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Analysis and Interpretation of Astronomical Spectra 52

13.8 The Rough Estimation of the Spectral Class

The rough, one-dimensional estimation of the spectral classes O, B, A, F, G, K, M, is easy
and even feasible for slightly advanced amateurs. The distinctive criteria are striking fea-
tures such as line- or band spectra, as well as absorption- or emission lines, which appear
prominently in certain spectral classes and vice versa are very weak or even completely ab-
sent in others. But the determination of the decimal subclasses and even more, the addi-
tional determination of the luminosity class (second dimension), require well-resolved spec-
tra with a large number of identified lines, as well as deeper theoretical knowledge. Possi-
ble distinctive criterions are eg the intensity ratio or the FWHM values of certain spectral
lines. On this topic exists an extensive literature eg [4]. Here follows just a brief introduc-
tion into the rough, one dimensional estimation of the spectral class. A further support is
the Spectroscopic Atlas for Amateur Astronomers [33]. The following figure shows super-

ifTmoAupnoFdsEeindL[a30n31d].lowly-resolÜvebdethreseicnthirte sSeqpueekncteraolfkthlaesspseecntral classes O - M, as it can be

Hε 3970
Hδ 4101
Hγ 4340
He I 4388
He I 4471
C III 4647/51
Hβ 4861
He I 4922
He I 5016
He I 50486
He II 5411

He I 5876
Na I 5890/95
Telluric O2
Hα 6562
He I 6678

O9.5 Alnitak
25‘000°K

B1 Spica
22‘000°K

B7 Regulus
A1 15‘000°K
A7
F0 Sirius
10‘000°K

Altair
7‘550°K
Adhafera
7‘030°K

F5 Procyon
6330°K

G2 Sonne
5‘700°K

G8 Vindemiatrix
4‘990°K

K1.5 Arcturus
4‘290°K

K5 Alterf
3‘950°K

M1.5 Antares Richard Walker 2010/05©
3‘600°K

M5 Rasalgethi
3‘300°K

KH TiO
Ca ll Mg l 5167-83
Ca I 4227 „Mg Triplet“ TiO TiO TiO
CH 4300
TiO
TiO