Confirmation of the Stellar Binary Microlensing Event, Macho 97-BLG-28

Abstract

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 and more recent models of stellar limb darkening. We find a lensing system with a larger mass ratio, q = 0.28±0.01, and smaller projected separation, s = 0.61±0.01, than that presented in the original study. We revise the estimate of the lens-source relative proper motion to µ rel = 2.8 ± 0.5 mas yr −1 , which indicates that 16.07 years after the event maximum the lens and source should have separated by 46±8 mas. We revise the source star radius using more recent reddening maps and angular diameter-color relations to R * = (10.3 ± 1.9)R . 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 , and distance, D L = 7.0 ± 1.0 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 , close to the boundary between being a star and a brown dwarf.

A Jovian analogue orbiting a white dwarf star

“…The goal of these observations was to determine the composition of the source-lens blend by obtaining a refined photometric and astrometric solution. We apply flat-field and dark-field corrections using standard techniques (Blackman et al 2020;Beaulieu et al 2016). The images were stacked using SWARP (Bertin & Emmanuel 2010).…”

OGLE-2017-BLG-1434Lb: Confirmation of a Cold Super-Earth using Keck Adaptive Optics

“…For simplicity in the rest of this paper we will drop the subscript and refer to the magnitudes simply as K. The wide camera has a plate scale of 0.03968 arcsec pixel −1 and a field of view of 40 arcseconds. The best 15 of these images were stacked using SWARP (Bertin & Emmanuel 2010) and calibration performed by cross-matching with the VVV catalog, following the process described in Blackman et al (2020) and Vandorou et al (2020). The mean full-width halfmaximum (FWHM) is 120 mas along the North axis and 90 mas along the east, indicating an elongation of the point spread function (PSF).…”