MAGNETIC STARS. 6-th Scientific Conference of the Subcommission No.4 of the Multilateral Cooperation of the Academies of Sciences of Socialist Countries "Physics and Evolution of Stars". Riga, April 10-12, 1984, p. 68
The variable star ET And - a triple system?
E. Gerth, G. Scholz
Academy of Sciences of the GDR, Central Institute of Astrophysics, Potsdam (GDR)
Zentralinstitut für Astrophysik der Akademie der Wissenschaften der DDR, DDR-1500 Potsdam Telegrafenberg
Bulgarian National Astronomical Observatory, Smolian
Simultaneous spectroscopic and photometric observations of the variable ET And carried out in the years 1981-83 at the Bulgarian National Astronomical Observatory in Rozhen suggest that this star consists of three components. The binary nature of the star is already known; after Grygar and Ouhrabka the orbital period is 48.308 days. Hildebrandt, Hempelmann and Panov determined a rotational period for the main star of 1.61881 day. The analysis of our data yields - besides the known periods - a variation of the radial velocity with a period of 0.1989 day and a photometric variation with half of this value, i.e. with 0.0994 day.
The phase relation between the waves of the radial velocity and the light curves is hardly to be explained by a spot model or by pulsations. A reasonable explanation is given by the assumption, that the main component is a binary itself. The companion produces tidal waves, which are running around the surfaces of both components with a phase shift, so that the large axes of the star bodies are nearly arranged crosswise to the radial direction. Under the assumption that ET And is a main-sequence B9 star, the orbital radius of the inner binary system of the triple has to be smaller than the stellar radius.
To overcome this contradiction it is assumed, that the star is located in the domain of the horizontal branch stars in the HR diagram. A magnetic field is not detected yet. But it can be concluded that the contraction of the star in the action of tidal forces may result in a considerable magnetic field.
(This is a summary of a lecture held by E. Gerth at the conference 1984 in Riga, which was printed as a manuscript in the conference booklet on page 68.
The conception of the lecture and the booklet are preserved in the personal archives of E. Gerth.)
P 62. Gerth, E., Scholz, G., Panov, K.:
The variable star ET And - a triple System?
MAGNETIC STARS. 6-th Scientific Conference of the Subcommission No. 4
of the Multilateral Cooperation of the Academies of Sciences of Socialist Countries
on Physics and Evolution of Stars, Riga 1984, p. 68
Further publications of the authors on this item:
P 69. Gerth, E.:
Short-periodic radial velocity variations of the B9p star ET And
IAU-Symposium No. 90, (1985) on Crimea (USSR) on
Upper Main Sequence Stars with Anomalous Abundances
eds. C.R. Cowley et al., Reidel Publ. Company 1986, p. 235-238
P 74. Scholz G., Gerth E.:
Remarks on Photometric and Spectroscopic Variations
of the B9p Star ET And
Meeting on Observation and Interpretation of Pulsating Stars,
Sonneberg 4-8 Sep 1989. Ed. W. Wenzel,
Veroeff. d. Sternwarte Sonneberg 10 (1990) 5, 413-415
P 75. Gerth E., Scholz G.:
The Variable Star ET Andromedae - a Tidally Exited Pulsator?
Meeting on Observation and Interpretation of Pulsating Stars, Sonneberg 4-8 Sep. 1989
ed. W. Wenzel, Veroeff. d. Sternwarte Sonneberg 10 (1990) 5, 415-420