View source for CG4 photometry: more detailed instructions

Follow the instructions on the [[Units]] page under "getting the number APT needs" (near the bottom of the page).  These are the numbers I got for my SA101 mosaics. Are they right? Are they the same as what you'd use for the online mosaics? 

 	step 1	        step 1	         step2	        step 3	        step 4	    step 5 -- # for APT
 chan	CDELT1	        CDELT2	        sq deg/px	sr/sq deg	sr/px	     convert to Jy/px
 i1	0.000169	0.000169	2.8561E-08	0.000304847	8.70674E-12	8.70674E-06
 i2	0.000169	0.000169	2.8561E-08	0.000304847	8.70674E-12	8.70674E-06
 i3	0.000169	0.000169	2.8561E-08	0.000304847	8.70674E-12	8.70674E-06
 i4	0.000169	0.000169	2.8561E-08	0.000304847	8.70674E-12	8.70674E-06
 m1	0.0006944	0.0006944	4.82191E-07	0.000304847	1.46995E-10	0.000146995

Then:
#stick this value in the conversion value under "more settings" (lower left)
#turn on background subtraction in more settings (option B)
#Apply settings. Close window
#change settings to 6, 6-14 px for aperture, annulus
#do photometry (click on object, calculate or recalculate values)
#write down "source_intensity (sky-included)" because this is the sky minus the scaled background from the annulus
#repeat for each object of interest
#multiply measured fluxes by aperture correction (band-dependent -- see below)
#compare these final flux densities to other people's flux densities

Aperture corrections. See photometry pages for explanation of what and why. The aperture corrections are a function of the aperture and annulus you used, compared to what the IRAC team uses to calibrate the instrument. Here are the aperture corrections for a NATIVE PIXEL 3, 3-7 combination; we have half the pixel size, so this corresponds to 6, 6-14 in arcseconds.  Different pixel scales require different combinations.
For this combination, the aperture corrections for the four IRAC channels are 1.124, 1.127, 1.143, 1.234.  Operationally, this means, using IRAC-1 as an example, that the 6/6-14 combination misses 12.4% of the flux, so take the flux you measure using 6/6-14, and multiply it by 1.124.  Do the same thing for the rest of the channels.  

FOR MIPS, use 1.4 px aperture, 2.8-5.2 px radius, aperture correction 2.8 (!).

real reference (e.g, see other combinations): http://ssc.spitzer.caltech.edu/irac/iracinstrumenthandbook/32/

Had we been able to do this in real time, I'd have created a spreadsheet with the measurements of the same stars from all 5 channels (irac1234mips1) and we'd have looked at the scatter in the values you measured, and compared them to my values. There's no guarantee I have it right!!  

<font color="red">HOMEWORK</font> Do the photometry once we solve these problems. Watch your email to see when/exactly what to do.  Then we can have you all post your photometry here by a particular deadline, and we'll THEN do the comparison among us all. Sigh.