New spectroscopic observations of the B[e]/K binary system MWC 623

Abstract

The B[e]/K binary system MWC 623 was reinvestigated using new spectroscopic observations. The absorption lines of the K and the B star do not exhibit any significant radial velocity variations over a time interval of 14 years. The spectral classification using a recent echelle spectrum yielded spectral types of K2II-Ib and B4III. The luminosity class of the K star gives an estimate of the distance towards MWC 623 of 2.4(+1.4/-0.9) kpc. This is consistent with the kinematic distance of 2.0(+0.6/-0.3) kpc. The masses derived from the locations of the binary components in the H-R diagram are 7+-1.5 Msun and 7.5+-2.5 Msun for the B and K star, respectively, i.e. the mass ratio is close to 1. Both stars are coeval with an age of 50+10/-20 Myr as shown by the comparison with isochrones. The high luminosity of the K star excludes a pre-main sequence evolutionary phase as explanation for the strong LiI lambda 6708 absorption line observed in the late-type component. Rather, the high lithium abundance is a consequence of the young age. Likewise, the B[e] star is a slightly evolved object starting it post-main sequence evolution.