[Mesa-users] metallicity in binary systems

[Aaron Dotter]

Taking this discussion off list for the time being.

Aaron

On Thu, Jan 3, 2019 at 7:28 PM Margaret Streamer <
Margaret.Streamer at anu.edu.au> wrote:

> 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> 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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>
>
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