Composite spectraPaper 10: the equal-mass binary HR 2030 (K0 IIb+B8 IV)

Abstract

We separate the spectra of the individual components of HR 2030, a sixth-magnitude composite-spectrum binary system, and show that they have types close to K0 IIb and B8 IV, and masses that are equal to within the precision of the measurements (mass The orbit appears to have a very small eccentricity, although reasons are given for believing that such eccentricity is spurious; it has a period of 66 d and an inclination estimated at 30° to the line of sight. Our photometric model of the system confirms the luminosity types derived from the spectra and indicates an interstellar absorption of 0.4 mag, in accord with the observed strength of the interstellar K line. We derive the physical parameters (Teff, Mbol, R, L) of the components, and calculate that the mass of each star is close to 4.0 M⊙. We further show that the hot component has already evolved to a position significantly above the zero-age main sequence (ZAMS), and we propose that the primary is making its first ascent of the red-giant branch. From comparisons with evolutionary tracks, we deduce that the age of the binary (since its arrival at the ZAMS) is in the range While we suspect that the components are sufficiently close for some tidal distortion to occur, the effects are not discernible in our data owing to the rather low orbital inclination. The system shows Si i in emission as a result of irradiation of the primary by the hot secondary, but in the optical spectrum we see little other clear evidence of interaction between the components even though the object has a relatively short period and is a strong X-ray source. On the other hand, Hipparcos photometry suggests the existence of a major non-uniformity of the surface of the primary star.