Re: [mesa-users] instability strip definition (no MESA content)

[Earl B. <bel...@mp...>]

errata: I found a little mistake in my previous email - I meant to say
that RR Lyrae are core-and-shell burning, not double-shell burning.

Best regards,
Earl Bellinger

---
www.earlbellinger.com
Department of Astronomy, Yale University
Stellar Ages & Galactic Evolution Group, Max Planck Institute


On Thu, Jun 1, 2017 at 12:03 PM, Earl Bellinger <bel...@mp...> wrote:
> Dear Aaron,
>
> I am probably not going to say anything you don't already know, but
> here are my two cents on the matter...
>
> From a theoretical point of view, the instability strip is found by
> determining when stars become unstable to fundamental (or
> low-overtone) radial oscillations. More specifically, this occurs when
> the imaginary component of radial mode eigenfrequencies change sign.
>
> This happens at several stages during evolution: on the main sequence
> (delta Scuti and other types of stars), during a "blue straggle" (SX
> Phoenicis variables), during the Hertzsprung gap in the sub-giant
> phase (first-crossing Cepheids), during blue loops after ignition of
> core helium burning in the star's ascent up the giant branch
> (Cepheids), on the horizontal branch with double-shell burning (RR
> Lyraes), etc...
>
> On the red edge, the location of the sign change depends on the
> details of pulsation-convection interaction which, as far as I know,
> is neglected in pulsation codes such as GYRE and ADIPLS, and as such
> is typically regarded as being unreliable. The location of the blue
> edge is more reliable but depends for example on one's choice of the
> mixing length parameter. So a theoretical definition of the
> instability strip in terms of Teff, log g, or L will depend on
> potentially arbitrary assumptions. That being said, one can find
> empirical instability strips from real stars in the literature.
>
> I hope what I have said is correct. If there are any errors, I hope
> someone will please correct me.
>
> Best regards,
> Earl Bellinger
>
> ---
> www.earlbellinger.com
> Department of Astronomy, Yale University
> Stellar Ages & Galactic Evolution Group, Max Planck Institute
>
>
> On Thu, Jun 1, 2017 at 11:13 AM, Aaron Dotter <aar...@gm...> wrote:
>> Hi all,
>>
>> (Sorry for the non-MESA request.  Too much expertise on this mailing list to
>> resist asking here!)
>>
>> Does anyone have a favorite definition of the realm of the instability strip
>> in the H-R diagram?  There are lots of cartoons out there, most of which are
>> vague and/or conflicting.  I'm not aware of a solid theoretical or empirical
>> definition of the bounds of the IS in terms of Teff, surface gravity, and/or
>> luminosity.
>>
>> Thanks,
>> Aaron
>>
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