[mesa-users] Vink_wind_eta

[Bill Paxton]

Thanks --- that is very helpful.  it looks like we're still using a scheme from the infancy of mesa when there were only a few options, but now it isn't a good fit for the range of options that have been added since then.  time for a cleanup. 

the RGB/AGB split was meant to provide a simple way for users to select different wind schemes for different stages of evolution.
and since the scheme could change on the fly, there needs to be a way to change the wind_scaling_factor too.
that is taken care of by providing separate values of scaling factor for the different kinds of winds.

I can easily do the renaming to replace "eta" by "scaling factor" while keeping different scaling factors for different types of wind.

Do you have suggestions for a way to replace the crude RGB/AGB by something better?  RGB/AGB/OB?  or what?
and please include precise details of the partitioning so that I can translate it into code! 

Thanks again,
Bill




On May 26, 2015, at 3:26 AM, Zsolt Keszthelyi wrote:

> Hi Bill, 
> 
> thanks for your reply. 
> 
> I think the issue is that eta is used in different contexts with different meanings in the literature. 
> 
> 
> 1. In the context of RGB / AGB stars (Reimers 1975, Blöcker 1995) eta is a scaling factor to match observed mass loss rates with their empirical mass loss formulas.  
> 
> 
> 2. On the other hand, in the context of WR stars (Cassinelli 1991 and references therein) eta was introduced with a physical meaning, to describe the wind with the ratio of stellar wind momentum flux and the photon momentum flux, eta = Mdot * vinf / (L / c).
> 
> This eta is used in the context of OB stars (e.g., Lamers & Leitherer 1993, Puls et al. 1996) as the performance number.
> 
> 
> 
> Even though the idea of eta as a scaling factor is stated (and used), a user was looking for eta in the Vink paper, so that is why I think calling it simply 'wind_scaling_factor' might make it easier for the users. 
> 
> 
> Also my understanding is that you must set either 'RGB_wind_scheme' or 'AGB_wind_scheme' to apply one of the wind recipes, however the Kudritzki, Vink (OB) and Nugis & Lamers, Gräfener & Hamann (WR) prescriptions are not valid for these stars. This might also be a source of confusion since in a previous email the vink_wind_eta and RGB mass loss was mentioned together. 
> 
> 
> I hope this is helpful. 
> 
> Cheers, 
> 
> Zsolt 
> 
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>> Von: Bill Paxton <paxton at kitp.ucsb.edu>
>> An: Zsolt Keszthelyi <Z.Keszthelyi at campus.lmu.de>
>> Kopie: mesa-users at lists.sourceforge.net users <mesa-users at lists.sourceforge.net>
>> Datum: Tue May 26 06:46:15 CEST 2015
>> 
>> 
>> On May 23, 2015, at 4:25 AM, Zsolt Keszthelyi wrote:
>> 
>>> It's a little bit unlucky nomenclature though, since in stellar wind physics the
>> eta is the so-called wind efficiency / performance number and has nothing to do with
>> a numerical scaling factor. (It might be useful to change it in the next version.)
>> 
>> 
>> Hi,
>> 
>> In star/defaults/controls.defaults we describe the various etas like this for Reimers
>> and Blocker winds:
>> 
>>         !### Reimers_wind_eta
>>         ! Parameter for mass loss by Reimers wind prescription.
>>         ! Reimers mdot is `eta*4d-13*L*R/M` (Msun/year), with L, R, and M in solar
>> units.
>> 
>>         !### Blocker_wind_eta = 0
>>         ! Parameter for mass loss by Blocker's wind prescription.
>>         ! Blocker mdot is `eta*4.83d-9*M**-2.1*L**2.7*4d-13*L*R/M` (Msun/year),
>> 
>> Having stated that idea twice, we just hope the reader will make the leap to understand
>> that they work similarly for the remaining kinds of winds.
>> 
>> So we use "parameter for mass loss" where you would use "wind efficiency / performance
>> number".
>> 
>> In practice of course it is a numerical scaling factor for the strength of the wind.
>> At least it looks like that to me.  And it does that in the code.
>> 
>> If I'm missing something important about the role of eta in stellar wind physics,
>> please educate me.  
>> 
>> Thanks,
>> Bill
>> 
>> 
>> 
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