We present a technique to model the instrumental polarization in the focal plane of a telescope. It takes into account that different rays of an incoming beam suffer different variation of the original polarization in their paths through the system. It also considers that the net effect depends on the way in which the different rays interfere with

Long-slit spectroscopy of the extended gas in the Seyfert galaxy NGC 3516 reveals considerable substructure in the narrow emission lines with several kinematically distinct components visible in H-alpha and N II lambda 6583. The velocity measurements cover almost all of the 3 kpc scale, Z-shaped emission-line structure seen in narrow-band images

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The discovery of lithium in the spectrum of the binary system V404 Cygni is described. A high lithium abundance in the secondary star, close to that of very young stars, is derived. Without lithium production, the secondary would have to be comparable in age to the Pleiades cluster. If the system is not being seen at an early moment in its lifetime

Spectroscopy and mapping of the type I postmain-sequence source CRL 618, taken with the 45-m antenna of the Nobeyama Radio Observatory and the 12-m NRAO facility at Kitty Peak, are presented. It is shown that the exterior constant velocity envelope has a typical aspect ratio of about 0.8, extends over a range not less than 70 arcsec, and has an

We present the results of a spectroscopic analysis of 25 galactic luminous OB stars. The gravities are in general lower than previously assumed, especially for giants. The helium abundances are also higher than normal in many cases. Using data from the spectroscopic analysis, radii, luminosities and masses are derived. The observed wind terminal