This is Week 2 of the Early Operations period for ongoing system optimization before starting sustained observations for the 10-year LSST survey. The primary emphasis continues to be improving the reliability of the delivered image quality.
In active optics system (AOS) optimization, the team completed a set of on-sky validation tests for the two-dimensional look-up table (LUT) for the camera hexapods accounting for telescope elevation angle and camera physical rotator angle, as well as on-sky validation for a refined filter focus offset LUT. Nightly AOS stability tests continued efforts to characterize stochastic variations in wavefront measurement while holding a fixed optical configuration. The team initiated more extensive investigation, on-sky testing, and modeling efforts for intrinsic aberrations related to spatial variations of the intrinsic wavefront across the focal plane considering the as-built mirror figure of the primary-tertiary (M1M3) and secondary (M2) mirrors as well as micron-scale height variations between the individual Camera sensors.
Efforts to improve control of the dome thermal environment are progressing in parallel with on-sky testing. Four sonic anemometers were installed on the telescope. The team continued a multi-week campaign to compare strategies for evening twilight dome ventilation. A second dome louver was qualified for nighttime operation on 6 November. In addition, the team is monitoring and reducing heat sources around the telescope.
The night of 6 November was dedicated for in-dome calibration tests, including filter wavelength scans with the collimated beam projector as well as monochromatic flats with the tunable laser light source illuminating the flat field screen.
During the week, the team acquired an average of ~150 visits per night with the Feature Based Scheduler (FBS) using the LSST configuration to evaluate the distribution of delivered image quality in wide-area survey operations. The currently deployed scheduler configuration is slightly modified relative to the standard LSST configuration to include periodic AOS “triplets” of intra-, extra-, and in-focus images to allow detailed characterization of the wavefront across the full field of view. Relative to the commissioning-era Science Validation surveys, the delivered image quality has generally been more stable and more uniform across the field of view during the past week.