 3 with the correct headers. The same unfortunate event happened in table 4. In this case, the header of table 4 at the beginning of page 4060 is incorrect. The correct one is that present at mid page 4059, listing columns from (14) to (24). Tables from 1 to 4 are also available at Centre de Donn ées astronomiques de Strasbourg as VizierR Catalogue ht tps://cdsarc.cds.unist ra.fr/viz-bin/cat/J/MNRA S/ 508/ 4047. Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated by the Fundaci ón Galileo Galilei (FGG) of the Istituto Nazionale di Astrofisica (INAF) at the Observatorio del Roque de los Muchachos (La Palma, Canary Islands, Spain).

Cornell University - arXiv, Apr 26, 2022

Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third... more Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic sources in the (E)DR3 catalogue. Aims. We describe the construction of Gaia-CRF3 and its properties in terms of the distributions in magnitude, colour, and astrometric quality. Methods. Compact extragalactic sources in Gaia DR3 were identified by positional cross-matching with 17 external catalogues of quasi-stellar objects (QSO) and active galactic nuclei (AGN), followed by astrometric filtering designed to remove stellar contaminants. Selecting a clean sample was favoured over including a higher number of extragalactic sources. For the final sample, the random and systematic errors in the proper motions are analysed, as well as the radio-optical offsets in position for sources in the third realisation of the International Celestial Reference Frame (ICRF3). Results. Gaia-CRF3 comprises about 1.6 million QSO-like sources, of which 1.2 million have five-parameter astrometric solutions in Gaia DR3 and 0.4 million have six-parameter solutions. The sources span the magnitude range G = 13 to 21 with a peak density at 20.6 mag, at which the typical positional uncertainty is about 1 mas. The proper motions show systematic errors on the level of 12 µas yr −1 on angular scales greater than 15 deg. For the 3142 optical counterparts of ICRF3 sources in the S/X frequency bands, the median offset from the radio positions is about 0.5 mas, but it exceeds 4 mas in either coordinate for 127 sources. We outline the future of Gaia-CRF in the next Gaia data releases. Appendices give further details on the external catalogues used, how to extract information about the Gaia-CRF3 sources, potential (Galactic) confusion sources, and the estimation of the spin and orientation of an astrometric solution.

Astronomy & Astrophysics, 2022

Context. Classical Cepheids (DCEPs) represent a fundamental tool to calibrate the extragalactic d... more Context. Classical Cepheids (DCEPs) represent a fundamental tool to calibrate the extragalactic distance scale. However, they are also powerful stellar population tracers in the context of Galactic studies. The forthcoming Data Release 3 of the Gaia mission will allow us to study, with unprecedented detail, the structure, the dynamics, and the chemical properties of the Galactic disc, and in particular of the spiral arms, where most Galactic DCEPs reside. Aims. In this paper we aim to quantify the metallicity dependence of the Galactic DCEPs’ period-Wesenheit (PWZ) relation in the Gaia bands. Methods. We adopted a sample of 499 DCEPs with metal abundances from high-resolution spectroscopy, in conjunction with Gaia Early Data Release 3 parallaxes and photometry to calibrate a PWZ relation in the Gaia bands. Results. We find a significant metallicity term, of the order of −0.5 mag dex−1, which is larger than the values measured in the near-infrared (NIR) bands by different authors. Ou...

VizieR Online Data Catalog: Gaia DR2 sources in GC and dSph (Gaia Collaboration+, 2018)

The files contains lists of possible members of each of the objects (75 globular clusters, 9 dwar... more The files contains lists of possible members of each of the objects (75 globular clusters, 9 dwarf spheroidal galaxies, the Bootes I UFD, the LMC and SMC). The stars in these lists have been selected and used to determine the astrometric parameters of the corresponding objects following either the procedures described in Sec. 2.1 (for the clusters and dwarfs) or in Sec. 2.2 (for the LMC and SMC). The first column is the "source_id" as given by Gaia, the ra and declination of the star in degrees, and its G-band magnitude (known as "photgmean_mag" in the Gaia archive). (2 data files).

VizieR Online Data Catalog: Properties of 70 RR Lyrae stars in the LMC bar (Muraveva+, 2015)

International Astronomical Union Colloquium, 2004

We present an overview of our study of the short period variable stars in the Large Magellanic Cl... more We present an overview of our study of the short period variable stars in the Large Magellanic Cloud, and in the dwarf galaxies Fornax, Leo I, and NGC 6822. Light curves are presented for RR Lyrae stars, Anomalous Cepheids and, for the first time, for Dwarf Cepheids in the field and in the globular cluster #3 of the Fornax galaxy.

Proceedings of the International Astronomical Union, 2006

We have applied the Image Subtraction to B,V time-series photometry of four globular clusters of ... more We have applied the Image Subtraction to B,V time-series photometry of four globular clusters of the Fornax dwarf spheoridal galaxy, which were observed with the 2.2m ESO-MPI, the 6.5m Magellan/Clay, the 4m CTIO/Blanco telescopes and the WFPC2 on board of HST. We have identified RR Lyrae stars and obtained well sampled light curves for the clusters' variables. From the periods and pulsation properties of their RR Lyrae stars Fornax globular clusters seem to be of Oosterhoff intermediate type.

The Fornax Project aims at mapping the classical instability strip of the Fornax dwarf spheroidal... more The Fornax Project aims at mapping the classical instability strip of the Fornax dwarf spheroidal galaxy, from the faint Dwarf Cepheids (V ˜ 24-25 mag) to the bright Anomalous Cepheids (V ˜ 19 mag). To achieve this goal, deep B,V time-series photometry of the galaxy has been obtained with the Wide Field Imagers (WFIs) of the ESO 2.2 m and CTIO 4 m telescopes, and the Clay camera at the Magellan 6.5 m telescope. Preliminary results are presented on the Oosterhoff classification of the RR Lyrae stars identified in a northern portion of Fornax field and in three of its globular clusters.

BVI photometry of LMC bar variables (Di Fabrizio+, 2005)

We present the Johnson-Cousins B,V and I time series data obtained for 162 variable stars (135 RR... more We present the Johnson-Cousins B,V and I time series data obtained for 162 variable stars (135 RR Lyrae, 4 candidate Anomalous Cepheids, 11 Classical Cepheids, 11 eclipsing binaries and 1 delta Scuti star) in two 13x13 square arcmin areas close to the bar of the Large Magellanic Cloud. The photometric observations presented in this paper were carried out at the 1.54m Danish telescope located in La Silla, Chile, on the nights 4-7 January 1999, UT, and 23-24 January 2001, UT, respectively. In the paper we give coordinates, finding charts, periods, epochs, amplitudes, and mean quantities (intensity- and magnitude-averaged luminosities) of the variables with full coverage of the light variations, along with a discussion of the pulsation properties of the RR Lyrae stars in the sample. (8 data files).

Proceedings of the International Astronomical Union, 2006

We have combined B, V, I time-series photometry from three different telescopes (SUBARU, TNG and ... more We have combined B, V, I time-series photometry from three different telescopes (SUBARU, TNG and HST) to study the variable star population of the remote Galactic globular cluster NGC 2419 and derive hints on a possible extragalactic origin for this cluster. We have discovered 40 new variables (34 RR Lyrae stars, 3 SX Phoenicis stars, 1 eclipsing binary system and 2 red irregular variables) doubling the number of known variable stars in NGC 2419.

We present a project devoted to a comprehensive study of the Small Magellanic Cloud (SMC) and of ... more We present a project devoted to a comprehensive study of the Small Magellanic Cloud (SMC) and of the Bridge toward the Large Magellanic Cloud. We plan to use the VLT Survey Telescope (VST) to image 65 squared degrees on both targets to V˜24.5 with S/N˜10 in two years. These observations, in conjunction with HST and VLT data will allow us

We have carried out an extensive observing campaign on the new dwarf spheroidal galaxies (dSphs) ... more We have carried out an extensive observing campaign on the new dwarf spheroidal galaxies (dSphs) recently discovered by the SDSS, with the aim of characterizing their stellar populations and structural properties, as well as their variable star content. First preliminary results are presented for the Canes Venatici II, the Coma and the Ursa Major II dSphs, based on data collected

The Astrophysical Journal, 2010

Take-down policy If you believe that this document breaches copyright please contact us providing... more Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

The Astrophysical Journal, 2011

The evolutionary properties and spatial distribution of I Zwicky 18 stellar populations are analy... more The evolutionary properties and spatial distribution of I Zwicky 18 stellar populations are analyzed by means of HST/ACS deep and accurate photometry. The comparison of the resulting Colour-Magnitude diagrams with stellar evolution models indicates that stars of all ages are present in all the system components, including objects possibly up to 13 Gyr old, intermediate age stars and very young ones. The Colour-Magnitude diagrams show evidence of thermally pulsing asymptotic giant branch and carbon stars. Classical and ultra-long period Cepheids, as well as long period variables have been measured. About 20 objects could be unresolved star clusters, and are mostly concentrated in the NorthWest (NW) portion of the Main Body (MB). If interpreted with simple stellar population models, these objects indicate a particularly active star formation over the past hundred Myr in IZw 18. The stellar spatial distribution shows that the younger ones are more centrally concentrated, while old and intermediate age stars are distributed homogeneously over the two bodies, although more easily detectable at the system periphery. The oldest stars are best visible in the Secondary Body (SB) and in the South East (SE) portion of the MB, where crowding is less severe, but are present also in the rest of the MB, although measured with larger uncertainties. The youngest stars are a few Myr old, are located predominantly in the MB and mostly concentrated in its NW portion. The SE portion of the MB appears to be in a similar, but not as young evolutionary stage as the NW, while the SB stars are older than at least 10 Myr. There is then a sequence of decreasing age of the younger stars from the Secondary Body to the SE portion of the MB to the NW portion. All our results suggest that IZw18 is not atypical compared to other BCDs.

The Astrophysical Journal, 2007

We present new V and I-band HST/ACS photometry of I Zw 18, the most metal-poor blue compact dwarf... more We present new V and I-band HST/ACS photometry of I Zw 18, the most metal-poor blue compact dwarf (BCD) galaxy in the nearby universe. It has been argued in the past that I Zw 18 is a very young system that started forming stars only 500 Myr ago, but other work has hinted that older (1 Gyr) red giant branch (RGB) stars may also exist. Our new data, once combined with archival HST/ACS data, provide a deep and uncontaminated optical color-magnitude diagram (CMD) that now strongly indicates an RGB. The RGB tip (TRGB) magnitude yields a distance modulus (m−M) 0 = 31.30 ±0.17, i.e., D = 18.2 ± 1.5 Mpc. The time-series nature of our observations allows us to also detect and characterize for the first time three classical Cepheids in I Zw 18. The time-averaged Cepheid V and I magnitudes are compared to the V I reddening-free Wesenheit relation predicted from new non-linear pulsation models specifically calculated at the metallicity of I Zw 18. For the one bona-fide classical Cepheid with a period of 8.63 days this implies a distance modulus (m − M) 0 = 31.42 ± 0.26. The other two Cepheids have unusually long periods (125.0 and 129.8 d) but are consistent with this distance. The coherent picture that emerges is that I Zw 18 is older and farther away than previously believed. This rules out the possibility that I Zw 18 is a truly primordial galaxy formed recently (z 0.1) in the local universe.

The Astrophysical Journal, 2009

We present the first V, B − V color−magnitude diagram of the Leo IV dwarf spheroidal galaxy, a fa... more We present the first V, B − V color−magnitude diagram of the Leo IV dwarf spheroidal galaxy, a faint Milky Way satellite recently discovered by the Sloan Digital Sky Survey. We have obtained B, V time-series photometry reaching about half a magnitude below the Leo IV turnoff, which we detect at V = 24.7 mag, and have performed the first study of the variable star population. We have identified three RR Lyrae stars (all fundamental−mode pulsators, RRab) and one SX Phoenicis variable in the galaxy. In the period−amplitude diagram the Leo IV Based on data collected at the 2.5 m Isaac Newton Telescope, La Palma, Canary Island, Spain, at the 4.2 m William Herschel Telescope, Roche de los Muchachos, Canary Islands, Spain, and at the 4.

arXiv: Solar and Stellar Astrophysics, 2019

Stellar variability studies are now reaching a completely new level thanks to ESA's Gaia miss... more Stellar variability studies are now reaching a completely new level thanks to ESA's Gaia mission, which enables us to locate many variable stars in the Hertzsprung-Russell diagram and determine the various instability strips/bands. Furthermore, this mission also allows us to detect, characterise and classify many millions of new variable stars thanks to its very unique nearly simultaneous multi-epoch survey with different instruments (photometer, spectro-photometer, radial velocity spectrometer). An overview of what can be found in literature in terms of mostly data products by the Gaia consortium is given. This concerns the various catalogues of variable stars derived from the Gaia time series and also the location and motion of variable stars in the observational Hertzsprung-Russell diagram. In addition, we provide a list of a few thousands of variable white dwarf candidates derived from the DR2 published data, among them probably many hundreds of new pulsating white dwarfs. O...

Stellar Populations, 1995

We discuss typicalities and atypicalities in the stellar population of a Galactic globular cluster.

The Oosterhoff Dichotomy in the Milky Way and Other Local Group Galaxies

Bulletin of the …, 2010

The Oosterhoff Dichotomy in the Milky Way and Other Local Group Galaxies ... Horace A. Smith1, M.... more The Oosterhoff Dichotomy in the Milky Way and Other Local Group Galaxies ... Horace A. Smith1, M. Catelan2, G. Clementini3, C. Kuehn1, B. Pritzl4, TC Beers1, N. De Lee5, K. Kinemuchi5, C. Greco6, V. Ripepi7, M. Marconi7, I. Musella7,

Arxiv preprint arXiv: …, 2008

As first Paper of a series devoted to study the old stellar population in clusters and fields in ... more As first Paper of a series devoted to study the old stellar population in clusters and fields in the Small Magellanic Cloud, we present deep observations of NGC 121 in the F555W and F814W filters, obtained with the Advanced Camera for Surveys on the Hubble Space ...

Monthly Notices of the Royal Astronomical Society

This is an erratum to the paper Cepheid metallicity in the Leavitt law (C-metall) surv e y-I. HAR... more This is an erratum to the paper Cepheid metallicity in the Leavitt law (C-metall) surv e y-I. HARPS-N@TNG spectroscopy of 47 classical Cepheids and 1 BL Her variables, published in MNRAS, 2021, 508, 4047-4071. In the original version, during the preparation of the proofs, the header of the second page of table 3 was erroneously substituted with the header of the first page, while the numbers in the table were not affected. In this erratum we provide the entire Table 3 with the correct headers. The same unfortunate event happened in table 4. In this case, the header of table 4 at the beginning of page 4060 is incorrect. The correct one is that present at mid page 4059, listing columns from (14) to (24). Tables from 1 to 4 are also available at Centre de Donn ées astronomiques de Strasbourg as VizierR Catalogue ht tps://cdsarc.cds.unist ra.fr/viz-bin/cat/J/MNRA S/ 508/ 4047. Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated by the Fundaci ón Galileo Galilei (FGG) of the Istituto Nazionale di Astrofisica (INAF) at the Observatorio del Roque de los Muchachos (La Palma, Canary Islands, Spain).

Cornell University - arXiv, Apr 26, 2022

Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third... more Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic sources in the (E)DR3 catalogue. Aims. We describe the construction of Gaia-CRF3 and its properties in terms of the distributions in magnitude, colour, and astrometric quality. Methods. Compact extragalactic sources in Gaia DR3 were identified by positional cross-matching with 17 external catalogues of quasi-stellar objects (QSO) and active galactic nuclei (AGN), followed by astrometric filtering designed to remove stellar contaminants. Selecting a clean sample was favoured over including a higher number of extragalactic sources. For the final sample, the random and systematic errors in the proper motions are analysed, as well as the radio-optical offsets in position for sources in the third realisation of the International Celestial Reference Frame (ICRF3). Results. Gaia-CRF3 comprises about 1.6 million QSO-like sources, of which 1.2 million have five-parameter astrometric solutions in Gaia DR3 and 0.4 million have six-parameter solutions. The sources span the magnitude range G = 13 to 21 with a peak density at 20.6 mag, at which the typical positional uncertainty is about 1 mas. The proper motions show systematic errors on the level of 12 µas yr −1 on angular scales greater than 15 deg. For the 3142 optical counterparts of ICRF3 sources in the S/X frequency bands, the median offset from the radio positions is about 0.5 mas, but it exceeds 4 mas in either coordinate for 127 sources. We outline the future of Gaia-CRF in the next Gaia data releases. Appendices give further details on the external catalogues used, how to extract information about the Gaia-CRF3 sources, potential (Galactic) confusion sources, and the estimation of the spin and orientation of an astrometric solution.

Astronomy & Astrophysics, 2022

Context. Classical Cepheids (DCEPs) represent a fundamental tool to calibrate the extragalactic d... more Context. Classical Cepheids (DCEPs) represent a fundamental tool to calibrate the extragalactic distance scale. However, they are also powerful stellar population tracers in the context of Galactic studies. The forthcoming Data Release 3 of the Gaia mission will allow us to study, with unprecedented detail, the structure, the dynamics, and the chemical properties of the Galactic disc, and in particular of the spiral arms, where most Galactic DCEPs reside. Aims. In this paper we aim to quantify the metallicity dependence of the Galactic DCEPs’ period-Wesenheit (PWZ) relation in the Gaia bands. Methods. We adopted a sample of 499 DCEPs with metal abundances from high-resolution spectroscopy, in conjunction with Gaia Early Data Release 3 parallaxes and photometry to calibrate a PWZ relation in the Gaia bands. Results. We find a significant metallicity term, of the order of −0.5 mag dex−1, which is larger than the values measured in the near-infrared (NIR) bands by different authors. Ou...

VizieR Online Data Catalog: Gaia DR2 sources in GC and dSph (Gaia Collaboration+, 2018)

The files contains lists of possible members of each of the objects (75 globular clusters, 9 dwar... more The files contains lists of possible members of each of the objects (75 globular clusters, 9 dwarf spheroidal galaxies, the Bootes I UFD, the LMC and SMC). The stars in these lists have been selected and used to determine the astrometric parameters of the corresponding objects following either the procedures described in Sec. 2.1 (for the clusters and dwarfs) or in Sec. 2.2 (for the LMC and SMC). The first column is the "source_id" as given by Gaia, the ra and declination of the star in degrees, and its G-band magnitude (known as "photgmean_mag" in the Gaia archive). (2 data files).

VizieR Online Data Catalog: Properties of 70 RR Lyrae stars in the LMC bar (Muraveva+, 2015)

International Astronomical Union Colloquium, 2004

We present an overview of our study of the short period variable stars in the Large Magellanic Cl... more We present an overview of our study of the short period variable stars in the Large Magellanic Cloud, and in the dwarf galaxies Fornax, Leo I, and NGC 6822. Light curves are presented for RR Lyrae stars, Anomalous Cepheids and, for the first time, for Dwarf Cepheids in the field and in the globular cluster #3 of the Fornax galaxy.

Proceedings of the International Astronomical Union, 2006

We have applied the Image Subtraction to B,V time-series photometry of four globular clusters of ... more We have applied the Image Subtraction to B,V time-series photometry of four globular clusters of the Fornax dwarf spheoridal galaxy, which were observed with the 2.2m ESO-MPI, the 6.5m Magellan/Clay, the 4m CTIO/Blanco telescopes and the WFPC2 on board of HST. We have identified RR Lyrae stars and obtained well sampled light curves for the clusters' variables. From the periods and pulsation properties of their RR Lyrae stars Fornax globular clusters seem to be of Oosterhoff intermediate type.

The Fornax Project aims at mapping the classical instability strip of the Fornax dwarf spheroidal... more The Fornax Project aims at mapping the classical instability strip of the Fornax dwarf spheroidal galaxy, from the faint Dwarf Cepheids (V ˜ 24-25 mag) to the bright Anomalous Cepheids (V ˜ 19 mag). To achieve this goal, deep B,V time-series photometry of the galaxy has been obtained with the Wide Field Imagers (WFIs) of the ESO 2.2 m and CTIO 4 m telescopes, and the Clay camera at the Magellan 6.5 m telescope. Preliminary results are presented on the Oosterhoff classification of the RR Lyrae stars identified in a northern portion of Fornax field and in three of its globular clusters.

BVI photometry of LMC bar variables (Di Fabrizio+, 2005)

We present the Johnson-Cousins B,V and I time series data obtained for 162 variable stars (135 RR... more We present the Johnson-Cousins B,V and I time series data obtained for 162 variable stars (135 RR Lyrae, 4 candidate Anomalous Cepheids, 11 Classical Cepheids, 11 eclipsing binaries and 1 delta Scuti star) in two 13x13 square arcmin areas close to the bar of the Large Magellanic Cloud. The photometric observations presented in this paper were carried out at the 1.54m Danish telescope located in La Silla, Chile, on the nights 4-7 January 1999, UT, and 23-24 January 2001, UT, respectively. In the paper we give coordinates, finding charts, periods, epochs, amplitudes, and mean quantities (intensity- and magnitude-averaged luminosities) of the variables with full coverage of the light variations, along with a discussion of the pulsation properties of the RR Lyrae stars in the sample. (8 data files).

Proceedings of the International Astronomical Union, 2006

We have combined B, V, I time-series photometry from three different telescopes (SUBARU, TNG and ... more We have combined B, V, I time-series photometry from three different telescopes (SUBARU, TNG and HST) to study the variable star population of the remote Galactic globular cluster NGC 2419 and derive hints on a possible extragalactic origin for this cluster. We have discovered 40 new variables (34 RR Lyrae stars, 3 SX Phoenicis stars, 1 eclipsing binary system and 2 red irregular variables) doubling the number of known variable stars in NGC 2419.

We present a project devoted to a comprehensive study of the Small Magellanic Cloud (SMC) and of ... more We present a project devoted to a comprehensive study of the Small Magellanic Cloud (SMC) and of the Bridge toward the Large Magellanic Cloud. We plan to use the VLT Survey Telescope (VST) to image 65 squared degrees on both targets to V˜24.5 with S/N˜10 in two years. These observations, in conjunction with HST and VLT data will allow us

We have carried out an extensive observing campaign on the new dwarf spheroidal galaxies (dSphs) ... more We have carried out an extensive observing campaign on the new dwarf spheroidal galaxies (dSphs) recently discovered by the SDSS, with the aim of characterizing their stellar populations and structural properties, as well as their variable star content. First preliminary results are presented for the Canes Venatici II, the Coma and the Ursa Major II dSphs, based on data collected

The Astrophysical Journal, 2010

Take-down policy If you believe that this document breaches copyright please contact us providing... more Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

The Astrophysical Journal, 2011

The evolutionary properties and spatial distribution of I Zwicky 18 stellar populations are analy... more The evolutionary properties and spatial distribution of I Zwicky 18 stellar populations are analyzed by means of HST/ACS deep and accurate photometry. The comparison of the resulting Colour-Magnitude diagrams with stellar evolution models indicates that stars of all ages are present in all the system components, including objects possibly up to 13 Gyr old, intermediate age stars and very young ones. The Colour-Magnitude diagrams show evidence of thermally pulsing asymptotic giant branch and carbon stars. Classical and ultra-long period Cepheids, as well as long period variables have been measured. About 20 objects could be unresolved star clusters, and are mostly concentrated in the NorthWest (NW) portion of the Main Body (MB). If interpreted with simple stellar population models, these objects indicate a particularly active star formation over the past hundred Myr in IZw 18. The stellar spatial distribution shows that the younger ones are more centrally concentrated, while old and intermediate age stars are distributed homogeneously over the two bodies, although more easily detectable at the system periphery. The oldest stars are best visible in the Secondary Body (SB) and in the South East (SE) portion of the MB, where crowding is less severe, but are present also in the rest of the MB, although measured with larger uncertainties. The youngest stars are a few Myr old, are located predominantly in the MB and mostly concentrated in its NW portion. The SE portion of the MB appears to be in a similar, but not as young evolutionary stage as the NW, while the SB stars are older than at least 10 Myr. There is then a sequence of decreasing age of the younger stars from the Secondary Body to the SE portion of the MB to the NW portion. All our results suggest that IZw18 is not atypical compared to other BCDs.

The Astrophysical Journal, 2007

We present new V and I-band HST/ACS photometry of I Zw 18, the most metal-poor blue compact dwarf... more We present new V and I-band HST/ACS photometry of I Zw 18, the most metal-poor blue compact dwarf (BCD) galaxy in the nearby universe. It has been argued in the past that I Zw 18 is a very young system that started forming stars only 500 Myr ago, but other work has hinted that older (1 Gyr) red giant branch (RGB) stars may also exist. Our new data, once combined with archival HST/ACS data, provide a deep and uncontaminated optical color-magnitude diagram (CMD) that now strongly indicates an RGB. The RGB tip (TRGB) magnitude yields a distance modulus (m−M) 0 = 31.30 ±0.17, i.e., D = 18.2 ± 1.5 Mpc. The time-series nature of our observations allows us to also detect and characterize for the first time three classical Cepheids in I Zw 18. The time-averaged Cepheid V and I magnitudes are compared to the V I reddening-free Wesenheit relation predicted from new non-linear pulsation models specifically calculated at the metallicity of I Zw 18. For the one bona-fide classical Cepheid with a period of 8.63 days this implies a distance modulus (m − M) 0 = 31.42 ± 0.26. The other two Cepheids have unusually long periods (125.0 and 129.8 d) but are consistent with this distance. The coherent picture that emerges is that I Zw 18 is older and farther away than previously believed. This rules out the possibility that I Zw 18 is a truly primordial galaxy formed recently (z 0.1) in the local universe.

The Astrophysical Journal, 2009

We present the first V, B − V color−magnitude diagram of the Leo IV dwarf spheroidal galaxy, a fa... more We present the first V, B − V color−magnitude diagram of the Leo IV dwarf spheroidal galaxy, a faint Milky Way satellite recently discovered by the Sloan Digital Sky Survey. We have obtained B, V time-series photometry reaching about half a magnitude below the Leo IV turnoff, which we detect at V = 24.7 mag, and have performed the first study of the variable star population. We have identified three RR Lyrae stars (all fundamental−mode pulsators, RRab) and one SX Phoenicis variable in the galaxy. In the period−amplitude diagram the Leo IV Based on data collected at the 2.5 m Isaac Newton Telescope, La Palma, Canary Island, Spain, at the 4.2 m William Herschel Telescope, Roche de los Muchachos, Canary Islands, Spain, and at the 4.