Supernova remnant precursor width

1.Assuming that the line widths represent thermal broadening, an upper limit on the precursor width is obtained by requiring that it must be small enough to avoid complete ionization of neutral H before it enters the shock (Hester et al. 1994; Smith et al. 1994).

The limit on the diffusion coefficient is then $κ<v_S^2 /n_e q_i(T_e)$, where $n_e$ is the preshock electron density and $q_i(T_e)$ is the ionization rate coefficient at the preshock electron temperature $T_e$.

ref: https://www.aanda.org/articles/aa/pdf/2003/31/aah4405.pdf  sec. 4.4

2. simulations show that the magnetic field amplification expected to accompany efficient particle acceleration results in a very high thermal energy density, making the survival of neutrals directly in the acceleration region unlikely (Reville & Bell 2013).

“Bohm limit,” the smallest possible diffusion coefficient for isotropic turbulence is assumed.

What is Balmer emission

The Balmer serirs is the name give to a series of spectral emission line of the hydrogen atom that result from electron transitions from higher levels down to the energy level with principal quantum number 2. Four transitions are visible in the optical waveband.

The wavelength is given by
\[ \lambda_0 = R_H(\frac{1}{n_1^2}- \frac{1}{n_2^2})  ,\]
where $R_H$ is constant $1.0968e^7$ per meter, and $n_1,n_2$ are integers corresponfing to the principal quantum numbers involved in the transition with $n_2>n_1$.
The red $H\alpha$ line is resulted from the electron transition from $n_2=3$ to $n_1=2$ energy level.

Some of the neutral hydrogen atoms entering the shock are occasionally excited and emit narrow Blamer lines, whose width is related to the kinetic temperature of the upstream neutrals;

part of the original neutrals undergo instead a charge-exchange process, and then the new fast moving neutrals (formerly being shocked ions) will emit broad Balmer lines; these second-generation neutrals have some change to undergo charge exchange again and so to create further generations of neutrals, until all neutrals will eventually get ionized. Due to this chain of processes, Balmer lines are expected to show a broad and narrow component.


Reference:

http://astronomy.swin.edu.au/cosmos/B/Balmer+series

https://arxiv.org/pdf/1811.11551.pdf

Virtual Desks In Chromebook

Master your multitasking with virtual desks. Now, with different sets of screens, you can compare tasks, organize projects, or simply separate work and play. To create a new virtual desk, click the “show all windows” button on your keyboard, and select “new desk”.