Gammas and polytropes..

Is the gamma from the polytropic index, the same as gamma in astrobear. I think gamma in astrobear is the 'adiabatic index', a ratio of specific heats — but this is not the case for the polytrope according to this -

​http://en.wikipedia.org/wiki/Polytropic_process#Notation

and here is a write up detailing the math

​https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&ved=0CGYQFjAG&url=http%3A%2F%2Fads.harvard.edu%2Fbooks%2F1989fsa..book%2FAbookC02.pdf&ei=pkLxUdWqMpTw8ATRn4G4Bw&usg=AFQjCNFb5iY-uoiYQBlORjGivOReZLsyqw&sig2=YSHBULwBSG1bzKmXQAMVMw&bvm=bv.49784469,d.eWU

Comments

1. Jonathan -- 11 years ago

In AstroBEAR, the adiabatic index does not affect hydrostatic equilibrium. However once gas is compressed - the adiatbatic index determines how 'stiff' the compressed material acts. So it would matter with regards to stability. The polytropic index is based upon an assumed 'adiabatic index' - and I imagine that using a lower adiabatic index than used to setup the polytrope could make the polytropes unstable…