Simone R. Zaggia

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The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium; almost all other elements were subsequently created in stars and supernovae. The mass fraction of elements more massive than helium, Z, is known as 'metallicity'. A number of very metal-poor stars has been found, some of which have a low iron abundance but(More)
Astronomical wide field imaging deals with Terabytes data sets and requires new strategies for data reduction and analysis. We discuss here the application of different types of neural nets to the detection and extraction of celestial objects. Preliminary tests show that neural nets are more effective than traditional techniques.
Observations of the Vela pulsar region with the Chandra X-ray observatory have revealed the fine structure of its synchrotron pulsar-wind nebula (PWN), which showed an overall similarity with the Crab PWN. However, contrary to the Crab, no firm detection of the Vela PWN in optical has been reported yet. To search for the optical counterpart of the X-ray(More)
In this paper we present a new, accurate determination of the three components of the absolute space velocity of the Galactic globular cluster NGC 6397 (l ≃ 338 • , b ≃ −12 •). We used three HST/WFPC2 fields with multi-epoch observations to obtain astrometric measurements of objects in three different fields in this cluster. The identification of 33(More)
Aims. In this paper we derive the structure of the Galactic stellar warp and flare. Methods. We use 2MASS red clump and red giant stars, selected at mean and fixed heliocentric distances of R ⊙ ≃ 3, 7 and 17 kpc. Results. Our results can be summarized as follows: (i) a clear stellar warp signature is derived for the 3 selected rings, proving that the warp(More)
We have used extensive V , I photometry (down to V = 20.9) of 33615 stars in the direction of the globular cluster M 55 to study the dynamical interaction of this cluster with the tidal fields of the Galaxy. An entire quadrant of the cluster has been covered, out to 1.5 times the tidal radius. A CMD down to about 4 magnitudes below the turn-off is presented(More)
  • Stefano Rubele, Léo Girardi, +17 authors Jacco Th. van Loon
  • 2015
We analyse deep images from the VISTA survey of the Magellanic Clouds in the Y JK s filters, covering 14 deg 2 (10 tiles), split into 120 subregions, and comprising the main body and Wing of the Small Magellanic Cloud (SMC). We apply a colour–magnitude diagram reconstruction method that returns their best-fitting star formation rate SFR(t), age–metallicity(More)
We use near-infrared observations obtained as part of the Visible and Infrared Survey Telescope for Astronomy (VISTA) Survey of the Magellanic Clouds (VMC), as well as two complementary Hubble Space Telescope (HST) data sets, to study the luminosity and mass functions as a function of clustercentric radius of the main-sequence stars in the Galactic globular(More)
We derive the star formation history (SFH) for several regions of the Large Magellanic Cloud (LMC), using deep near-infrared data from the VISTA near-infrared Y JK s survey of the Magellanic system (VMC). The regions include three almost-complete 1.4 deg 2 tiles located ∼ 3.5 • away from the LMC centre in distinct directions. They are split into 21.0 ′ ×(More)
1E 161348-5055 (1E 1613) is a point-like, soft X-ray source originally identified as a radio-quiet, isolated neutron star, shining at the center of the 2000 yr old supernova remnant RCW103. 1E 1613 features a puzzling 6.67 hour periodicity as well as a dramatic variability over a time scale of few years. Such a temporal behavior, coupled to the young age(More)