High-resolution ALMA Study of the Proto-Brown-Dwarf Candidate L328-IRS
  This paper presents our observational attempts to precisely measure the
central mass of a proto-brown dwarf candidate, L328-IRS, in order to
investigate whether L328-IRS is in the substellar mass regime. Observations
were made for the central region of L328-IRS with the dust continuum and CO
isotopologue line emission at ALMA band 6, discovering the detailed outflow
activities and a deconvolved disk structure of a size of $\sim$87 AU $\times$
37 AU. We investigated the rotational velocities as a function of the disk
radius, finding that its motions between 130 AU and 60 AU are partially fitted
with a Keplerian orbit by a stellar object of $\sim0.30 ~\rm\,M_\odot$, while
the motions within 60 AU do not follow any Keplerian orbit at all. This makes
it difficult to lead a reliable estimation of the mass of L328-IRS.
Nonetheless, our ALMA observations were useful enough to well constrain the
inclination angle of the outflow cavity of L328-IRS as $\sim 66^{\circ}$,
enabling us to better determine the mass accretion rate of $\sim 8.9\times
10^{-7} \rm\,M_\odot~yr^{-1}$. From assumptions that the internal luminosity of
L328-IRS is mostly due to this mass accretion process in the disk, or that
L328-IRS has mostly accumulated the mass through this constant accretion rate
during its outflow activity, its mass was estimated to be $\sim 0.012 -
0.023\rm\,M_\odot$, suggesting L328-IRS to be a substellar object. However, we
leave our identification of L328-IRS as a proto-brown dwarf to be tentative
because of various uncertainties especially regarding the mass accretion rate.
