The high-magnification microlensing event MACHO-97-BLG-28 was previously determined to be a binary system composed either of two M dwarfs , or an M dwarf and a brown dwarf .
We present a revised light-curve model using additional data from the Mt .
Stromlo 74 ” telescope , model estimates of stellar limb darkening and fitting the blend separately for each telescope and passband .
We find a lensing system with a larger mass ratio , q = 0.28 \pm 0.01 , and smaller projected separation , s = 0.61 \pm 0.01 , than that presented in the original study .
We revise the estimate of the lens-source relative proper motion to \mu _ { rel } = 2.8 \pm 0.5 \mathrm { mas\ > yr ^ { -1 } } , which indicates that 16.07 years after the event maximum the lens and source should have separated by 46 \pm 8 \si { mas } .
We revise the source star radius using more recent reddening maps and angular diameter-color relations to R _ { * } = ( 10.3 \pm 1.9 ) R _ { \odot } .
K and J-band adaptive optics images of the field taken at this epoch using the NIRC2 imager on the Keck telescope show that the source and lens are still blended , consistent with our light-curve model .
With no statistically significant excess flux detection we constrain the mass , M _ { L } = 0.24 ^ { +0.28 } _ { -0.12 } M _ { \odot } , and distance , D _ { L } = 7.0 \pm 1.0 \si { kpc } , of the lensing system .
This supports the interpretation of this event being a stellar binary in the galactic bulge .
This lens mass gives a companion mass of M = 0.07 ^ { +0.08 } _ { -0.04 } M _ { \odot } , close to the boundary between being a star and a brown dwarf .