Search

We present the results of a systematic search for molecular outflows in 68 Very Low Luminosity Objects (VeLLOs) from single-dish observations in CO isotopologues which find 16 VeLLOs showing clear outflow signatures in the CO maps. With additional three VeLLOs from the literature, we analyzed the outflow properties for 19 VeLLOs, identifying 15 VeLLOs as proto-Brown Dwarf (BD) candidates and four VeLLOs as likely faint protostar candidates. The proto-BD candidates are found to have a mass accretion rate ($\sim 10^{-8} - 10^{-7}$ $\rm M_{\odot}$ yr$^{-1}$) lower than that of the protostar candidates ($\gtrsim 10^{-6}$ $\rm M_{\odot}$ yr$^{-1}$). Their accretion luminosities are similar to or smaller than their internal luminosities, implying that many proto-BD candidates might have had either small accretion activity in a quiescent manner throughout their lifetime, or be currently exhibiting a relatively higher (or episodic) mass accretion than the past. There are strong trends that outflows of many proto-BDs are less active if they are fainter or have less massive envelopes. The outflow forces and internal luminosities for more than half of the proto-BD candidates seem to follow an evolutionary track of a protostar with its initial envelope mass of $\sim$0.08 $\rm M_{\odot}$, indicating that some BDs may form in less massive dense cores in a way similar to normal stars. But, because there also exists a significant fraction (about 40%) of proto-BDs with much weaker outflow force than expected by the relations for protostars, we should not rule out the possibility of other formation mechanism for the BDs., Comment: 32 pages, 9 Figures, 5 Tables, Accepted for publication in ApJS

We performed mapping observations of the Class I protostellar binary system L1551 NE in the C$^{18}$O ($J$=3-2), $^{13}$CO ($J$=3-2), CS ($J$=7-6), and SO ($J_N$=7$_8$-6$_7$) lines with Atacama Submillimeter Telescope Experiment (ASTE). The ASTE C$^{18}$O data are combined with our previous SMA C$^{18}$O data, which show a $r \sim$300-AU scale Keplerian disk around the protostellar binary system. The C$^{18}$O maps show a $\sim$20000-AU scale protostellar envelope surrounding the central Keplerian circumbinary disk. The envelope exhibits a northeast (blue) - southwest (red) velocity gradient along the minor axis, which can be interpreted as a dispersing gas motion with an outward velocity of 0.3 km s$^{-1}$, while no rotational motion in the envelope is seen. In addition to the envelope, two $\lesssim$4000 AU scale, high-velocity ($\gtrsim$1.3 km s$^{-1}$) redshifted $^{13}$CO and CS emission components are found to $\sim$40$^{\prime\prime}$ southwest and $\sim$20$^{\prime\prime}$ west of the protostellar binary. These redshifted components are most likely outflow components driven from the neighboring protostellar source L1551 IRS 5, and are colliding with the envelope in L1551 NE. The net momentum, kinetic and internal energies of the L1551 IRS 5 outflow components are comparable to those of the L1551 NE envelope, and the interactions between the outflows and the envelope are likely to cause the dissipation of the envelope and thus suppression of the further growth of the mass and mass ratio of the central protostellar binary in L1551 NE., Comment: 37 pages, 14 figures