[Mesa-users] ask for help to use the rsp_Delta_scuti mode

[Radek Smolec]

Dear Ma Shuguo,

What is your scientific goal? It seems you are interested in evolutionary
status and would like to take into account rotation. My guess is that you
need evolutionary calculations coupled with computing pulsation properties
of the models with gyre (linear pulsation code). RSP is nonlinear pulsation
code.
Below is a brief summary of what you can/cannot do with gyre compared with
what you can/cannot do with RSP.

with gyre:
- you can run pulsation models on top of evolutionary models computed with
MESA
- your pulsation model takes into account full internal structure at a
given point in evolution
- you can include rotation (both in evolutionary and pulsation calculations)
- you can get frequencies of radial and nonradial modes
- you cannot get any information whether your model is in fact double-mode
pulsator
- you cannot get any information about mode amplitudes
- you can do this modelling on a relatively short time scale

with RSP
- you can only compute static, chemically homogeneous envelope model and
its pulsation properties for a given set of parameters (M, L, Teff, X, Z)
- you can set those parameters (M, L, Teff, X, Z) based on evolutionary
tracks computed with MESA
- you cannot include rotation in pulsation calculations with RSP
- you can get frequencies of radial modes only
- you can get some insight into mode-content and amplitude of the excited
modes in large amplitude (nonlinear) regime, but
- time needed to do such modelling may be extremely long

For delta Scuti stars, nonlinear modelling with RSP may simply be not
practical because of very small growth rates of pulsation modes. Take a
look at Section 2.4.6 of MESA V to see the point. You may need to compute
tens of thousands of pulsation cycles to arrive at a full amplitude
solution. If you are interested in mode selection (i.e. whether your model
can pulsate in two radial modes simultaneously) then you need to run
several models with different initializations (see Figure 24 in MESAV).
Amplitudes and mode selection may also depend on other parameters (eg.,
convective parameters) so to make a thorough study of delta Sct models with
RSP several months of calculations on a cluster may be needed. Keep in mind
that RSP was designed for large amplitude classical pulsators (Cepheids and
RR Lyrae). While applications to other classes of pulsating stars are
possible, there are some limitations which can make a scientific project
impractical or difficult to implement with RSP.

If you are interested in reproducing pulsation frequencies (standard
asteroseismic analysis), then go for MESA+gyre.

pon., 25 wrz 2023 o 04:59 mashuguo at xao.ac.cn <mashuguo at xao.ac.cn>
napisał(a):

> Dear professors，
> Greetings. On the official website of MESA, I learn that the
> rsp_Delta_Scuti model is applicable to stars with large amplitude radial
> pulsations . I intend to use this model to analyze the evolution of
> double-mode delta variable stars.
>
> The physical parameters and pulsation frequency of the star are provided
> in the attachment. The star has a fundamental frequency with amplitude of
> 1.35 mmag and a first overtone amplitude of 0.24 mmag. The star has a
> rotational frequency of 0.45813 c/d (with an angular frequency of 3.
> 3299*10*(-5) rad/s) and a rotational velocity of about 75 km/s, which is
> based on a radius of R = 3.2(2) R☉ provided by the tess input catalog.
>
> Is it appropriate to use the rsp_Delta_Scuti model to analyze the physical
> parameters and evolutionary stages of low-amplitude bimodal delta Scuti
> stars?
>
> Also, in the inlist_rsp_Delta_Scuti file for the model, there are some
> parameters whose meaning I don't understand. These parameters are as
> follows,
>
> x_integer_ctrl(1) = 10                                            ! Is it
> the number of times the model loops?
>
> x_ctrl(1) = 0.1280758d0                                        ! Is it the
> period of the observed fundamental mode? Is it possible to add another
> parameter for the period of the first overtone?
>

The above two controls control the test_suite run. The first
(x_integer_ctrl(1)) is a cycle number at which the pulsation period will be
recorded and compared with the value stored in x_ctrl(1). If the value
agrees, the test is passed. You can safely remove those controls.



>
> rsp_kick_vsurf_km_per_sec = 3.0d0                      ! Is this velocity
> amplitude related to the pulsation mode amplitude? What is the basis for
> setting the velocity amplitude?
>
> rsp_fraction_1st_overtone = 0.5d0                       ! Is the weight of
> the first overtone related to the ratio of the fundamental mode and the
> first overtone mode? Or, when there are only two radial pulsation
> frequencies, the weight for the other frequency is artificially set to 0.5?
>

These controls set the initial perturbation for nonlinear calculations.
Please read the first sections (up to 2.4) of MESA V to learn more and to
get a better feeling of what RSP does.
Best wishes,
Radek Smolec



>
> Also, at &controls, is it possible to add surface angular velocity? like
> that:
> !Rotation control
> Osurf = 3.3299d-5                                                ! The
> unit is rad/sec.
>
> Attached is my inlist_rsp_Delta_Scuti file. Do you have any better
> suggestions on how to set the other parameters in that file ?
>
>
> I would appreciate if you could help in any way. If you wish, I would like
> to invite you to be one of the collaborators in this research work.
>
> Sincerely
> Ma Shuguo
>
> ------------------------------
> mashuguo at xao.ac.cn
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>
>
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