The Enigma of AA Dor

Abstract

AA Dor (LB 3459) is an eclipsing, close binary (P = 0.26d) consisting of a sdOB primary star and an unseen secondary with an extraordinary small mass. The secondary is possibly a former planet which may have survived a common-envelope phase and has even gained mass. In order to investigate on an existing discrepancy between the components' mass derived from NLTE spectral analysis and subsequent comparison to evolutionary tracks and masses derived from radial-velocity and the eclipse curves, we performed phase-resolved high-resolution and high-SN spectroscopy with the UVES attached to the ESO VLT. From the obtained spectra, we have determined AA Dor's orbital parameters (P = 22600.702 +/- 0.005 sec, A = 39.19 +/- 0.05 km/sec, T0 = 2451917.152690) and the rotational velocity (v = 47 +/- 5 km/sec) of the primary.