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By using dark nebulae as opaque outer screens, the luminosity function of white dwarfs and M dwarfs has been studied. High-extinction areas towards the Orion A, Serpens and rho Oph cloud complexes were observed, covering a volume corresponding to 464 pc3 in the solar neighbourhood, complete to Mv=16.5. Foreground stars were selected by VRI photometry and photometric parallaxes. The resulting foreground sample consists of 21 M dwarfs and 7 white dwarfs. The derived M-dwarf luminosity function is consistent with previous studies, showing no substantial upturn beyond Mv=16. The 7 white dwarfs imply a local density of 0.013(+-0.005)Msun/pc3 (~15% of the dynamical mass in the solar neighbourhood) supporting other recent results but obtained with a completely different method. For the clouds, foreground-star data were used to derive independent cloud distances, while the background stars and a simple model of the Milky Way gave reliable cloud extinctions., Comment: 12 pages, 15 figures, to be published in A&A

The brown dwarf population in the Pleiades cluster has been probed in a deep 850 arcmin2 RIJK survey. The survey is complete to I=21.4 in 76% of the area and to I=20.2 in the remaining 24%. Photometry of 32 previously known members is presented together with 8 new candidates, four of which are below the brown dwarf limit. The faintest one is the lowest mass brown dwarf candidate found hitherto in the Pleiades (I=20.55, 0.04Msun). The derived Pleiades luminosity function is compared to the most recent theoretical mass-luminosity relations and is consistent with a power-law index in the mass function between 0 and 1 to the limit of this survey., Comment: 8 pages, A&A in press

The large-redshift (z=3.8) quasar 1208+1011 has recently been discovered to be a gravitational lens candidate with a separation of 0.47" between the two imaged components (A and B). NOT (Nordic Optical Telescope) and HST (Hubble Space Telescope) studies from 1992 probing primarily the continuum light show that the amplification of A relative to B is almost achromatic with the canonical value A:B=4+/-0.1. In this paper we present high-resolution optical images (FWHM=0.4"-0.5") from 1993 of the quasar. From our narrow-band CCD frames centred on the redshifted Ly-alpha/Nv line at 5900 A we find that A:B=3.85+/-0.2. Our broad-band I images uncontaminated by line-emission are found to be affected by PSF variation over a range of 20\arcsec. However, by iteratively determining the PSF from the images themselves we show that the data can be accounted for by two point sources with A:B=3.35+/-0.2. These results imply that the continuum intensity ratio has decreased during 1992-1993 and that the amplification of the emission-line regions relative to the continuum emitting regions is different in the two components (under the gravitational lens hypothesis). The most conservative interpretation of these results is that 1208+1011 is a gravitationally lensed quasar in which component B is being microlensed, but the possibility that 1208+1011 is a binary quasar is not excluded by the present data., Comment: 6 pages. To appear in A&A 1995