标题： 早期凯克/NIRC2-PWFS高对比度成像结果：SR 21盘 显示英文标题

标题： Early High-contrast Imaging Results with Keck/NIRC2-PWFS: The SR 21 Disk

摘要： 系外行星和原行星盘的高对比度成像依赖于自适应光学仪器进行波前探测与校正。传统上，波前探测是在光学波长范围内进行的，这使得红目标（如M型星或被遮蔽的T型金牛座星）的高对比度成像变得困难。凯克/NIRC2结合了近红外（NIR）探测器技术和金字塔波前传感器（PWFS）。利用这个新模块，我们观测了SR~21，一颗在近红外波段比光学波段更亮的年轻恒星。与使用光学波前探测的SR~21存档数据相比，在相似的自然视宁条件下，我们获得了$\sim$20%更高的斯托列尔比值。进一步利用角差成像和参考星差分成像的后处理确认了VLT/SPHERE偏振观测报告的螺旋特征，这是在$L^\prime$波段总强度下首次检测到SR~21的螺旋结构。我们还比较了我们的结果（$10^{-4}$在$0\farcs4$和$2\times10^{-5}$在$1\farcs0$）的对比极限与使用光学波前探测的存档数据，并确认了性能提升，特别是在$\leq0\farcs5$。我们的观测表明，近红外金字塔波前传感器提升了自适应光学系统的性能，并将为未来的红目标提供更多的观测机会。 显示英文摘要

摘要： High-contrast imaging of exoplanets and protoplanetary disks depends on wavefront sensing and correction made by adaptive optics instruments. Classically, wavefront sensing has been conducted at optical wavelengths, which made high-contrast imaging of red targets such as M-type stars or extincted T Tauri stars challenging. Keck/NIRC2 has combined near-infrared (NIR) detector technology with the pyramid wavefront sensor (PWFS). With this new module we observed SR~21, a young star that is brighter at NIR wavelengths than at optical wavelengths. Compared with the archival data of SR~21 taken with the optical wavefront sensing we achieved $\sim$20\% better Strehl ratio in similar natural seeing conditions. Further post-processing utilizing angular differential imaging and reference-star differential imaging confirmed the spiral feature reported by the VLT/SPHERE polarimetric observation, which is the first detection of the SR~21 spiral in total intensity at $L^\prime$ band. We also compared the contrast limit of our result ($10^{-4}$ at $0\farcs4$ and $2\times10^{-5}$ at $1\farcs0$) with the archival data that were taken with optical wavefront sensing and confirmed the improvement, particularly at $\leq0\farcs5$. Our observation demonstrates that the NIR PWFS improves AO performance and will provide more opportunities for red targets in the future.