arXiv subjects

L. Pulone

Publications and source records attributed to L. Pulone.

60 records · Page 4Linked to original sources

arXiv1999

Search for the optical counterpart of the 16ms X-ray pulsar in the LMC

The 16ms X-ray pulsar PSR J0537-6910 in SNR N157B is the fastest known isolated (non-recycled) pulsar and, with a rotational energy loss dE/dt ~ 4.8 10^38 erg/s, is the most energetic (together with the Crab). Here we report the results of optical observations of the field, recently performed with the SUSI2 camera of the NTT. Few objects are observed inside the ~ 3 arcsec X-ray error circle but none of them can be convincingly associated to the pulsar, which appears undetected down to V ~ 23.4. With a corresponding optical luminosity Lopt < 1.3 10^33 erg/s, PSR J0537-6910 is, at best, comparable to the other very young pulsars Crab and PSR B0540-69.

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arXiv1998

The mass function of M4 from near IR and optical HST observations

Deep images of the galactic globular cluster M4 taken at various locations with the NIC3 and the WFPC2 cameras on HST were used to derive detailed local optical and near IR luminosity functions. White dwarfs have been detected for the first time on a color sequence at constant luminosity in the F110W band. Transformation of the observed luminosity functions into mass functions via the most up to date theoretical mass luminosity relations currently available results in best fit local mass functions, that consist of a power-law with single exponent x = -0.8 for the inner regions and a two-segment power-law which rises with x = 1 down to M_{814}=8.5 and then drops all the way to the detection limit with x = -0.3 for the outer regions.

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arXiv1998

Theoretical vs. semi-empirical relative ages of globular clusters

Theoretical relative ages of galactic globular clusters have recently been challenged by a semi-empirical relation. It was used to point out that tested sets of isochrones were unable to reproduce the relation and yield internally inconsistent relative ages. We find that differential cluster ages derived with the isochrones by Salaris & Weiss (1998) are reliable and internally consistent. We also show that this consistency depends on using the lower absolute ages determined by SW98, which therefore receive more empirical support. Moreover, we discuss the effect of the clusters absolute age on the evaluation of their differential ages, and its connection with the question of their age dispersion.

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arXiv1998

Old open clusters: the interesting case of Berkeley 21

We present CCD BVI photometry of the old open cluster Berkeley 21, one of the most distant clusters in the Galactic anticentre direction, and possibly the lowest metallicity object in the open clusters sample. Its position and metal abundance make it very important for the study of the Galactic disc. Using the synthetic Colour - Magnitude Diagram method, we estimate values for distance modulus (m-M)0=13.4-13.6, reddening E(B-V)=0.74-0.78 (with possible differential absorption), and age=2.2-2.5 Gyr.

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arXiv1997

The stellar content of the Sagittarius Dwarf Galaxy

We present V,I deep CCD photometry for three fields of the dwarf galaxy in Sagittarius (Sgr). One of the fields is centered on the globular cluster NGC 6715 (M54), which lies in one of the dense clumps of the Sgr galaxy. Comparing the CMD of Sgr with those of globular clusters which are believed to be kinematically associated with the dwarf galaxy, we conclude that the stellar population of Sgr presents a spread in metallicity, and that the dominant population (about 10 Gyr old) is extremely similar to the star content of the associated globular cluster Terzan 7. The estimated distance to Sgr is about d=24.55 Kpc.

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arXiv1994

The Hot End of Evolutionary Horizontal Branches

In this paper we investigate the hot end of the HB, presenting evolutionary constraints concerning the CM diagram location and the gravity of hot HB stars. According to the adopted evolutionary scenario, we predict an upper limit for HB temperatures of about logTe = 4.45, remarkably cooler than previous estimates. We find that such a theoretical prescription appears in good agreement with available observational data concerning both stellar temperatures and gravities.

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