We present improved visual and near-infrared empirical mass-luminosity relations for very low mass stars (M

We have obtained adaptive optics images and accurate radial velocities for 7 very low mass objects, In the course of a long term effort to determine accurate masses for very low mass stars (M

In this paper, we present meteorological and photometric studies of the Oukaimeden astronomical site in Morocco. The meteorological measurements were obtained over 537 days. The photometric data were measured by both FIP and GONG instruments over 1182 days. We have also analysed the weather parameters at the Observatorio del Roque de los Muchachos

We have used a flux-calibrated mosaiced CCD image of M33 in Hα emission to produce a catalogue of the positions and Hα luminosities of 9190 HII regions complete down to a limiting luminosity LHα of 1036 erg/s and constructed a luminosity function (LF) from this catalogue. In contrast to previously published M33 LFs we find the slope of the function

Spectroscopic observations of this X-ray nova with the new 6.5-m MMT on Dec. 1 & 4 show that it contains a black hole primary of at least 6 solar masses. Our prior photometric observations using the FLWO 1.2-m telescope showed that the X-ray nova was near its pre-outburst brightness (IAUC 7390) at V = 18.8 on Oct. 26.

Spectroscopic observations of the fast X-ray transient and superluminal jet source SAX J1819.3-2525 (V4641 Sgr) reveal a best fitting period of P spect=2.81678+/- 0.00056 days and a semiamplitude of K2=211.0+/- 3.1 km s-1. The optical mass function is f(M)=2.74+/- 0.12 Msun. We find a photometric period of P photo=2.81730 +/- 0.00001 days using a