[mesa-users] Radiation pressure at zero optical depth

[Konstantin Pavlovskii]

Hello Bill,

I suggest to make

Pextra = 5.12d-5 / tau * kap * (L/Lsun) / (M/Msun)

Kind regards. Kostya.


On Sat, May 3, 2014 at 4:09 PM, Bill Paxton <paxton at kitp.ucsb.edu> wrote:

> Hi Konstantin,
>
> Thanks very much for your report.  Here are the lines of code in
> atm/private/mod_atm that you are referring to:
>
>          ! P = (tau*g/kap)*(1 + 1.6d-4*kap*(L/Lsun)/(M/Msun))
>          ! the factor comes from including nonzero Prad at tau=0
>          ! see, e.g., Cox & Giuli, Section 20.1
>          P0 = tau*g/kap
>          Pextra = 1.6d-4*kap*(L/Lsun)/(M/Msun)
>
> What precisely do you suggest for a fix -- what should replace the 1.6d-4
> factor?
>
> Bill
>
>
> On May 3, 2014, at 2:31 PM, Konstantin Pavlovskii wrote:
>
> > Dear MESA developer(s),
> >
> > I'd like to report a couple of issues in simple grey atmosphere boundary
> condition in MESA/atm.
> >
> > Prescription from Cox & Giuli is used there to take into account
> radiation pressure at zero optical depth -- 1.6d-4*kap*(L/Lsun)/(M/Msun).
> First, the numerical factor in this prescription is designed by Cox & Giuli
> to contain tau=2/3 embedded into it, whereas tau is supposed to be a
> parameter of the boundary condition in MESA. Second, the value of this
> factor -- 1.6d-4 is apparently not correct for tau=2/3 due to error in Cox
> & Giuli, it should be approximately two times smaller.
> >
> > Kind regards. Konstantin.
> >
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