Velocity definitions

[tonywong]

I am confused about how MIRIAD interprets datasets with ctype3='VELO-LSR' or 'VELO-HEL'. It sounds like these should still be interpreted as Doppler velocities in the "radio" convention, yet some routines like 'imspec' and 'imstat' now report the 3rd axis to be 'Relativistic velocity'. Can someone verify that old MIRIAD datasets are still being interpreted the same way? I suggest that for the old AIPS linetypes, imspec use the same x-axis labeling as uvspec, e.g. Velocity(radio,LSR). Also, the online MIRIAD manual doesn't seem to have been updated to reflect the changes to 'velsw'.

[Mark.Wieringa]

Hi Tony,

I'm afraid I must claim ignorance in this area. Maybe some other spectral line observer has worked this out and can enlighten us.
What I can offer is Mark Calabretta's email on the topic that went out to the atnf-data-reduction list:

http://www.atnf.csiro.au/lists/atnf-dat ... /0027.html

Could you try the task 'impos' on the same dataset - it appears to have been updated for spectral coordinate handling more recently. If impos does the right thing, we could look at fixing imspec and imstat to report the same spectral axis info. A small test dataset displaying the issue would help.

Jamie will have a look at updating the Miriad manual text for velsw.

Cheers,

Mark