[mesa-users] The Cepheid phase

[Bill Paxton]

On Jul 30, 2016, at 12:26 PM, Jakub Ostrowski wrote:

> Hi,
> 
> This loop is really weird. I’ve studied blue loops pretty extensively and I can’t recall seeing anything like it. You can take a look at my paper (2015, MNRAS 447, 2378). We tried to determine whether pulsating B-type supergiants can be on blue loops or not. The considered masses are higher (M >= 13 Ms) but our loops behave better. I intend to publish a paper solely focused on the blue-loop problem in massive stars but that’s that's not going to happen until the end of the year.

Thanks Jakub.    Perhaps the message is that mesa/star will do weird things if you give it weird parameters!   The real question is whether can we get reasonable blue loops by some settings -- my plot shows how easy it is to get strange results.   In my book, you're the mesa expert on this, so we'll be interested to see what you have found.   

> Anyway, the problem is extremely complicated so even the easiest questions might be difficult to answer.

that sums it up nicely!

Bill





> 
> Jakub
> 
> 
>> On 30 Jul 2016, at 20:18, Bill Paxton <paxton at kitp.ucsb.edu> wrote:
>> 
>> Hi Earl,
>> 
>> While Radek is off on holiday for the month of August, you might want to play with these.  I believe I'm using tricks that Radek taught me about getting blue loops in mesa -- but don't count on it.  Here's an example (9Msun; Z=0.02) showing that we can get multiple loops ending in a return to the L-Teff at the base of the RGB.  Very weird.
>> <H_R.pdf>
>> 
>> i did this run on my current development version, but i expect it will work with minor revisions in the current mesa (8845)
>> <inlist_to_instability_strip><run_star_extras.f>
>> 
>> Good luck,
>> Bill
>> 
>> 
>> 
>> 
>> On Jul 30, 2016, at 9:11 AM, Earl Bellinger wrote:
>> 
>>> Excellent, thank you very much! Inlists would be very helpful.
>>> 
>>> Best regards,
>>> Earl Bellinger
>>> Stellar Ages & Galactic Evolution Group
>>> Max-Planck-Institut für Sonnensystemforschung
>>> 
>>> 
>>> On Fri, Jul 29, 2016 at 9:07 PM, Radek Smolec <smolec at camk.edu.pl> wrote:
>>>> Hi Earl,
>>>> 
>>>> The statement in Dziembowski's paper was about helium burning loop and
>>>> relatively low mass Cepheids; Fig 14 in the third instrument paper shows the
>>>> first crossing only.
>>>> 
>>>> The loop is, and was tricky. In many published evolutionary tracks the
>>>> presence or extent of the loop do not vary smoothly with mass or Z. It is
>>>> difficult to get the loop for near solar metallicities and low masses,
>>>> 3-5Ms. For lower metallicities and higher masses loops are quite easy to
>>>> get. Adding some overshooting from the envelope convection zone helps.
>>>> 
>>>> Note that we still have the Cepheid mass discrepancy problem, although it is
>>>> significantly reduced, to 10-15%. We know that pulsation theory is right
>>>> (Pietrzynski et al., 2010, Nature; other papers with determination of
>>>> Cepheid's masses in eclipsing binaries), the evolution calculations need
>>>> improvement. The recent papers point that rotation might be a solution.
>>>> 
>>>> To summarize, Cepheids can be investigated with MESA, and there are still
>>>> some problems to be solved (and lots of parameters to play with :-)
>>>> 
>>>> I'm now on holidays; at the end of August I can send you the inlists I used
>>>> for Cepheid calculations (but these are old; for MESA 4xxx, I think).
>>>> Kind regards,
>>>> Radek
>>>> 
>>>> 
>>>> 2016-07-29 16:40 GMT+02:00 Earl Bellinger <bellinger at mps.mpg.de>:
>>>>> 
>>>>> Hello everybody,
>>>>> 
>>>>> In Dziembowski's 2012 paper [1] the claim is made that:
>>>>> 
>>>>>> "BaSTI (Pietrinferni et al. 2006) models at M = 4 and 5 do not reach
>>>>>> the instability strip [in the helium burning phase] but the maximum
>>>>>> values of L in this evolutionary phase are in a good agreement with
>>>>>> the relation given by Eq. (2). Similar conclusion was reached by
>>>>>> Smolec (private communication), who used public domain code MESA
>>>>>> (Paxton et al. 2011). Apparently, new evolutionary codes do not
>>>>>> describe well the Cepheid phase."
>>>>> 
>>>>> Can anyone corroborate/evaluate this claim for me please? That is: is
>>>>> MESA suitable for investigating Cepheid stars? If not, why not?
>>>>> 
>>>>> For example, can a theoretical Cepheid Period-Luminosity relation be
>>>>> derived using MESA plus a pulsation code (ADIPLS/GYRE/etc)?
>>>>> 
>>>>> Thanks for any insights.
>>>>> 
>>>>> [1] http://acta.astrouw.edu.pl/Vol62/n4/pdf/pap_62_4_1.pdf
>>>>> 
>>>>> Best regards,
>>>>> Earl Bellinger
>>>>> Stellar Ages & Galactic Evolution Group
>>>>> Max-Planck-Institut für Sonnensystemforschung
>>>>> 
>>>>> 
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