On the Diversity of Asymmetries in Gapped Protoplanetary Disks

Abstract

Protoplanetary disks with large inner dust cavities are thought to host massive planetary or substellar companions. These disks show asymmetries and rings in the millimeter continuum caused by dust trapping in pressure bumps and potentially vortices or horseshoes. The origin of the asymmetries and their diversity remains unclear. We present a comprehensive study of 16 disks for which the gas surface density profile has been constrained by CO isotopologue data. First, we compare the azimuthal extents of the dust continuum profiles with the local gas surface density in each disk and find that the asymmetries correspond to higher Stokes numbers or low gas surface density. We discuss which asymmetric structures can be explained by a horseshoe, a vortex, or spiral density waves. Second, we reassess the gas gap radii from the 13CO maps, which are about a factor of 2 smaller than the dust ring radii, suggesting that the companions in these disks are in the brown dwarf (∼15–50 M Jup) or super-Jovian (∼3–15 M Jup) mass regime on eccentric orbits. This is consistent with the estimates from contrast curves on companion mass limits. These curves rule out (sub)stellar companions (q > 0.05) for the majority of the sample at the gap location, but it remains possible at even smaller radii. Third, we find that spiral arms in scattered-light images are primarily detected around high-luminosity stars with disks with wide gaps, which can be understood by the dependence of the spiral arm pitch angle on disk temperature and companion mass.

A faint companion around CrA-9: protoplanet or obscured binary?

“…This value may be slightly overestimated due to the lack of an absolute calibration (Peterson et al 2011). van der Marel et al (2016) found ∼ 1.8 mag from SED fitting, which we use as prior for our SED fitting (Section 4.3), adopting an uncertainty of 0.3 mag.…”

“…The SED of CrA-9 is characteristic of a protoplanetary disc with a large dust cavity (Romero et al 2012;van der Marel et al 2016), i.e. a transition disc.…”

“…Based on both the positive slope of the IR excess and the high stellar accretion rate, Romero et al (2012) recognised it as one of the transition discs of their sample whose properties are the most compatible with giant planet(s) dynamically carving the dust depletion. van der Marel et al (2016) inferred a cavity radius of ∼14 au based on SED modeling. Sicilia-Aguilar et al (2008) had already noted the larger fraction of transition discs in the R CrA cloud core (∼ 50%) compared to other dark clouds of similarly young age, suggesting they were not tracing a short-lived transition phase but rather that they formed with these "transition-like" feature, e.g.…”

“…Visual inspection of the PSF of the STD stars suggests similar Strehl ratios as achieved for CrA-9, for each respective pair of observations. We measured the average flux (in ADUs) in a 1-FWHM aperture, and used the physical fluxes tabulated in van der Bliek et al (1996) to compute zero points. The absolute fluxes calculated for CrA-9 in the 2017 and 2018 datasets are 1.63 ± 0.16 × 10 −14 W m −2 m −1 and 1.08 ± 0.11 × 10 −14 W m −2 m −1 respectively, where we considered a 10% relative uncertainty based on our procedure (e.g.…”

“…In this context, protoplanetary discs with large cavities, also known as transition discs, constitute prime targets to search for nascent giant planets, since they may be carving the cavity (e.g. Espaillat et al 2014;Casassus 2016;Owen 2016;van der Marel et al 2021).…”