Re: Estimation of emission measure for a single line

On Thu, Feb 10, 2005 at 13:17 +0530, V Rana wrote:
> Dear ISIS users,
>
>     I have recently installed the ISIS package and started using it for
> analysis of HETG grating data for my sources.  I want to generate the
> emission measure vs. temperature curve for various lines from different
> elements that are present in the spectra. I first loaded the spectrum
> and fitted a single gaussian to one perticular line and obtained the
> observed flux for that, ignoring the other part of the spectrum. I
> followed the istructions given in section 4.6 of the user manual to get
> the emission measure vs temperature curve for that line using the
> observed flux. But it gave me error saying there is no data for x-axis
> and nothing was plotted. I guess there is some problem with the value of
> "k" in the command "em = line_em(k, t);" that I am  suppling. Similarly
> for generating the ratio vs. temperature plot also it gave me same
> error.  There also it demands the value of two line indices n1 and n2.
>
>       Since I am a new user, it will be of great help for me if I can
> get a little detailed reply regarding this.
>        Thank you very much.
> Regards.
> Vikram

It sounds like the X-axis range specified for the plot did not
overlap with the X-axis range in the data.  If no axis ranges
are specified, the plot scale should automatically be set to
span the data.  For example, try:

  xrange;
  yrange;
  plot (t,em);        % should plot on a linear scale

  xlog; ylog;         % log-scale might be better here
  plot (t, em);

If the problem is not associated with the X-axis range, it
would help if I could see the commands input to isis and the
exact error messages generated.

The function line_em1() might also be of interest.  While
line_em() returns the line emissivity interpolated onto a
specified temperature grid, line_em1() returns the grid
points contained in the database.

Thanks,
-John
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