2018-01-25
==========

J. Kielkopf

CDK20N
grizbV



22:27  40.6 F 69% H

Slew to M67

128s exposures 

g m67_00020.fits
r m67_00021.fits
i m67_00022.fits
z m67_00022.fits
V m67_00023.fits


The color image

m67_log_rgb.png 

was made with ds9 using 

Sloan r'           --> red
Johnson Cousins V  --> green
Sloan g'           --> blue

to approximate visual color.  The log of the light signal is shown so that
faint and bright stars may be seen in the same image.  The faintest stars are
distinctly redder, as expected for cluster members.

The coadded fits file is the sum of 46 images, each 128 seconds, through the V
filter, for a total exposure time of 5888 seconds (1.6 hours).  In the png file
it is shown on a linear scale where black is just above sky background, and
white is 50,000 on the digital scale were 1 count is approximately 1.5 photons. 
The brightest stars in the image are saturated, and at that register over
1,000,0000 photons per pixel at their peak.