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\centerline{\bf YOHKOH BCS Synthetic Spectra}
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\+&&&					A. Sterling (3/2/92)\cr
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\centerline{\bf Introduction}
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A set of synthetic spectra covering a range of temperatures is available for
some of the channels covered by the YOHKOH BCS.  One can estimate the
temperature of BCS spectra by comparing the synthetic spectra at a given
temperature with the BCS spectra, and line full width at half maximum (FWHM)
values are fixed for each channel's spectra.  Continuum values are not
calculated.  This method is intended to give a quick estimate of temperatures
of the spectra-producing plasma.

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{\bf 1.0 Synthetic Spectra}
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Spectra for Fe XXV and Fe XXVI were generated by A. Sterling from codes
obtained from George Doschek of NRL.  Intensities are scaled to unity (or to a
specified maximum value when overplotting -- see below), so only
the relative sizes of the lines have meaning (i.e., emission measure
information is not included in these spectra).  Synthetic spectra for S XV
will be available shortly.  


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Fe XXVI spectra:
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Only lines produced by Fe XXV are included in the generation of these spectra. 
The code to produce the spectra was written by G. Doschek and modified by R.
Summers.  Gaussian profiles are assumed, and line FWHMs are set to 0.001 \AA. 
Relative strengths of L$\alpha$ and J lines are temperature sensitive.

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Fe XXV spectra:
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The Fe XXV spectra use multiplicative factors for lines x, y, and z based on
the Ni tokomak results presented by Zastrow {\it et al.}, Phys. Rev. A, 41,
1427 (1990) for line x, and EBIT results presented by Brown {\it et al.}, Phys.
Rev. A., 40, 4089 (1989) for lines y and z.  Fractional ionization abundances
for Fe XX - XXVI are from Arnaud \& Rothenflug (Astro. \& Astrophy. Supplement
Series 1985, 60, 425).  Gaussian profiles are assumed, and line FWHMs are set
to 0.001 \AA.  Relative strengths of w and j lines are temperature sensitive.

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Ca XIX spectra:
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Fractional ionization abundances for Ca XVII - XX are from Arnaud \& Rothenflug
(Astro. \& Astrophy. Supplement Series 1985, 60, 425).  Gaussian profiles are
assumed, and line FWHMs are set to 0.0025 \AA.  The line q to line w ratio, and
D13 to line w ratio are temperature sensitive.  Normally the Yohkoh BCS does
not detect the q line, so the D13/w ratio must be used for temperature
estimates.  But this is not too easy to do since D13 is often poorly resolved. 
Moreover, the D13/w ratio is not strongly dependent on temperature (cf. the q/w
ratio).  Therefore please exercise caution when estimating the temperatures
from Ca spectra. 

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{\bf 2.0 Accessing the Spectra} 
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The synthetic spectra can be accessed via the idl code SYNTH.PRO written by D.
Pike.  To run, enter idl from the BCS VAX. Then input:

IDL$>$ synth[,chan\#,temp,/over,xarr,yarr,/noplot]

where chan\# is the channel to be fit(1 for Fe XXVI, 2 for Fe XXV, 3 for Ca XIX,
and 4 for S XV), and temp is the temperature in millions of degrees K.  So, for
example, 

IDL$>$ synth,2,15

generates a 15 million degree Fe XXV spectrum.   Including the option, /over,
will overplot the spectra onto displayed bcs spectra.  You will be prompted to
position the cursor on the location where you would like the maximum of the
resonance line (w-line) to be in the plot for Fe XXV, Ca XIX, or S XV, or the
maximum of the L$\alpha_1$ line to be for Fe XXVI.  The xarr and yarr options
are for storing the output wavelengths and spectral data in arrays xarr and
yarr.  Including the /noplot option with xarr and yarr will store the data in
the xarr and yarr arrays without plotting.  If none of the options are
selected, you will be prompted for the channel number and the temperature, with
the current range of available temperatures being given. 

Plots of the synthetic spectra are available in the BCS SYNTHETIC SPECTRA
folder in D-toh.

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