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 \sim 0.30 ~ { } { 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 } { 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 { 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 .