This is the sixth week of on-sky commissioning with ComCam.
Observing efficiency continued to improve during the past week, due to multiple factors. First, the commanded telescope motion has increased once again as the team gains experience with the systems that control inertial forces experienced by the glass mirrors during slew and settle. Second, optimization of the control software has reduced the time between successive visits for short slews. Third, the team continues to identify and mitigate the root causes of various interruptions to nighttime observing and is able to recover more quickly when interruptions do occur.
With these gains in observing efficiency, the number of in-focus visits for Science Pipelines commissioning has continued to increase during the past week, roughly doubling the nightly rate compared to prior weeks of the ComCam on-sky campaign. The team took advantage of dark time around the new moon to install the ugr filter set and expand coverage in the bluest bands for several target fields. Currently, the gri filters are installed.
Commissioning of the Active Optics System (AOS) has continued to refine the open-loop look-up tables for elevation and camera rotator angle. Other testing has sought to correct higher order Zernike coefficients in the measured wavefront and to exercise the closed loop system using the sparser samples of high signal-to-noise stars seen in u band. Following iteration of the closed-loop system at a target field, the estimated residual contribution of the AOS to the delivered image quality PSF FWHM reaches below 0.2 arcseconds.
Most of the in-focus imaging during the ComCam campaign has used visits consisting of a single 30-second exposure. In order to characterize higher frequency contributions (e.g., 1-100 Hz) to the delivered image quality attributed to effects on shorter timescales than a typical visit (e.g., atmosphere and observatory seeing, mount motion), the team acquired ComCam observations in both stuttered imaging mode and guider imaging mode. In stuttered imaging mode, rows of pixels on the CCD are shifted during an exposure to produce a time-series measurement of the PSF. In guider imaging mode, small regions of the sensor centered on bright stars are read out at high frequency during an exposure. LSSTCam has dedicated sensors on the four corner rafts for guider mode measurements.
One of the calibration hardware systems, the collimated beam projector (CBP), was installed inside the dome on 22 November. The CBP is designed to precisely measure the throughput by illuminating various paths through the optical system with a set of collimated, monochromatic beams. Functional testing and commissioning of the CBP using ComCam is starting this week.
The final night of the ComCam on-sky commissioning campaign is now planned to be 11 December so that preparatory work needed for LSSTCam installation on the telescope can proceed.