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Astron. Astrophys. 328, 617-627 (1997)

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Appendix A: collision rates [FORMULA] O [FORMULA] O-He

To obtain the de-excitation rates of 16 O18 O-He, the collisional transitions are separated into 9 groups:


[TABLE]

For each group, N indicates the initial level, N', the final one and [FORMULA] and we have used the following hypothesis to obtained the de-excitation rates:

  • For odd values of N and [FORMULA], the rates are equal to those of O2.
  • For odd values of N and even values of [FORMULA], the rates are obtained by averaging the rates of the transition [FORMULA] and the transition [FORMULA]. For odd values of N and ([FORMULA] =0, [FORMULA] =1), the rates are obtained by extrapolation from all the rates from the same N to [FORMULA] [FORMULA] 0.
  • For even values of N and [FORMULA] (even values of [FORMULA]), the rates are obtained by averaging the rates of N -1 and N +1 (equal to those of O2) for the same value of [FORMULA]. For even values of N and ([FORMULA] =0, [FORMULA] =1), the rates are obtained by extrapolation from all the rates with the same value of [FORMULA] and [FORMULA] [FORMULA] 0.
  • For even values of N and odd values of [FORMULA], the rates are obtained by averaging the rates of the transition [FORMULA] and transition [FORMULA].

The excitation rates are obtained by the usual reversibility law and the collisional rates of 16 O18 O-H2 are equal to those of 16 O18 O-He multiplied by the reduced mass factor [FORMULA] (see MVB).

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© European Southern Observatory (ESO) 1997

Online publication: March 26, 1998

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