Page 31 - analysis-and-interpretation-of-astronomical-sp

Analysis and Interpretation of Astronomical Spectra 31

hydrogen lines, according to sect. 20 and 21. Practical example are the strongly attenu-
ated hydrogen lines of P Cygni.

8.9 Rectification of the Continuum Intensity

The most simple correction process is the rectification of the recorded profile by dividing of

the pseudo-continuum by its own “smoothed” or fitted intensity course . Ac-

cording to [11], this method is appropriate even for most professional applications. This
way the continuum-intensity is unified or "normalised" through the entire range, and set
to . The resulting profile is called „Residual Intensity“

Due to this division, the profile runs now horizontally and the intensity of the emissions -

and absorptions is related to the unified continuum intensity . This process

proportionally scales by the intensities of all spectral lines from their individual -

values in the pseudo-continuum, up to the level . This corresponds now to the origi-

nal, not attenuated profile of a virtual star which shows a horizontally running, but physi-

cally impossible radiation characteristic. For the intensity of the emission lines this correc-
tion process is just a rough approximation (see sect. 8.8).

Consequences and benefits of Rectifying the Pseudo-Continuum

 Useful for certain applications – the profile normalisation allows the elimination, of

the often irrelevant, or even hindering, wavelength-dependent distribution, of the stellar
radiation intensity. It generates a "quasi neutralisation", but never a real correction of the

attenuating effects.

 Between individual absorption lines, enables the direct comparison of the peak in-

tensities between individual absorption lines, according to . The scaling effect of

a rectified profile is impressively demonstrated at the absorptions in the solar spectrum
by the two Fraunhofer H- and K- lines of ionised calcium (Ca II). The blue profile of the
pseudo-continuum shows these lines only stunted at the short wavelength end of the
spectrum (blue arrow). After rectifying of the continuum (red profile), the H- and K- lines
appear now obviously as the strongest absorptions, which the sun generates itself (red
arrow).

 The original ratio of the individual emission lines is maintained just as a rough
approximation {7h}.

 , with the unified and normalised radiation-intensity , enables for the re-
corded emission lines the intensity comparison with those of the original, unattenuated
Balmer-Decrement (sect. 20).