Hydrogen-alpha emissions (top graph)
Hydrogen-alpha emissions is one factor that has to be closely monitored when revitalizing a star.
When Doctor Timicin attempted to revitalize Praxillus, two increases of hydrogen-alpha levels were an early sign that the experiment was going wrong, signaling that neutron migration was taking place during the experiment. This was unexpected, and ultimately led to Praxillus going nova. (TNG: "Half a Life")
As an in-joke, the console that La Forge was working on during the experiment on the star is labeled as sensor analysis 4077. This was the M*A*S*H unit that David Ogden Stiers was a member of while he played the character of Charles Winchester on the television series M*A*S*H. (Star Trek Encyclopedia)