Optical Spectra of Zeta-Aurigae Binary Systems - Part Three - the 1989 Eclipse of Tau-Persei

Details Optical Spectra of Zeta-Aurigae Binary Systems - Part Three - the 1989 Eclipse of Tau-Persei Optical Spectra of Zeta-Aurigae Binary Systems - Part Three - the 1989 Eclipse of Tau-Persei

Feb 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...254..289g&link_type=abstract

Astronomy and Astrophysics, Vol.254, NO. FEB(I), P. 289, 1992

Astronomy and Astrophysics

Astrophysics

24

Stars, Atmospheres Of, Stars: Chromospheres Of, Stars: Individual: Τ Per, Stars: Binaries: Spectroscopic

Scientific paper

We present a detailed study of the composite-spectrum eclipsing system τ Per. From new radial-velocity measurements and high-dispersion spectroscopy, together with photometric data taken from the literature, we refine the orbital and physical parameters of the system, and uncover the secondary's spectrum for the first time by our subtraction technique. The primary appears to have a spectral type near to G 8 III a, slightly later than previously thought; the secondary, a rapidly rotating early-A dwarf, is suspected of belonging to the Boo class of objects. Spectra secured during the system's partial eclipse of 1989 January reveal strong chromospheric absorption lines of Ca ii but only weak lines of other elements. Analysis of those spectra, together with photometric observations made during the eclipse, indicates that the eclipse had maximum depths ΔV = 0m.16, ΔB = 0mm.45, when about 80% of the light from the dwarf was obscured. A measurement of the mass ratio has enabled us to present an improved model for the system; we find radii R1 = 16 Rsun, R2 = 2.2 Rsun for the giant and dwarf, respectively, masses m1 = 2.4 Msun and m2 = 1.8 Msun, and an inclination of the plane of the orbit of about 87°. The eclipse appears to take place at a latitude of 69° on the disk of the giant, or at a minimum projected linear separation between the centre of the giant and the eclipse trajectory of D = 14.9 Rsun. The chromospheric features, isolated by our subtraction technique and analyzed by a modified curve of growth that takes into account the size of the dwarf's disk in relation to the density gradient of the giant's chromosphere through which it is radiating, gives strong evidence that the chromospheric material is distributed inhomogeneously, or at least without radial symmetry. From a tentative model of such a chromosphere, and from the corresponding density distributions of various atoms and ions within it, we conclude that the giant star possesses a thin, clumpy chromosphere and probably a hot, solar-like corona.

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