In this work, we are interested in the diagnostics in electronic temperature of a plasma purely photoionized, based on the intensity ration of lines emitted by ions helium-like, which have an atomic number Z relatively small.We considered the three lines corresponding to the transitions starting from the excited levels 1s2l towards the fundamental level 1s2 1S0, like appropriate lines.More precisely, the line of resonance w due to the transition 1s2p 1P1 --- 1s2 1 S0, click here the line of intercombinaison (x,y) 1s2p 3 P2,1 --- 1s2 1 S0 as well as prohibited line z due to the transition 1s2 3 S1 --- 1s2 1 S0.These lines appear clearly in the spectra of astrophysical plasmas.
As helium-like ion, we chose two, the oxygen O6+ (Z=8) and neon Ne8+ (Z=10).We carried out calculations of the ration of lines intensity G=(z+x+y)/w of O6+ and Ne8+ according to the electronic temperature in the range going from 105 to 107 K.We will see that, like it was shown by Gabriel and Jordan in 1969 [1], this intensity ration can be very sensitive to the temperature electronic and practically independent of the electronic density.Consequently, the ration G can be used to determine in a reliable way the electronic alarecre.com temperature of plasma observed [2].