(abrupt change in stellar spectrum at end of Balmer series)
The Balmer jump (or Balmer discontinuity)
is an abrupt change in the intensity of some stars' spectra
for wavelengths shorter than
the "infinity" end of the Balmer series spectral lines,
i.e., 364.6 nm.
It occurs when the star is sufficiently hot that hydrogen atoms
with electrons at level II are generally being ionized rather
than moving to a higher level of atomic excitation.
Then, any photon of sufficient energy can be absorbed, i.e.,
a lowering of the continuum at the above-mentioned wavelength.
Its shape is an indication of the star's density and temperature.
The jump is strongest in young stars, e.g., A-type star.
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Balmer-break galaxy (BBG)