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Date: Thu, 16 Apr 1998 17:38:00 +0100
From: M.Villar-Martin@sheffield.ac.uk (Montse Villar-Martin)
Message-Id: <199804161638.RAA10465@kepler.Sheffield.ac.uk>
To: rfosbury@eso.org
Subject: Re: Letter of reference to Michael Rowan-Robinson?
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Status: RO

        Dear Bob,

        Mappings crushes if I use dust/gas ratio larger than
2  to compute depletion of elements. The results for dust/gas
ratios of 0,1,2 are :


 Dust/Gas    N/C      N/C (relative to solar)    
 0           0.30     1.00   
 1           0.77     2.57   
 2           0.91     3.03    


        This suggests that N/C is quite sensitive to dust depletion, but
we would need   large amounts of dust to make N/C 5-10 times solar. This
gas should be mixed with the ionized gas. 

        I don't think that Ca depletion is the reason for the large NV/CIV 
values. Table 2 shows that those objects with larger NV/CIV values have also 
the largest NV/HeII values (4C41.17 is an exception, low NV/CIV and high
NV/HeII). This suggests to me that the overabundance of N is also relative 
to elements like He (non sensitive to depletion) and not only to C. Moreover, 
CIV/HeII is not  smaller in objects where NV is stronger. Again, this sugests 
that C is not depleted.

                NV/CIV    NV/HeII   CIV/HeII
4c23.56a         0.654    0.89      1.37        
4c23.56b         0.471    0.57      1.21
4c00.54          0.5      0.67      1.33
TXS0211-122      0.563    1.10      1.96

B30731+438       0.132    0.16      1.21
TXS0828+193      0.213    0.32      1.50
MRC0943-242      0.271    0.27      1.01
4C41.17          0.294    0.70      2.38

        Cheers

        Montse

------- Message 61