[Mesa-users] STELLA Fe II Velocities

Jared Goldberg goldberg at physics.ucsb.edu
Wed May 1 19:47:12 EDT 2019 

Hi,

I know this domain hasn't been tested, but can you offer any insight into
> why early times give apparently unphysical results?
>

I do not believe this fully resolves the question, but it does not seem
totally surprising that the Sobolev optical depth calculation, which is
used to calculate the location in the ejecta where the Fe II 5169 Angstrom
line is formed, does not yield physically meaningful results within the
first ~20 days or so. A short bit of insight: "This simple equation only
holds for atmospheres in homologous expansion; for other velocity laws,
will depend on the direction in which the photon packet is traveling" ~
Kasen et al 2006.


A more thorough exploration of exactly why or how the calculation breaks
down at early times would require thinking more carefully about how the
Sobolev optical depth is calculated. Consider that the Sobolev optical
depth is calculated (see, e.g. Paxton et al 2018 section 6.5, and Kasen,
Thomas, and Nugent 2006, and the references therein) by the simple
criterion
[image: image.png]
where texp is the time since the explosion, nFe is the number density of Fe
at a given location, eta_i is the fraction of iron atoms that are in the
lower level of the transition and depends on the properties of the gas as
found in a table (which ranges over log(rho/cgs) = -16 to -8 and
log(Teff/K)=3.3 to 4.3). This expression assumes that texp >> t(shock
breakout) and that the material is homologous in the sense that R ~ v texp,
which is not precisely true for the envelope in the first 30 days even in
the outer ejecta (see, for example, Mesa IV figure 32).

Hope this helps provide at least a little intuition, and/or points you
somewhat in the right direction if you want to dive further into it.
Otherwise, the usual tau=2/3 photospheric calculation might prove
sufficient at early times.

Let us know if anything interesting turns up!

Best,
~Jared

On Wed, May 1, 2019 at 3:44 PM Bill Paxton <paxton at kitp.ucsb.edu> wrote:

>
> On May 1, 2019, at 3:37 PM, Wilson Ricks <wilson.ricks at gmail.com> wrote:
>
> Having done several new STELLA runs, I can say that the new early time
> results are definitely wonky (falling off sharply before 20 days before
> increasing again as we approach the explosion time). I know this domain
> hasn't been tested, but can you offer any insight into why early times give
> apparently unphysical results?
>
>
> nope.  that’s way out of my area.
>
> do you have any basis for expecting the Fe velocities to be significantly
> different that the photosphere velocities at the early time?   if not, then
> don’t push the code into places it wasn’t meant to cover.
>
> -b
>
>
>
>
> On Wed, May 1, 2019, 12:44 PM Wilson Ricks <wilson.ricks at gmail.com> wrote:
>
>> Thanks for the heads up. I'll definitely do a sanity check on what comes
>> out.
>>
>> On Wed, May 1, 2019, 12:33 PM Bill Paxton <paxton at kitp.ucsb.edu> wrote:
>>
>>>
>>> On May 1, 2019, at 7:02 AM, Wilson Ricks <wilson.ricks at gmail.com> wrote:
>>>
>>> Hi Bill,
>>>
>>> This solves it - thanks for the help.
>>>
>>> Best,
>>> Wilson
>>>
>>>
>>> Glad that produces the output you want.
>>>
>>> But use those results with caution since you are going beyond the usual
>>> range where the approximations for the Fe velocity have been used and
>>> tested.  That doesn’t mean they are bad, but it does mean you need to be
>>> careful to ensure you haven’t just driven your Maserati over a cliff
>>> expecting it to fly.   If the results in the new domain look crazy, they
>>> don’t use them.
>>>
>>> -Bill
>>>
>>>
>>>
>>> On Tue, Apr 30, 2019, 8:50 PM Bill Paxton <paxton at kitp.ucsb.edu> wrote:
>>>
>>>>
>>>> On Apr 30, 2019, at 5:19 PM, Wilson Ricks <wilson.ricks at gmail.com>
>>>> wrote:
>>>>
>>>> Hi Bill,
>>>>
>>>> I did another run and I think the method you referred to only adds
>>>> "mesa.dayxxx_post_Lbol_max.data" files, while I'm looking to control output
>>>> times in "mesa.vel_fell".  This file is still only giving data points
>>>> starting around 25-30 days, and I'm interested in getting earlier ones.
>>>>
>>>>
>>>> Ahh.
>>>>
>>>> Search in stella_extras.f90 for ‘.vel_feII’.   you’ll find this
>>>>
>>>>    fname = trim(filestr)//'.vel_feII'
>>>>    open(24,file=fname, status='unknown')
>>>>
>>>> Then search from that location for ‘write(24’.   first you find where
>>>> it writes the header info.   then you’ll find this
>>>>
>>>>             if (k > k_phot - 10) &
>>>>                write(24,'(i5,99(1pe18.4,x))') k,time-t0, &
>>>>                   v_sob_lo_tau*1d3, v_sob_med_tau*1d3,
>>>> v_sob_hi_tau*1d3, &
>>>>                   10**logRho, 10**logT, eta, &
>>>>                   m_sob_lo_tau, r_sob_lo_tau, &
>>>>                   m_sob_med_tau, r_sob_med_tau, &
>>>>                   m_sob_hi_tau, r_sob_hi_tau
>>>>
>>>> Try commenting out the line "if (k > k_phot - 10) &” so that the write
>>>> is always done.
>>>>
>>>> -Bill
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Thanks,
>>>> Wilson
>>>>
>>>> On Tue, Apr 30, 2019, 5:27 PM Wilson Ricks <wilson.ricks at gmail.com>
>>>> wrote:
>>>>
>>>>> Alright, thank you very much for the help. I'll see if I can get
>>>>> things working.
>>>>>
>>>>> Best,
>>>>> Wilson
>>>>>
>>>>> On Tue, Apr 30, 2019, 4:42 PM Bill Paxton <paxton at kitp.ucsb.edu>
>>>>> wrote:
>>>>>
>>>>>>
>>>>>> On Apr 30, 2019, at 1:26 PM, Wilson Ricks <wilson.ricks at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>> Hi Bill,
>>>>>>
>>>>>> Do you mind explaining how output times can be adjusted using this
>>>>>> file? I think the relevant section is between lines 185 and 200, but I'm
>>>>>> having trouble interpreting the code.
>>>>>>
>>>>>>
>>>>>> times in the stella code itself use t=0 at start of run.
>>>>>> but the output from stella_extras are at times since Lbol max.
>>>>>> typically there is no stella output for the times since breakout when
>>>>>> we want to see results.
>>>>>> so the code has to interpolate between the available stella data
>>>>>> snapshots.
>>>>>> the output times are determined by the calls
>>>>>> on save_day_post_Lbol_max starting at line 458.
>>>>>> for example, if you want to get interpolated results for 33.7 days
>>>>>> post Lbol max, then insert a new line between the ones for output at 30
>>>>>> days and at 40 days.  the final arg to save_day_post_Lbol_max is a string
>>>>>> that goes in the filename - you need to change that as well.
>>>>>>
>>>>>> good luck,
>>>>>> bill
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>> Wilson
>>>>>>
>>>>>> On Tue, Apr 30, 2019, 3:29 PM Bill Paxton <paxton at kitp.ucsb.edu>
>>>>>> wrote:
>>>>>>
>>>>>>> The Fe II 5169 velocities are calculated during the post-processing
>>>>>>> done by stella_extras.f90 which lives in stella/res.
>>>>>>>
>>>>>>> So they are actually derived from STELLA data rather than being
>>>>>>> output directly by STELLA.
>>>>>>>
>>>>>>> -Bill
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> > On Apr 30, 2019, at 12:24 PM, Wilson Ricks via Mesa-users <
>>>>>>> mesa-users at lists.mesastar.org> wrote:
>>>>>>> >
>>>>>>> > Hi all,
>>>>>>> >
>>>>>>> > I'm currently having trouble controlling when STELLA outputs Fe II
>>>>>>> 5169 velocities.  The "stella/strad/run/mesa.dat" file which controls all
>>>>>>> the other STELLA outputs does not seem to affect these, and whatever the
>>>>>>> default is gives fairly sparse data at early times. Is there another file
>>>>>>> which can be used to control the Fe II velocity outputs?
>>>>>>> >
>>>>>>> > Thanks,
>>>>>>> > Wilson Ricks
>>>>>>> > _______________________________________________
>>>>>>> > mesa-users at lists.mesastar.org
>>>>>>> > https://lists.mesastar.org/mailman/listinfo/mesa-users
>>>>>>> >
>>>>>>>
>>>>>>>
>>>>>>
>>>>
>>>
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20190501/b7a5f7cd/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 2618 bytes
Desc: not available
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20190501/b7a5f7cd/attachment.png>

More information about the Mesa-users mailing list