IC 348-SMM2E: a Class 0 proto-brown dwarf candidate forming as a scaled-down version of low-mass stars

Abstract

We report on Submillimeter Array observations of the 870 µm continuum and CO (3-2), 13 CO (2-1) and C 18 O (2-1) line emission of a faint object, SMM2E, near the driving source of the HH 797 outflow in the IC 348 cluster. The continuum emission shows an unresolved source for which we estimate a mass of gas and dust of 30 M Jup , and the CO (3-2) line reveals a compact bipolar outflow centred on SMM2E, and barely seen also in 13 CO (2-1). In addition, C 18 O (2-1) emission reveals hints of a possible rotating envelope/disk perpendicular to the outflow, for which we infer a dynamical mass of ∼ 16 M Jup . In order to further constrain the accreted mass of the object, we gathered data from Spitzer, Herschel, and new and archive submillimetre observations, and built the Spectral Energy Distribution (SED). The SED can be fitted with one single modified black-body from 70 µm down to 2.1 cm, using a dust temperature of ∼ 24 K, a dust emissivity index of 0.8, and an envelope mass of ∼ 35 M Jup . The bolometric luminosity is 0.10 L ⊙ , and the bolometric temperature is 35 K. Thus, SMM2E is comparable to the known Class 0 objects in the stellar domain. An estimate of the final mass indicates that SMM2E will most likely remain substellar, and the SMM2E outflow force matches the trend with luminosity known for young stellar objects. Thus, SMM2E constitutes an excellent example of a Class 0 proto-brown dwarf candidate which forms as a scaled-down version of low-mass stars. Finally, SMM2E seems to be part of a wide (∼ 2400 AU) multiple system of Class 0 sources.

The Gas Disk: Evolution and Chemistry

“…The ejected fragments, upon cooling and contraction, can form freely floating brown dwarfs and very-low-mass stars (Basu and Vorobyov 2012;Vorobyov 2016). This phenomenon is distinct from previously suggested scenarios of brown dwarf formation via disk fragmentation, wherein finished point-sized objects are ejected (Bate 2009;Stamatellos and Whitworth 2009), and is more consistent with observations of isolated proto-brown dwarf clumps (André et al 2012;Palau et al 2014). b) Dust processing in the depths of massive fragments and formation of solid cores.…”

Molecular Outflows and the Formation Process of Very Low-Mass Objects

“…As discussed in Section 2.2, more observations are needed to confirm the episodicity of the outflow process in VLM objects and hence clarify these two possibilities. Second, the basic properties of the outflow process in our VLM objects such as masses, and mass-loss rates are comparable to those observed in proto BD candidates at earlier stages, e.g., L1014-IRS (class I, Bourke et al 2005) or IC 348-SMM2E (class 0, Palau et al 2014). The similarity implies that the mass-loss rate, and hence the associated accretion rate in VLM objects does not change considerably at different stages of the VLM object formation.…”

“…These VLM cores are dense enough to be gravitational unstable and collapse. Recent detections of proto BD candidates (e.g., André et al 2012;Palau et al 2014) support these models. However, it is still unclear how the physical processes of VLM object formation occur at later stages (e.g., class 0, I, and II).…”

A search for pre- and proto-brown dwarfs in the dark cloud Barnard 30 with ALMA

“…Palau et al (2012) or André et al (2012). Up to now, several objects have been identified as VeLLOs whose properties are consistent with proto-BDs (see e.g., Young et al 2004;Bourke et al 2006;Lee et al 2009;Barrado et al 2009;Palau et al 2012Palau et al , 2014Morata et al 2015). However, the samples of proto-BD candidates are still very small.…”

“…The study of the most embedded and youngest BDs requires observations in the mm/sub-mm regime, where they emit the bulk of their energy as they are dominated by cold envelopes (e.g., Bourke et al 2006;Lee et al 2013;Palau et al 2014).…”