Page 32 - analysis-and-interpretation-of-astronomical-sp

Analysis and Interpretation of Astronomical Spectra 32

 Like in the recorded pseudo-continuum , also in changes the intensity ratio of

any two emissions or absorptions , measured in the original profile {7i}, {7j}.

 The rectified profile, normalised to , enables the determination of the -values

and facilitates the measurement of the , the Doppler-shift , as well as the de-

termination of the spectral class.

 By the rectification of the profile, by the information gets lost, which allows, by

means of the known attenuation function , to approximately reconstruct the

original profile (according to formula ).

 Anyway, even for most professional applications – with just a few exceptions –, the pro-
file normalisation is clearly the best and easiest option [11].

8.10 Relative Radiometric Flux Calibration by a Synthetic Continuum

The goal of this procedure is a rough approximation of the recorded profile with the

pseudo-continuum , to the original- and therefore not reddened continuum . This

procedure is described in the manual of the Vspec software. With dividing by correction
curves, the spectral lines of the pseudo-continuum are directly transferred to the syn-

thetically produced and fitted continuum course of a virtual model star with the

same spectral class and unreddened by any interstellar dust. Similar to sect. 8.9, this proc-

ess proportionally scales the intensities of all spectral lines from their individual -values in

the pseudo-continuum, up to the level of . For specific applications this procedure

is also applied in the professional field [301].

In the following chart the blue spectrum is the recorded profile with the pseudo-continuum
of Sirius. The red profile is the aimed, fitted continuum course of the syn-

thetic model star of the same spectral type, from the Vspec library (CDS Database). It ap-

pears cleaned from all spectral lines and thus roughly corresponds to the black body radia-
tion characteristics of this star:

.

Smoothed reference profile of
the model star

Ms Fit (λ)

Pseudo-continuum Ps(λ)

On the following graph, the green correction curve is generated by division of the fit-

ted blue pseudo-continuum with the red synthetic reference profile . It is

called by Vspec “Instrumental Response” and is denoted hereinafter with correction func-

tion .