Week ten of the LSSTCam On-sky Campaign. The Rubin Observatory team was delighted to share on-sky images and to celebrate First Look events and activities around the world.
New highlights this week:
Pilot observations for the Science Validation (SV) surveys began this week, running for at least one hour on each night that the environmental conditions allowed for on-sky engineering. During these full system integration tests, the Feature Based Scheduler (FBS) drove the selection of targets across the SV survey footprint and cycled the online filter to acquire observations in multiple bands. The team demonstrated continuous, uninterrupted operation for periods of up to 4 hours. As part of the ongoing effort to optimize the interaction and timing of control system components, the median time between successive visits, typically ~3.5 deg slews between adjacent LSSTCam pointings, was reduced to ~10 seconds.
The sustained, wide-area sky scanning observations of the SV surveys provide valuable diagnostic information for continued optimization of the Active Optics System (AOS) open loop and closed loop control systems. The delivered image quality varied throughout the week, due to both atmosphere and system contributions. On one night with good atmosphere seeing, the system maintained a sub-arcsecond PSF FWHM across the field of view while covering a range of telescope pointing directions for a full hour. Across the week, the delivered image quality has generally been stable between 1.0" and 1.5" PSF FWHM, with occasional deviations where the optics needed to be brought back into focus and alignment.
Two additional sensors on LSSTCam were turned on this week, such that 188 of 189 science sensors are now operational. The team has also been testing sequencer configurations that control the timing and readout for the sensors, with the goal of further reducing the readout noise.
The currently loaded filter set is ugriz. The team plans to load swap in the pinhole next week for additional stray and scattered light testing, and then swap in the y filter as we enter bright time in early July.
The Auxiliary Telescope (AuxTel) resumed on-sky spectroscopic observations to characterize the atmosphere transparency. During the week, the team demonstrated autonomous operations for both the Simonyi Survey Telescope and AuxTel on-sky simultaneously using the FBS. Currently, the Simonyi Survey Telescope and AuxTel are observing independently in parallel, rather than performing coordinated observations (e.g., with AuxTel following the Simonyi Survey Telescope.)
AuxTel is the smaller (1.2 m) sibling telescope to the Simonyi telescope, located in a separate, adjacent dome. It will be used mainly to monitor atmospheric conditions for nightly calibration of LSST images and photometry. The telescope itself was formerly the Calypso telescope at Kitt Peak; it was donated to the Rubin Observatory. Its main instrument is LATISS (LSST Atmospheric Transmission Imager and Slitless Spectrograph). As indicated by the name, it’s a slitless spectrograph, used to get simultaneous spectra for many bright stars at once. It uses a single one of the 4k x 4k CCDs that are used by ComCam and LSSTCam.
If I have my info right, AuxTel has been operational since July 2019, though I think LATISS wasn’t put onto it until a year later.
I believe LATISS can also take regular images for photometry (someone please correct me if I’m wrong). If I recall correctly, regular images from AuxTel provided the first real-data from-the-summit test of the Rubin LSST pipeline software (before ComCam on the Simonyi telescope).
There’s lots of info on AuxTel online, though some of the more technical content takes a bit of effort to find. The Rubin site has a brief description:
There are two slide decks there, the first on its main use as a spectrograph, and the latter on AuxTel photometry (which I think was done with LATISS, but not operating as a spectrograph). Here’s a slide deck from last November’s LSST-France meeting with a recent update on AuxTel activity:
I believe Chris Stubbs (shoutout to @CStubbs) is one of the leads for LATISS; he may want to weigh in with more details. Here is a thesis by his student Nicholas Mondrik with LATISS construction details, and a SPIE paper on AuxTel:
Hello, here are a few details about the spectrograph that equips the auxiliary telescope.
The spectrograph of the auxiliary telescope is equipped with a custom-made hologram, the original idea and realization of which came from a French team at IJCLab (formerly LAL).
Holographic technology, best known for its ability to reproduce three-dimensional vision, makes it possible here to combine in a single optical element the functions of light dispersion, as would an ordinary prism or periodic grating, and focusing, without which spectra cannot be sharp over the entire color range, since the spectrograph is not angled.
The software for analyzing the spectra obtained with this hologram was also developed in France. By comparing star spectra obtained on the ground and measured from space, we can deduce, among other things, the absorption of light by atmospheric water vapour. At present, we measure the amount of precipitable water in the atmosphere to an accuracy of 1/10mm, which is sufficient to reconstruct the fluxes in the Z and y bands as they arrive at the top of the atmosphere to an accuracy of a few per thousand.
