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

[Bill Paxton]

Hi Earl,

this is just to say how much I appreciate your input to mesa-users.  keep it up!

cheers,
bill


On Jun 1, 2017, at 10:11 AM, Earl Bellinger wrote:

> 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 <bellinger at mps.mpg.de> 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 <aaron.dotter at gmail.com> 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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