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Spectroscopic Atlas for Amateur Astronomers 34

9.3 Classification System for WR Stars in the Optical Spectral Range

The following tables show, according to [232], the Smith classification-system (1968) for
the decimal subclasses based on the ionisation stage and the intensity of dedicated emis-
sion lines. This system was amended by many authors, including K. van der Hucht et al
[232]. The subtypes are here sorted so, that the age and temperature of the individual WR-
stages increase from top to bottom. Within each WR subclass the development takes place
against the "semantic logic", ie from "late" to "early".

WN Nitrogen Emission Lines Other Emission Criteria Temp.

WN11 N II ≈ He II, N III weak or absent Balmer lines, He I P-Cyg WN11: 30kK
WN10 N III ≈ N II Balmer lines, He I P-Cyg WN8: 40kK
WN9 N III > N II, N IV absent He I P-Cyg WN2: 100kK
WN8 N III >> N IV, N III ≈ He II 4686 He I strong P-Cyg [234]
WN7 N III > N IV, N III < He II 4686 He I weak P-Cyg
WN6 N III ≈ N IV, N V present but weak
WN5 N III ≈ N IV ≈ N V He II strong
WN4.5 N IV > N V, N III weak or absent
WN4 N IV ≈ N V, N III weak or absent
WN3 N IV << N V, N III weak or absent
WN2.5 N V present, N IV absent
WN2 N V weak or absent

WC Carbon Emission Lines Other Emission Criteria Temp.

WC9 C III > C IV C II present, O V weak or absent WC9: 50kK
WC8 C III > C IV C II absent, O V weak or absent WC8: 70kK
WC7 C III < C IV C III >> O V WC4: >>100kK
WC6 C III << C IV C III > O V [234]
WC5 C III << C IV C III < O V
WC4 C IV strong, C II weak or absent O V moderate intensity

WO Oxygen Emission Lines Other Emission Criteria Temp.
~200kK
WO4 O VII weak or absent C IV >> O VI, C III absent
WO3 O VII < O V C IV ≈ O VI, C III absent
WO2 O VII ≥ O V, O VIII present C IV < O VI, C III absent
WO1 C III absent

Classification Lines:

WN Stars: He I λ3888, He I λ4027, He I λ4471, He I λ4921, He I λ5875, He II λ4200, He II
λ4340, He II λ4541, He I λ4686, He II λ4861, He II λ5411, He II λ6560, N II λ3995, N III
λλ4634–4641, N III λ5314, N IV λ4058, N V λ4603, N V λ4619, and N V λλ4933–4944.

WC Stars: C II λ4267, C III λ5696, C III/C IV λ4650, C IV λλ5801–12, and
O V λλ5572–98.

WO Stars: C IV λλ5801–12, O V λλ5572–98, O VI λλ3811–34, O VII λ5670, and
O VIII λ6068.