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The typical 5σ point-source depth in a single visit in r will be ∼24.5 (AB). The project is in the construction phase and will begin regular survey operations by 2022. The survey area will be contained within 30,000 deg2 with δ<+34.5∘, and will be imaged multiple times in six bands, ugrizy, covering the wavelength range 320--1050 nm. About 90% of the observing time will be devoted to a deep-wide-fast survey mode which will uniformly observe a 18,000 deg2 region about 800 times (summed over all six bands) during the anticipated 10 years of operations, and yield a coadded map to r∼27.5.

I believe 'five-sigma' refers to standard deviations in a Gaussian distribution (statistics), but am unclear what it has to do with a 'point-source depth'.

And I am even more confused by 'r' and 'lowercase-delta'....

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The quote appears to be from the Ivezić et al. 2019 paper about LSST. In this context, σ quantifies the noise level in the images, and r is a photometric passband of ~620±70 nm wavelength. In single r-band images, they expect stars of AB magnitude 24.5 to stand out 5σ above the background level.

δ refers to declination; they plan to cover the sky from the south celestial pole to 34.5° north of the equator.

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