Page 30 - analysis-and-interpretation-of-astronomical-sp

Analysis and Interpretation of Astronomical Spectra 30

8.6 Summary of the consequences:

 For absorption lines, absolutely connected with the continuum, the -related measure-

ments – peak intensity and equivalent width – remain untouched by the attenua-

tion due to . The original ratio of remains the same also in the pseudo-

continuum .

 The emission lines, superimposed to the pseudo continuum , stay independent of

the continuum level . In contrast to the absorption lines, their values appear here

to be attenuated, depending on the specific wavelength. This effect excludes an attenua-

tion, acting proportional to the dampened continuum-level , and shows up by the so-

called Balmer-Decrement of the hydrogen emissions according to sect. 20. Nevertheless
as a rough approximation, sometimes an attenuation is assumed, which acts propor-
tional to .

 The intensity values and , which are measured in arbitrary measuring units, and in-
dependently from the continuum-level, appear to be attenuated in the pseudo-continuum
,.

 The original intensity ratios between two different absorptions , or emissions ,

which are measured within the original profile in arbitrary measuring units, ap-

pears to be modified in the pseudo-continuum , .

8.7 The Importance of the Pseudo-Continuum

If the attenuation-function is approximately known, the pseudo continuum

contains the information, to enable the approximate reconstruction of the original profile

, applying formula . Further, according to sect. 3.2 and 3.3, the wavelength of the

maximum intensity is, even in the strongly dampened pseudo-continuum, a very rough indi-
cator at least for the order of magnitude of the effective temperature .

Apart from these effects the course of the recorded pseudo-continuum , is useless.

Depending on the wavelength, just shows the amount of electrons, which has been

read out of the individual pixels, amplified by the camera electronics and finally averaged by
the spectral processing software over a defined height of the vertical pixel rows. Thus it re-
flects roughly proportional the recorded photon flux which however is loaded with all the

mentioned attenuating influences. As intensity unit for raw profiles therefore often [ADU]
(Analog – Digital Units) is used.

8.8 Proportional Radiometric Corrections of the Pseudo-Continuum

In the following sections 8.9 – 8.12 several proportional-radiometric correction processes
are presented, which transform the recorded pseudo-continuum for different applica-

tions to appropriate forms. All are based on the division of by empirical correction-

functions. Thus , the intensities of the embedded absorption lines and also the su-

perimposed appearing emission lines , are scaled proportionally to a new value.

Important:

 The -related measurements – peak intensity and equivalent width – remain un-
touched by the division. Just the intensity values and , which are measured in arbi-
trary measuring units, and independently from the continuum-level, are concerned.
These effects are appropriate only for the absorption lines.

 For the emission lines, however, only a rough approximation is achieved this way. Be-
cause, related to , the original equivalent widths can't be reconstructed by a

simple division, and the original -values can just very roughly be approximated. The

original intensity ratios of the emission lines can only be determined by individual, ar-
ithmetical scaling, proportional to the values of the theoretical Balmer-Decrement of the