On the basis of Synthetic Horizontal Branches computed with Sweigart and Gross (1976) Horizontal Branch evolutionary tracks, and by means of Sweigart and Gross (1978) Red Giant Branch star models, the calibration of the ratio R = N(HB)/N(RGB) in terms of helium abundance (Y), He-core mass (Mc) and Horizontal Branch morphology is derived. The

The authors have made observations of the spectrum of comet Halley on various dates between September 1985 and December 1986, obtaining multipositional long-slit absolute spectrophotometry of the inner region of the coma in the visible range. They present a study of the emission in the 3883 Å line of the (0-0) transition of CN. The observed CN

Energy transport by radiation is an important contribution to the energy budget in stellar atmospheric structures. In this paper, radiative relaxation of small-scale structures is investigated. The authors show in a linear analysis: (1) Already at structural lengths of 10 opacity scale heights, horizontal photon exchange is important for the energy

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Infrared magnitudes in the J, H, K and L bands for 64 metal-deficient stars spanning a wide range in effective temperature, luminosity and metal content are presented. An accuracy of 0.02 magnitude is obtained for the JHK bands and 0.03 for the L filter. Infrared-infrared and optical-infrared colour-colour diagrams are discussed and compared with