Reply To: Astrofest 2024

Forums Spectroscopy Astrofest 2024 Reply To: Astrofest 2024

Ken Whight

Hi Dominic, Thanks for your interesting reply. In my career within Philips research I learned that modelling silicon devices was difficult enough even with the luxury of having them on the bench infront of you! However assuming thermal equilibrium got you a long way. We did go to a “hydrodynamic” model where the silicon lattice, electrons and holes could be at different temperatures but I couldn’t claim that that was a major advance in terms of designing better devices. I also know that “Monte Carlo” methods were necessary for modelling GaAs devices but I never had to get into that thankfully!
Yes stellar photospheres are not in a global thermal equilibrium but I was hoping that estimates of photosphere pressure and thickness would be “reasonable” for a fair number of stellar types (my estimates for the Sun seemed OK – see the attached file and others under my “Spectral Line Modelling topic). Having developed a global equilibrium model it could fairly easily be extended to a local equilibrium model (but not by me!) to cover more (main sequence?) stars.
However, the particular “insight” that I wanted to discuss was that whilst detailed balance under thermal equilibrium allows you to calculate the Einstein B coefficients in terms of a cross-section area (if you express the Planck function as a photon flux). These cross-sections infuriatingly only apply in the monochromatic case. In the polychromatic case they proved useless as each atom now has a choice of photon to capture. I think this is what necessitated the additional calculation of “oscillator strengths”. However if you use the properties of thermal equilibrium you can relate the polychromatic capture cross-sections simply to the Einstein A coefficients of any elemental spectral series as demonstrated in my attached paper Europa.pdf (equation A.4.12) and I’m hoping to test this out on the Sodium principle series for the Sun if I can get the necessary data, sadly my experimental setup is somewhat moribund (offers of data anyone?).