ALMA observations of the early stages of substellar formation in the Lupus 1 and 3 molecular clouds

Abstract

Context. The dominant mechanism leading to the formation of brown dwarfs (BDs) remains uncertain. While the census of Class II analogs in the substellar domain continues to grow, the most direct keys to formation, which are obtained from younger objects (pre-BD cores and proto-BDs), are limited by the very low number statistics available. Aims. We aim to identify and characterize a set of pre-and proto-BDs as well as Class II BDs in the Lupus 1 and 3 molecular clouds to test their formation mechanism. Methods. We performed ALMA band 6 (1.3 mm) continuum observations of a selection of 64 cores previously identified from AzTEC/ASTE data (1.1 mm), along with previously known Class II BDs in the Lupus 1 and 3 molecular clouds. Surveyed archival data in the optical and infrared were used to complement these observations. We expect these ALMA observations prove efficient in detecting the youngest sources in these regions, since they probe the frequency domain at which these sources emit most of their radiation. Results. We detected 19 sources from 15 ALMA fields. Considering all the pointings in our observing setup, the ALMA detection rate was ∼23 % and the derived masses of the detected sources were between ∼0.18 and 124 M Jup. We classified these sources according to their spectral energy distribution as 5 Class II sources, 2 new Class I/0 candidates, and 12 new possible pre-BD or deeply embedded protostellar candidates. We detected a promising candidate for a Class 0/I proto-BD source (ALMA J154229.778-334241.86) and inferred the disk dust mass of a bona fide Class II BD. The pre-BD cores might be the byproduct of an ongoing process of large-scale collapse. The Class II BD disks follow the correlation between disk mass and the mass of the central object that is observed at the low-mass stellar regime. Conclusions. We conclude that it is highly probable that the sources in the sample are formed as a scaled-down version of low-mass star formation, although disk fragmentation may be responsible for a considerable fraction of BDs.

The Initial Conditions of Clustered Core Collapse: Multiwavelength Analysis of Oph A SM1N and N6 at 100 au Resolution

“…Assuming a ∼30% mass accretion efficiency (Alves et al 2007), the final source mass would fall on the border between a brown dwarf and stellar object. The N6-mm mass and luminosity upper limit are similar to values found for proto-or Class 0 brown dwarfs identified in Lupus (Santamaría-Miranda et al 2021).…”

Early Planet Formation in Embedded Disks (eDisk). VI. Kinematic Structures around the Very-low-mass Protostar IRAS 16253-2429

“…Protostars around the BD threshold, i.e., proto-BDs or very-low-mass protostars, are then important to determine down to which mass such a scaling law of protostars holds. Recent observational studies have aimed to identify and characterize proto-BDs, as well as pre-BDs (de Gregorio-Monsalvo et al 2016;Huélamo et al 2017;Santamaría-Miranda et al 2021). To study star formation in this very-low-mass regime, it is, therefore, necessary to establish a method for precisely estimating the central mass of each protostar down to the mass regime around M * ∼ 0.1 M ☉ .…”

The origin of free-floating planets

“…Some evidence in favour of this scenario is that the disc (Luhman et al 2005;Monin et al 2010), outflow (Santamaría-Miranda et al 2020, and binary (Burgasser et al 2003;Bouy et al 2003Bouy et al , 2006bFontanive et al 2018) properties of substellar objects resemble those of low-mass stars. Additionally, several studies have detected candidates of prestellar cores with a mass below the hydrogen-burning limit and proto-brown dwarfs (André et al 2012;Palau et al 2012Palau et al , 2014Lee et al 2013;de Gregorio-Monsalvo et al 2016;Riaz et al 2016;Huélamo et al 2017;Santamaría-Miranda et al 2021).…”