It is the fourth week of on-sky commissioning with ComCam, and we are now about halfway through the planned duration of the campaign.
Active Optics System (AOS) commissioning continues to test both the closed loop and open loop systems. The AOS closed loop is now running with more than 90% of the optical degrees of freedom enabled, including the camera and secondary mirror (M2) hexapods that control the rigid-body relative positioning of the optics, and all of the lower order bending modes for the primary-tertiary mirror (M1M3) and M2 optical surfaces. Tests have been performed to evaluate the closed-loop convergence, for example, using shorter exposure times, adjusting the gain of the control loop to converge quickly while avoiding overfitting with noisy measurements, using various approaches to optimize image quality while avoiding movement along degenerate degrees of freedom, and using an alternative wavefront estimation algorithm that requires observations on only one side of focus. The team has begun scans in telescope elevation to verify the open loop look-up tables. Collectively, these tests are gradually making the AOS more efficient and reliable across a range of conditions.
Science Pipelines commissioning observations are continuing as opportunities allow between the AOS tests. Filter exchanges for ComCam are occurring roughly once per week, coinciding with routine mirror cleaning. This week, the z filter was exchanged for y, providing the first opportunity to obtain full-color six-band ugrizy coverage of a field, the Extended Chandra Deep Field South (ECDFS) LSST Deep Drilling Field. Flux measurements of stars in this field from observations across multiple nights and a range of airmass from 1.0 to 1.4 are repeatable at the 1% level for the u band, and 0.5% level for griz, before using the full set of planned calibration systems. The repeated observations of ECDFS have also been used to build prototype templates for difference imaging tests. The Data Management System demonstrated, for the first time with ComCam data, Prompt Processing with Difference Image Analysis (DIA) running to completion and producing candidate DIA sources and associated Alerts for the purpose of internal pipeline verification and validation. Observations within a second LSST Deep Drilling Field, the Euclid Deep Field South, began this past week, and there is currently rizy band coverage. The team currently plans to exchange the y filter for g during the upcoming dark time around the new moon.
One continued area of emphasis is increasing the overall efficiency and reliability during nighttime operations. The shutter open efficiency time has gradually improved during the first weeks of the campaign. The telescope commanded speed also continues to increase gradually, reaching up to 10% of maximum motion during the past week, while testing and analysis of the inertial forces on the mirrors continues. The slew-and-settle time will be optimized as the telescope motion increases. As telescope motion increases, tests to verify the telescope pointing model over the full range of elevation and azimuth angles will also become more efficient.
To maximize the utility of observations for Science Pipelines commissioning during the late stages of the ComCam on-sky campaign, repeated visits distributed across multiple bands will be collected for the same fields across many nights. The team has identified a set of target fields that are visible over the next weeks, and plans to concentrate the available time for preliminary survey-mode observations on these fields. Details will be described in more detail in the Rubin Observatory Plans for an Early Science Program document (RTN-011).