ORCID Profile
0000-0002-3182-3574
Current Organisations
Università degli Studi di Pisa
,
Université de Strasbourg
,
University of Victoria
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Publications
The Pristine Inner Galaxy Survey (PIGS) I: tracing the kinematics of metal-poor stars in the Galactic bulge
Publisher: Oxford University Press (OUP)
Date: 26-11-0011
Abstract: Our Galaxy is known to contain a central boxy eanut-shaped bulge, yet the importance of a classical, pressure-supported component within the central part of the Milky Way is still being debated. It should be most visible at low metallicity, a regime that has not yet been studied in detail. Using metallicity-sensitive narrow-band photometry, the Pristine Inner Galaxy Survey (PIGS) has collected a large s le of metal-poor ($\\rm {[Fe/H]}\\, \\lt -1.0$) stars in the inner Galaxy to address this open question. We use PIGS to trace the metal-poor inner Galaxy kinematics as function of metallicity for the first time. We find that the rotational signal decreases with decreasing [Fe/H] , until it becomes negligible for the most metal-poor stars. Additionally, the velocity dispersion increases with decreasing metallicity for $-3.0 \\lt \\rm {[Fe/H]}\\, \\lt -0.5$, with a gradient of −44 ± 4 km s−1 dex−1. These observations may signal a transition between Galactic components of different metallicities and kinematics, a different mapping on to the boxy eanut-shaped bulge for former disc stars of different metallicities and/or the secular dynamical and gravitational influence of the bar on the pressure-supported component. Our results provide strong constraints on models that attempt to explain the properties of the inner Galaxy.
The Pristine Inner Galaxy Survey (PIGS) – IV. A photometric metallicity analysis of the Sagittarius dwarf spheroidal galaxy
Publisher: Oxford University Press (OUP)
Date: 07-10-2022
Abstract: We present a comprehensive metallicity analysis of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) using Pristine CaHK photometry. We base our member selection on Gaia EDR3 astrometry, applying a magnitude limit at G0 = 17.3, and our population study on the metallicity-sensitive photometry from the Pristine Inner Galaxy Survey (PIGS). Working with photometric metallicities instead of spectroscopic metallicities allows us to cover an unprecedented large area (∼100 square degrees) of the dwarf galaxy, and to study the spatial distribution of its members as function of metallicity with little selection effects. Our study compares the spatial distributions of a metal-poor population of 9719 stars with [Fe/H] & −1.3 and a metal-rich one of 30 115 stars with [Fe/H] & −1.0. The photometric Sgr s le also allows us to assemble the largest s le of 1150 very metal-poor Sgr candidates ([Fe/H] & −2.0). By investigating and fitting the spatial properties of the metal-rich and metal-poor population, we find a negative metallicity gradient which extends up to 12 degrees from the Sgr centre (or ∼5.5 kpc at the distance of Sgr), the limit of our footprint. We conclude that the relative number of metal-poor stars increases in the outer areas of the galaxy, while the central region is dominated by metal-rich stars. These findings suggest an outside-in formation process and are an indication of the extended formation history of Sgr, which has been affected by the tidal interaction between Sgr and the Milky Way.
The Pristine Inner Galaxy Survey (PIGS) VII: a discovery of the first inner Galaxy CEMP-r/s star
Publisher: Oxford University Press (OUP)
Date: 19-05-2023
Abstract: Well-studied very metal-poor (VMP, [Fe/H] & −2) stars in the inner Galaxy are few in number, and they are of special interest because they are expected to be among the oldest stars in the Milky Way. We present high-resolution spectroscopic follow-up of the carbon-enhanced metal-poor (CEMP) star Pristine_184237.56-260624.5 (hereafter Pr184237) identified in the Pristine Inner Galaxy Survey. This star has an apocentre of ∼2.6 kpc. Its atmospheric parameters (Teff = 5100 K, log g = 2.0, and [Fe/H] = −2.60) were derived based on the non-local thermodynamic equilibrium (NLTE) line formation. We determined abundances for 32 elements, including 15 heavy elements beyond the iron group. The NLTE abundances were calculated for 13 elements from Na to Pb. Pr184237 is strongly enhanced in C, N, and O, and both s- and r-process elements from Ba to Pb it reveals a low carbon isotope ratio of 12C/13C = 7. The element abundance pattern in the Na–Zn range is typical of halo stars. With [Ba/Eu] = 0.32, Pr184237 is the first star of the CEMP-r/s subclass identified in the inner Galaxy. Variations in radial velocity suggest binarity. We tested whether a pollution by the s- or i-process material produced in the more massive and evolved companion can form the observed abundance pattern and find that an i-process in the asymptotic giant branch star with a progenitor mass of 1.0–2.0 $\\, {\\rm M}_{\\odot }$ can be the solution.
GHOST Commissioning Science Results: Identifying a New Chemically Peculiar Star in Reticulum II
Publisher: American Astronomical Society
Date: 09-2023
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Related Funding Activities
No related grants have been discovered for Federico Sestito.