As I understand it, the current upper limit of brightness is about magnitude +17 for Rubin/LSST. How will the suggestion that exposures be increased to 30 seconds from 15 seconds affect this boundary? Does this impact the science being planned for the solar system? What is the primary benefit to the overall mission in making this change?
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The idea is that moving from 2x15 “snaps” to 1x30 for each pointing means the observatory skips one shutter open + close per pointing, which corresponds to around 2 seconds fewer of overhead per pointing, or around 8% more time with the shutter open. I haven’t looked into the simulations too closely (to do a real investigation I would dig into the baseline vs one-snap baseline files here: Index of /sim-data/sims_featureScheduler_runs4.0/ ), but more time with the shutter open frees up time for many good things: more repeat coverings, higher-frequency cadence, deeper coadds, etc.
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Thanks @sdcorle1 for this question, and @Gerenjie for the reply.
I think Section 3.6 on Snaps, in the document “Survey Cadence Optimization Committee’s Phase 3 Recommendations”, released October 2024, summarizes the answers to @sdcorle1’s questions pretty well. The boundary will be slightly fainter (i.e., slightly fainter stars will saturate), but impacts on science across all areas will be minimal, and as @Gerenjie mentions, one of the primary benefits is an ~8% gain in survey efficiency.
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Thanks to both of you @MelissaGraham and @Gerenjie. I took a look at both the Recommendations document and the “snaps” simulation files.
Our work with exoplanets falls into one of those areas that will need reinforcement from other missions like GAIA. I know that the saturation boundary for LSST (circa mag 17) and the observability boundary for GAIA (mag 20.6) define a region where there is overlap that we can utilize for our needs. I’ll remain open to finding a quantification of the saturation boundary. If you become aware of one, I would appreciate a pointer. Thanks again. I think we can consider this issue closed.
Stars that are marginally saturated in coadds may not be saturated in the visits with the worst seeing, so if that limit is important you might consider combining coadd object tables with those single visit catalogs.
Interesting. Thanks Dan. We’ll look into how to implement this within our environment.
Regarding the use of other assets with a brighter magnitude limit, I suggest considering use of the La Silla Schmidt Southern Survey https://sites.northwestern.edu/ls4/survey/, and the associated Wide, Fast, Deep with DECam survey 2024B-388081 (Peter Nugent PI), both with zero proprietary time for the data, and designed to complement and enhance the LSST.
@ARW Thanks for the information. I did a quick scan of the web-site. Is there an opportunity at this point to gain access to documentation on the data and on the process for gaining access to the data as it becomes available?
Best to contact one of the people mentioned on the website, I am not a Co-I.