L.S.,
I want to determine the spatial extent of line emission in several
maps taken at JCMT with HARP-B/ACSIS. Assuming a simple structure of
my source, I could describe it by a 2D Gaussian. As output, I would
like to have numbers that tell me how extended the emission is (long
axis and short axis at 50% intensity), and the shape (ellipticity,
position angle), including uncertainties for all these numbers. I have
already 'collapsed' the relevant part of the cube over the width of
each line, so I have 2D maps to work with.
The 'GAUFIT' task in ESP in starlink seems to be able to do exactly
what I want. However, I am not completely clear what is in the output
file. The description at
http://www.starlink.rl.ac.uk/star/docs/sun180.htx/node17.html does not
seem to explain what the output parameters are.
1. I can guess what X and Y mean, and they correspond to what I expect
looking at where my emission is in the GAIA display window. No problem
there.
2. 'Angle' is probably a position angle (in degrees?) of the fitted
ellipse, but relative to what direction? North would be logical, but
that doesn't really make sense in the numbers I'm getting.
3. FWHMa/as and FWHMb/as are probably supposed to be the FWHM values
of the long axis and short axis, respectively, in units of arcseconds.
However, FWHMa is sometimes smaller than FWHMb...
Is there documentation available somewhere that explains what the
output values mean?
Or should I refrain from using this GAUFIT altogether? Maybe the
'object detection' routine embedded in GAIA is an option, but that
seems to be more suited for photometry with data that has a bit more
than 16x16 pixels per map.
In addition, on my Mac OS X 10.5 system, there seems to be a problem
with PATH settings. Upon initiializing ESP, I get a message:
"
Environment Variable ESP_DIR is not set. Setting ESP_DIR to be INSTALL_BIN
Environment Variable ESP_HELP is not set. Setting ESP_HELP to be
INSTALL_HELP/esp
ESP commands are now available -- (Version 0.11-4)
"
Subsequently, calling GAUFIT from the command line looks for the
INSTALL_BIN/gaufit file, which does not exist. When I type,
"/star/bin/esp/gaufit", it does run as expected. This also goes for
'display', which is needed to interactively work with GAUFIT: it only
works on my system when I call the full path /star/bin/kappa/display .
I guess this is also the reason why the ESP help file cannot be found
on my system, since "/star/bin/esp/esphelp" returns the following:
"
!! Error accessing help on topic ' ' in library INSTALL_HELP/esp.shl. Reason
! was "HLP: help library error on open".
! Application exit status SAI__ERROR, Error
"
This PATH problem is of course not a big issue, as long as I can
figure out the full path to the relevant tasks.
Best regards,
Matthijs
--
M.H.D. van der Wiel
Kapteyn Astronomical Institute, University of Groningen
& SRON Netherlands Institute for Space Research
e-mail: [log in to unmask]
homepage: http://www.astro.rug.nl/~wiel/
room: ZG 183 [Landleven 12]
tel: +31 (0)50 363 4083
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