An M-dwarf star in the transition disk of Herbig HD 142527

Abstract

HD 142527A is one of the most studied Herbig Ae/Be stars with a transitional disk, as it has the largest imaged gap in any protoplanetary disk: the gas is cleared from 30 to 90 AU. The HD 142527 system is also unique in that it has a stellar companion with a small mass compared to the mass of the primary star. This factor of $\approx20$ in mass ratio between the two objects makes this binary system different from any other YSO. The HD142527 system could therefore provides a valuable testbed for understanding the impact of a lower mass companion on disk structure. This low-mass stellar object may be responsible for both the gap and the dust trapping observed by ALMA at longer distances. We have observed this system with the NACO and GPI instruments using the aperture masking technique. Aperture masking is ideal for providing high dynamic range even at very small angular separations. We present here the SEDS for HD 142527A and B from the $R$ band up to the $M$ band as well as the orbital motion of HD 142527B over a period of more than 2 years. The SED is compatible with a $T=3000\pm100\,$K object in addition to a 1700\,K black body environment (likely a circum-secondary disk). From evolution models, we find that HD142527B is compatible with an object of mass $0.13\pm0.03\,$Msun, radius $0.90\pm0.15\,$Rsun and age $1.0^{+1.0}_{-0.75}\,Myr$. This age is significantly younger than the age previously estimated for HD142527A. Computations to constrain the orbital parameters found a semi-major axis of $140^{+120}_{-70}$\,mas, an eccentricity of $0.5 \pm 0.2$, an inclination of $125 \pm 15$ degrees, and a position angle of the right ascending node of $-5 \pm 40$ degrees. Despite its high eccentricity, it is unlikely that HD142527B is responsible for truncating the inner edge of the outer disk.