Hello!
I'm trying to get photometry from archival DECam single-epoch image cutouts, in order to calibrate some spectra (the calibration is time-sensitive, otherwise I would just pull numbers from the coadd catalogues). I'm using proctype=Resampled and the images are specifically from the DES supernova survey -- object='DES supernova hex SN-X1 tiling 20'. The BUNIT in the cutouts is ADU, so I'm trying to convert flux values to magnitudes with the equation:
m = m0 - 2.5*log(flux)
where flux = gain * counts [ADU] / exptime.
The issue I'm having is with the gain -- each header lists two gain values, one for each of amplifier A and B, and I can't tell which spaxel belongs to which amplifier. How do I find out which gain to use? Here's an example of the relevant part of the header:
EXCLUDED= '' / DECam components not used for this frame
HEX = 339 / DES Hex number
TILING = 20 / DES Tiling number
DETECTOR= 'S3-40_124750-19-1' / Detector Identifier
CCDNUM = 4 / CCD number
DETPOS = 'S25 ' / detector position ID
GAINA = 4.061 / [electrons/adu] Gain for amp A
RDNOISEA= 6.05089 / [electrons] Read noise for amp A
SATURATA= 42059.0 / [adu] Saturation for amp A
GAINB = 4.249 / [electrons/adu] Gain for amp B
RDNOISEB= 6.080319 / [electrons] Read noise for amp B
SATURATB= 42605.0 / [adu] Saturation for amp B
Thanks!
Delaney