Retrieve the Data

The data are on the server in /home/data/m67. Look for a file called
m67_cmd.dat. The file contains only the apparent magnitudes and (B-V) colors for the stars in the cluster. This file has been extracted from the primary data file table3.dat using the program make_cmd.f which is also in this directory for reference. Use the m67_cmd.dat data file to make a Grace file following steps such as these:

• Make a directory to store your work with mkdir m67
• Copy the data to this directory with
  • cd /home/data/m67
  • cp m67_cmd.dat /home/username/m67 where ``username'' is your login name
• Go back to your directory (cd then cd m67)
• Start Grace with xmgr
• Load the data using Data -> Import
  This will make one data set where x is the magnitude and y is the color.
• Use Data -> Transformations -> Evaluate Expression to create a new set where x is the color and y is the magnitude. You could do this in two steps this way:
  • Select S0 and then use y=x. Press Apply.
  • Now select S1 and use x=S0.y . This makes a third set labeled S2 which has the ordering you need.
  • Use the left mouse button, select the first two sets, and with the right mouse button press Hide to make them disappear from the graph. Press the AS button to autoscale and you should see a plot of apparent magnitude versus color.
• Customize the plot using the Plot -> Axis properties menu. You should select the y-axis and press the Invert button so that it plots smaller magnitudes (brighter stars) at the top. Adjust the scales and label the axes.
• Plot each star as a point instead of a ``pen down'' plot by selecting Plot -> Set appearance and changing the Line properties from ``Straight'' to ``None'' and the Symbol properties from ``None'' to ``Circle''. Make the circle size small. Select a color you like. Press ``Apply'' so this takes effect. You can also fill the circle by using the Symbol menu in Set appearance.
• Save your work. Select File -> Save as (not just Save, since that will write over your data file), and giving it a name. The correct extension for Grace files is ``.agr''. It may also be useful to save a new data file that you can easily load on top of the Hipparcos Grace file you made earlier. Do this with the Data -> Export menu and give it a distinct name, usually with a ``.dat'' extension. This file would not contain information about how to plot the data, but it would have the x column as the color and the y column as the magnitude.