Try and find a way to make a table of the ROSAT point source catalog that contains only the RA, Dec, and count rate.
from astropy.table import Table
t = Table.read('data/rosat.vot')
t.keep_columns(['RAJ2000', 'DEJ2000', 'Count'])
t
Note that you can also do this with:
t_new = t['RAJ2000', 'DEJ2000', 'Count']
t_new
Make an all-sky equatorial plot of the ROSAT sources, with all sources shown in black, and only the sources with a count rate larger than 2. shown in red.
from astropy.table import Table
from matplotlib import pyplot as plt
t = Table.read('data/rosat.vot')
t_bright = t[t['Count'] > 2.]
fig = plt.figure()
ax = fig.add_subplot(1,1,1, aspect='equal')
ax.scatter(t['RAJ2000'], t['DEJ2000'], s=1, color='black')
ax.scatter(t_bright['RAJ2000'], t_bright['DEJ2000'], color='red')
ax.set_xlim(360., 0.)
ax.set_ylim(-90., 90.)
ax.set_xlabel("Right Ascension")
ax.set_ylabel("Declination")
Try and write out the ROSAT catalog into a format that you can read into another software package.
from astropy.table import Table
t = Table.read('data/rosat.vot', format='votable')
t.write('rosat2.csv', format='ascii', delimiter=',')