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

We report on the initial results of the Large Adaptive optics Survey for Substellar Objects (LASSO). The purpose of LASSO is to directly image new substellar companions (<70 M_Jup) at wide orbital separations (>50 AU) around stars that are young (<300 Myrs), nearby (<100 pc), and low-mass (0.1-0.8 M_Sun). Large observational studies of substellar companions on wide-orbits are necessary to better understand their formation and evolution mechanisms by comparing trends in orbital architectures, primary and companion masses, age, and environments with population model predictions. We conducted observations with Robo-AO at the Kitt Peak 2.1-m telescope in 2017-2018 and the Maunakea UH 2.2-m telescope in 2019. We commissioned a low-noise high-speed SAPHIRA near-infrared detector as the new science infrared camera on Robo-AO. It is one of the earliest uses of these detectors for science and we report on our data reduction process. We directly imaged 428 stars in the visible and near-infrared simultaneously with median FWHM of 0.2" in the near-infrared. We detected 127 companion candidates around 114 stars, of which 51 are physically associated, another 66 require follow-up observations to confirm physical association, and 10 are background objects. The majority of confirmed and pending candidates are stellar companions, with ~5 being potentially substellar and requiring follow-up for confirmation. We also detected a 43±9 M_Jup and an 81±5 M_Jup companion that were previously reported in the literature. The companion separations range from 2-1112 AU and reach contrasts of 7.7 magnitudes in the near infrared compared to the primary. 34 of our observed targets have acceleration measurements derived from Hipparcos-Gaia proper motions. We find that 58% of the 12 with a companion candidate have significant accelerations (χ² >11.8), while only 23% of the 22 with no detected companion have significant accelerations. Furthermore, the significance of the acceleration decreases with increasing companion separation.