[Mesa-users] CCSN_IIp module: infall up to what radius?

[Jared Goldberg]

What physicists call intuition is often 'I've seen a problem like that
before and remember the solution'  ;-)

~Jared

On Thu, Jul 3, 2025 at 5:55 PM Mandal, Soham (uqa7ur) <soham at virginia.edu>
wrote:

> Yes, yes, yes! The handoff is the issue. The infall was modest before that
> (1700 km to 1693 km in 10^5 seconds), but just switching from Lagrangian to
> Riemannian hydro before excising the core fixed everything.
>
> Thank you so much, Jared! I think it's miraculous the way you spotted that
> bug with so little information.
>
> Best,
> Soham
> ------------------------------
> *From:* Jared Goldberg <jgoldberg at flatironinstitute.org>
> *Sent:* Thursday, July 3, 2025 5:01 PM
> *To:* Mandal, Soham (uqa7ur) <soham at virginia.edu>
> *Cc:* mesa-users at lists.mesastar.org <mesa-users at lists.mesastar.org>
> *Subject:* Re: [Mesa-users] CCSN_IIp module: infall up to what radius?
>
> What is the *initial* R_center? Is it falling in at all?
>
> There can sometimes be an issue with changing from lagrangian hydro
> (v_flag) to riemann hydro (u_flag) in the same timestep that you excise the
> core. This used to be done in make_pre_ccsn_IIp in old revisions but has
> been taken out of *_pre_ms_to_core_collapse in newer revisions.
> (Re-)improving compatibility between the pre_ccsn and ccsn setups is on my
> agenda for when I get some time...
>
> If the handoff is the issue and it's not infalling, possible fixes
> include: add a step where you take a few very small timesteps where you
> just switch from v_flag to u_flag, without excising the core. Sometimes
> simply setting okay_to_remesh = .true. in inlist_infall works. Also, it may
> help to change to use_Skye = .true. in &eos, if it's false.
>
> Another option might be to do the infall in lagrangian hydro rather than
> riemann hydro, i.e. commenting out the following in inlist_infall:
> ! change_initial_v_flag = .true.
> ! change_initial_u_flag = .true.
> ! new_v_flag = .false.
> ! new_u_flag = .true.
>
> Also, 400 km comes from a slightly arbitrary engineering choice that
> (probably Bill Paxton) deemed "close enough to the ~100 km PNS radius, but
> also still within the acceptable scope of MESA's eos and opacity tables",
> probably also motivated by old work with the Kepler code.
>
> ~Jared
>
> On Thu, Jul 3, 2025 at 4:31 PM Mandal, Soham (uqa7ur) <soham at virginia.edu>
> wrote:
>
> Thanks again, Jared! You're right, R_center in my model is not going below
> 1600 km in the ccsn_IIp setup. I was of the opinion that I should then just
> replace  "center_R_lower_limit = 4d+07" with "center_R_lower_limit =
> 1.6d+08", but was apprehensive that this might mean I'm doing something
> horribly wrong!
>
> Will go through the works you mentioned and try to figure out why the
> stalling happens at such a large radius. Can you please also help me
> understand where the choice of R_center = 400 km comes from? Thanks a lot!
>
> Best,
> Soham
> ------------------------------
> *From:* Jared Goldberg <jgoldberg at flatironinstitute.org>
> *Sent:* Thursday, July 3, 2025 3:41 PM
> *To:* Mandal, Soham (uqa7ur) <soham at virginia.edu>
> *Cc:* mesa-users at lists.mesastar.org <mesa-users at lists.mesastar.org>
> *Subject:* Re: [Mesa-users] CCSN_IIp module: infall up to what radius?
>
>
> Do we then expect the inner radius to gradually halt at some value? For
> example, in my model, R_center won't go below ~1600 km. How does one
> determine that infall has ended and now it's time to inject energy?
>
> In *_to_core_collapse, Fe infall velocity.  In ccsn_IIp, a central radius
> is specified (center_R_lower_limit = 4d+07). Is your R_center not going
> below 1600 km in the ccsn_IIp setup?
>
> Exploding a star in MESA is a feat of engineering as much as it is a feat
> of physics, if not moreso.
>
> Some people have calculated the evolution further in GR1D and STIR and
> PUSH and some other frameworks, then ported back to MESA (see works by
> Sanjana Curtis, Brandon Barker, others). It turns out that lightcurve
> modeling is often *not* so sensitive to when you halt the infall and put
> in the bomb, since you're using a thermal bomb that is the asymptotic
> energy + the binding energy at that time, and not doing a "self-consistent"
> explosion anyway (this is something many people have found through
> experimentation, including myself, though I don't know of a great reference
> that shows it). For the composition and explosive burning, it matters more,
> but then you run into the problem that 1D explosion models don't get
> mixing at the proto-neutron star boundary right, the explosion isn't
> actually 1D, et cetera.
>
> ~Jared
>
> On Thu, Jul 3, 2025 at 3:17 PM Mandal, Soham (uqa7ur) <soham at virginia.edu>
> wrote:
>
> Thanks for that prompt clarification, Jared! So if I understand correctly,
> MESA choking at higher core densities sets an upper limit to the Fe core
> infall velocity stopping condition. In that case, one eventually has to
> calculate the rest of the core infall in the ccsn_IIp, after excising the
> proto-NS core.
>
> Do we then expect the inner radius to gradually halt at some value? For
> example, in my model, R_center won't go below ~1600 km. How does one
> determine that infall has ended and now it's time to inject energy?
>
> Thanks,
> Soham
> ------------------------------
> *From:* Jared Goldberg <jgoldberg at flatironinstitute.org>
> *Sent:* Thursday, July 3, 2025 2:38 PM
> *To:* Mandal, Soham (uqa7ur) <soham at virginia.edu>
> *Cc:* mesa-users at lists.mesastar.org <mesa-users at lists.mesastar.org>
> *Subject:* Re: [Mesa-users] CCSN_IIp module: infall up to what radius?
>
> The *_pre_ms_to_core_collapse models end with an Fe core infall velocity
> stopping condition -- to get to smaller radii, you can increase that
> velocity (see fe_core_infall_limit). However, MESA often chokes at higher
> and higher core densities, which is why the rest of the core infall is
> carried out *after *excising the proto-NS core in inlist_infall in the
> ccsn_IIp setup.
>
> ~Jared
>
> On Thu, Jul 3, 2025 at 2:22 PM Mandal, Soham (uqa7ur) via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
>
> Dear all,
>
> I am running into an issue while trying to use the CCSN_IIp test_suite
> problem. So the inlist_infall continues evolution of the star till the
> inner radius falls below 400 km. I'm not sure how to compute this value
> (400 km) for any arbitrary model.
>
> For example, in a pre-core-collapse model I ran, the inner radius won't go
> below ~1600 km (found by trial and error). Is there a way to compute the
> lower threshold of the inner radius and set the center_R_lower_limit parameter
> to that before the test problem is run? Any insight will be
> greatly appreciated!
>
> Thanks,
> Soham
>
>
>
> ------------------------------------------------
> Dr. Soham Mandal
> VITA postdoctoral research fellow
> Department of Astronomy
> University of Virginia
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>
>
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