[mesa-users] Pulsating star in the HB using GYRE

Cyrus Zalian thebigkiwi2003 at yahoo.fr
Sun Jan 24 16:35:06 EST 2016


Hi László and thanks for your answer.

Concerning your question on turbulent convection, my lack of knowledge will
limit my answer. No semi-convection nor overshoot or anything else fancy
taken into account. Just Henyey's convection model with an alpha = 1.5 plus
default MESA parameters. I don't know if the turbulent convection is
related to what I consider to the usual convection. Still, I remarked that
the core convection zone fades rapidly at a certain moment during the HB
(figure in attachment). That surprised me at first so I look for any
publication on that. I found papers showing figures with the same
phenomenon happening, but no comment at all. Maybe the fact that my
convection zone disappear is linked to the absence of barrier on the red
side for the instability strip.

Following your comment, I checked my results. The green zone corresponds to
both fundamental and 1st overtone being excited (negative imaginary part).
But, after further investigation, if the fundamental period is above 1.2
days, the first overtone was below. So I changed my program, and plotted
again in blue the zone where the first overtone was excited and in the good
range (in attachment).

The plot isn't great for two reasons : 1) I feel like the right side blue
plot are not relevant 2) We still have a green zone meaning modes are
excited but both fundamental and first overtone are not in the good range.

Last thing, concerning the second point, I checked the second overtone :
it's also excited and in the good range.

That's all.

Thanks again for your help.
Cyrus.


2016-01-24 19:37 GMT+01:00 László Molnár <molnar.laszlo at csfk.mta.hu>:

> Hi Cyrus,
>
> that's odd... are those periods longer than 1.2 day? A naiive question
> would be that is turbulent convection on in your model? Because that's
> what creates the red edge of the instability strip.
>
> Cheers,
> László
>
> László Molnár
> -------------------------------------------
> research fellow, PhD
> IBVS editor
> Konkoly Observatory
> Budapest
> -------------------------------------------
>
>
> 2016-01-24 14:26 GMT+01:00 Cyrus Zalian <thebigkiwi2003 at yahoo.fr>:
> > Hi to everybody,
> >
> > First of all, I've started using Mesa a year ago, and it has been the
> most
> > instructive tool by far. I thus wanted to thank the developers and all
> the
> > mesa community for their help (as I had some silly questions sometimes).
> >
> > To sum it up : I'm studying RR Lyrae stars. I've been able to compute
> > different models of HB stars (Masses from 0.5 to 0.88 by 0.05, and Z =
> > 0.0001, 0.001, 0.002, 0.004 and 0.01) with no fancy option (no rotation,
> no
> > mass loss, no semi convection nor overshoot).
> >
> > Now, I'm using GYRE to look for RR Lyrae among the HB stars following the
> > procedure used in this excellent site :
> > http://www.ster.kuleuven.be/~pieterd/mesa/instability_strip.html
> >
> > The problem was that there were more excited models than I thought. In
> > attachment I've put an image of one HB star (can't remember the M and Z
> > value) with the following color code :
> >
> > red = not excited
> > blue = no fundamental excited but first overtone excited in the 0.2/1.2
> days
> > period range of RR Lyrae
> > orange = fundamental excited (and maybe also overtones) in the 0.2/1.2
> days
> > period range of RR Lyrae
> > green = excited mode but not in the range of RR Lyrae period
> >
> > Here is my problem : from what I know, there shouldn't be any pulsating
> star
> > in the green range. So, is it normal that I have excited radial mode in
> this
> > range ? If yes, how do I discriminate these stars from RR Lyrae (I did
> it by
> > focusing on the one with the appropriate period, but it don't like that
> > criteria that much) ?
> >
> > Thanking you all in advance.
> >
> >
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