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

Abstract

Aims. HD 42527A 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 ≈20 in mass ratio between the two objects makes this binary system different from any other YSO. The HD 142527 system could therefore provide a valuable test bed 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 dust trapping observed by ALMA at longer distances. Methods. We 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 the spectral energy distribution (SED) for HD 142527A and B. Brightness of the companion is now known from the R band up to the M band. We also followed the orbital motion of HD 142527B over a period of more than two years. Results. The SED of the companion is compatible with a T = 3000 ± 100 K object in addition to a 1700 K blackbody environment (likely a circum-secondary disk). From evolution models, we find that it is compatible with an object of mass 0.13 ± 0.03 M , radius 0.90 ± 0.15 R , and age 1.0 +1.0 −0.75 Myr. This age is significantly younger than the age previously estimated for HD 142527A. Computations to constrain the orbital parameters found a semimajor axis of 140 +120 −70 mas, an eccentricity of 0.5 ± 0.2, an inclination of 125 ± 15 degrees, and a position angle of the right ascending node of −5 ± 40 degrees. Inclination and position angle of the ascending node are in agreement with an orbit coplanar with the inner disk, not coplanar with the outer disk. Despite its high eccentricity, it is unlikely that HD 142527B is responsible for truncating the inner edge of the outer disk.

Spiral Arms in Disks: Planets or Gravitational Instability?

“…Whereas a massive planet exterior to the arms can generate the observed two-arm spirals, a stellar companion closer than ∼5″ could produce a similar spiral structure in a disk with a typical size of ∼1-2″ (e.g., as in the HD 100453 disk; Wagner et al 2015;Dong et al 2016c;Wagner et al 2018). The companion to HD142527, which is located well within the gap in the disk, is commonly interpreted as having too low a mass (0.13 M e ; Lacour et al 2016) and eccentricity to generate the observed spiral arms, so this object is included in our sample (although see Price et al 2018). Lastly, we removed HD141569 from the sample, because its low dust mass (on the order of 1 M ⊕ or less; Flaherty et al 2016;White et al 2016) makes the system prone to radiation pressure and photoelectric instability, which can also produce spiral arm structures (e.g., Richert et al 2018b).…”

A Close-up View of the Young Circumbinary Disk HD 142527

“…Recent simulations by Lacour et al (2016) have shown that the companion is probably orbiting on the inner disk plane, not coplanar with the outer disk, with an eccentricity of about 0.6 not sufficient to explain the dust cavity size. Furthermore, this interaction should lead to the formation of a gas density maximum very close to the cavity edge, i.e., between 40-60 AU.…”

“…The primary star is an Herbig FeIIIe star with a mass of 2.4 M (Verhoeff et al 2011) which is accreting material at the rate of about 10 −7 M yr −1 (Garcia Lopez et al 2006;Mendigutía et al 2014). The secondary star has a mass between 0.1-0.3 M , an orbital radius between 15-20 AU, and a mass accretion rate of ∼ 6 × 10 −10 M yr −1 (Biller et al 2012;Close et al 2014;Lacour et al 2016). The binary system is at the center of a large elliptical dust cavity of about 120 AU in radius and of an asymmetric disk with a dense dust crescent on the north side (Ohashi 2008;.…”

Characterization of exoplanets from their formation

“…The comparison with LkCa 15b is found in the next section. The L Hα of HD 142527 B (Close et al 2014), which is a low-mass M dwarf (Lacour et al 2016), is also shown for comparison.…”