The GYRE Forums

May I ask for a reference explaining how gyre calculates non-adiabatic effect please?

I am interested in g modes in white dwarfs. There is an outer convection zone. Does gyre only calculate non-adiabatic effect due to photon diffusion please? If yes, how does it treat the non-adiabatic effect in the convection zone and the atmosphere above the photosphere please?

Many thanks.

Sincerely,
Jing

jingluan wrote:May I ask for a reference explaining how gyre calculates non-adiabatic effect please?

I am interested in g modes in white dwarfs. There is an outer convection zone. Does gyre only calculate non-adiabatic effect due to photon diffusion please? If yes, how does it treat the non-adiabatic effect in the convection zone and the atmosphere above the photosphere please?

Many thanks.

Sincerely,
Jing

Hi Jing --

Thanks for your question. GYRE currently includes non-adiabatic effects due to radiative transport, as modeled by the radiative diffusion equation. These effects are included in both radiative and convective regions. However, in convection regions the convection is frozen by ignoring the perturbations to the convective heating/cooling term in the energy equation.

cheers,

Rich

Hi Rich,

Thank you so much for your quick response May I ask what you mean specifically (exactly) by
'the convective heating/cooling term in the energy equation' please? Do you mean that gyre ignores the perturbation to the background(unperturbed-state) entropy gradient please?

Sincerely,
Jing

Hi Rich,

Another question please , to make sure I understand you.

By 'convection frozen', do you mean that gyre ignores the fact that convection can mix the entropy perturbations throughout the convection zone please?

Thank you very much

Sincerely,
Jing

jingluan wrote:Hi Rich,

Thank you so much for your quick response May I ask what you mean specifically (exactly) by
'the convective heating/cooling term in the energy equation' please? Do you mean that gyre ignores the perturbation to the background(unperturbed-state) entropy gradient please?

Sincerely,
Jing

Being specific, GYRE ignores the perturbations to the term

rho^{-1} div F_c

in the energy equation, where rho is the density and F_c is the convective flux. There are a number of other ways to 'freeze' convection -- see Unno et al, 1989 (Nonradial oscillations of stars).

cheers,

Rich

jingluan wrote:Hi Rich,

Another question please , to make sure I understand you.

By 'convection frozen', do you mean that gyre ignores the fact that convection can mix the entropy perturbations throughout the convection zone please?

Thank you very much

Sincerely,
Jing

No, I don't think so. 'Frozen convection' is simply the common way of saying that the effects of pulsation on convective energy transport are neglected.

Hi Rich,

Thank you for answering my questions about the convection zone .

For the optically thin part of the stellar model, does gyre not calculate any non-adiabatic effect please? I ask this question because the mesa model I use includes the part with optical depth << 2/3. So I am wondering how gyre treats the energy equation in this part please.

Many thanks!

Sincerely,
Jing

jingluan wrote:Hi Rich,

Thank you for answering my questions about the convection zone .

For the optically thin part of the stellar model, does gyre not calculate any non-adiabatic effect please? I ask this question because the mesa model I use includes the part with optical depth << 2/3. So I am wondering how gyre treats the energy equation in this part please.

Many thanks!

Sincerely,
Jing

Hi Jing --

GYRE does not distinguish between optically thin and optically thick regions. So, in the optically thin region the diffusion equation is still used to calculate the radiative flux. This is a crude approximation, but has little effect on the global stability (or instability) of modes. In the near future, I plan to replace the diffusion approximation with the Eddington approximation, which works well in both optically thin and optically thick limits.

cheers,

Rich

Hi Rich,

Thank you very much for clarifying my questions. It is very helpful . Have a nice day .

Sincerely,
Jing

It's very helpful, Rich. Thanks!