We present ESO-NTT low resolution spectroscopy of the neutron star X-ray transient Cen X-4 in quiescence over a complete orbital cycle. Our data reveal the presence of a K3-7 V companion which contributes 63% to the 5600-6900 Å flux and orbits the neutron star with a velocity semi-amplitude of K_2=145.8± 1.0 km s-1. This, combined with a previous

A good alternative to traditional methods of passing on astronomical concepts is to use a 'collateral' story that catches the public's attention. It may also simultaneously give a vital opportunity to awaken the critical faculty that often seems so perilously close to extinction these days. The recipe is simple: nothing but an actor or actress, his

We report the discovery of twin kilohertz quasi-periodic oscillations (kHz QPOs) in the X-ray flux of XTE J1807-294, the fourth accreting millisecond pulsar (AMP). This is the second AMP exhibiting twin kHz QPOs. In contrast to the first case, SAX J1808.4-3658, the frequency separation Δν between these kHz QPOs is consistent with the pulse

It is well known that when measuring electron densities in H II regions locally via emission line ratios the values observed are 100cm-3, but gobal values obtained via emission measure using surface brightness as the observed parameter are ~1cm-3. This difference is attributable to density fluctuations,and traditional models for these is the `

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We have studied here for the first time the use of the log(H 0/[N 0]), log (H 0/[S 0]) diagnostic diagram for determining the metallicities and ionization parameters of the H 0 regions in the Local Group. An important advantage of using these lines is their proximity in wavelength, which both simplifies the observations and makes the de-reddening