[Mesa-users] metallicity in binary systems

[Margaret Streamer]

Hi Aaron,
Many thanks for the reply and you are correct that I was simply using the default simple_photosphere, and also the default mixing_length_alpha.  I’ve now read the paper you suggested and it seems I need to investigate my models further.
Firstly though, to summarise what I found for TT Hor:
My binary initial conditions are donor ~ 1.6Msun; accretor ~ 1.3Msun
                    Final conditions are donor ~ 0.7Msun; accretor ~2.2Msun
The final temperature of the donor (now a red giant) from MESA models fits within uncertainties of 50K for my binary model.  It’s the temperature of the accretor that is the problem(now a delta Sct pulsator).  The difference is ~800K higher with solar metallicity, compared to my binary model.  This is far greater than the effects you are seeing with red giant stars.  My primary interest is with the delta Sct pulsator.  Thus far I have not changed my input conditions  as the stars evolve.

Given the above, I am trying to decide which boundary conditions to use.  As a start, I think I should be using model atmosphere tables with solar metallicity and use tau=1e-1, and decrease ML alpha from the default.   Does this seem a realistic starting point to you?

Many thanks for your advice,
Cheers,
Margaret


From: Aaron Dotter [mailto:aaron.dotter at gmail.com]
Sent: Thursday, January 3, 2019 2:29 AM
To: Margaret Streamer
Cc: mesa-users at lists.mesastar.org
Subject: Re: [Mesa-users] metallicity in binary systems

Hi Margaret,

From your inlist, it looks like you’re not explicitly setting ‘which_atm_option’ in the controls section.  Thus, you get the default simple_photosphere, which is not a good choice for low mass stars.

The atmosphere boundary condition and your choice of the mixing_length_alpha have a significant influence on the Teff of your models.  For a thorough discussion of this topic (using MESA) see

https://arxiv.org/abs/1805.04112

Cheers,
Aaron



On Wed, Jan 2, 2019 at 12:40 AM Margaret Streamer via Mesa-users <mesa-users at lists.mesastar.org<mailto:mesa-users at lists.mesastar.org>> wrote:
Hi MESA team,


I recently had a paper published (Streamer, M., Ireland, M.J., Murphy, S.J., Bento, J., 2018. A window into δ Sct stellar interiors: understanding the eclipsing binary system TT Hor. Mon Not R Astron Soc 480, 1372-1383. https://doi.org/10.1093/mnras/sty1881) but I now have a more general query about the way MESA deals with binary systems.

Inlists are attached.

For TT Hor, I needed to change from solar metallicity to one higher (Z=0.0281, [M/H] =0.15) before I could match the temperature of the accretor in the evolutionary models to that of my binary model.  This difference was more than uncertainties of my binary model.

I am now working on a different system which has similar masses, is also an Algol-type and has conservative mass transfer. I'm still using MESA version r-8845.

Again I am finding that I need to increase the metallicity before I can match the temperature of my evolutionary models to the binary model.

Both systems lie slightly above the galactic plane at 786pc (TT Hor) and 1190pc (current target), so a higher than solar metallicity is feasible.

As the metallicity also affects the calculated pulsations, I need to be sure that this is a 'real' effect and not something I am doing wrong in my MESA modelling.



Are any of the MESA team able to offer any advice or assurances in this matter?



Many thanks for your time,

Regards,

Margaret

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