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

Tue Jul 18 05:46:40 UTC 2023

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.

> 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 <mailto: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 <mailto: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 <mailto: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 <mailto: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$>
>>>>> Bhubaneswar, INDIA
>>>>> 
>>>>> 
>>>>> 
>>>>> _______________________________________________
>>>>> mesa-users at lists.mesastar.org <mailto:mesa-users at lists.mesastar.org>
>>>>> https://urldefense.com/v3/__https://lists.mesastar.org/mailman/listinfo/mesa-users__;!!IKRxdwAv5BmarQ!dPs0I_NtKoQRnpfmatdrcvp3atkIEBt9Cn2kPKqPIy-lnf3EwwHGazY74Dp19ztpDcIcxkwWPxnEGTAAm0IMGyGA$ 
>>>>> 
>>> 
>>> 
>>> -- 
>>> 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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20230718/d910a375/attachment-0001.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Screenshot 2023-07-18 at 11.15.37 AM.png
Type: image/png
Size: 1199868 bytes
Desc: not available
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20230718/d910a375/attachment-0001.png>