An Upper Limit on the Mass of the Circumplanetary Disk for DH Tau b^*

Abstract

DHTau is a young (∼1 Myr) classical TTauri star. It is one of the few young PMS stars known to be associated with a planetary mass companion, DHTaub, orbiting at large separation and detected by direct imaging. DHTaub is thought to be accreting based on copious a H emission and exhibits variable Paschen Beta emission. NOEMA observations at 230 GHz allow us to place constraints on the disk dust mass for both DHTaub and the primary in a regime where the disks will appear optically thin. We estimate a disk dust mass for the primary,, which gives a disktostar mass ratio of 0.014 (assuming the usual gas todust mass ratio of 100 in the disk). We find a conservative disk dust mass upper limit of 0.42 M ⊕ for DHTaub, assuming that the disk temperature is dominated by irradiation from DH Tau b itself. Given the environment of the circumplanetary disk, variable illumination from the primary or the equilibrium temperature of the surrounding cloud would lead to even lower disk mass estimates. AMCFOST radiative transfer model, including heating of the circumplanetary disk by DHTaub and DHTauA, suggests that a mass-averaged disk temperature of 22 K is more realistic, resulting in a dust disk mass upper limit of 0.09 M ⊕ for DHTaub. We place DHTaub in context with similar objects and discuss the consequences for planet formation models.

An Explanation of the Very Low Radio Flux of Young Planet-mass Companions

“…Compact dust continuum emission is optically thick, rather than optically thin as usually assumed. We note that similar thoughts have been discussed and applied to derive an upper limit on disk size MacGregor et al 2017;Ricci et al 2017;Wolff et al 2017). Here, we further study the brightness and implications of compact optically-thick disks.…”

The Young Substellar Companion ROXs 12 B: Near-infrared Spectrum, System Architecture, and Spin–Orbit Misalignment*

“…Paβ emission was not observed in the moderate-resolution spectroscopy of GQ Lup B presented by McElwain et al (2007) and Lavigne et al (2009), which suggests that the emission observed by Seifahrt et al (2007) was variable. Similarly, Wolff et al (2017) also found variable emission for DH Tau B. This suggests that other companions without Paβ emission could be observed during a quiescent state of low accretion.…”

A Rotation Rate for the Planetary-mass Companion DH Tau b

“…This observation is in good agreement with models of magnetic coupling between the planet and its circumplanetary disk (Takata & Stevenson 1996;Batygin 2018), which predict that this mechanism should provide an efficient means of angular momentum dissipation. Interestingly, previous studies have found active accretion signatures for DH Tau b, suggesting that it may still possess a cicumplanetary gas disk (Zhou et al 2014;Bonnefoy et al 2014;Wolff et al 2017).…”

“…In this model, the disk extracts angular momentum from the planet, while meridional circulation of gas within the Hill sphere recycles this angular-momentum rich gas back into the circumstellar nebula, thereby decreasing the planet's rotation rate. In fact, there is indirect evidence that DH Tau b is actively accreting, as this object has both Hα and Paβ emission lines in its spectrum (Zhou et al 2014;Bonnefoy et al 2014;Wolff et al 2017). This accretion would presumably be mediated via a circumplanetary gas disk, but Wu et al (2017) did not find any evidence for such a disk when they observed this object with ALMA.…”