Context: The young σ Orionis cluster is an important location for studying the formation and evolution of stars, brown dwarfs, and planetary-mass objects. Its metallicity, although it is a fundamental parameter, has not been well determined yet. Aims: We present the first determination of the metallicity of nine young late-type stars in σ Orionis

The accreting millisecond X-ray pulsar SAX J1808.4-3658 recently exhibited another outburst in September and October 2008 (ATel #1728). During this outburst, on 2008 Oct 2, we obtained a ~40 ks observation with Suzaku. The XIS detectors were operated in 1/4 window mode, with 1 sec burst, leading to a good time exposure of 21 ks for the XIS 0, 1 and

Context: Current atmospheric models cannot reproduce some of the characteristics of the transition between the L dwarfs with cloudy atmospheres and the T dwarfs with dust-depleted photospheres. It has been proposed that a majority of the L/T transition brown dwarfs could actually be a combinaison of a cloudy L dwarf and a clear T dwarf. Indeed

We present observations for three star clusters, Kron 11, Kron 63 and NGC 121, in the Small Magellanic Cloud. We have studied their structure and derived their fundamental parameters by means of their luminosity functions, their colour magnitude diagrams and the Padova suite of isochrones. NGC 121 is a well-studied object, for which we confirm

Nova V458 Vul erupted on 2007 August 8 and reached a visual magnitude of 8.1 a few days later. Hα images obtained 6 weeks before the outburst as part of the IPHAS Galactic plane survey reveal an 18th magnitude progenitor surrounded by an extended nebula. Subsequent images and spectroscopy of the nebula reveal an inner nebular knot increasing

The AGILE gamma-ray burst GRB 080514B is the first detected to have emission above 30 MeV and an optical afterglow. However, no spectroscopic redshift for this burst is known. We report on our ground-based optical/NIR and millimeter follow-up observations of this event at several observatories, including the multi-channel imager GROND on La Silla