[Mesa-users] A Query regarding swithcing off magnetic braking

Ebraheem Farag ekfarag at asu.edu
Tue Jul 18 15:45:11 UTC 2023 

To close this out, one other approach to letting your model run further
could be to switch to using the Freedman lowT opacities: low_T_opacities
<https://docs.mesastar.org/en/release-r23.05.1/kap/overview.html#low-temperature-t-lesssim-10-4-rm-k>,
which extend down to logT = 1.88.

-EbF

On Tue, Jul 18, 2023 at 9:38 AM Ebraheem Farag <ekfarag at asu.edu> wrote:

> Hello,
>
> > But in other cases, it stopped automatically with both mb on and off.
> For example, I am sharing a screenshot of one of the runs with mb = on.
>
> In the screenshot you shared, your model is crashing because of a timestep
> dive, since the solver cannot find an acceptable solution. This is likely
> for the same reason I previously stated.
> You have a cold ~1d-2 Msun model which is sampling opacities from outside
> the tabulated opacity table regime, and the solver is trying its best to
> find a solution.
>
> If your goal is to run the model further,  it was suggested to me by
> Giulia Cinquegrana that  "you can make custom molecular opacities with
> AESOPUS that extend further than logT=2.7". However do keep in mind that
> you might encounter other unforeseen issues as your model descends lower in
> mass. My recommendation is to establish a universal stopping condition for
> your runs that satisfies your project goal.
>
> > If I manually stop a seemingly unending evolution in the terminal after
> a huge number of retries, can that be considered a final result for that
> evolution?
>
> I guess, but this is not a consistent approach. I would recommend finding
> a good stopping condition that you can use for all your runs. e.g.
> star_mass_min_limit = 2d-2.
>
> -EbF
>
> On Mon, Jul 17, 2023 at 11:58 PM ABHIJNAN KAR 20064 <
> abhijnank20 at iiserbpr.ac.in> wrote:
>
>> Also another trivial question: If I manually stop a seemingly unending
>> evolution in the terminal after a huge number of retries, can that be
>> considered a final result for that evolution?
>>
>> On 18-Jul-2023, at 11:16 AM, ABHIJNAN KAR 20064 <
>> abhijnank20 at iiserbpr.ac.in> wrote:
>>
>> Hi Ebraheem,
>> Thanks for the help! However, in my case, this unending MESA evolution
>> occurred only in some cases(that too with all of the cases being mb on).
>> But in other cases, it stopped automatically with both mb on and off. For
>> example, i am sharing a screenshot of one of the runs with mb = on.
>> <Screenshot 2023-07-18 at 11.15.37 AM.png>
>>
>> On 18-Jul-2023, at 2:23 AM, Ebraheem Farag <ekfarag at asu.edu> wrote:
>>
>> Hello Ojha,
>>
>> Both models, with and without magnetic braking, reach a point where the
>> doner's mass is sufficiently small ~ 1e-2 Msun. At this point, both models
>> are simultaneously quite cold and low in density.  A large portion of these
>> very low mass models live in the "extended" section of opacity tables (at
>> logR > 1, where logR = logrho - 3*logT + 18). In this regime the MESA
>> opacity tables are extrapolated from the logR = 1 edge. The Fa05_gs98 lowT
>> opacity tables being extended in this regime only extend down to logT =
>> 2.7. It doesn't look like there is a condition in MESA to generate opacity
>> values for temperatures lower than logT = 2.7, so it appears the code is
>> returning a NaN for the opacity here, for both models.
>>
>>  rho =     2.5146799359618161D-06
>>  lnrho =    -1.2893365024554088D+01
>>  T =     4.9966225551057875D+02
>>  lnT =     6.2139323811978784D+00
>>  logKap =                        NaN
>>  opacity =    -9.9999999999999997D+98
>>  dlnkap_dlnd =                        NaN
>>  dlnkap_dlnT =                        NaN
>>  d_opacity_dlnd =    -2.4822215369416772D-08
>>  d_opacity_dlnT =     7.2510282819076687D-03
>>
>> for:
>>  logrho ~ log10(2.5d-6) = -5.602059,
>>  logT ~ logT(500) = 2.69897 < 2.7d0,
>>  logR = 4.3010 >> 1d0
>>
>> One model timestep dives and crashes, while the other rides the edge of
>> the table finding hotter solutions with logT>= 2.7 which still satisfy the
>> structure equations, though both models effectively stall for the same
>> reason. With or without magnetic braking, this result is inevitable.
>> This appears to be a bug that could be fixed, and I will open up a bug
>> report on the topic, but for the time being, I would recommend setting a
>> lower limit on your model to step the evolution when the doner's mass
>> decreases beyond 0.02 Msun?
>>
>> star_mass_min_limit = 2d-2
>>
>>
>>
>> Hope this helps.
>>
>> -EbF
>>
>>
>> On Sat, Jul 15, 2023 at 10:41 AM ABHIJNAN KAR 20064 <
>> abhijnank20 at iiserbpr.ac.in> wrote:
>>
>>> A gentle reminder!
>>>
>>> On 12-Jul-2023, at 12:45 AM, Pulkit Ojha <pulkit.ojha at niser.ac.in>
>>> wrote:
>>>
>>> Hello,
>>> Thank you for your reply.
>>>
>>> I'm using MESA version r22.05.01. I do not have any desired stopping
>>> condition. In my runs, the evolution stops when the donor mass becomes very
>>> small and software isn't able to find any consistent solution, stating "dt
>>> < min_timestep_limit" or "no. of redo exceeding redo_limit".
>>>
>>> In the case of "keep_mb_on = .true." , it is true that the timestep
>>> becomes so small after first 5k+ steps. I'm attaching binary_history files
>>> for both the cases and the same set of initial parameters. I'm also
>>> attaching a snippet of terminal output of MESA run with "keep_mb_on =
>>> .true." .
>>>
>>> Truly
>>> Pulkit
>>>
>>> On Tue, Jul 11, 2023 at 12:06 AM Ebraheem Farag <ekfarag at asu.edu> wrote:
>>>
>>>> Hello Ojha,
>>>>
>>>> Would you mind sharing which version of MESA you are using?
>>>>
>>>> What is your desired stopping condition?
>>>>
>>>> > but if case we do not switch it off i.e. "keep_mb_on = .true."
>>>> , evolution isn't stopping at all. After running for 12-13k steps, the mass
>>>> transfer rate as well as the masses of both the stars become constant but
>>>> the steps are just repeating themselves, even till 40k steps.
>>>>
>>>> It sounds like your timesteps have become very small. Can you comment
>>>> on the difference in time step size between both runs with and without
>>>>  "keep_mb_on = .true." ? Are the size of timesteps different between
>>>> runs? What is controlling the timesteps in your terminal output in both
>>>> runs? A short print out attachment of a snippet from your terminal output
>>>> would be useful.
>>>>
>>>> Thanks,
>>>> EbF
>>>>
>>>>
>>>> On Sun, Jul 9, 2023 at 12:16 AM Pulkit Ojha via Mesa-users <
>>>> mesa-users at lists.mesastar.org> wrote:
>>>>
>>>>> Dear All,
>>>>>
>>>>> I'm evolving LMXB models with NS accretors with the specifications
>>>>> described in the attached inlist_project file. There is this option of
>>>>> "keep_mb_on" for calculating the angular momentum loss due to magnetic
>>>>> braking. It decides whether to switch off magnetic braking when the star
>>>>> becomes fully convective. If we choose to switch it off, models are running
>>>>> fine (stopping after 5-8k timesteps) but if case we do not switch it off
>>>>> i.e. "keep_mb_on = .true." , evolution isn't stopping at all. After running
>>>>> for 12-13k steps, the mass transfer rate as well as the masses of both the
>>>>> stars become constant but the steps are just repeating themselves, even
>>>>> till 40k steps.
>>>>>
>>>>> Can anyone help me to understand what's going on there? Is the
>>>>> software getting stuck in some loop or the values of mass transfer become
>>>>> so low that they do not appear changing?
>>>>> Please find attached the inlist and extras files.
>>>>>
>>>>> --
>>>>> Pulkit Ojha
>>>>> 5th Year Integrated MSc.,
>>>>> School of Physical Sciences,
>>>>> National Institute of Science Education and Research
>>>>> <https://urldefense.com/v3/__https://www.niser.ac.in/__;!!IKRxdwAv5BmarQ!dPs0I_NtKoQRnpfmatdrcvp3atkIEBt9Cn2kPKqPIy-lnf3EwwHGazY74Dp19ztpDcIcxkwWPxnEGTAAm7DH0uOT$>
>>>>> Bhubaneswar, INDIA
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> mesa-users at lists.mesastar.org
>>>>>
>>>>> https://urldefense.com/v3/__https://lists.mesastar.org/mailman/listinfo/mesa-users__;!!IKRxdwAv5BmarQ!dPs0I_NtKoQRnpfmatdrcvp3atkIEBt9Cn2kPKqPIy-lnf3EwwHGazY74Dp19ztpDcIcxkwWPxnEGTAAm0IMGyGA$
>>>>>
>>>>>
>>>>>
>>>
>>> --
>>> Pulkit Ojha
>>> 5th Year Integrated MSc.,
>>> School of Physical Sciences,
>>> National Institute of Science Education and Research
>>> <https://urldefense.com/v3/__https://www.niser.ac.in/__;!!IKRxdwAv5BmarQ!axq4MEK3mDgQQ8m_6A2KCQLaV38v1CbzecDpFCIx6dqG_MieRMpbp4w1S8wrqNwM7R7SdMByZ-FHfLQNagHMZ72LjA$>
>>> Bhubaneswar, INDIA
>>>
>>> <snippet_MESA__run.png><data_compare_mb_on_and_off.zip>
>>>
>>>
>>> Regards,
>>> Abhijnan Kar(He/his/him)
>>> BS-MS,IISER Berhampur
>>>
>>
>> Regards,
>> Abhijnan Kar(He/his/him)
>> BS-MS,IISER Berhampur
>>
>>
>> Regards,
>> Abhijnan Kar(He/his/him)
>> BS-MS,IISER Berhampur
>>
>>
>>
>>
>>
>>
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20230718/93ce2887/attachment.htm>

More information about the Mesa-users mailing list