Herschel/SPIRE observations of the TWA brown dwarf disc 2MASSW J1207334–393254

Abstract

We present Herschel/SPIRE observations for the 2MASS 1207334−393254 (2M1207) system. Based on radiative transfer modelling of near‐infrared to submillimetre data, we estimate a disc mass of 3 ± 2 MJup and an outer disc radius of 50–100 au for the 2M1207A disc. The relative disc mass for 2M1207A is similar to the T Tauri star TW Hya, which indicates that massive discs are not underabundant around substellar objects. In probing the various formation mechanisms for this system, we find that core accretion is highly uncertain mainly due to the large separation between the primary and the companion. Disc fragmentation could be a likely scenario based on analytical models, and if the disc initially was more massive than its current estimate. Considering that the TW Hydrae Association (TWA) is sparsely populated, this system could have formed via one of the known binary formation mechanisms (e.g. turbulent fragmentation of a core) and survived disruption at an early stage.

HerschelPACS and SPIRE observations of TW Hydrae association brown dwarf disks

“…The upper limit to the disk mass of ∼0.1 M Jup obtained from modeling the 2M1207 SED thus does not rule out disk fragmentation, since the system is relatively old and we have not observed it during its early stages when fragmentation might have occurred (<0.1 Myr). This system may be considered as a very low-mass wide binary rather than a planetary system, and some alternative formation mechanisms, such as the turbulent fragmentation of a core, were discussed in Riaz et al (2012a). Figure 8a compares the relative disk mass upper limits for 2M1207, SS1102, and 2M1139 with the other disk sources in the TWA (using data from Calvet et al 2002;Low et al 2005;Andrews et al 2010).…”

“…However, we cannot rule out that the non-detection for both 2M1207 and SS1102 in the SPIRE bands is caused by the limitations of the confusion noise. We discussed in Riaz et al (2012a) the possibility of the formation of the ∼5 M Jup secondary in the 2M1207 disk via disk fragmentation. Our argument is that even a very low mass disk could produce a fragment of ∼0.035 M Jup , which can then grow over time to form a 5 M Jup mass object.…”

“…In Riaz et al (2012a), we reported a detection for 2M1207 in the SPIRE bands of 250 and 350 μm, but a comparison now with the PACS images indicates that this was a misidentification. The revised SPIRE fluxes (upper limits) for 2M1207 were presented in Riaz et al (2012a), where we noted that the source may be unresolved in the SPIRE bands, given the large positional offset of ∼14 .…”

“…The revised SPIRE fluxes (upper limits) for 2M1207 were presented in Riaz et al (2012a), where we noted that the source may be unresolved in the SPIRE bands, given the large positional offset of ∼14 . However, the contamination from the nearby bright object would likely dominate the composite photometry in such a scenario.…”

ALMA Observations of the Young Substellar Binary System 2M1207

“…2M1207A and b have an angular separation of 0 77, which corresponds to a projected separation of 40.6 au at a distance of 52.8 pc (Ducourant et al 2008). Given the large companion-to-host mass ratio and large separation, Lodato et al (2005) proposed gravitational fragmentation of the 2M1207A disk (Sterzik et al 2004;Riaz et al 2012) as the most likely formation mechanism for 2M1207b.…”