geordie666
commented
7 years ago I'm happy to code this into desitarget (cuts.py), although we should probably have a discussion on the targeting telecon about whether this is a "proposed" cut or a "decided" one. If this was decided on the previous telecon, which I missed, then let me know and I'll code it up as soon as I find time.
We have verified with simulations and real observations from SDSS/SEGUE that the current baseline color cut for spectrophotometric F-type standards is not optimal. Even though it is based in the cuts used in SDSS (aimed for standard stars to be similar to BD +17 4708), lacking the u band lets in too many thick-disk stars at higher metallicity ([Fe/H]~ -0.7). Shifting the midpoint of the g-r range used to select F-type standards to the blue will increase the number of targets from the metal-poor halo.
We explored first a common shift in both g-r and r-z, which seemed quite useful, and later fine tuned independent shifts in g-r and r-z, finding that leaving r-z alone and shifting the center of the interval in g-r by 0.06 mag would work well.
This is described in more detail on the wiki at https://desi.lbl.gov/trac/wiki/TargetSelectionWG/STDalgorithms#ProposalforachangeinthebaselineselectionforF-typespectrophotometricstandards