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

Mon Jul 17 20:53:10 UTC 2023

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
>
>
>
>
>
>
>
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