Summary: A&A 378, 936945 (2001)
c ESO 2001
BI Lyncis: A hydrogen-deficient binary consisting
of two low-mass giants of spectral types
early-B and G
C. S. Jeffery and R. Aznar Cuadrado
Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
Received 21 June 2001 / Accepted 4 September 2001
Abstract. BI Lyn has previously been misclassified as an evolved binary system containing either a hot subdwarf
or white dwarf and a thick accretion disk. New intermediate dispersion spectra are presented which demonstrate
clearly that the hot component is a luminous low-mass helium star and the cool companion is a rapidly rotating
G-type giant. Techniques of spectrum synthesis have been used to establish the dimensions of both components.
Although the orbital period of the system remains unknown, other phenomena are entirely consistent with these
observed dimensions. A 0.34 d periodic photometric variation could be explained by pulsations in the B-type
primary and, by analogy with other H-deficient binaries, it is suggested that the variable absorption in H may
be due to a gas stream flowing through the inner Lagrangian point.