In chandra-users, you wrote:
>
>After happily doing many RMF-less gaussian fits a la Sherpa thread to
>HETG emission lines in the standard data products of two observations of
>one star separated by a few months, I started to include the standard
>CIAO 2.1/CALDB RMF files (that were used, incidentally, to make the garf
>files). This worked fine for one observation and fine for the +/-1 MEG
>spectra in the second observation but the later +/-1 HEG spectra now
>have emission features shifted by +0.5 Angstroms. It looks like +0.500
>Angstroms. So the same HEG RMF file seems to work OK for one observation
>but not for the second. If I blank out the RMF, the scale goes back to
>normal. Anyone know what I'm doing wrong ?
>
>Andy Pollock
>
>
>
You didn't do anything worng, we did. This is a flashback to some
ancient HEG/MEG schizophrenia. At one time, we decided to reconcile
disparate HEG and MEG grids so they both start at 1A in 1st order.
Prior to that, we had grids scaled by grating and order, so the MEG 1A
scaled to 0.5 for HEG.
The solution is to either:
- use a different HEG rmf
- re-run tgextract to make a new pha file w/ updated HEG grid.
There are a couple utility scripts on the ciao web pages:
check the grids
- http://asc.harvard.edu/ciao/download/scripts/query_heg_grid
make a grid from pha file
- http://asc.harvard.edu/ciao/download/scripts/mk_tggrid
(top level page is http://cxc.harvard.edu/ciao/download_scripts.html)
Ciao 2.2 also has a mkgrmf tool which can also take a grid spec (2,
actually - one for the energy axis, another for the channel), and make
customized grating rmfs.
-- Dave
David Huenemoerder (617-253-4283; fax: 253-8084)
MIT Center for Space Research/Chandra X-ray Center
70 Vassar St., NE80-6023,
Cambridge, MA 02139
[Admin. Asst.: Deborah Gage 617-253-0228, dgage@space.mit.edu]
This archive was generated by hypermail 2b29 : Tue Feb 12 2013 - 01:00:10 EST