A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » FITS
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

[fitsbits] frequency definitions



 
 
Thread Tools Display Modes
  #1  
Old May 4th 09, 06:38 PM posted to sci.astro.fits
Tom Kuiper[_2_]
external usenet poster
 
Posts: 7
Default [fitsbits] frequency definitions

I'd like to get it clear in my mind what the various frequency
definitions are. Is the following right?
If there is a place where all this is clearly laid ou, please refer me
to that.

CRVALx - the value corresponding to the pixel CRPIXx in frame
defined by CTYPEx.
OBSFREQ - the actual frequency to which the receiver is tuned
corresponding to the center of the IF.
RESTFREQ - the receiver frequency (corresponding to the center of the
IF) in the reference frame defined in TTYPEx.

( Vdop )
OBSFREQ = RESTFREQ * ( 1 - ------)
( c )

where Vdop is the velocity of the reference frame with respect to the
observer.

If we assume that CRPIXx is the pixel corresponding to the center of the
IF, then
CRVALx = RESTFREQ if CTYPEx = FREQ-LSR,
CRVALx = OBSFREQ if CTYPEx = FREQ-OBS

What is the difference between FREQ-OBS and FREQREST?

Thanks and regards

Tom
  #2  
Old May 5th 09, 11:44 AM posted to sci.astro.fits
LC's No-Spam Newsreading account
external usenet poster
 
Posts: 6
Default [fitsbits] frequency definitions

On Mon, 4 May 2009, Tom Kuiper wrote:

I'd like to get it clear in my mind what the various frequency
definitions are. Is the following right? If there is a place where
all this is clearly laid ou, please refer me to that.


Not a spectral WCS expert, but the standard and official references
are :

- http://fits.gsfc.nasa.gov/fits_standard.html
the latest release of the FITS standard, in particular chapter 8

- the full WCS paper III, either as published or
http://www.atnf.csiro.au/people/mcalabre/WCS/scs.pdf

(the other WCS papers are all listed in
http://www.atnf.csiro.au/people/mcalabre/WCS/index.html

--
----------------------------------------------------------------------
is a newsreading account used by more persons to
avoid unwanted spam. Any mail returning to this address will be rejected.
Users can disclose their e-mail address in the article if they wish so.
  #3  
Old May 6th 09, 07:54 AM posted to sci.astro.fits
David Berry
external usenet poster
 
Posts: 4
Default [fitsbits] frequency definitions

It looks like Tom's query was about dual sideband data, which is not
covered by paper III. OBSFREQ, etc, are not in the standard. There are
probably various different schemes in use out there. For instance JCMT
and CLASS software use a system based on a keyword called IMAGFREQ,
which holds the image sideband rest frequency (with RESTFREQ holding
the observed sideband rest frequency).

David


2009/5/5 LC's No-Spam Newsreading account :
On Mon, 4 May 2009, Tom Kuiper wrote:

I'd like to get it clear in my mind what the various frequency
definitions are. *Is the following right? If there is a place where
all this is clearly laid ou, please refer me to that.


Not a spectral WCS expert, but the standard and official references
are :

- http://fits.gsfc.nasa.gov/fits_standard.html
* the latest release of the FITS standard, in particular chapter 8

- the full WCS paper III, either as published or
* http://www.atnf.csiro.au/people/mcalabre/WCS/scs.pdf

* (the other WCS papers are all listed in
* http://www.atnf.csiro.au/people/mcalabre/WCS/index.html

--
----------------------------------------------------------------------
is a newsreading account used by more persons to
avoid unwanted spam. Any mail returning to this address will be rejected.
Users can disclose their e-mail address in the article if they wish so.
_______________________________________________
fitsbits mailing list

http://listmgr.cv.nrao.edu/mailman/listinfo/fitsbits


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Subsolar and Sublunar Points definitions Oct. 11, 2008 E.D.G. Astronomy Misc 4 October 18th 08 01:10 AM
Conference to Grapple with Planet Definitions (Forwarded) Andrew Yee Astronomy Misc 0 May 21st 08 03:39 PM
Conference to Grapple with Planet Definitions (Forwarded) Andrew Yee[_1_] News 0 May 21st 08 03:29 PM
definitions Mike Amateur Astronomy 0 March 29th 06 08:04 PM
Definitions Astro "Messier Objects" Mark F. Amateur Astronomy 11 March 8th 04 04:02 AM


All times are GMT +1. The time now is 12:54 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.