Subject: Standard kywrds for energy & channel ranges (OFWG prelim recomm p20.2)

From: "Ian M George, Code 668, NASA/GSFC, USA (Usque ad mortem bibendum)" <[email-masked]>
Date: Thu, 12 May 94 00:58 EDT

STANDARD KEYWORDS FOR ENERGY & CHANNEL BOUNDARIES IN DERIVED FILES 
 ------------------------------------------------------------------

At a meeting on 1994 May 11 of the OGIP FITS Working Group (OFWG) 
there was a review of keywords used to store information relating to 
the energy & channel ranges used to construct derived products. 

In an attempt to standardize the various conventions which have been 
adopted in the past, the OFWG made the following preliminary 
recommendation.

As always, comments from the rest of the community are invited. The 
OFWG plans to take a final vote on this proposal in a couple of weeks. 

Ian M George 					
on behalf of the OFWG

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OFWG Prelim Recommendation p20.2

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 | STANDARD KEYWORDS FOR ENERGY & CHANNEL BOUNDARIES IN DERIVED FILES |
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					            Version: 1994 May 11

 Typically, in the FITS header of a 'derived' file (such as an image, a
 lightcurve or a spectrum), it is desirable to have keywords which 
 carry the information of the channel or energy boundaries/ranges used 
 to select the data.
 
 The OFWG recommends that channel and/or energy boundaries be recorded using 
 the following keywords.

 Channel boundary:
 -----------------
 The keywords to define lower and higher channel bounderies are:

    CHANMIN = n       /n= numeric (integer) value for the lower boundary      
    CHANMAX = m       /m= numeric (integer) value for the higher boundary

 For those experiments which derived files could be created selecting 
 on diffent channel coodinates (eg. PHA or PI), the coodinates type 
 should be specified using the keyword 

    CHANTYPE= 'value' / value=character string  
			{currently the allowed values are 'PHA' and 'PI'}

 Energy boundary:
 ----------------
 To define the energy range of the data in a derived/product file, the 
 keywords recommended are :

    E_MIN   =  n.n    /n.n numerical value of the lower energy boudary
    E_MAX   =  m.m    /m.m numerical value of the higher energy boundary
    EUNIT   =  'keV'  /character string for unit of E_MIN and E_MAX  
			{where the string must conform to the rules given
			 in OGIP memo OGIP/93-001}

 Deprecated Alternatives
 -----------------------

 Within the OGIP a number of files and /or documents have used or defined 
 different keywords to specify energies or channels boundaries.
 Below is a list of those different/old definitions. 
 These old keywords should no longer be used unless they are required 
 by existing instrument-specific software. It is strongly suggested that 
 any such software be updated to handle the above keywords as soon as 
 possible.

a) The memo number OGIP/93-003 defines the keywords MINCHAN and MAXCHAN
   for the channel boundaries.
b) The previous versions of the ROSAT standard processing software (SASS) 
   created images containing the following keywords:
    XS-CHAN
    XS-MINCH
    XS-MAXCH
    PHACHANS
    PICHANS
    MINPI
    MAXPI
    MINPHA
    MAXPHA 
c) The latest version of the ROSAT standard processing software (SASS) 
   creates images where the above 9 keywords have been replaced by 
    PIMIN
    PIMAX
   in the case of PSPC instrument
    PHAMIN
    PHAMAX
   in the case of HRI instruments.

----------------------------------- END ---------------------------------- 
Ian M George 					
NASA/GSFC OFWG
1994 May 11