OSSOS XII: Variability studies of 65 Trans-Neptunian Objects using the Hyper Suprime-Cam

TL;DR

This study used the Hyper Suprime-Cam on the Subaru Telescope to measure brightness variations of 65 Trans-Neptunian Objects, revealing common variability patterns and correlations with size, but not with orbital inclination or dynamical class.

Contribution

First large-scale variability survey of small TNOs using HSC, providing new insights into their brightness fluctuations and correlations with physical properties.

Findings

Approximately half of the objects show variability greater than 0.4 magnitudes.

Light curve amplitude correlates with absolute magnitude but not with orbital inclination.

Variability is common among small TNOs, affecting detection and color measurement strategies.

Abstract

We present variability measurements and partial light curves of Trans-Neptunian Objects (TNOs) from a two-night pilot study using Hyper Suprime-Cam (HSC) on the Subaru Telescope (Maunakea, Hawai'i, USA). Subaru's large aperture (8-m) and HSC's large field of view (1.77 square degrees) allow us to obtain measurements of multiple objects with a range of magnitudes in each telescope pointing. We observed 65 objects with m_r = 22.6--25.5 mag in just six pointings, allowing 20--24 visits of each pointing over the two nights. Our sample, all discovered in the recent Outer Solar System Origins Survey (OSSOS), span absolute magnitudes H_r = 6.2--10.8 mag and thus investigates smaller objects than previous light curve projects have typically studied. Our data supports the existence of a correlation between light curve amplitude and absolute magnitude seen in other works, but does not support a correlation between amplitude and orbital inclination. Our sample includes a number of objects from different dynamical populations within the trans-Neptunian region, but we do not find any relationship between variability and dynamical class. We were only able to estimate periods for 12 objects in the sample and found that a longer baseline of observations is required for reliable period analysis. We find that 31 objects (just under half of our sample) have variability greater than 0.4 magnitudes during all of the observations; in smaller 1.25 hr, 1.85 hr and 2.45 hr windows, the median variability is 0.13, 0.16 and 0.19 mags, respectively. The fact that variability on this scale is common for small TNOs has important implications for discovery surveys (such as OSSOS or the Large Synoptic Survey Telescope) and color measurements.