Spectral analysis of two directly imaged benchmark L dwarf companions at the stellar-substellar boundary

We used multiple epochs of high-contrast imaging spectrophotometric observations to determine the atmospheric characteristics and thermal evolution of two previously detected benchmark L dwarf companions, HD 112863 B and HD 206505 B. We analyzed IRDIS and IFS data from VLT/SPHERE of each companion, both of which have dynamical masses near the stellar-substellar boundary. We compared each companion with empirical spectral standards, and constrained their physical properties through atmospheric model fits. From these analyses, we estimate that HD 112863 B is spectral type L3 ± 1 and that HD 206505 B is spectral type L2 ± 1. Using the BT-Settl atmospheric model grids, we found a bimodal solution for the atmospheric model fit of HD 112863 B where T eff = 1757 −36 +37 K or 2002 −24 +23 K and log g = 4.973 −0.063 +0.057 or 5.253 −0.033 +0.037 , while for HD 206505 B, T eff = 1754 −13 +13 K and log g = 4.919 −0.029 +0.031 . The results of a comparison of the bolometric luminosities of the companions with evolutionary models imply that both companions are likely above the hydrogen burning limit.