2006MNRAS.373.1351G

HR 1129 is a 4.8-mag star in the constellation Camelopardus, strangely (in view of its brightness) lacking a constellation designation. It has long been known to exhibit a composite spectrum consisting of a late-type primary and an early-type secondary. The radial velocity of the primary is easily measured, and was announced as variable nearly 100 years ago. A preliminary orbit with a period of 6150 d was given for it by one of the present authors in 1990; our new value is 6124±3 d. The system has been resolved by speckle interferometry, but has not been measured systematically by that technique. The spectrum of the primary is found to be very similar to that of α Aqr (G2Ib), although the parallax shows HR 1129 to be somewhat less luminous. The secondary spectrum has been isolated by subtraction and has proved to be that of a B7 star that is somewhat above the main sequence and may itself already be a giant. We present a comprehensive discussion of the spectra of both stars, and deduce that the system is considerably reddened: E(B - V) ∼ 0.30, A_V∼ 0.9 mag. By incorporating 25 measurements of the radial velocity of the secondary, we calculate a double-lined orbit solution which gives the mass ratio for the components as 1.109±0.022; we determine individual masses of 4.8-5.2 M_☉(primary) and 4.3-4.7 M_☉(secondary). The orbit is viewed at an inclination of ∼ 87°, but there are no eclipses. However, around the phases of conjunction the Mgii doublet near λ2800 Å, as seen in IUE spectra, exhibits evidence of two circumstellar absorption systems, which we interpret as a wind from the cool giant and a static shell around it. Substantial 100-µm emission recorded by IRAS points to the presence of warm circumbinary dust enveloping the system, and is likely to have originated in the stellar wind.