Notes for Asif on Chandra data analysis, model fitting, etc.
D. Cohen - 31Oct05

First of all, we'll be using the standard Chandra data reduction and analysis package, CIAO, as well as XSPEC for fitting our Owocki-Cohen line profile models.  We'll also be using some IDL code we wrote to plot best fit models, data, and fit residuals, as well as to calculate and plot the confidence regions for a given fit.  (You can use my current zeta Ori draft as a guide to the kind of things we'll be doing - a draft and other related information is posted at: http://astro.swarthmore.edu/~cohen/projects/zori/)

Basic Chandra information (including "threads" - basically recipes for running common CIAO tasks - and the interface for searching the archives) is available at the Chandra X-ray Center site: http://cxc.harvard.edu/

To run CIAO and XSPEC, a couple of start-up scripts need to be run.  The standard way to do this is to put the following lines in your .cshrc file: 

-----
if (-e /opt/lheasoft/i686-pc-linux-gnu-libc2.3/lhea-init.csh) then
    setenv LHEASOFT /opt/lheasoft/i686-pc-linux-gnu-libc2.3/
#   /usr/local/astro/xspec/lheasoft/Linux_2.2_i686
    source $LHEASOFT/lhea-init.csh
endif

source /opt/ciao/bin/ciao.csh
-----

Note: it might be advisable to put a " -o" at the end of that last line. 

Since we'll be starting out by doing some analysis and plotting of models and zeta Ori data - and since we've already got the zeta Ori data all processed - we won't need to access the archives or run CIAO with this dataset.  So, let's start with using XSPEC. 

My working directory is 
/home/cohen/xspec/2005/

Maybe you should make your own working directory, and then we can sit down together and do some simple reading-in of the data to XSPEC, screen plotting, model fitting...

The relevant files are: 

All the fits files in that directory.  The one with "pha2" contains the spectrum itself.  The ones with "grmf" contain the response matrix (which describes the spectral resolution of the instrument) and the ones with "garf" contain the detector effective area (so that models calculated in flux units can be compared to data measured in counts units). 

The two files "loaddata.xcm" and "setup.xcm" are scripts that contain some often-invoked commands; so you should copy them over too. 

OK... let's start there.  I'm now making a "project" directory on my webserver for you/us: 

http://astro.swarthmore.edu/~cohen/projects/Asif/

Right now, I've put two things there: A copy of this very document, and another rtf file that contains a record of a few different analysis sessions I ran with my student Kevin, who'd worked on the zeta Ori project this summer.  These include XSPEC sessions very much like you and I should get started on, and also some of Kevin's IDL code for making plots and calculating confidence limits.  

Maybe you and I should try to reproduce some of these calculations. 

David