Capabilities of SST* and CHROMIS Göran Scharmer Institute for Solar Physics Stockholm University *Swedish 1-m Solar Telescope Hinode 9, Belfast, 16 September 2015
Strengths of SST Outstanding image quality (=> low spatial straylight, high S/N) High transmission (=> high S/N) Powerful instrumentation: CRISP, TRIPPEL in progress: CHROMIS Hinode 9, Belfast, 16 September 2015
Can this be improved? (Yes, we can!) Broad-band movie at 396 nm (SST; V. Henriques 2011)
SST image quality improvements 2013-2015 New (2013) adaptive mirror (by CILAS) of extremely high optical quality (λ/100 rms wavefront) Improved AO wavefront sensing (24x24 pix FOV, 2kHz) Previous 60 EUR tip-tilt mirror replaced with mirror (from ICOS) of exceptional quality 2015 Field mirror (inside vacuum) re-aluminized in 2015 (first time since 2001) Note: Tip-tilt and adaptive mirrors close to pupil plane => high optical quality crucial
SST AO and seeing monitor AO electrode and microlens layout 4 micro lenses measure seeing from differential image motion at 2 khz update rate Real-time seeing monitor (2 sec averages obtained every second, using 20 sec reference for calculating variances) Using AO log file, we calculate granulation rms contrast for the same 2 sec intervals using science cameras of CRISP narrowband (NB) & wideband (WB)
2 sec averages! Higher ro (Fried s parameter) means better seeing
2 sec averages! Not saturated! Seeing not good enough. Higher ro (Fried s parameter) means better seeing
Shift and add 2 sec raw images Top row: CRISP narrowband (NB) 525 nm 557 nm 630 nm 854 nm Bottom row: CRISP wideband (WB)
2 sec MFBD reconstructed images Top row: CRISP narrowband (NB) 525 nm 557 nm 630 nm 854 nm Bottom row: CRISP wideband (WB)
CRISP narrowband continuum CRISP Wideband
Table 1. Observed granulation contrasts with SST/CRISP Wavelength (nm) 525.0 557.6 630.1 853.5 NB WB NB WB NB WB NB WB No corr. 10.9 10.5 10.7 10.6 9.2 9.2 6.3 5.6 MTF corr. 11.8 11.5 11.8 11.6 10.2 10.2 7.2 6.2 MFBD corr. 13.9 13.7 13.4 13.1 11.7 11.5 8.2 7.2 r 0 (m) 0.164 0.239 0.238 0.270 Compare Sunrise: 8-8.5% Compare Hinode: 7% The above are 2 sec averages! (From Scharmer et al. in prep.)
Table 1. Observed granulation contrasts with SST/CRISP Wavelength (nm) 525.0 557.6 630.1 853.5 NB WB NB WB NB WB NB WB No corr. 10.9 10.5 10.7 10.6 9.2 9.2 6.3 5.6 MTF corr. 11.8 11.5 11.8 11.6 10.2 10.2 7.2 6.2 MFBD corr. 13.9 13.7 13.4 13.1 11.7 11.5 8.2 7.2 r 0 (m) 0.164 0.239 0.238 0.270 Compare Sunrise phase diversity restored: 13-15% The above are 2 sec averages! (From Scharmer et al. in prep.)
Concepts for CRISP (and CHROMIS) Telecentric optical system (=> diffraction limited image quality) R (reflectivity) of LR etalon << R of HR etalon (=> min. impact of cavity errors on spectral transmission profile) Compact optical design (avoid multiple reflections/mirrors) Wideband anchor channel for MOMFBD image reconstruction Modest spectral resolution (adopted to required S/N and cadence!) (Scharmer 2006; Scharmer et al. 2008)
SST transmission Simple optics => High transmission => High S/N Optics / Wavelength: 396 nm 630 nm 1083 nm SST (incl. re-imaging triplet) 46% 41% 48% TRIPPEL (excluding prefilter) 37% 51% 39% SST * TRIPPEL 17% 21% 19% e.g, CRISP: 10-3 noise requires 0.5 sec integration at 630 nm (0.9 sec wall clock time) (Courtesy of Dan Kiselman)
SST optics field mirror AO DM tip-tilt mirror
SST optical setup with CRISP and CHROMIS. CHROMIS narrowband Overall length: 1.5 m (CRISP) 1.6 m (CHROMIS) AO WFS CHROMIS Polarizing BS CRISP CRISP wideband CRISP narrowband CHROMIS wideband Filter wheel AO lens Dichroic BS tip tilt From telescope Filter wheel Chopper Correlation tracker camera Filter wheel
CHROMIS features 390-490 nm Ca H and K first priority, Hβ second Low spectral resolution (80 må FWHM at Ca H) Diffraction limited spatial resolution (0.04 pixels) High cadence: 10 wavelengths with S/N > 200 in 8 sec Polarimetry: maybe later
CHROMIS features Compact, 1.6 m overall length HR reflectivity 90%, LR reflectivity 80% (to mitigate effects of cavity errors) Etalon clear apertures 78 mm, oversized by 50% (to mitigate effects of cavity errors) High transmission (64% calculated) Short exposures (30 ms) + MOMFBD image reconstr. Number of photons per exp. (Ca H core): 1500-2500 (based on scaling from 1.1 Å Ca H filter)
Calculated Strehl values with CHROMIS FOV Wavelength (nm) 380 390 400 420 440 460 480 490 0.7 x0.7 0.986 0.995 0.992 0.987 0.993 0.998 0.994 0.987 1.0 x1.0 0.983 0.986 0.977 0.968 0.977 0.991 0.999 0.999 1.2 x1.2 0.947 0.962 0.958 0.952 0.963 0.980 0.994 0.997
Ca K line scanned with CHROMIS (FWHM 0.078 Å)
Courtesy of: Carolina Robustini Jorrit Leenaarts Jaime de la Cruz Rodriguez Luc Rouppe van der Voort
SST/CRISP at Ca II 8542 Courtesy of J. de la Cruz Rodriguez
Conclusions New AO system and tip-tilt mirror strongly improve SST image quality (Strehl) On a good site, seeing is not the ultimate limit to high image quality, it is the quality and complexity of the telescope optics The etalons and telecentric optics of CRISP do not degrade imaging performance SST will be well equipped for future studies of the chromosphere with CRISP (Hα, Ca II 8542, He I D3) and CHROMIS (Ca H+K, Hβ) SST will remain a world-leading solar telescope
Extra slides
How to measure Strehl values in the absence of point-like objects (stars)? Use granulation!
Granulation contrast = Strehl!! (for AO corrected telescopes) (Scharmer et al. in prep.)
CHROMIS beam footprint (explains high image quality of CRISP!) L1 Pupil L2 FPI-1 RGB rays above corresponds to three different points of the FOV but each ray actually shows the beam footprint from entire SST pupil. Small footprint on optics => high optical quality easily achievable.
Granulation contrast = Strehl!! (for AO corrected telescopes) (Scharmer et al. in prep.)