Is the sky the limit? Performance of the revamped Swedish 1-m Solar Telescope and its blue- and red-beam re-imaging systems

Abstract

We demonstrate that for data recorded with a solar telescope that uses adaptive optics and/or post-processing to compensate for many low- and high-order aberrations, the RMS granulation contrast is directly proportional to the Strehl ratio calculated from the residual (small-scale) wavefront error. We demonstrate that the wings of the high-order compensated PSF for SST are likely to extend to a radius of not more than about 2 arcsec, consistent with earlier conclusions drawn from straylight compensation of sunspot images. We report on simultaneous measurements of seeing and solar granulation contrast averaged over 2 sec time intervals at several wavelengths from 525 nm to 853.6 nm on the red-beam (CRISP beam) and wavelengths from 395 nm to 484 nm on the blue-beam (CHROMIS beam). These data were recorded with the Swedish 1-m Solar Telescope (SST) that has been revamped with an 85-electrode adaptive mirror and a new tip-tilt mirror, both of which were polished to exceptionally high optical quality. The highest 2-sec average image contrast measured in April 2015 through 0.3-0.9 nm interference filters at 525 nm, 557 nm, 630 nm and 853.5 nm with compensation only for the diffraction limited point spread function of SST is 11.8%, 11.8%, 10.2% and 7.2% respectively. Similarly, the highest 2-sec contrast measured at 395 nm, 400 nm and 484 nm in May 2016 through 0.37-1.3 nm filters is 16%, 16% and 12.5% respectively. The granulation contrast observed with SST compares favorably with that of other telescopes. Simultaneously with the above wideband red-beam data, we also recorded narrow-band continuum images with the CRISP imaging spectropolarimeter. We find that contrasts measured with CRISP are entirely consistent with the corresponding wide-band contrasts, demonstrating that any additional image degradation by the CRISP etalons and telecentric optical system is marginal or even insignificant.

In press in Astronomy & Astrophysics

References in corpus (6)

• The Solar Optical Telescope for the Hinode Mission: An Overview
• The intensity contrast of solar granulation: comparing Hinode SP results with MHD simulations
• Non-LTE inversions of the Mg II h&k and UV triplet lines
• Radiative diagnostics in the solar photosphere and chromosphere
• Point spread functions for the Solar Optical Telescope onboard Hinode
• The Anisoplanatic Point Spread Function in Adaptive Optics

Cited by in corpus (16)

• The European Solar Telescope
• Spicules and downflows in the solar chromosphere
• GREGOR: Optics Redesign and Updates from 2018-2020
• Signatures of ubiquitous magnetic reconnection in the lower solar atmosphere
• Ultra-high resolution observations of plasmoid-mediated magnetic reconnection in the deep solar atmosphere
• High-resolution observations of the solar photosphere, chromosphere and transition region. A database of coordinated IRIS and SST observations
• The chromosphere underneath a Coronal Bright Point
• Evidence of multithermal nature of spicular downflows. Impact on solar atmospheric heating
• Signatures of ubiquitous magnetic reconnection in the deep atmosphere of sunspot penumbrae
• Design and Performance Analysis of a Highly Efficient Polychromatic Full-Stokes Polarization Modulator for the CRISP Imaging Spectrometer
• IBIS-A: The IBIS data Archive. High resolution observations of the solar photosphere and chromosphere with contextual data
• Improved reconstruction of solar magnetic fields from imaging spectropolarimetry through spatio-temporal regularisation
• Investigating the effect of solar ambient and data characteristics on Ca II K observations and line profile measurements
• Formation of H$\epsilon$ in the solar atmosphere
• Wavelength Dependence of Image Quality Metrics and Seeing Parameters and their Relation to Adaptive Optics Performance
• Image Quality Specification for Solar Telescopes