Changes between Version 4 and Version 5 of u/adebrech/Papers

Timestamp:

11/01/17 13:16:30 (7 years ago)

Author:

adebrech

Comment:

—

u/adebrech/Papers

@@ +1 @@
+= Radiation Pressure =
+
+[attachment:'Shaikhislamov ea 2016 NegRadPress.pdf' Shaikhislamov et al.] estimate the effects of radiation pressure on optically thick gas near 0.045 AU to be negligible for all of their models of the near-planet environment.
+
+[attachment:'Bourrier&desEtangs 2013 PartRadPress.pdf' Bourrier and des Etangs] use calculated Lyman-alpha profiles for HD209458 and HD189733 in particle simulations to model radiation pressure on neutral hydrogen escaping the planet. They used a parameter which decreased the effect of stellar gravity, but unlike many studies, their parameter is a function of velocity (Doppler shift, from the stellar Lyman-alpha profiles) and penetration depth (effectively optical depth):
+
+{{{#!latex
+$F = (1-\beta)F_{\star}$
+
+$\beta(v,\Lambda)=\beta(v,0)e^\frac{{-\sigma_{v0} \lambda_0}}{\Delta v}\int_0^\Lambda n_H(\mu,v)d\mu$
+}}}
+
+They argue that the absorption signature in the blue wing could be due to radiation pressure accelerating neutral hydrogen away from the star in the radial direction (up to ~120 km/s), but the absorption in the red wing cannot be explained in this manner.
+
+[attachment:'Khodachenko ea 2017 RadPress.pdf' Khodachenko et al.] use a simplified version of the Lyman-alpha flux to calculate radiation pressure in hydrodynamic simulations. They appear to have radially averaged the radiation pressure -- the pertinent equations we would apply are:
+
+{{{#!latex
+$x(v_i,T) = \frac{v_i - v_R}{\sqrt{\frac{2kT}{m_P}}}$
+
+$z(x^2) = \frac{x^2-0.855}{x^2+3.42}$
+
+$q(x^2) = \begin{cases}
+\frac{21+x^2}{1+x^2}z(x^2)(0.1117+z(x^2)(4.421+z(x^2)(5.674z(x^2)-9.207))), z(x^2)>0 \\
+0, z(x^2) < 0
+\end{cases}$
+
+$\sigma(v_i, T) \approx 5.9\times 10^{-14}\sqrt{\frac{10^4 \text{K}}{T}}e^{-x^2} + 2.9\times10^{-19}\left (\frac{100 \text{km s}^{-1}}{v_i - v_R}\right )^2 q(x^2)$
+}}}
+
+where $v_i$ is the Doppler-shifted velocity for each frequency bin, $v_R$ is the radial velocity of the cell, and $T$ is the temperature. They find that radiation pressure is negligible in comparison to charge exchange (in 2D).
+
 = Wind Launching =