iraf.net

Dear sirs,Thank you in advance for the email support. I am an amateur doing radial
velocity work and I do not have easy access to the academic community for
help.1. In Do3fibers every time I process a spectra I have to manually select
the apertures to process. I have 9 apertures in my flat field but only use
2 in processing. It constantly picks 4+5, I want it to stay on 1+2, how do
I get them to stay on 1,2 in subsequent spectra after I select them once?2. In Fxcor when I compare the subject spectra to the template spectra I
get a pixel offset of say .008 at the bottom of the screen and right next
to it is +/- 1.92 pixels. I would think this is the error factor but it
seems high, so I wanted to verify exactly what it represented.3. I have multiple exposures of the same star with file names
Pollux_1.imh, Pollux_2.imh, Pollux_3.imh etc. I want to batch process
these files from the subdirectory and have them end up Pollux_1.ms etc. It
is not clear how to go about this any hints?Thank you VERY much for the help,Tom Kayespectrashift.com

Hi Tom,
I can reply to your FXCOR question but somebody else will have to
handle the others since I'm not familiar with the tasks involved. The
error quoted on the initial command line is the error in the heliocentric
velocity in km/s and represents the uncertainty in the shift derived from
fitting the peak. Depending on the fitting function used, it is either simply
the error of the center parameter of the fitting function times the
velocity-per-pixel dispersion, or when a FWHM is available it is an error
estimate derived from the Tonry & Davis 'R' value. The R-value is a ratio
of the true peak height to the height of the average peaks in the correlation
function, the actual error is computed as error = [ (TWO_PI * width) / 8.0 / (1.0 + R) ] * deltavwhere 'width' is the FWHM in pixels of the peak and 'deltav' is the velocity
per pixel dispersion. The actual equations used are eqns 20-24 in the
Tonry & Davis paper (1979, Astron. J. 84, 1511) on which the program is based.
With all that said, I wouldn't take the error too seriously since it
tends to greatly overestimate the real errors. Most people use repeated
observations and/or multiple templates and derive their own values. The
height of your peak, the number of points fit, and the function used to
derive the center all affect this value and reported errors will vary widely.
The verbose output log files will give you all the fit parameters and
associated errors which you may wish to use in computing an error.
BTW, I had a look at your web page and it sounds like an impressive
project. Two quick comments you might already be aware of: IRAF V2.11
can use FITS images directly so there is no need to convert to .imh format
unless you prefer it. The FXCOR task will do all the velocity calculations
and corrections for you provided the image has the proper header keywords
(see the KEYWPARS pset help page). If you haven't already found it there is
a lot of documentation available from the /iraf/docs directory on
iraf.noao.edu, the README file serves as a TOC (all these are available from
the web page as well). There are also introductory exercises available from
/iraf/misc as 'exer211.tar.Z', see the readme for what it contains.
Hope this helps, let me know if you still have questions.Cheers,
Mike Fitzpatrick