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Spectroscopic Atlas for Amateur Astronomers 73
The intensity maximum of the real continuum is now clearly located within the visible range
of the spectrum. The graph shows the theoretical continuum for a synthetic F5 V standard
star (Vspec/Tools/Library). Highlighted with a red circle is here the “Line-double” of the G-
band and Hγ, the striking “Brand” of the F-class.
G Band Hγ
16.4 Commented Spectra
Tafel 30: Adhafera (ζ Leo) und Procyon (α CMi)
The development of the F-subclasses is demonstrated here by two superposed overview
spectra (200L grating) representing an early and middle subtype.
Adhafera (260 ly), classified as F0 III, is located at the top of the F-class and has already
reached the Giant stage (III). The surface temperature is about 7,030 K and its apparent ro-
tation speed some 84 km/s [506]. Even within this early F-class, the Fraunhofer-H and K
lines have already surpassed the intensity of the H-Balmer series, where the K-line at
λ 3968 has overprinted the Hε absorption.
Procyon (11 ly) is classified as F5 IV-V and thus representing approximately the “center” of
the F-class. Like Sirius, it has a white dwarf companion. The luminosity class IV-V reveals
that it has begun to leave the Main Sequence in the HRD towards the Giant Branch. The
apparent rotation speed is only some 6 km/s. The surface temperature with about 6,630 K
is expectedly lower than for the earlier classified Adhafera. At the first glance this has little
effect on the spectral profile.
The most noticeable and important difference relates to the "Brand" of the F-class - the in-
creasing intensity of the CH molecular absorption band (at λ 4300) and conversely the
shrinking of the neighbouring Hγ line. Further the growing intensity of the Ca l line
(λ 4227), at this resolution clearly visible only by the somewhat colder Procyon. Some fur-
ther differences may be caused by the difference in luminosity class.
Line identification:
The line identification is based amongst others on [1], [5], [51], [52], [59]
