We report on a comprehensive analysis of the kilohertz (≥600 Hz) quasi-periodic oscillations (kHz QPOs) detected from the neutron star X-ray transient Aquila X-1 (Aql X-1) with the Rossi X-ray Timing Explorer, between 1997 and 2007. Among kHz QPO sources, Aql X-1 is peculiar because so far only 1-kHz QPO has been reported, whereas in most sources, 2-kHz QPOs are usually detected (a lower and an...

Using an Extreme Ultraviolet Explorer (EUVE) spectrum, we confirm the identification of a white dwarf companion to the B9.5V star 16 Dra (HD150100), and constrain its surface temperature to lie between 29,000 K and 35,000 K. This is the third B star + white dwarf non-interacting Sirius-type binary to be confirmed, after y Pup (HR2875, HD59635) and θ Hya (HR3665, HD79469). 16 Dra and its white d...

0-7803-7231-X/01/$10.00/© 2002 IEEE 2 IEEEAC paper #050, Updated November 29, 2001 Abstract—Italian Space Agency has funded, as one of the possible Italian experiment on board the International Space Station, the development of a new star tracker, called StarNav III, which observes the sky by means of three orthogonal fields of view and focuses all the star images onto a single CCD/CMOS imager....

Using an Extreme Ultraviolet Explorer (EUVE) spectrum, we confirm the identification of a white dwarf companion to the B9.5V star 16 Dra (HD150100), and constrain its surface temperature to lie between 29,000K and 35,000K. This is the third B star + white dwarf non-interacting Sirius-type binary to be confirmed, after y Pup (HR2875, HD59635) and θ Hya (HR3665, HD79469). 16 Dra and its white dwa...

We report on the identification of the optical/IR counterpart of the 29.5-s transient X–ray pulsar GS 1843+009. We re–analysed an archival ROSAT HRI observation of GS 1843+009 obtaining a new refined position. The optical and IR follow–up observations carried out for the new error circle allowed us to find a relatively faint (V = 20.9) and variable early type reddened star (V − R = 2.1). The op...

Recent discovery of the afterglow emission from short gamma-ray bursts suggests that binary neutron star or black hole-neutron star binary mergers are the likely progenitors of these short bursts. The accretion of neutron star material and its subsequent ejection by the central engine implies a neutron-rich outflow. We consider here a neutron-rich relativistic jet model of short bursts, and inv...

Recent discovery of the afterglow emission from short gamma-ray bursts suggests that binary neutron star or black hole-neutron star binary mergers are the likely progenitors of these short bursts. The accretion of neutron star material and its subsequent ejection by the central engine implies a neutron-rich outflow. We consider here a neutron-rich relativistic jet model of short bursts, and inv...

We report on a comprehensive analysis of the kilo-Hz (> 600 Hz) quasi-periodic oscillations (kHz QPOs) detected from the neutron star X-ray transient Aquila X-1 (Aql X-1) with the Rossi X-ray Timing Explorer, between 1997 and 2007. Among kHz QPO sources, Aql X-1 is peculiar because so far only one kHz QPO has been reported, whereas in most sources, two kHz QPOs are usually detected (a lower and...

We have carried out a series of small scale collisional N-body calculations of single-mass star clusters to investigate the dependence of the lifetime of star clusters on their initial parameters. Our models move through an external galaxy potential with a logarithmic density profile and they are limited by a cut-off radius. In order to find scaling relations between the lifetime of star cluste...

Context. The discovery of photospheric absorption lines in XMM-Newton spectra of the X-ray bursting neutron star in EXO 0748−676 by Cottam and collaborators allows us to constrain the neutron star mass-radius ratio from the measured gravitational redshift. A radius of R = 9 − 12 km for a plausible mass range of M = 1.4 − 1.8 M⊙ was derived by these authors. Aims. It has been claimed that the ab...