[mesa-users] Vink_wind_eta

Tue May 26 13:30:13 EDT 2015

Hi Bill, hi all,
I think a reasonable naming that also takes care of generality could be something like mass_loss_h_burning, and mass_loss_he_burning. Then whether or not one deals with OB stars or an RGB, the former applies, and after the core He ignition, the latter enters the stage.
Just a suggestion …

Cheers
Ehsan.

> On 26 May 2015, at 17:57, Bill Paxton <paxton at kitp.ucsb.edu> wrote:
> 
> 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 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>>> 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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> 
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