Large Adaptive optics Survey for Substellar Objects (LASSO) at wide separations around young, nearby, low-mass stars with Robo-AO

The purpose of the Large Adaptive optics Survey for Substellar Objects (LASSO) is to directly image new substellar companions (<70 M_Jup) at wide orbital separations (\(\gtrsim\)50 AU) around young (\(\lesssim\)300 Myrs), nearby (<100 pc), low-mass (0.1-0.8 M_Sun) stars. We report on 427 young stars imaged in the visible (i') and near-infrared (J or H) simultaneously with Robo-AO on the Kitt Peak 2.1-m telescope and later the Maunakea UH 2.2-m telescope. To undertake the observations, we commissioned a new infrared camera on Robo-AO that uses a low-noise high-speed SAPHIRA detector. We detected 122 companion candidates around 110 stars, of which 58 companions are physically associated based on Gaia DR2 parallaxes and proper motions, another 52 require follow-up observations to confirm physical association, and 12 are background objects. The majority of confirmed and pending candidates are stellar companions, with ~5 being potentially substellar and requiring follow-up observations for confirmation. We also detected a 43\(\pm\)9 M_Jup and an 81\(\pm\)5 M_Jup companion that were previously reported. The companion separations range from 2-1112 AU and reach contrast ratios of 7.7 magnitudes in the near infrared compared to the primary. We found 34 of our targets have acceleration measurements derived from Hipparcos-Gaia proper motions. Of those, 58% of the 12 stars with companion candidates have significant accelerations (\(\chi\)² >11.8), while only 23% of the remaining 22 stars with no detected companion have significant accelerations. The significance of the acceleration decreases with increasing companion separation. These young accelerating low-mass stars with companions will eventually yield dynamical masses with future orbit monitoring.