A Deep Search for Binary TNOs

The Latitude Density Search utilized Hyper Suprime-Cam on Subaru Telescope to discover 60 moving objects in the outer Solar System, 54 of which have semi-major axes beyond 30 AU. The images were acquired in exceptional seeing (0.4) and reached a detection limit of m_r~=25.2. The two night arcs were used to calculate orbits which are poorly constrained, however, the distance and inclination are the parameters best constrained by short arcs and a reasonable determination can be made of which objects are cold classical TNOs and which are dynamically excited. We identify 10 objects as likely cold classical objects. We searched all of the detections for binary sources using a trailed Point Spread Function subtraction method, and identified one binary object with a separation of 0.34 and a secondary with 17% the brightness of the primary (2.0 magnitudes fainter). This is the brightest TNO in the sample, the previously known object 471165 (2010 HE79), which has a dynamically excited orbit. Because of the excellent seeing, this search was sensitive to binaries with 0.34 separation and a brightness of >=50% the primary brightness for 7 objects, including one cold classical. This gives an intrinsic binary fraction of ~17% (1 of 6) for the dynamically excited objects within our detection limits. The trailed point spread function subtraction method to identify binaries, fit the two components, and determine the sensitivity limits, used in the Latitude Density Search is a useful tool that could be more broadly applied to identify binary TNOs and track known binary TNO orbits.