[mesa-users] Radiation pressure at zero optical depth

[Konstantin Pavlovskii]

Alternatively, if you find it more appropriate you can write

Pextra = (6.0 * pi * clight * cgrav * tau)**(-1.0) * lsol / msol  * kap *
(L/Lsun) / (M/Msun)

Kind regards. Kostya.


On Sat, May 3, 2014 at 6:15 PM, Konstantin Pavlovskii
<pavlovsk at ualberta.ca>wrote:

> 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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