I’m looking for an easy way to convert between DES, PanSTARRS and SDSS magnitudes and colors, and LSST values. Here’s a sample of what I’m looking for from DES, where it converts between PanSTARRS and SDSS values:
SDSS
Here, we matched stars from DES DR2 to stars in the Stripe 82 area of SDSS DR13, using the WAVG_PSF_MAG’s from DES and the PSF_MAG’s from SDSS. To reduce the effects of photon noise, we only considered stars with rms magnitude errors of ≤ 0.01 in DES and ≤ 0.02 in SDSS. For outlier rejection, we made use of iterated sigma-clipping, iterating over the fit 3 times and removing 3 σ outliers after each iteration. We found that the following to fall within reasonable bounds of accuracy, simplicity, and wide color coverage:
g{DES} = g{SDSS} - 0.061 (g - i){SDSS} + 0.008 ~(RMS: 0.017 mag) QA plot
r{DES} = r{SDSS} - 0.155 (r - i){SDSS} - 0.007 ~(RMS: 0.014 mag) QA plot
i{DES} = i{SDSS} - 0.166 (r - i){SDSS} + 0.032 ~(RMS: 0.018 mag) QA plot
z{DES} = z{SDSS} - 0.056 (r - i){SDSS} + 0.027 ~(RMS: 0.018 mag) QA plot
and
g{SDSS} = g{DES} + 0.060 (g - i){DES} - 0.005 ~(RMS: 0.018 mag) QA plot
r{SDSS} = r{DES} + 0.150 (r - i){DES} + 0.014 ~(RMS: 0.016 mag) QA plot
i{SDSS} = i{DES} + 0.167 (r - i){DES} - 0.027 ~(RMS: 0.015 mag) QA plot
z{SDSS} = z{DES} + 0.054 (r - i){DES} - 0.024 ~(RMS: 0.018 mag) QA plot
First-order polynomials based on a single color index (g-i for g and r-i for r,i,z). These equations are valid for stars with roughly -1.0 < g-i < 3.5 (g) and roughly -0.4 < r-i < 2.0 (r,i,z). (Note: the RMS listed after each transformation is RMS per star. The mean RMS for a collection of stars being transformed from one photometric system to the other – especially if that collection of stars covers a range of colors – should be correspondingly smaller.)
Pan-STARRS
As for the DES/SDSS transformation equations, here, we matched stars from DES DR2 to stars in the Stripe 82 area of PanSTARRS1 DR2, using the WAVG_PSF_MAG’s from DES and the MeanPSFMag’s from PanSTARRS1. Again, to reduce the effects of photon noise, we only considered stars with rms magnitude errors of ≤ 0.01 in DES and ≤ 0.02 in PanSTARRS1. Using the same type of outlier rejection and aiming for similar goals in accuracy, simplicity, and color coverage, we arrived at the following equations:
g{DES} = g{PS1} + 0.028 (g - i){PS1} + 0.020 ~(RMS: 0.017 mag) QA plot
r{DES} = r{PS1} - 0.142 (r - i){PS1} - 0.010 ~(RMS: 0.013 mag) QA plot
i{DES} = i{PS1} - 0.155 (r - i){PS1} + 0.015 ~(RMS: 0.012 mag) QA plot
z{DES} = z{PS1} - 0.114 (r - i){PS1} - 0.010 ~(RMS: 0.015 mag) QA plot
Y{DES} = y{PS1} - 0.031 (r - i){PS1} + 0.035 ~(RMS: 0.017 mag) QA plot
and
g{PS1} = g{DES} - 0.026 (g - i){DES} - 0.020 ~(RMS: 0.017 mag) QA plot
r{PS1} = r{DES} + 0.139 (r - i){DES} + 0.014 ~(RMS: 0.015 mag) QA plot
i{PS1} = i{DES} + 0.153 (r - i){DES} - 0.011 ~(RMS: 0.010 mag) QA plot
z{PS1} = z{DES} + 0.112 (r - i){DES} + 0.013 ~(RMS: 0.015 mag) QA plot
Y{PS1} = y{DES} + 0.031 (r - i){DES} - 0.034 ~(RMS: 0.017 mag) QA plot
– which are valid for stars with roughly -0.9 < g-i < 3.8 (g) and -0.4 < r-i < 2.4 (r,i,z,Y).