We present observational evidence of high-temperature spiral structure on the accretion disk of the dwarf nova IP Peg during outburst. The Doppler tomogram of ionized helium He II 4686 shows a two-arm spiral pattern on the disk image. The spiral shocks are generated by the tides raised by the secondary star on the disk and shows that a new

New improvements in the measurement of both the optical solar spectrum and laboratory wavelengths for lines of neutral iron are combined to extract central wavelength shifts for 1446 lines observed in the Sun. This provides the largest available database of accurate solar wavelengths useful as a reference for comparison with other solar-type stars

Data from five continuous years (1984 to 1989) at Teide Observatory (Iza na, Tenerife, Canary Islands) obtained with a full-disc solar multichannel photometer devoted to the detection of solar intensity oscillations has now been used for a detailed study of the extinction coefficient behaviour at several wavelengths (from 450 nm to 870 nm) and

Three different types of evidence are presented in favour of the hypothesis that the HII regions in disk galaxies with H-alpha luminosities greater than a critical value of 10^(38.6)^ erg s^(-1)^ are density bounded, and that the escaping Lyman continuum photons from these are the principal ionizing agents for the diffuse ISM in disk galaxies. This

IAUC 6875 available at Central Bureau for Astronomical Telegrams.

We present echelle spectroscopy in the 3500- to 7060-Å range for two positions of the Orion nebula. The data were obtained using the 2.1-m telescope at Observatorio Astrónmico Nacional in San Pedro Mártir, Baja California. We have measured the intensities of about 220 emission lines, in particular 81 permitted lines of C+, N+, N++, 0°, 0+, Ne0, Si+