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Spectroscopic Atlas for Amateur Astronomers 18

HD: Henry Draper Catalogue

HRD: Hertzsprung-Russel Diagram

HST: Hubble Space Telescope LBV: Luminous Blue Variable (sect. 11)

MK: Morgan, Keenan, Kellman: spectral classification system and spectral atlas

mV: Apparent visual magnitude, MV: Absolute Magnitude at a distance of 10 parsec
PN: Planetary Nebula

PMS: Pre-Main sequence Star. Young Protostar, not yet established on main sequence

RGB: Red Giant Branch (HRD) RSG: Red Supergiant

SB1: SB 1 system. Spectroscopic binary stars with strongly different bright components.
Only the spectrum of the brighter component can therefore be observed.

SB2: SB 2 system. Spectroscopic binary stars with two similar bright components.
A composite spectrum of both components is therefore observed.

SN: Supernova

VLT: Very Large Telescope, ESO telescope group at Cerro Paranal, Chile

WR: Wolf-Rayet stars

SuW: German astronomical journal: Sterne und Weltraum

K: Kelvin temperature unit K ≈ °Celsius + 273°
Å: unit of wavelength Angstrom. 1 Å = 10-10m
ly: light year [ly] 1 ly = 9,46 x 1012 km parsec: [pc] 1 pc = 3.26 ly

Labeling of the Balmer Series: Hα, Hβ, Hγ, Hδ, Hε, H8, H9, H10 etc: Further lines after Hε
are labelled with the affected shell number, involved in the according electron transition.

200L / 900L: reflection grating of the DADOS spectrograph with 200 or 900 lines/mm.

V: Spectral line identified with help of the Vspec Tool

: Molecular absorption band

: Comparison to the sun: M : solar mass, L : Luminosity of the sun

4.6 Identifying of the Elements and Ions

As usual in astrophysics, all the elements, except of hydrogen and helium, are called "met-
als" and identified in the astrophysical form - for details see [30].

The term “Ionisation stage” refers here to the number of electrons, which an ionized atom
has lost to the space (Si IV, Fe II, H II, etc.). The Roman numeral I is used for spectral lines
associated with the neutral element, numeral II for those from the first ionization stage, –
III for those from the second-, and so on. This must not be confused with the term “Degree
of ionisation” in plasma physics. It defines for a gas mixture the ratio of atoms (of a certain
element) that are ionised into charged particles, regarding the temperature, density and the
required ionisation energy of the according element. This “Degree” is determined in astro-
physics with the famous Saha equation.

So-called "Forbidden lines" are written within brackets, eg [O III].

4.7 The Metal Abundance Z (Metallicity)

Of great importance is the iron to hydrogen ratio ܰி௘/ܰு, considering the relative number
of atoms ܰ and not the mass! The Metallicity ܼ in a stellar atmosphere, also called "ሾ‫݁ܨ‬/‫ܪ‬ሿ",

is expressed as the decadic logarithm in relation to the sun:

ܼ = ሾ‫݁ܨ‬/‫ܪ‬ሿ = ݈‫݃݋‬ଵ଴ ሺ ܰி௘ /ܰு ሻ ௌ௧௔௥
ሺܰி௘/ܰு ሻௌ௨௡

ܼ values, smaller than found in the atmosphere of the Sun, are considered to be metal poor
and carry a negative sign (–).The existing range reaches from approximately +0.5 to –5.4
(SuW 7/2010).