[Mesa-users] How to make a model a neutron star together with thick atomsphere ?

[Rob Farmer]

Hi
The inner radius is set by relax_R_center and should be the size of the
neutron star itself. The outer radius will be what ever it wants to be as
dictated by the composition, temperature, and entropy of the material you
accrete onto the neutron star.

If you need you neutron star + envelope to be a certain radius then you
will need accrete material until it reaches the radius you want. This will
also depend on whether you allow the accreted material to burn. It is a
non-trial to get from the accretion rate and total mass of accreted
material (which is what you can vary with mesa) to a certain radius.

Rob

On Wed, 22 Jan 2020 at 10:00, Chen DDan <ChenDDan at outlook.com> wrote:

> Hi Rob,
>
> Thank you for your reply. And if i want to extend the radius out when the
> mass gain, should i relax radius explicitly with any parameter (since i see
> in the neutron_star_envelope there are relax_R_center parameter, but i
> guess maybe it only apply to inner boundary..?)?
>
> Best Regards
> Chen
>
> ------------------------------
> *发件人:* Rob Farmer <r.j.farmer at uva.nl>
> *发送时间:* 2020年1月21日 23:34
> *收件人:* Chen DDan <ChenDDan at outlook.com>
> *抄送:* mesa-users at lists.mesastar.org <mesa-users at lists.mesastar.org>
> *主题:* Re: [Mesa-users] How to make a model a neutron star together with
> thick atomsphere ?
>
> If you just want the atmosphere then it will be easier with just using the
> mass change controls (
> http://mesa.sourceforge.net/controls_defaults.html#mass_gain_or_loss)
> rather than doing this in a binary.
>
> You say you don't want any burning, but it depends what you want to do
> with the star,
>
> If you want the energy but not the composition change from burning then
> you can use (so the outer layers of the envelope will be supported by the
> burning)
> dxdt_nuc_factor = 0
>
> and composition change, but without the energy release (so that the
> material will change composition but wont release energy thus you wont get
> any x-ray flashes on the surface)
> eps_nuc_factor = 0
>
> and you can set both to 0 to turn of all composition change and energy
> release from nuclear burning.
>
> Rob
>
>
>
> On Tue, 21 Jan 2020 at 11:07, Chen DDan <ChenDDan at outlook.com> wrote:
>
> Hi Rob,
>
> Thank you for your reply. I try you suggestion to take the saved model
> from neutron_star_envelope (ns9.mod that do not accrecte he4) and
> make_he_wd (wd4.mod) to binary test_suite evolve_both_stars and run. It
> give out below errors:
>
> stopping because of problems dt < min_timestep_limit
>                                                      dt
>  1.0834630960693358D-07
>                                      min_timestep_limit
>  9.9999999999999995D-07
>
> attached output.log file give out the whole screen output. I attached all
> the file in this letter. I do not modify the *.f files in the src directory
> of test_suite evolve_both_stars.
> I just want to make neutron star with its atomsphere, but do not want to
> burn it. I don't know why it could not run. I search the archive and find
> that if this system do not convergence, it can give out such error. So how
> can i analyze to solve the error and make a proper one? Could you give me
> any help? Thank you for any help in advance.
>
> Best Wishes
> Chen
>
> ------------------------------
> *发件人:* Rob Farmer <r.j.farmer at uva.nl>
> *发送时间:* 2020年1月20日 20:45
> *收件人:* Chen DDan <ChenDDan at outlook.com>
> *抄送:* mesa-users at lists.mesastar.org <mesa-users at lists.mesastar.org>
> *主题:* Re: [Mesa-users] How to make a model a neutron star together with
> thick atomsphere ?
>
> Hi,
>
> The 10km radius specific in the neutron_star_envelope test case only
> relates to the size of the inner boundary of the neutron star. You can
> accrete material using the same mass change controls as for a normal star (
> http://mesa.sourceforge.net/controls_defaults.html#mass_gain_or_loss) or
> take the final saved model from neutron_star_envelope and load that into a
> binary system and do accretion from a companion.
>
> Rob
>
> On Mon, 20 Jan 2020 at 10:56, Chen DDan via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
>
> Hi,
>
> I use mesa version 11701 and the test_suite seems only have neutron star
> envelope system. I want to model the neutron star envelope together with
> the thick atomsphere around it. The radius should not be only around
> 10-12km but extends out. The matter can be either accrected from the donor
> or mass loss from the neutron star itself. How can i make such system with
> mesa? Could anyone give me any suggestion?
> Thank you for any help in advance.
>
> Best Wishes
> Chen
>
>
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