HIPPARCOS Astrometric Orbit and Evolutionary Status of HR 6046

Abstract

The previously known, 6-yr spectroscopic binary HR 6046 has been speculated in the past to contain a compact object as the secondary. A recent study has re-determined the orbit with great accuracy, and shown that the companion is an evolved but otherwise normal star of nearly identical mass as the primary, which is also a giant. The binary motion was detected by the Hipparcos mission but was not properly accounted for in the published astrometric solution. Here we use the Hipparcos intermediate data in combination with the spectroscopic results to revise that solution and establish the orbital inclination angle for the first time, and with it the absolute masses M(A) = 1.38 [-0.03,+0.09] M(Sun) and M(B) = 1.36 [-0.02,+0.07] M(Sun). Aided by other constraints, we investigate the evolutionary status and confirm that the primary star is approaching the tip of the red-giant branch, while the secondary is beginning its first ascent.