The spectral region is dominated by the CaII triplet lines at
8498 Å, 8542 Å and 8662 Å. The Paschen lines disappear at G0 for
class V and III and at G2 for supergiants. Many lines of FeI
and TiI become visible and strengthen with advancing spectral
type. We quote specially the FeI lines at 8621 Å, 8688 Å and
8514 Å and the TiI lines at 8426 Å, 8435 Å and 8518 Å. Notice also
the appearance of molecular bands of TiO in the coolest stars.
All these features can be used for the determination of the
spectral type.
Luminosity effects are evident in the line depth. Lines become
wider and deeper with higher luminosity (see Figs. 4 (click here) to 17 (click here)).
This effect is specially noticeable for the CaII triplet lines.
Another good luminosity criterion is the behavior of the blend
at 8468 Å (TiI and FeI).
We have provided in Figs. 22 (click here) to 27 the curves relating measured
equivalent widths to spectral type and luminosity class. These
curves are averages based on the measurements from many
spectra. The measurements itself were given in Ginestet et al.
(1994). The purpose of including these figures is twofold. In
first place the figures illustrate very well how the different
criteria behave in different spectral types and luminosity
classes, so that no lengthy explanation regarding the
usefulness of each criterion is needed. In second place the
figures illustrate that the equivalent widths can be used to
refine the classifications based upon the visual inspection of
spectra.
From the Atlas it is clear that it should be possible to obtain
from the infrared spectral region classifications which are as
precise as those obtained from the blue region. This is a point
of real interest for the classification of all red and faint
objects.
Acknowledgements
We express our gratitude to Dr. Y. Andrillat from the Université de Montpellier for permitting the use of four spectra for this Atlas. We thank also Prof. P.C. Keenan for useful discussions.
Figures 6, 7, 8, 9 10 and 11:
Figures 12 and 13, 14 and 15, 16, 17, 18:
Figures 19, 20, 21:
Figure 22: The equivalent width (in Angström units) of the
blend 8468 line as a function of
spectral type and luminosity class
Figure 23: The equivalent width (in Angström units) of the
CaII 8542 line as a function of
spectral type and luminosity class
Figure 24: The equivalent width (in Angström units) of the
FeI 8621 line as a function of
spectral type and luminosity class
Figure 25: The equivalent width (in Angström units) of the
FeI 8688 line as a function of
spectral type and luminosity class
Figure 26: The equivalent width (in Angström units) of the
TiI 8426 line as a function of
spectral type and luminosity class
Figure 27: The equivalent width (in Angström units) of the
TiI 8435 line as a function of
spectral type and luminosity class
