17:15 〜 19:15
[PPS04-P03] Daytime observation of Mercury with a visible adaptive otpics installed on Tohoku 60-cm telescope at Haleakala observatory
キーワード：水星、ナトリウム、外圏、補償光学
We report on the development of a visible Adaptive Optics for the Tohoku 60-cm telescope (T60-AO) at Haleakala Observatory in Hawaii. Our current goal is to provide ground-based support observations for the ESA-JAXA joint Mercury mission, BepiColombo, which will be in orbit around Mercury in 2026.
Mercury has a tenuous exosphere composed of alkali metal atoms. In particular, bright resonance scattering emissions of the Na D-lines (589.0 and 589.6 nm) allow us to derive its distribution and velocity field via high-dispersion spectroscopy. The typical time scales for variability expected from the interaction with the solar wind are on the order of a few minutes. Previous ground-based observations have shown that the north-south ratio of brightness in the Na exosphere changes on a time scale of several tens of minutes, which is consistent with the brightness response due to magnetospheric particle sputtering. However, previous observations using the slit scanning technique took about an hour to get Mercury's global Na brightness distribution. Using a high-resolution spectrograph (R=67,000) equipped with an integral field unit (IFU) installed on the T60, our objective is to obtain 2-dimensional spectroscopic observation with a cadence of a few minutes. Because Mercury's maximum elongation from the Sun is only about 25 degrees, daytime observations are indispensable for continuous monitoring. The T60-AO aims to achieve stable daytime observations with a spatial resolution better than 1.5 arcseconds, even under poor seeing conditions.
T60-AO employs a 12×12, 140-element MEMS deformable mirror and a Shack-Hartmann wavefront sensor. The wavefront sensor has an 18'' field of view and divides the pupil into 11×11 sub-apertures. In August 2024, we conducted on-sky test observations of Mercury during daytime to evaluate the T60-AO performance. With a closed-loop AO control frequency of 600 Hz, the AO correction improved the FWHM from 3.5-7'' (with AO off) to about 2.0±0.2'' (with AO on). Furthermore, we upgraded the Shack-Hartmann wavefront sensor in December 2024, enabling a higher closed-loop AO control frequency of up to 1.1 kHz. In this presentation, we will report on the latest development status of the T60-AO.
Mercury has a tenuous exosphere composed of alkali metal atoms. In particular, bright resonance scattering emissions of the Na D-lines (589.0 and 589.6 nm) allow us to derive its distribution and velocity field via high-dispersion spectroscopy. The typical time scales for variability expected from the interaction with the solar wind are on the order of a few minutes. Previous ground-based observations have shown that the north-south ratio of brightness in the Na exosphere changes on a time scale of several tens of minutes, which is consistent with the brightness response due to magnetospheric particle sputtering. However, previous observations using the slit scanning technique took about an hour to get Mercury's global Na brightness distribution. Using a high-resolution spectrograph (R=67,000) equipped with an integral field unit (IFU) installed on the T60, our objective is to obtain 2-dimensional spectroscopic observation with a cadence of a few minutes. Because Mercury's maximum elongation from the Sun is only about 25 degrees, daytime observations are indispensable for continuous monitoring. The T60-AO aims to achieve stable daytime observations with a spatial resolution better than 1.5 arcseconds, even under poor seeing conditions.
T60-AO employs a 12×12, 140-element MEMS deformable mirror and a Shack-Hartmann wavefront sensor. The wavefront sensor has an 18'' field of view and divides the pupil into 11×11 sub-apertures. In August 2024, we conducted on-sky test observations of Mercury during daytime to evaluate the T60-AO performance. With a closed-loop AO control frequency of 600 Hz, the AO correction improved the FWHM from 3.5-7'' (with AO off) to about 2.0±0.2'' (with AO on). Furthermore, we upgraded the Shack-Hartmann wavefront sensor in December 2024, enabling a higher closed-loop AO control frequency of up to 1.1 kHz. In this presentation, we will report on the latest development status of the T60-AO.