Swiss Telescope Research Articles

Contribution à l'étude des spectres composites

HD 174016-7, listed by [Hynek (1938)] as a star having a composite spectrum, was on our observing programmes of such objects carried out both at the Cambridge Observatories and at the Observatoire Midi-Pyrenees. Most of the observations were made with the CORAVEL spectrovelocimeter of the Swiss telescope at the Observatoire de Haute-Provence. We find that this star is a long-period spectroscopic binary with two correlation dips; we obtain the following orbital elements: days; T = JD 2450605.2; ; ; km s-1 ; km s-1 ; km s-1 ; Gm; Gm; ; . The primary is a giant star of spectral type near G6III, and the hot dwarf secondary is found to be a peculiar A star of type A0p Sr, Cr, Eu, Si; so HD 174016-7 is, to our knowledge, the second discovered composite-spectrum binary with a Ap-type hot component. A confrontation with Hipparcos data suggests and mv = 0.6 mag. On the basis of very accurate masses of main sequence stars by [Andersen (1991),] we estimate the mass, , of the giant primary, the orbital inclination, , and the mean linear separation of the components, AU. The evolutionary status of the system is discussed using [Schaller et al. (1992)] diagram for stars of solar metallicity. Theoretical masses suggested by this diagram confirm the proposed model.

Photometric and Spectroscopy Observations of Peculiar Nuclei of Planetary Nebulae

Photometric and spectroscopic observations of some bright central stars of planetary nebulae (PN) have been conducted between 1984 and 1987 with the following tools: differential photometer P7 (70-cm swiss telescope, La Silla c/o ESO); radial velocity scanner CORAVEL (1-m swiss telescope, Observatoire de Haute-Provence = OHP); spectrograph CARELEC with CCD detector (193-cm telescope, OHP).

Activity and Secondary Minimum of RZ Eridani

RZ Eridani is an eclipsing binary star with Algol-type light curve of rather long period of 39.28 days. As this star exhibits emission lines of Ca 11 H and K it was classified also as RS CVn type. RZ Eri has been occasionally observed with the GENEVA photometric system with 40cm and later 70cm Swiss telescope at La Silla, Chile, since 1977 mainly for obtaining a complete light curve and for detecting the secondary minimum. The observation showed, that the brightness outside minima really varies as the RS CVn stars usually do. The secondary minimum has been detected at the phase 0.67. Apart from that, the variation of the brightness outside the minima occasionally drops for a short time (about one day or even less). These drops may be due to rotation and uneven distribution of active regions on the surface of the secondary or by the gas streams between the two components. The variation of the light outside minima is certainly not caused by the primary component, because such jumps in the brightness were detected during the total eclipse, when the primary component is not visible. This star certainly deserves more both photometric and spectroscopic attention. Preliminary search for periodicities by G. Burki showed that apart from the orbital period no other periods within the range of days are present. Further details will be published later elsewhere.

Temperature Effect in Zero-Point Drift

The relationship between the observed magnitude of a star and the air-mass takes the shape of a loop. These loops are caused by the zero-point drift of the photometer in use and by the variations of the atmospheric extinction taking place during the observation (Kviz 1979). From observations where the temperature drift of the photometer and of the photomultiplier were recorded, it is evident that the sense of the loops is correlated with the physical temperature of the photo-multiplier. Measurements have been made with the Swiss telescope and the 7-colour Geneva photometer P 7 using pulse counting with PM tube EMI9798 — described in Burnet (1976) and Burnet, Rufener (1979) — at La Silla, Chile.