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 Teff = 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, Teff = 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.