A. Piersimoni - Academia.edu (original) (raw)

Papers by A. Piersimoni

Proceedings of the International Astronomical Union, 2006

We present optical-near infrared photometry of the peculiar Galactic globular cluster NGC 6441. B... more We present optical-near infrared photometry of the peculiar Galactic globular cluster NGC 6441. By using the K-band Period-Luminosity-Metallicity (PLZK) of its RR Lyrae stars, we supply a new estimate of its distance. With this distance, we discuss the comparison in the K-(J − K) plane between observations and "canonical" evolutionary models.

We present iron abundance measurements, based on high resolution spectroscopy, and accurate dista... more We present iron abundance measurements, based on high resolution spectroscopy, and accurate distance determinations, based on near infrared photometry, for 34 Galactic Cepheids. The new data are used to constrain the Galactic iron abundance gradient in the outer disk, namely from 10 to 14 kpc. We confirm the flattening of the gradient toward the outer disk. In this region we

EAS Publications Series, 2007

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 low-mass stars. Moreover, we discuss

The Astrophysical Journal, 2005

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 1 Based on observations made with the ESO Telescopes at the La Silla and Paranal Observatories, programme IDs: 63.L-0686,

The Astrophysical Journal, 2007

We present new intermediate-band Strömgren photometry based on more than 300 u, v, b, y images of... more We present new intermediate-band Strömgren photometry based on more than 300 u, v, b, y images of the Galactic globular cluster ω Cen. Optical data were supplemented with new multiband nearinfrared (NIR) photometry (350 J, H, K s images). The final optical-NIR catalog covers a region of more than 20 × 20 arcmin squared across the cluster center. We use different optical-NIR color-color planes together with proper motion data available in the literature to identify candidate cluster red giant (RG) stars. By adopting different Strömgren metallicity indices we estimate the photometric metallicity for ≈ 4, 000 RGs, the largest sample ever collected. The metallicity distributions show multiple peaks ([Fe/H] phot = −1.73 ± 0.08, −1.29 ± 0.03, −1.05 ± 0.02, −0.80 ± 0.04, −0.42 ± 0.12 and −0.07 ± 0.08 dex) and a sharp cut-off in the metal-poor tail ([Fe/H] phot −2 dex) that agree quite well with spectroscopic measurements. We identify four distinct sub-populations, namely metalpoor MP, [Fe/H] ≤ −1.49), metal-intermediate (MI, −1.49 < [Fe/H] ≤ −0.93), metal-rich (MR, −0.95 < [Fe/H] ≤ −0.15) and solar metallicity (SM, [Fe/H] ≈ 0). The last group includes only a small fraction of stars (∼ 8 ± 5%) and should be confirmed spectroscopically. Moreover, using the difference in metallicity based on different photometric indices, we find that the 19 ± 1% of RGs are candidate CN-strong stars. This fraction agrees quite well with recent spectroscopic estimates and could imply a large fraction of binary stars. The Strömgren metallicity indices display a robust correlation with α-elements ([Ca+Si/H]) when moving from the metal-intermediate to the metal-rich regime ([Fe/H] −1.7 dex). 1 Based on observations collected in part with the 1.54m Danish Telescope and with the NTT@ESO Telescope operated in La Silla, and in part with the VLT@ESO Telescope operated in Paranal. The Strömgren data were collected with DFOSC2@Danish (proprietary data), while the NIR data were collected with SOFI@NTT, proposals: 66.D-0557 and 68D-0545 (proprietary data), 073.D-0313 and 59.A-9004 (ESO Science archive) and with ISAAC@VLT, proposal 075.D-0824 (proprietary data).

Astronomy and Astrophysics, 2009

Aims. The iron abundance gradient in the Galactic stellar disk provides fundamental constraints o... more Aims. The iron abundance gradient in the Galactic stellar disk provides fundamental constraints on the chemical evolution of this important Galaxy component. However the spread around the mean slope is, at fixed Galactocentric distance, larger than estimated uncertainties. Methods. To provide quantitative constraints on these trends we adopted iron abundances for 265 classical Cepheids (more than 50% of the currently known sample) based either on high-resolution spectra or on photometric metallicity indices. Homogeneous distances were estimated using near-infrared Period-Luminosity relations. The sample covers the four disk quadrants and their Galactocentric distances range from ∼5 to ∼17 kpc. We provided a new theoretical calibration of metallicity-index-color (MIC) relation based on Walraven and NIR photometric passbands. We estimated the photometric metallicity of 124 Cepheids. Among them 66 Cepheids also have spectroscopic iron abundances and we found that the mean difference is −0.03 ± 0.15 dex. We also provide new iron abundances, based on high-resolution spectra, for four metal-rich Cepheids located in the inner disk. The remaining iron abundances are based on high-resolution spectra collected by our group (73) or available in the literature (130). Results. A linear regression over the entire sample provides an iron gradient of -0.051 ± 0.004 dex kpc −1 . The above slope agrees quite well, within the errors, with previous estimates based either on Cepheids or on open clusters covering similar Galactocentric distances. However, Cepheids located in the inner disk appear systematically more metal-rich than the mean metallicity gradient. Once we split the sample in inner (R G <8 kpc) and outer disk Cepheids we found that the slope (-0.130±0.015 dex kpc −1 ) in the former region is ≈3 times steeper than the slope in the latter one (-0.042 ± 0.004 dex kpc −1 ). We found that in the outer disk the radial distribution of metal-poor (MP, [Fe/H] < −0.02 dex) and metal-rich (MR) Cepheids across the four disk quadrants does not show a clear trend when moving from the innermost to the external disk regions. We also found that the relative fractions of MP and MR Cepheids in the 1st and in the 3rd quadrant differ at 8σ (MP) and 15σ (MR) level. Finally, we found that iron abundances in two local overdensities of the 2nd and of the 4th quadrant cover individually a range in iron abundance of ≈0.5 dex.

Astronomy & Astrophysics, 2013

Context. Classical Cepheids are excellent tracers of intermediate- mass stars, since their distan... more Context. Classical Cepheids are excellent tracers of intermediate- mass stars, since their distances can be estimated with very high accuracy. In particular, they can be adopted to trace the chemical evolution of the Galactic disk. Aims. Homogeneous iron abundance measurements for 33 Galactic Cepheids located in the outer disk together with accurate distance determinations based on near-infrared photometry are adopted

Astronomy and Astrophysics Supplement Series, 1997

In this paper, all the light-curves obtained during the PHEMU91 campaign of observations of the m... more In this paper, all the light-curves obtained during the PHEMU91 campaign of observations of the mutual phenomena of the Galilean satellites are presented. These observations give accurate astrometric positions of major interest for dynamical studies of the motion of the Galilean satellites. The aim of this work is to give observational data directly usable for theoretical studies. We made 374 observations of 111 mutual events from 56 sites. The corresponding data are given in this paper 1 . The accuracy of each observation has been deduced from a comparison with the theoretical predictions. For each observation, information is given about the telescope, the receptor, the site and the observational conditions. Send offprint requests to: J.-E. Arlot 1 Tables 3 and figure 3 are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

Arxiv preprint astro-ph/ …, 2000

ABSTRACT. Deep (I,VI) and (I,BI) color-magnitude diagrams (CMDs) of the Antlia dwarf galaxy, base... more ABSTRACT. Deep (I,VI) and (I,BI) color-magnitude diagrams (CMDs) of the Antlia dwarf galaxy, based on Science Verification (SV) data collected with the FORS I camera on the ESO Very Large Telescope (VLT) are presented. By adopting the new calibration of the Tip of ...

Monthly Notices of the Royal Astronomical Society, 2011

We present new and accurate near-infrared (NIR) J, K-band time series data for the Galactic globu... more We present new and accurate near-infrared (NIR) J, K-band time series data for the Galactic globular cluster (GC) M5 = NGC 5904. Data were collected with SOFI at the NTT (71 J + 120 K images) and with NICS at the TNG (25 J + 22 K images) and cover two orthogonal strips across the center of the cluster of ≈ 5 × 10 arcmin 2 each. These data allowed us to derive accurate mean K-band magnitudes for 52 fundamental (RR ab ) and 24 first overtone (RR c ) RR Lyrae stars. Using this sample of RR Lyrae stars, we find that the slope of the K-band Period Luminosity (PLK) relation (−2.33 ± 0.08) agrees quite well with similar estimates available in the literature. We also find, using both theoretical and empirical calibrations of the PLK relation, a true distance to M5 of 14.44 ± 0.02 mag. This distance modulus agrees very well (1σ) with distances based on main sequence fitting method and on kinematic method (14.44±0.41 mag, Rees 1996), while is systematically smaller than the distance based on the white dwarf cooling sequence (14. 67±0.18 mag, Layden et al. 2005), even if with a difference slightly larger than 1σ. The true distance modulus to M5 based on the PLJ relation (14.50 ± 0.08 mag) is in quite good agreement with the distance based on the PLK relation further supporting the use of NIR PL relations for RR Lyrae stars to improve the precision of the GC distance scale.