Type: Talk
Session: Stellar Science and Crowded Fields
Author: Zhoujian (ZJ) Zhang

Abstract: Spectroscopy has emerged as a vital tool for studying the atmospheres and origins of exoplanets. However, the interpretive power of spectroscopic data hinges on the fidelity of theoretical models, a cornerstone that has not been thoroughly anchored. In this presentation, I will highlight the significant value of gas-giant exoplanets and brown dwarfs that orbit stars at wide separations (> 500au); these companions are crucial analogs for directly imaged exoplanets, offering an excellent opportunity to empirically constrain the systemic errors of exoplanet models. To expand the census of these "benchmark companions", I have been leading the COol Companions ON Ultrawide orbiTS (COCONUTS) program. Using multi-epoch astrometry and multi-wavelength photometry from Pan-STARRS1, 2MASS, UKIDSS, and WISE, our efforts have yielded over 50 new brown dwarf companions to stars, doubling the existing census. We also discovered an exoplanet, COCONUTS-2b, the nearest directly imaged exoplanet to Earth with among the lowest mass (~6 Mjup) and coldest temperature (~430K). I will present the design and findings of our COCONUTS program and their implications for forthcoming large sky surveys, such as LSST. I will also discuss the anticipated properties of exoplanets and benchmark brown dwarfs that could be detected by the Rubin Observatory over the coming years.