Wilson-Bappu effect
(Wilson-Bappu relation, WBR)
(a relation between a star's spectral line and luminosity)
The Wilson-Bappu effect is a relation discovered in
the 1950s between the luminosity of
G-type stars, K-type stars and M-type stars
(both their main-sequence and giant variants)
and the width (line broadening) of a particular emission line:
the Ca II K line
(ionized calcium, 393.366 nm,
a Fraunhofer line),
a width is referred to as W0.
The relation provides a means of stellar distance determination, especially
useful for groups of stars, in which case the effects of some
variance can be reduced.
The relationship seems odd to me, that the luminosity of the entire star
somehow correlates to the broadening of an emission line
despite the fact that this luminosity reflects a combination of
surface temperature and radius, and a single relation holds
for stars of such varying radii. The line is produced in the
chromosphere and the effect is potentially a clue to the
chromosphere of "stars in general" as opposed to specifically that
of the Sun. An obvious candidate-mechanism is Doppler broadening
from chromosphere turbulence, but this passes on the mystery
to how such chromosphere turbulence could be affected by the
total luminosity in such manner.
(stars,relation)
Further reading:
https://en.wikipedia.org/wiki/Wilson-Bappu_effect
https://ui.adsabs.harvard.edu/abs/1957ApJ...125..661W/abstract
https://ui.adsabs.harvard.edu/abs/1991Ap%26SS.179..293G/abstract
https://ui.adsabs.harvard.edu/abs/2003A%26A...401..997P/abstract
WaveL | Freq | Photon Energy | | |
393.366nm | 762THz | 3.2eV | | Wilson-Bappu effect |
|
Index