[Mesa-users] stellar wind velocity

[Francis Timmes]

hi saul,

ok. well, at least my message pointed out to the larger community
what the output quantity is and how it is being calculated. 

in some regimes the formula being used seems to makes some sense:

> It seems that as the star is starting to leave the MS, the wind mass loss rate approaches 10^(-6) Msun/year, and at the same time, V_wind goes up to ~50 km/sec (which is what I would expect).  

but in other regimes it does not seem to make sense:

> Then, when the star really grows to huge proportions with a radius of ~1000 Rsun, the wind rate grows to ~10^(-5) Msun/year.  However, V_wind abruptly drops to 0.01 km/sec (10 meters/sec). What does that mean when the escape speed is still 10’s of km/sec? 


i don't know what your model looks like, but its possible that 
the atmosphere is not resolved enough to give a consistent 
optical depth at the base of the envelope. or maybe the atmosphere
is sufficiently resolved and the solution lies elsewhere, up to 
and including using a different formula.

i know there are several mass loss wind speed experts lurking 
on this mailing list. perhaps one of them can chime in.

fxt


p.s. - always cc mesa-users on replies. its how we track resolving issues.









> On Oct 7, 2021, at 6:27 AM, Saul A Rappaport <sar at MIT.EDU> wrote:
> 
> Hi Frank:
> 
>> lines 542-549 in $MESA_DIR/star/defaults/history_columns.list
>> say how v_wind_Km_per_s is calculated. 
>> 
>> clearer?
> 
> Actually this does not help me.  I had asked Josiah about this, and this is what he wrote:
> 
> If the answer is not obvious to you, could you recommend someone who can enlighten me?  Or, am I just not thinking about this correctly?
> 
> I can't answer this off the top of my head.  It looks like MESA is setting
> 
>   v_wind ~= kappa * Mdot / (4*pi*r) 
> 
> which implies r ~= 1/(kappa * rho), i.e., the photon mean free path at photosphere conditions is about the radius.  More specifically, star/private/history.f90 has the code for the history output
> 
>             case(h_v_wind_Km_per_s)
>                val = 1d-5*s% opacity(1)*max(0d0,-s% mstar_dot)/ &
>                         (4*pi*s% photosphere_r*Rsun*s% tau_base)
> 
> I don't think I understand why that approach makes sense generically.  My best suggestion is to ask on the mesa-users list (mesa-users at lists.mesastar.org).  The developers read it and usually someone with some relevant expertise will come along.
> 
> I’m asking why the values seem non-physical, and appear to fly in the face of what I had believed to be winds of ~20 km/sec being blown out via dust grains.
> 
> Can you point me to the literature where winds of 10 m/sec are discussed?
> 
> 
> Saul 
>