next up previous contents
Next: The cora program package Up: Manual for Cora line Previous: New in version 3.0   Contents

Summary

Cora is a program package that implements a line fitting procedure based on the Maximum Likelihood technique and developed for emission line spectra, as introduced in Ness & Wichmann 2002.

Basically the program seeks to obtain emission line counts (total number of photons). Energy fluxes or intensities are not calculated during the procedure, since the response from the specific instrument must be processed. Our aim is to provide a tool applicable to all kinds of different spectra. However, we provide some tools to calculate fluxes from effective areas to be given after the calculation of line counts. In addition, line positions and line widths can be iterated in order to get most accurate line fluxes. For line profiles we provide Gauss- and Lorentz profiles. A Pseudo-Voigt profile is implemented consisting of a weighted sum of a Gauss- and a Lorentz profile, with common line-widths also calculated from individual Gauss and Lorentz line-widths. More profiles can be used by giving an ASCII file containing data points representing the line profile and line width. The program is especially applicable to spectra with low count numbers like UV spectra or X-ray spectra. It has been developed in the context of analyzing CHANDRA LETGS data, and is especially useful for these data, but sufficiently general to be applicable for other data as well. A supplemental program cora_rgs is provided, converting the fits files returned by the XMMSAS task rgsproc into the CORA format, such that XMM-RGS data can easily be analyzed with CORA.

In Sect. 3, installation instructions are given. The basic fit routine is delivered with a Graphical User Interface (GUI) supporting the specification of the input parameters. The acceptable ranges of the input parameters are described in Sect. 6.

The output is organized in two ways: In order to obtain a visual impression of the fit result, a plot can be produced, thus allowing comparison of the fit result with the original spectrum. This plot can be produced in different formats, i.e., as postscript file designed for inclusion in publications and as GIF and PPM file for inclusion in, e.g., power point presentations, or in an X window. In addition the numerical fit results, i.e., the parameters with their errors, can be written into an ASCII file for further processing. This is useful when the program is to be used for searching a whole spectrum automatically, listing all lines with wavelengths, fluxes, etc. in a log-file. This log-file can be converted into a LATEX table for publication etc. A detailed description can be found in Sect. 8.

We would like to point out that the program is still being developed and improved. Some new features that are provided may not yet be included in the manual.



Subsections
next up previous contents
Next: The cora program package Up: Manual for Cora line Previous: New in version 3.0   Contents
Jan-Uwe Ness
2003-05-23