The general appearance of the spectra of the supergiants of types A-K is different from that of stars of lower luminosity; and, when an attempt is made to classify the high-luminosity stars by the ratios used for ordinary giants and dwarfs, a number of difficulties are encountered. Ratios which include a hydrogen line are strongly affected by absolute-magnitude effects in classes B8-F0 and G8-K5; in the first spectral interval the H lines are greatly weakened in the supergiants, and in the second they are considerably strengthened. The lines used to classify the A5-F5 spectra are disturbed by blends in the supergiants which have a marked absolute-magnitude effect. In addition, the G band appears as a fairly continuous absorption only for types later than F8 in the supergiants; while in ordinary giants and dwarfs it is present at F5 on plates similar to the ones used in preparing the Atlas.
For these reasons, if a highly accurate system is to be defined for supergiants and Cepheids, it is important to set up a sequence of standard supergiants by criteria suitable for the high-luminosity stars. The system defined by the supergiants in Table 31 is in fairly good systematic agreement with the Henry Draper Catalogue. The stars listed define the system accurately to about a tenth of a class, except in the case of the late A and early F subdivisions, where the accuracy is appreciably lower.
Some ratios useful in determining the spectral type of the supergiants are: 4128- 4130: 4172- 4179 (A0-F0), 4226: H (F5-G5), 4045: H (F5-G8), 4226: H (F5-K5), 4325: H (F5-G2), blend at 4176: blend at 4200 (G5-K5), 4383: 4406 (G8-K5), and the appearance of the region of the G band (F0-K5).
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No stars have been classified as Ia between F8 and M2; it is possible that certain luminous irregular variable stars may belong to this class in the G and K types. It is also possible that stars of the highest luminosity develop TiO bands at slightly lower temperatures than the F8 Ia stars CMa and Cas; they might then be classified among the M stars, while their line spectra correspond to class G or K.
Star | MKK | a | m | HD | Notes | |
Ori ..... | B8 Ia | 05:09 | -08°19' | 0.3 | B8p | |
4 Lac ..... | B8 Ib | 22:20 | +48 58 | 4.6 | B8p | |
Cyg ..... | B9 Ia | 21:13 | +38 59 | 4.3 | A0p | |
HR 1040 .. | A0 Ia | 03:21 | +58 32 | 4.8 | A0p | 1 |
13 Mon .... | A0 Ib | 06:27 | +07 24 | 4.5 | A0p | |
Leo ..... | A0 Ib | 10:01 | +17 15 | 3.6 | A0p | |
a Cyg ..... | A2 Ia | 20:38 | +44 55 | 1.3 | A0p | |
Cep ..... | A2 Ia | 21:42 | +60 40 | 4.5 | A0p | |
Cas ..... | A5 Ia | 01:13 | +57 42 | 5.3 | F5P | |
Aur ..... | F0 Ia | 04:54 | +43 41 | (3.3) | F5p | |
a Lep ..... | F0 Ib | 05:28 | -17 54 | 2.7 | F0 | |
a Per ..... | F5 Ib | 03:17 | +49 30 | 1.9 | F5 | |
CMa ..... | F8 Ia | 07:04 | -26 14 | 2.0 | F8p | |
Cas ..... | F8 Ia | 23:49 | +56 57 | (4.4) | F8p | |
Cyg ..... | F8 Ib | 20:18 | +39 56 | 2.3 | F8p | |
Aqr ..... | G0 Ib | 21:26 | -06 01 | 3.1 | G0 | |
Leo ..... | G0 I-II | 09:40 | +24 14 | 3.1 | G0p | |
a Aqr ..... | G1 Ib | 22:00 | -00 48 | 3.2 | G0 | |
Cap ..... | G4 Ib? | 21:21 | -22 51 | 3.9 | G5p | 2 |
9 Peg ..... | G5 Ib | 21:39 | +16 53 | 4.5 | G5 | |
Gem ..... | G8 Ib | 06:37 | +25 14 | 3.2 | G5 | |
56 Peg .... | G8 Ib | 23:02 | +24 56 | 5.0 | K0 | |
Cep ..... | K1 Ib | 22:07 | +57 42 | 3.6 | K0 | |
Peg ..... | K3 Ib | 21:39 | +09 25 | 2.5 | K0 | |
Aql ..... | K3 I-II | 19:41 | +10 22 | 2.8 | K2 | |
Cyg ..... | K5 Ib | 21:01 | +43 32 | 3.9 | K5 | |
a Sco ..... | M1 Ib | 16:23 | -26 13 | 1.2 | Ma | 3 |
µ Cep ..... | M2 Ia | 21:40 | +58 19 | var | Ma | 3 |
a Ori ..... | M2 Ib | 05:49 | +07 23 | var | Ma | 3 |
NOTES | ||||||
1. The H lines are slightly stronger than in Ori. | ||||||
2. The line Sr II 4077 is very Strong. | ||||||
3. The Mount Wilson spectral types of the M giants have been assumed. |
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