BLACKWEL GUI

Before attempting to use this shell, please read over the documentation for BLACKWEL. This shell is included in the SPECTRUM distribution and is called blackwell_sh.tcl. It likewise will have been moved to /usr/local/bin if you executed the make install script discussed in § . To invoke this shell, type at the prompt:

> blackwell_sh.tcl

The GUI illustrated in Figure should appear.

Figure: The Tcl/Tk GUI for BLACKWEL.

To run this shell, you must have installed on your machine the latest version (4.0 or later) of gnuplot (see http://www.gnuplot.info/).

To test this shell, select the stellar atmosphere model 67244k2p00.mod provided in the distribution, the atomic data file (stdatom.dat) and an equivalent width file for a single species (the file feI.eqw is provided for this test). Select a range of microturbulent velocities (say 0.5 to 3 km/s) over which you want BLACKWEL to do its computations and then press Execute. For this set of files, you will get the graph in Figure , courtesy of gnuplot.

Figure: Sample output from the BLACKWEL GUI.

Each sloping line in this graph corresponds to a spectral line in the file feI.eqw. This is a plot of the abundance of iron as determined from Fe I lines against the microturbulent velocity. Notice that (somewhat ideally!) all of the lines seem to converge at a point in the plot. This gives the optimal value for the abundance of iron and the characteristic microturbulent velocity in the atmosphere of the star under consideration. If you have chosen the temperature and gravity of the star correctly, you will get nearly the same answer for Fe II lines. And, for other species, you should get, within the errors, the same value of the microturbulent velocity. The figure above is an example of a ``Blackwell Diagram'', which is a useful tool for determining microturbulent velocities and abundances in a consistent way in stellar atmospheres.

Please note that the lines can fail to converge in a Blackwell diagram if 1) one or more of your lines is in an undetected blend, 2) the gf values for one or more of your lines are not good, 3) your choice of a stellar atmosphere to model your star is not good, or 4) your line is strongly affected by non-LTE effects. You should use a stellar atmosphere computed with a microturbulent velocity which is as close as possible to the value indicated by the Blackwell diagram, for the sake of consistency. The model atmosphere 67244k2p00.mod was computed with a microturbulent velocity of 2km/s. Since the diagram above indicates that the microturbulent velocity is closer to 1.2 km/s, it would be better to select a model computed with a microturbulent velocity of 1 km/s.

Please note that BLACKWEL cannot be used with hydrogen or helium lines (both He I and He II). Ideally, lines used to compute Blackwell diagrams should be weak to medium strength lines. The cores of strong lines are often not well reproduced in the LTE approximation. A range of line strengths is required in a Blackwell diagram. The weak lines (which are not strongly affected by microturbulence) are nearly horizontal in a Blackwell diagram. Stronger lines have a steeper slope.

Note that blackwell_sh.tcl outputs data you can use to reconstruct the above graph in individual data files labeled with the wavelength of the line.

The shell blackwell_sh.tcl can be directed to give the above plot in postscript format.