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)
I-band CCD images of two large regions of the Galactic globular cluster NGC 1261 have been used to construct stellar luminosity functions (LF) for 14000 stars in three annuli from 1. 4 from the cluster center to the tidal radius. The LFs extend to M I ∼ 8 and tend to steepen from the inner to the outer annulus, in agreement with the predictions of the(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)
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 present iron and α element (Mg, Ca, Ti) abundances for a sample of 15 Red Giant Branch stars belonging to the main body of the Sagittarius dwarf Spheroidal galaxy. Abundances have been obtained from spectra collected using the high resolution spectrograph FLAMES-UVES mounted at the VLT. Stars of our sample have a mean metallicity of [Fe/H]=-0.41±0.20(More)
Context. The Sagittarius (Sgr) dwarf spheroidal galaxy is currently being disrupted under the strain of the Milky Way. A reliable reconstruction of Sgr star formation history can only be obtained by combining core and stream information. Aims. We present radial velocities for 67 stars belonging to the Sgr Stream. For 12 stars in the sample we also present(More)
Using the USNO CCD Astrograph all-sky Catalog (UCAC2), we measure the mean proper motion of the two Magellanic Clouds. Appropriately-selected LMC populations show a proper motion µα, µδ ≃ (+0.84, +4.32) that is significantly higher, in µδ, than currently accepted Hipparcos-like values; µα, µδ ≃ (+1.94, −0.14). A higher µα value is also found for the SMC.(More)