Program: GN-2020B-Q-214

Recent studies have found evidence for a correlation between photometric colour and viewing geometry of L and T type brown dwarfs. We have been running a survey to confirm this promising correlation, and to investigate the large diversity of brown dwarf properties over the narrow temperature range (1200-1400 K) of the L-T transition: a long-standing issue in substellar astrophysics. Given degenerate equations of state, brown dwarfs attain nearly constant 0.8-1.0 Jupiter radii at ages older than 500 Myr, and so rotation period and vsin(i) measurements reveal their viewing geometry. Since 2017 we have been collecting moderate- to high-dispersion near-infrared spectra of brown dwarfs with accurately known rotation periods from our two recent Spitzer Exploration Science programs. Our survey is nearly complete, save for two remaining targets, one included in this request. However, we have found that the theoretically calculated molecular line lists used to generate model spectra are inconsistent with each other and are even missing lines for some molecular species. This results in discrepant vsin(i) values when we compare our high-dispersion spectra to theoretical models. Fortunately, accurate vsin(i) estimates may also be obtained by comparisons to spectra of slowly rotating “template” brown dwarfs. We seek GNIRS and IGRINS spectroscopy of three such slow rotators to serve as empirical templates for our sample. These observations will calibrate to much higher accuracy our vsin(i) (and radial velocity) estimates from the 16 brown dwarfs that we have already observed with GNIRS and IGRINS during the course of our spectroscopic survey. We also seek to observe one of the two remaining science targets from our spectroscopic survey, the last one being visible only in the A semester.