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Meredith L. Rawls edited Beyond_a_stellar_evolution_model__.tex
almost 9 years ago
Commit id: ef12b02cc71c3824d2f7de9d88b4da489a793420
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The timescale $\tau_c$ on which orbital circularization occurs is given by
\begin{equation}
\frac{1}{\tau_c} \equiv \frac{\rm{d} \ln e}{\rm{d}t} = f \left( \frac{L}{M_{\rm{env}}R^2} \right)^{1/3} \frac{M_{\rm{env}}}{M}
q \frac{M_2}{M} \frac{M+M_2}{M} \left( \frac{R}{a} \right)^8.
\end{equation}
Here, $f$ is a factor of order unity
\citep{ver95}, \citep{ver95} and $M_{\rm{env}}$ is the mass of the convective envelope of the primary
star, and $q$ is the mass ratio. star.
We integrate this expression over the lifetime of the star to estimate the total expected change in orbital eccentricity, $\Delta \ln e$. We assume $a$ is constant, $f = 1$, and further assume no mass loss. Because KIC 9246715 is a well-separated binary, we can separate the integral into a part that is independent of the orbit and a part that must be integrated over time:
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\Delta \ln e = -1.7 \times 10^{-5} \ f \ {\left( \frac{M}{M_{\odot}} \right)}^{-11/3} \ q(1+q)^{-5/3} \ I(t) {\left( \frac{P_{\rm{orb}}}{\rm{day}} \right)}^{-16/3},
\end{equation}
where
$q$ is the mass ratio and
\begin{equation}
I(t) \equiv \int_0^t \left( \frac{T_{\rm{eff}}(t')}{4500 \rm{K}} \right)^{4/3} \ \left( \frac{M_{\rm{env}}(t')}{M_{\odot}} \right)^{2/3} \ \left( \frac{R(t')}{R_{\odot}} \right)^8 \ dt'.
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