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Spectroscopic Atlas for Amateur Astronomers 8

1 Introduction

Probably most amateur astronomers have a common experience at the beginning of their
spectrographic “career”. Full of expectations they test the new device for the first time and
look with great pride at the first self recorded spectrum. This first enthusiasm then quickly
gives way to the perplexity, how these numerous lines shall now be identified and even
analyzed. Fortunately, some recommendable introductory literature, e.g. [1], to the interpre-
tation of stellar spectra is available for amateurs. However, a real “Spectral Atlas”, which
systematically covers the classes O, B, A, F, G, K, M, by commenting most of the lines, visi-
ble in a medium resolved spectral profile, was still missing. In 2009 the extensive work
"Stellar Spectral Classification" was published by R. Gray and C. Corbally [2]. It is aimed
primarily at students and professional astronomers, but offers the significantly advanced
amateur valuable information, eg for determining the decimal subclasses or the spectral
characteristics of rare types of stars.

The project "Spectroscopic Atlas" launched in 2010, intended to close this publication gap,
which was particularly serious for the German-speaking amateurs. Originally intended was
just the complete documentation of the stellar spectral types, except of the Brown Dwarfs
L, T and Y, which remain exclusively reserved to professional infrared telescopes. Already
on the first edition followed a astonishingly positive and surprisingly broad international
feedback. This motivated me, in addition to the stellar classes, to document even further
object types, which are spectroscopically accessible for amateurs.

In the Internet we find many professional papers, mostly focused on small sections of a
spectral profile. Nevertheless, they often contribute valuable puzzle pieces to the exciting
“detective work” of line identification. Very well documented is the spectrum of the Sun (G2
V), where almost all of the lines are identified and commented. Here, at least two easily
readable and freely downloadable atlases are available on the net [80], [81]. These sources
can even help, with the necessary precautions, to identify spectral lines of adjacent spec-
tral classes.

Spectral atlases from professional sources, published on the internet, and covering all im-
portant spectral classes can rarely be found. Amazingly, even in such professional papers,
usually only a few intense lines, mostly in very lowly resolved spectra, are commented.
However, the focus of many practical applications, even in professional works, is mostly
reduced to relatively few, highly intense and isolated lines, e.g. for determination of the ro-
tation speed or the metal abundance. In such publications the ultraviolet, the blue- and red-
to far infrared part of the spectra are preferably treated - the sections "green" and "yellow"
however only rarely.

In Appendix 34.3 some excerpts from several historical as well as state of the art spectral
atlases are shown. Probably the best known and highly important one, even for the history
of science, is the out of print standard work "An atlas of stellar spectra, with an outline of
spectral classification" by Morgan, Keenan and Kellman [50]. This seminal work from 1943
can now be downloaded from the Internet but is limited to the short-wavelength part of the
visible spectrum, reflecting the state of technology in the 1940’s. It presents photographic
1D-spectral stripes, commented with handwritten notes! Made in a similar style is the “Re-
vised MK Spectral Atlas for Stars Earlier Than the Sun” from 1978 by Morgan, Abt, and
Tapscott [51].

Some spectral atlases were available in the past but are out of print today. The most com-
prehensive “reference work” is surely “Bonner Spektralatlas”, the title of the English edi-
tion: “Atlas for Objective Prism Spectra” by Waltraut C. Seitter, 1975 [5]). This atlas, cover-
ing the spectral types from O5 to M2, is out of print today, but recently available as
download [5]! Still based on photographic 1D-spectral stripes it’s the only reviewed work,
documenting most of the lines between about λ 3400 – 5000, which are visible with low to
medium resolving spectrographs. In the green-red range this atlas partly shows quite large