In this paper we estimate the ratio OB stars to red supergiants (OB/R) as a function of the distance from the centre of M 33. We found a gradient of the ratio (OB/R) really exists. Our study is based on a new approach in estimating the errors on the ratio (OB/R). On the other hand, by applying a new correlation technique between OB star candidates and red supergiant candidates in the central re...

Spectroscopic observations of 48 emission-line objects of M 33 have been obtained with the multi-object, wide field, fibre spectrograph AF2/WYFFOS at the 4.2m WHT telescope (La Palma, Spain). Line intensities and logarithmic extinction, cβ, are presented for 42 objects. Their location in the Sabbadin & D’Odorico diagnostic diagram (Hα/[S ii] vs Hα/[N ii]) suggests that >70% of the candidates ar...

The nearby galaxy M33 hosts the most luminous steady X-ray source in the Local Group. The high spatial resolution of Chandra allows us to confirm that this ultra-luminous X-ray source is within the nucleus and rule out at the 4.6σ level a previously proposed possible counterpart located 1 away. The X-ray spectrum is well fitted by a disc blackbody with kTin=1.18±0.02 keV and Rin(cos θ)=57±3 km,...