Title:
Two extremes of exoplanet direct imaging: detecting wide massive companions with the LASSO survey and pushing sensitivity to lower-mass planets by correcting for segment co-phasing errors
Speaker:
Maissa Salama (Santa Cruz) - Virtual Talk
Abstract:
In order to understand how directly imaged substellar companions (massive exoplanets and brown dwarfs) form and evolve, we need to analyze trends in their population demographics. However, studying directly imaged substellar companions as a population is difficult because of the technological challenges faced in detecting them combined with their rare existence. To address the challenge of searching for these rare massive substellar companions on wide orbits, I will present results from the Large Adaptive optics Survey for Substellar Objects (LASSO), where we directly imaged 930 young (<300 Myrs), nearby (<100 pc), low-mass (~0.1-0.8 MSun) stars. We used Robo-AO, a robotic adaptive optics instrument successively mounted on the Kitt Peak 2.1-m and Maunakea UH 2.2-m telescopes, to observe 427 stars and then used IRCS on Subaru and NIRC2 on Keck to observe another 503 stars. We detected 250 companion candidates. The majority of confirmed and pending candidates are stellar companions, with ~5 potentially new substellar companions that will require follow-up observations to confirm. To address the technical challenges of directly imaging fainter (lower-mass), closer-in, and more abundant planet populations, I will present results from the first on-sky demonstration of closed-loop control of Keck primary mirror segments with a Zernike Wavefront Sensor (ZWFS), improving the Strehl ratio on the NIRC2 science camera by up to 10 percentage points. Segment co-phasing errors are a primary contributor to contrast limits on Keck and will be necessary to correct for the next generation of space missions and ground-based extremely large telescopes (ELTs), which will all have segmented primary mirrors. The ZWFS is ideal for measuring phase discontinuities such as segment co-phasing errors and the low wind effect, as well as sensing non-common path aberrations. The ZWFS is extremely sensitive but has very limited dynamic range. The vector-ZWFS at Keck consists of a focal plane mask which imposes two different phase shifts on the core of the point spread function (PSF) to orthogonally polarized light, producing two pupil images. Compared to the scalar ZWFS (one phase shift and one pupil image), the vector-ZWFS has a superior dynamic range and enables the reconstruction of the wavefront's phase and amplitude. I will present the results of the ZWFS closed-loop tests and discuss the impact on NIRC2 science data. This work is also supported by laboratory experiments with the vector-ZWFS installed on the Santa Cruz Extreme AO Lab (SEAL) testbed, where we can simulate atmospheric conditions and analyze the performance of the vector-ZWFS in measuring and correcting segment co-phasing errors.
