FW Tau C or FW Tau c: Brown Dwarf or Massive Giant Planet?

On the nature of the tertiary companion to FW Tau: ALMA CO observations and SED modeling

Authors:

Caceres et al

Abstract:

It is thought that planetary mass companions may form through gravitational disk instabilities or core accretion. Identifying such objects in the process of formation would provide the most direct test for the competing formation theories. One of the most promising candidates for a planetary mass object still in formation is the third object in the FWTau system. We here present ALMA cycle 1 observations confirming the recently published 1.3 mm detection of a dust disk around this third object and present for the first time a clear detection of a single peak 12CO(2-1) line, providing direct evidence for the simultaneous existence of a gas disk. We perform radiative transfer modeling of the third object in FW Tau and find that current observations are consistent with a planetary mass object embedded in a disk which is externally irradiated by the binary companion and seen at an inclination of i less than 15 deg. However, we also find that a near edge-on disk around a more massive substellar object can explain the observations if cloud contamination causes the single peak shape of the 12CO(2-1) line. Although this possibility appears less likely, further observations with ALMA, aiming for the detection of less contaminated gas lines, are required to conclusively unveil the nature of the third object in FWTau.