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Analysis and Interpretation of Astronomical Spectra 44

Since by definition the energy on the level is set to , we shift the value of

the Balmer edge 3.40 eV with negative sign to the initial level of the Balmer Series .

3.40 eV corresponds also to the energy difference between the initial level and the

Balmer edge, as well as to the minimum required energy to ionise a hydrogen atom from

the initial level . For the calculation of the other energy levels the values of the

corresponding level differences must now be subtracted from 3.40 eV. For the energy level,
eg , the subtraction 3.40 eV – 1.89 eV = 1.51 eV is required (1.89 eV = EpHα). Per
definition the values of the energy levels have here negative signs.

10.4 Balmer- Paschen- and Bracket Continuum

Hot stars, with main radiation intensity in the UV region of the spectrum, show a steeply
rising continuum level toward shorter wavelengths. As already shown above, this tendency
is abruptly stopped by the Balmer Jump at 3646 Å. After a dramatic drop in intensity, the
continuum rises again in the UV range, until it reaches the final ionisation limit of hydrogen
(also called the Lyman limit) at 912 Å. The following graph shows the Balmer Jump at a
synthetic A0 I profile from the Vspec database.

A similar process occurs near the border to the infrared region at 8207 Å, the so-called
Paschen Jump. Somewhat confusing is the designation of the intermediate continuum sec-
tions which always bear the name of the preceding jumps or series. The Balmer Series

is therefore located within the so-called Paschen Continuum. On the shortwave

(UV) side of the Balmer Jump, follows the Balmer Continuum with the Lyman Series

. In the infrared region, the Paschen Series is located within the Bracket

Continuum. The dramatic influence of the hydrogen absorption on the continuum can be

explained by the extremely high occurrence of this element in most of stellar photospheres.

I

Paschen Jump
8207 Å

λ [Å]