Comet C/2014 UN271 (Bernardinelli-Bernstein) exhibited activity at 23.8 au
ATel #14759; Tony Farnham (University of Maryland)
on 6 Jul 2021; 16:19 UT
Credential Certification: Tony Farnham (farnham@astro.umd.edu)
Referred to by ATel #: 15356
We report on our analysis of TESS (Transiting Exoplanet Survey Satellite)
observations from September 21 to October 18, 2018 that suggests comet C/2014
UN271 was already exhibiting a coma at a heliocentric distance of 23.8 au.
We applied our comet studies pipeline, which uses the Difference Image
Analysis software (Oelkers & Stassun, AJ 156, 132, 2018) to
remove the background stars from each image, and then coadded 976 30-minute
Full Frame Images (total integration time 1.76e6 sec). For comparison, we
used the same pipeline on four Kuiper Belt Objects from the same TESS sector,
with comparable magnitudes, proper motions and number of observations. Each
of the KBOs shows a brightness profile dominated by the central pixel, and
fitting Gaussians to the radial profiles gives FWHMs between 1.75 and 2.06
pixels. In contrast, inspection of the resulting image of 2014 UN271 shows a
more extended profile around the center pixel with an asymmetry toward a
position angle ∼90 deg E of N. Fitting a Gaussian to the radial profile
gives a FWHM of 2.92 pixels, indicating there is coma present.
The consistency in C/2014 UN271's brightness between 2014 and 2018 suggests
that it may have become active even before it was discovered at 29.3 au. If
so, this has implications on the predicted size of the nucleus.
This work makes use of data collected by the TESS mission.
