A Guide to Reducing MMT/Megacam Imaging Data


by Matthew L. N. Ashby

Introduction

These notes are intended as a guide for those who need to reduce visible-wavelength imaging data acquired at the MMT atop Mt. Hopkins with Megacam. They are oriented toward those seeking the best outcome from deep-sky, highly redundant observing schemes. They draw heavily on the procedures and software described in Buell Jannuzi's KPNO/MOSAIC page developed for the NOAO Deep-Wide Field Survey (NDWFS).

Notes added 2008 Feb 25: CfA staffers can make use of the new, dedicated Megacam pipeline platform and software -- this is strongly recommended -- for details see the local wiki page.

If you're reducing i' or z' data, the procedures described in this cookbook are sufficient to permit defringeing to roughly the level of the RMS noise within each frame. It's possible to do better however. In fact defringeing artifacts limit Megacam's sensitivity for for long, deep-sky integrations involving the coadding of more than 10 frames unless you iterate the defringeing procedure. If you want to know more, ask me. I'll describe the algorithm on this website at the next possible update.

Send comments regarding defringeing or any other Megacam issues (especially errors in the cookbook) to Matthew Ashby at mashby@cfa.harvard.edu.

Getting Started

You will need the following:

1. A considerable amount of clear disk space -- a few hundred GB for a large project. Each Megacam exposure requires 340 MB when binned 2x2, and these frames will be multiplied by several stages of processing.

2. IRAF software, with specfically the nproto, mscred, and megacam packages installed. For this last item, you can set these lines to your existing loginuser.cl file: 

# This added to run MEGACAM package, 2006 May 27.
reset	megacam		= /data/oirperm2/bmcleod/Megared/
task 	$megacam.pkg	= megacam$megacam.cl
...or you can get the Megared package from Brian at
this URL if you are not working locally at the CfA.

3. Access to IDL (but only if you're using the SDSS-based calibration scheme; see below).

4. Access to various starbase programs and utilities. To get those, add these lines to your .myrc or .cshrc file if you are at the CfA: 

#       For running MEGACAM/STARBASE software, 2006 May 26.
setenv MEGARED /data/oirperm2/bmcleod/Megared/
if ($OS == "solaris") then
	set path=( $path /home/bmcleod/linux/starbase/bin )
	set path=( $path /data/oirperm2/bmcleod/Megared/ )
	set path=( $path /home/bmcleod/bin.linux )
else if ($OS == "linux") then
	set path=( /home/bmcleod/linux/starbase/bin $path )
	set path=( /data/oirperm2/bmcleod/Megared/ $path )
	set path=( /data/oirperm2/bmcleod/Megared/bin/ $path )
	set path=( /home/bmcleod/bin.linux $path )
else
	echo "ERROR -- OS version incorrectly set'
endif

The IRAF portions of the software, in other words, can be run on either a Linux or a Solaris platform (although Solaris is preferred for some important operations), and other programs are specific to Linux. You'll need both platforms. IMPORTANT: The commands that modify the path PRECEDE the existing path designation or you will encounter confusing problems later on.

Last modified February 25, 2008.