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Analysis and Interpretation of Astronomical Spectra 86
In the diagram below, the Hβ-equivalent widths (EW) of 24 Atlas stars [33] are plotted
against the effective temperatures . Due to the bell-shaped curve an ambigu-
ity arises, which requires a clarification by additional spectral information. A prominent fea-
ture, indicating the profile segment on the long wavelength side of 10,000 K, is the Fraun-
hofer K-line (Ca II) at 3934 Å – further details see [33]. The average temperature range is
here almost exclusively represented by main-sequence stars, the peripheral sections also
by giants of the luminosity class I – III.Despite of relatively few data points and a low reso-
lution (DADOS 200L/mm), the curve shape can clearly be recognised and is manually in-
serted here as an approximate "least square fit". It is just intended to demonstrate the prin-
ciple. For more accurate results the analysis of high-resolution spectra would be required
and further the separation between the luminosity classes.
α Gem
78 Virα CMa
α Aql
EW ζ Leo γ Vir γ Crv
Hβ α Cmi α Leo
[Å]
Sun α Vir 68 Cyg
η Boo δ Ori
α Ori
α Sco ε Vir ε Ori
61 Cyg ζ Ori
Effective temperature Teff [K]
