Uhuru observations of Hercules X-1
This light curve of Her X-1 shows long term and medium term variability. Each pair of vertical lines deliniate the eclipse of the compact object behind its companion star. In this case, the companion is a 2 Solar-mass star with a radius of nearly 4 times that of our Sun. This eclipse shows us the orbital period of the system, 1.7 days.
The long term variability shown here is precession of a disk of accreting matter around the neutron star. This precession has a 35-day period.
In addition, the neutron star in Her X-1 is also a pulsar with a 1.24 second pulse period.
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