[Mesa-users] Correct interpretation of dvdt_grav

[Farag, Ebraheem]

Hello Ishaan,

To investigate this a simple grep will reveal that the definitions for profile output are contained within $MESA_DIR/star/private/profile_getval.f90:

case (p_dvdt_grav)
    val = -s% cgrav(k)*s% m(k)/(s% r(k)*s% r(k))

So, to answer your question:  no, dvdt_grav != dvdt, dvdt_grav is just the gravitational term in the momentum equation, which you've already confirmed with your plot. Likewise, dvdt_dPdm is the pressure contribution.

Dvdt is not a default profile column, however we could consider making it a default. If you'd like to output dvdt directly, you must compute it as an additional profile column in the run_stars_extras.f90 , something like:

dvdt = s% dxh_v(k)/s% dt

-EbF
________________________________
From: Mesa-users <mesa-users-bounces at lists.mesastar.org> on behalf of Varshney, Ishaan via Mesa-users <mesa-users at lists.mesastar.org>
Sent: Friday, April 17, 2026 3:28 PM
To: mesa-users at lists.mesastar.org <mesa-users at lists.mesastar.org>
Subject: [Mesa-users] Correct interpretation of dvdt_grav

Dear MESA users,

I am trying to understand the correct definition of dvdt_grav output data. This output was given in the profile_column.list which I am using to study the X-ray bursts winds. I am trying to understand whether it's the same dv/dt which appears in the 1-D spherical momentum equation:
ρ*Dv_r/Dt=−dP/dr−ρ*GM/r^2    , because when on plotting, it is giving me gravitational acceleration. (Plot attached)

Also, plotting dvdt_grav / (GM/r^2) gives 1.

So, can anyone please help me understand the correct definition of this output…

Thank you,
Ishaan
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