Companions embedded in the cavities of transitional circumstellar disks have
been observed to exhibit excess luminosity at Hα, an indication that
they are actively accreting. We report 5 years (2013-2018) of monitoring of the
position and Hα excess luminosity of the embedded, accreting low-mass
stellar companion HD 142527 B from the MagAO/VisAO instrument. We use pyklip, a
python implementation of the Karhounen-Loeve Image Processing algorithm, to
detect the companion. Using pyklip forward modeling, we constrain the relative
astrometry to 1−2mas precision and achieve sufficient photometric
precision (±0.2mag,3% error) to detect changes in the Hα
contrast of the companion over time. In order to accurately determine the
relative astrometry of the companion, we conduct an astrometric calibration of
the MagAO/VisAO camera against 20 years of Keck/NIRC2 images of the Trapezium
cluster. We demonstrate agreement of our VisAO astrometry with other published
positions for HD 142527 B, and use orbitize! to generate a posterior
distribution of orbits fit to the relative astrometry of HD 142527 B. Our data
suggest that the companion is close to periastron passage, on an orbit
significantly misinclined with respect to both the wide circumbinary disk and
the recently observed inner disk encircling HD 142527 A. We translate observed
H-alpha contrasts for HD 142527 B into mass accretion rate estimates on the
order of 4−9×10−10M⊙yr−1. Photometric
variation in the H-alpha excess of the companion suggests that the accretion
rate onto the companion is variable. This work represents a significant step
towards observing accretion-driven variability onto protoplanets, such as PDS
70 b\&c.Comment: Accepted to the Astronomical Journal. 32 pages, 16 figures, 8 tables,
4 appendice