# [mesa-users] Brunt-Vaisala frequency

Ying Qin Ying.Qin at unige.ch
Thu Jan 21 16:38:53 EST 2016

```Dear Robert,

Cheers,
Ying

On 21 Jan 2016, at 22:11, Robert Farmer <rjfarmer at asu.edu<mailto:rjfarmer at asu.edu>> wrote:

Hi

It looks like, you want the brunt_N2 term then, as brunt_A= brunt_N2* r/g
which then should give you N^2. For the /x^2 term you just need to divide by the fractional radius at that cell. Which you could do in your run_star_extras file, where you just need to add:

s%brunt_N2(k)/(s% r(k)/s% r(1))**2

as an extra profile column

Rob

On Wed, Jan 20, 2016 at 4:04 PM, Ying Qin <Ying.Qin at unige.ch<mailto:Ying.Qin at unige.ch>> wrote:
Dear all,

For a specific profile, how to obtain the (N^2/x^2)’_f ( derivative of the N^2/x^2 at the boundary of the convective core ), where x = r/R ( x = r(k)/r(1) ), N^2 is defined in the Eq. 4 of MESA Paper II.
I want to use this parameter and combine a model to calculate the tidal torque constant.

At first, I checked the profile_columns.list and find:
brunt_A ! = N^2*r/g
brunt_A_div_x2 ! x = r(k)/r(1)

It is very close to what I expect, but not yet!  In the definition of N^2 in Eq. 4 of MESA Paper 2, the term r/g has already been involved in N^2.
So can any expert tell me is there a direct way to get the term N^2/x^2, as well as the derivative of N^2/x^2 ?

Cheers,
Ying

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