[mesa-users] Creating a gamma Dor model

[Aaron Dotter]

Hi folks,

I think Ehsan is on the right track.  Quoting Warner et al.,

"The equation of state (EOS)is a variation of that presented by Iben (1975
<http://iopscience.iop.org/article/10.1086/376727/fulltext/57524.text.html#rf26>)
using the Eggleton, Faulkner, & Flannery (1973
<http://iopscience.iop.org/article/10.1086/376727/fulltext/57524.text.html#rf9>
) EOS for temperatures greater than 4.5 × 106 K and the Vardya (1964
<http://iopscience.iop.org/article/10.1086/376727/fulltext/57524.text.html#rf37>)
EOS for lower temperatures, and it has been corrected for Coulomb shielding
(see, e.g., Clayton 1968
<http://iopscience.iop.org/article/10.1086/376727/fulltext/57524.text.html#rf6>
)."

Since the section of the model Rich is interested is in the
partially-ionized regime, the quality of the Iben EOS is not directly
relevant.  (As Bill says "stellar evolution is highly nonlinear" so it's
not irrelevant.)  Vardya (1964) does not seem to be readily available to
the interested reader but I'm willing to bet that it gives sufficiently
different results to the OPAL EOS that is a plausible culprit, though it
may be impossible to put this to the test in 2016.

Aaron



On Wednesday, July 13, 2016, Francis Timmes <fxt44 at mac.com> wrote:

> generally, the pressure and thermal energy from the iben eos
> is within 0.1% of other independent eos routines and the
> derivatives of those quantities are within 1%. the largest
> deficiency of the iben eos is that it does not include positrons,
> a very reasonable approximation for the main topics that icko pioneered.
>
> if one would like to basis for the statements above:
>
> http://adsabs.harvard.edu/abs/1999ApJS..125..277T
>
> and if one is so inclined, the iben eos can be downloaded here:
>
> http://cococubed.asu.edu/code_pages/eos.shtml
>
> fxt
>
>
>
>
>
> > On Jul 13, 2016, at 5:12 PM, Ehsan Moravveji <e.moravveji at gmail.com>
> wrote:
> >
> > Hi Rich,
> >
> > Naively, I just took a very quick peek at the Sect. 2 in Warner et al.
> (2003)  and noticed that there is a significant version difference between
> the EOS they use (Iben 1976), compared to that of MESA (updated OPAL 2005).
> Since nabla_ad is among the return columns of the EOS, “perhaps”, the
> difference you see in your boundary locations stems from different EOS
> values for nabla_ad through the two EOS versions.
> > If this is so, I do not have an immediate idea how to “downgrade” to the
> old EOS, and reproduce Warner's models; else, let’s hope that the more
> recent MESA EOS gives is more accurate in providing nabla_ad values.
> >
> > B.t.w. the clocks have ticked since the 70s, and our understanding of
> stellar EOS has advanced. Thus, your model “might be” a more accurate
> representation of gamma Dor stars: Your instability strips will tell ;-)
> >
> > The good thing is that your composition (Z=0.02, Y=0.28) and mixture
> (GN93) is identical to theirs.
> >
> > Best regards,
> > Ehsan.
> >
> >> On 13 Jul 2016, at 20:03, RICHARD H D TOWNSEND <townsend at astro.wisc.edu>
> wrote:
> >>
> >> Hi folks —
> >>
> >> I’m interested in creating a models for gamma Dor stars, in which
> gravity modes are unstable due to convective flux blocking. I’ll be using
> GYRE to do the stability calculations; I appreciate that the
> convection-pulsation interaction probably needs a more-sophisticated
> approach than GYRE’s current method (convective freezing), but for now GYRE
> should suffice.
> >>
> >> My first step is attempting to reproduce some of the gamma Dor models
> presented in Warner, Kaye & Guzik (2003, ApJ 593, 1049). However, try as I
> might, I seem to end up with models that don’t have the (relatively) thick
> outer convection zone reported by Warner et al.
> >>
> >> As a specific example, I attach a MESA inlist which aims to reproduce
> the M=1.55 Msun model reported in Table 1 of Warner et al. Running this
> inlist with MESA 8118 results in a final model with the following
> properties:
> >>
> >> Teff = 6927 K
> >> L/Lsun = 6.82
> >> Age = 1.049 Gyr
> >>
> >> This model is somewhat cooler than the model reported in Warner et al
> (their Teff = 6965K), but the difference is small. The luminosity matches
> exactly, and the age is close (their age = 1.076 Gyr). So, it looks like
> I’m in the right ballpark.
> >>
> >> However, when I look at the internal structure of the model, I’m struck
> by the fact that the inner edge of the envelope convection zone is at T ~
> 63 kK (logT ~ 4.75), rather than the ~ 240 kK (logT ~ 5.4) reported by
> Warner et al. Here’s a plot of the radiative vs total flux, as a function
> of temperature, which demonstrates this:
> >>
> >> <figure_1.png>
> >>
> >> Indeed, I find that to get the convection zone(s) to extend to deeper
> layers, I have to allow the star to be significantly cooler and more
> evolved.
> >>
> >> Since I’m not all too familiar with gamma Dor stars, I’m likely making
> a stupid mistake in my inlist file. Can anyone suggest what might be the
> problem?
> >>
> >> Many thanks,
> >>
> >> Rich
> >>
> >> <inlist><profile_columns.list>
> >>
> >>
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