Adaptive optics investigation of two VLM binaries

We report the discovery of a new binary companion to the M-dwarf LP 1033-31 and confirm the binarity of LP 877-72 using the high-resolution near-infrared adaptive optics imaging from the NaCo instrument of the Very Large Telescope. We have characterized both stellar systems and estimated the properties of their individual components. We have found that LP 1033-31 AB with the spectral type of M4.5+M4.5 has a projected separation of 6.7 ± 1.3 AU. Whereas with the spectral type of M1+M4, the projected separation of LP 877-72 AB is estimated to be 45.8 ± 0.3 AU. The binary companions of LP 1033-31 AB are found to have similar masses, radii, effective temperatures, and log g with the estimated values of 0.20 ± 0.04 Mʘ, 0.22 ± 0.03 Rʘ, 3200 K, 5.06 ± 0.04. However, the primary of LP 877-72 AB is found to be twice as massive as the secondary with the derived mass of 0.520±0.006 Mʘ. The radius and log g for the primary of LP 877-72 AB are found to be 1.8 and 0.95 times that of the secondary component with the estimated values of 0.492 ± 0.011 Rʘ and 4.768 ± 0.005, respectively. With an effective temperature of 3750 ± 15 K, the primary of LP 877-72 AB is also estimated to be ~ 400 K hotter than the secondary component. We have also estimated the orbital period of LP 1033-31 and LP 877-72 to be ~ 28 and ~ 349 yr, respectively. The binding energies for both systems are found to be > 1043 erg, which signifies both systems are stable.