Medium‐Separation Binaries Do Not Affect the First Steps of Planet Formation

Abstract

The first steps of planet formation are marked by the growth and crystallization of sub-micrometer-sized dust grains accompanied by dust settling toward the disk midplane. In this paper we explore whether the first steps of planet formation are affected by the presence of medium-separation stellar companions. We selected two large samples of disks around single and binary T Tauri stars in Taurus that are thought to have only a modest age spread of a few Myr. The companions of our binary sample are at projected separations between ∼10 and 450 AU with masses down to about 0.1 M ⊙ . We used the strength and shape of the 10 µm silicate emission feature as a proxy for grain growth and for crystallization respectively. The degree of dust settling was evaluated from the ratio of fluxes at two different mid-infrared wavelengths. We find no statistically significant difference between the distribution of 10 µm silicate emission features from single and binary systems. In addition, the distribution of disk flaring is indistinguishable between the single and binary system samples. These results show that the first steps of planet formation are not affected by the presence of a companion at tens of AU.

Spectral signatures of disk eccentricity in young binary systems

“…According to Zsom et al (2010), the aggregate sizes are lower in eccentric disks than in axisymmetric disk environments owing to the increase in the relative velocity between the dust particles. We note, however, that an investigation of the SED slopes of medium-separation T Tauri binaries by Pascucci et al (2008) showed that the extent of dust processing in the disk surface layer and the degree of dust settling in binary disks do not differ significantly from those in disks around single stars.…”

“…The binary eccentricity is neglected in this particular calculation. The distance unit is taken to be 40 AU accordingly to the measured separation (Pascucci et al 2008). The initial disk mass is set to 2 × 10 −3 M by the choice of Σ = 17.2 g/cm 2 at 1 AU.…”

“…A recent survey of Taurus medium-separation young binaries revealed that their secondary infrared fluxes are commensurable to their primary ones (Pascucci et al 2008), hence, young binaries might have also circumsecondary disks. In some cases, the infrared flux of a circumsecondary disk is equal to that of the primary, and the common spectra of a system may also contain the presumably distorted line profiles of the secondary.…”

Mid-IR observations of circumstellar disks

“…In case of the three spectroscopic binary (SB) systems, silicate dust is either seen in small amounts or is absent, which can be explained by the removal of dust inside the circumbinary disk. Pascucci et al (2008) demonstrated that companions at separations of tens of AU have no impact on the dust evolution, which would be interesting to study for a carefully defined target sample with closer companions. Table 4.…”

Prospects for planet formation in multiple stellar systems

“…Considering disks located in multiple systems, the properties of their innermost, planet-forming, regions are indistinguishable from those of single stars (e.g., White & Ghez 2001, Pascucci et al 2008. This suggests that the required initial conditions for planet formation are met equally well in the higher-mass component of a multiple system as in single stars, but that lower-mass components may have more adverse initial conditions to form planets.…”