Revolutionary exoplanet and brown dwarf science
Key parameters in the study of both planets and low-mass brown dwarfs are their mass and distance, which advanced astronomical AO systems such as the Gemini Planet Imager (GPI) do not measure directly. Rather, we indirectly measure parameters such as temperature or luminosity that can be combined with evolutionary tracks to produce mass estimates. A direct, independent measurement of mass allows us to estimate the specific entropy of the object separately from evolutionary tracks, constrain its equation of state, and distinguish between different formation models. The best way to do this is to measure the reflex motion of the parent star in the plane of the sky by comparison to reference stars.
As an exemplar of this technique, using novel multi-laser guide star technology installed on the Gemini telescopes, we made the first precise measurements of the closest known binary brown dwarf system, Luhman 16 AB. The observations yielded an estimate of its relative orbital parameters and thus a constraint of the brown dwarf masses. We also used the Keck laser guide star and the Shane adaptive optics system at Lick Observatory to obtain distance measurements for two extremely faint T-type brown dwarfs, WISE2154 and WISE1901.
Advancing technology
Through an analysis with Stanford University, we found that important performance limiters for high-contrast AO instruments, such as the GPI, are control system latencies and temporal wavefront errors. These issues affect the system’s ability to keep up with ever-evolving atmospheric turbulence. Addressing these issues is necessary for the success of future large telescopes, updating the performance of existing systems, and pushing adaptive optics to visible wavelengths.
Motivated by this finding, our team developed the Low-Latency Adaptive Mirror System (LLAMAS) testbed to advance the state of the art in adaptive optics latencies. LLAMAS is an onsite system that will test techniques and solutions in an integrated, real-time, closed-loop AO system. LLAMAS has demonstrated an order of magnitude improvement in closed-loop bandwidth (740 Hz), improved from about 30 Hz for the GPI.
The next generation of Extremely Large Telescopes (ELTs) require AO systems that challenge the current state of the art. These larger apertures of up to 42 meters require deformable mirrors with higher actuator counts, better performance at visible wavelengths, and faster computers to command deformable mirrors. LLNL’s AO research program is focused on developing prototypes that will advance the technology in preparation for ELTs.
