Color terms and Galactic extinction coefficients for DECam filters (including the Merian medium-band filters)

config/calibrate.py

@@ -30,4 +30,16 @@
 # See Slack: https://lsstc.slack.com/archives/C2B6X08LS/p1586468459084600
 config.astrometry.wcsFitter.order = 4
 
+# Photometric calibration: use color terms
+config.photoCal.applyColorTerms = True
+colors = config.photoCal.match.referenceSelection.colorLimits
+# The following two color limits are adopted from obs_subaru for HSC SSP survey.
+colors["g-r"] = ColorLimit(primary="g_flux", secondary="r_flux", minimum=0.0)
+colors["r-i"] = ColorLimit(primary="r_flux", secondary="i_flux", maximum=0.5)
+# The following magnitude limit is also adopted from obs_subaru for HSC SSP survey.
+config.photoCal.match.referenceSelection.doMagLimit = True
+config.photoCal.match.referenceSelection.magLimit.fluxField = "i_flux"
+config.photoCal.match.referenceSelection.magLimit.maximum = 22.0
+config.photoCal.colorterms.load(os.path.join(obsConfigDir, 'colorterms.py'))
+
 config.measurement.load(os.path.join(obsConfigDir, "hsm.py"))

config/colorAnalysis.py

@@ -0,0 +1,5 @@
+import os.path
+
+config.load(os.path.join(os.path.dirname(__file__), "extinctionCoeffs.py"))
+from lsst.obs.decam.decamFilters import DECAM_FILTER_DEFINITIONS
+config.physicalToBandFilterMap = DECAM_FILTER_DEFINITIONS.physical_to_band

config/colorterms.py

@@ -0,0 +1,51 @@
+from lsst.pipe.tasks.colorterms import Colorterm, ColortermDict
+
+# Average color terms for the DECam filters are calculated using the Pickles stellar spectra atlas.
+# The following values are provided by Song Huang (Tsinghua University; [email protected])
+# Color terms for u, Y, N964, and N419 bands are not available now.
+
+# The values for DECam g, r, & z-band are calculated independently and are different with the values from: https://www.legacysurvey.org/dr9/description/
+# A Jupyter notebook is available at https://github.com/MerianSurvey/caterpillar/blob/main/notebook/photocal/merian_filter_color_terms.ipynb 
+# to reproduce these values.
+
+# In obs_subaru, colorterms.py is also used in:
+# - config/jointcal.py
+# - config/skyAnalysis.py
+# - config/compareCoaddAnalysis.py 
+# - config/coaddAnalysis.py
+# - config/visitAnalysis.py
+# - config/fgcmBuildStarsTable.py and config/fgcmBuildStars.py
+# These files are not available for obs_decam yet.
+
+config.data = {
+    "decam*": ColortermDict(data={
+        'g': Colorterm(primary="g", secondary="g"),
+        'r': Colorterm(primary="r", secondary="r"),
+        'i': Colorterm(primary="i", secondary="i"),
+        'z': Colorterm(primary="z", secondary="z"),
+    }),
+    "sdss*": ColortermDict(data={
+        'g': Colorterm(primary="g", secondary="r", c0=-0.008015, c1=-0.089869, c2=-0.018398), # For -1.0 < g-r < 1.8
+        'r': Colorterm(primary="r", secondary="i", c0=-0.0077434, c1=-0.202615, c2=0.016042), # For -1.0 < r-i < 2.2
+        'i': Colorterm(primary="i", secondary="z", c0=0.00018887, c1=-0.2748281, c2=-0.029417), # For -1.0 < i-z < 1.2
+        'z': Colorterm(primary="z", secondary="i", c0=-0.0059858, c1=0.1131192, c2=0.0156471), # For -1.0 < z-i < 0.5
+        'N708': Colorterm(primary="r", secondary="i", c0=-0.01428724, c1=-0.71755905, c2=0.08959316), # For -1.0 < r-i < 2.0
+        'N540': Colorterm(primary="g", secondary="r", c0=-0.03359776, c1=-0.57665033, c2=-0.01510509), # For -1.0 < g-r < 1.5
+    }),
+    "hsc*": ColortermDict(data={
+        'g': Colorterm(primary="g", secondary="r", c0=0.0000509, c1=-0.0152487, c2=-0.0029937), # For -1.0 < g-r < 1.4
+        'r': Colorterm(primary="r", secondary="i", c0=-0.0078995, c1=-0.1695323, c2=0.0251978), # For -1.0 < r-i < 2.2
+        'i': Colorterm(primary="i", secondary="z", c0=0.0010196, c1=-0.1314031, c2=0.0054605), # For -1.0 < i-z < 1.0
+        'z': Colorterm(primary="z", secondary="y", c0=-0.0013244, c1=-0.2846684, c2=-0.1229817), # For -1.0 < z-y < 0.5
+        'N708': Colorterm(primary="r", secondary="i", c0=-0.01978413, c1=-0.64368838, c2=0.09132738), # For -1.0 < r-i < 2.0
+        'N540': Colorterm(primary="g", secondary="r", c0=-0.03015158, c1=-0.53715834, c2=-0.00202415), # For -1.0 < g-r < 1.5
+    }),
+    "ps1*": ColortermDict(data={
+        'g': Colorterm(primary="g", secondary="r", c0=0.006388, c1=0.045875, c2=-0.004484), # For -1.0 < g-r < 1.2
+        'r': Colorterm(primary="r", secondary="i", c0=-0.006775, c1=-0.187304, c2=0.018928), # For -1.0 < r-i < 2.2
+        'i': Colorterm(primary="i", secondary="z", c0=0.0012204, c1=-0.282956, c2=-0.011321), # For -1.0 < i-z < 1.4
+        'z': Colorterm(primary="z", secondary="y", c0=-0.0087868, c1=-0.5204795, c2=-0.057955), # For -1.0 < z-y < 1.0
+        'N708': Colorterm(primary="r", secondary="i", c0=-0.01508987, c1=-0.69377675, c2=0.09079348), # For -1.0 < r-i < 2.0
+        'N540': Colorterm(primary="g", secondary="r", c0=-0.02635164, c1=-0.50968428, c2=-0.00958104), # For -1.0 < g-r < 1.5
+    }),
+}

config/extinctionCoeffs.py

@@ -0,0 +1,15 @@
+# Extinction coefficients for DECam filters for conversion from E(B-V) to extinction, A_filter.
+# Numbers provided by Song Huang (NAOJ).
+#
+# Band, A_filter/E(B-V)
+# Values for N964 and N149 filters are not available at this point.
+config.extinctionCoeffs = {
+    "u": 3.994,
+    "g": 3.212,
+    "r": 2.164,
+    "i": 1.591,
+    "z": 1.211,
+    "y": 1.063,
+    "N708": 1.847,
+    "N540": 2.753
+}