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Spectroscopic Atlas for Amateur Astronomers 17
4 Terms, Definitions and Abbreviations
4.1 Parameters and Identification of the Stars
The information to the spectral and brightness classes comes largely from the Bright Stars
Catalogue [505] or James Kaler [506], the distance information, if there available, from the
Karkoschka Atlas [10]. The information to the "surface temperature" of the stars stems
from a variety of sources, e.g. [506]. It is also referred to herein as effective temperature
ܶ. It usually relates to the layer of the stellar photosphere, which is mainly responsible
for the formation of the spectral lines as well as for the spectral distribution of the stellar
radiation intensity (course of the continuum).
The rotation velocity of a star refers here to the part of the surface velocity ࢜, which is pro-
jected to the direction of the earth – ࢜ – ܖܑܛand can spectrographically be determined by
using the Doppler principle (details and procedures see [30], [31]). These values are mainly
derived from the Bright Stars Catalogue [505] or by James Kaler [506].
Brighter stars are referred in the atlas with the proper name and in the Bayer system with
small Greek letters, combined with the abbreviated Latin constellation name, e.g.
Sirius α CMa (see the corresponding lists in appendix 34.1). Fainter stars, lacking proper
names, are identified with the Bayer system, or if necessary, with the Flamsteed- or HD
number (Henry Draper Catalogue), e.g. φ Sagittarii, 61 Cygni, HD 22649.
4.2 Galactic Nebulae and Star Clusters
Such parameters are from NED [501], the NASA/IPAC Extragalactic Database or Kar-
koschka [10].
4.3 Extragalactic Objects
Parameters of galaxies and Quasars, e.g. the Z-values of the Redshift are from NED [501],
the NASA/IPAC Extragalactic Database. From understandable reasons, information about
the masses of such objects is missing there. Current estimates are still very uncertain, and
accordingly the subject of debate – not least about the existence of dark matter. Therefore
these values come from recent publications.
4.4 "Early" and "Late" Spectral Types
At the beginning of the 20th Century, a hypothesis wrongly postulated that the spectral se-
quence from O to M represents the chronological development stages in the life of a star
from very hot to cold. This misleading thesis has subsequently influenced the terminology,
which is still in use today. Therefore the classes O, B, A are still called “early-”, and K, M as
"late" types. In this Atlas the classes F and G are referred as “middle”.
This terminology is logically also applied within a class. So e.g. M0 is called an "early" and
M8 a "late" M-type. In consequence e.g. A2 is "earlier" than A7.
4.5 Abbreviations and Units
AU: Astronomical unit, 149.6M km
AGB: Asymptotic Giant Branch (HRD)
BSA: Bonner Spektralatlas
ESO: European Southern Observatory
ESL: Energy saving lamp
EW: Equivalent width of a spectral line [Å] [30]
FWHM: Full width at half maximum height [Å] [30]
HB: Horizontal Branch (HRD)
