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Table 1
Atomic and molecular features used to classify C, M- and S-type stars.
| λ (Å) | Feature | Comment |
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|
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| 4861 | Hβ F-line | Fraunhofer F-line. Seen in emission in some of our stars. |
| 4959 | [O III] | Forbidden emission line of doubly ionised oxygen, ~1/3 strength of the 5007 Å line. Seen in some of our stars. |
| 5007 | [O III] | Forbidden emission line of doubly ionised oxygen. Seen in some of our stars. |
| 5165 | C2 | Degrades blueward from bandhead. |
| 5167 | Mg I | Visible in all G, K, and M-type stars until M4 III or M6.5 V; greatly enhanced in dwarfs. |
| 5173 | Mg I | See comments for Mg I 5167 Å. |
| 5184 | Mg I | See comments for Mg I 5167 Å. |
| 5211 | MgH | Broad absorption feature in M-type dwarfs; degrades toward the violet. |
| 5298 | ZrO | Several ZrO bands beginning at 5298 Å. Visible in mid S-type stars. |
| 5577 | [O I] | Telluric oxygen emission line. |
| 5636 | C2 | Degrading blueward. |
| 5730 | CN | |
| 5810 | TiO | Visible at M2 to M3. |
| 5862 | TiO | Visible at M0 to M1. |
| 5890 | Na I D-line | Visible in all G-, K- and early M-type stars. Greatly enhanced in dwarfs; overwhelmed in M-type giants by M2. |
| 5896 | Na I D-line | As above. |
| 6005 | C2 | Molecular carbon feature degrading blueward. |
| 6059 | C2 | Molecular carbon feature degrading blueward. |
| 6132 | ZrO | Several ZrO bands beginning at 6132 Å. Increasing in strength with later spectral type. |
| 6159 | TiO | Bandhead degrades redward. |
| 6162 | Ca I | Enhanced in M-type dwarfs. |
| 6206 | CN | |
| 6300 | [O I] | Telluric oxygen line. |
| 6332 | CN | |
| 6363 | [O I] | Telluric oxygen emission line. |
| 6385 | CaH | Band used as an M-type dwarf indicator. |
| 6478 | CN | |
| 6532 | VO | Seen in S-type stars. |
| 6548 | [N II] | Forbidden emission line of singly ionised nitrogen, ~1/3 strength of the 6583 Å line. Seen in some of our stars. |
| 6563 | Hα C-line | Fraunhofer C-line. Seen in emission or absorption in some of our stars. |
| 6569 | TiO | Several TiO bands beginning at 6569 Å that are marginally visible in early M-types. |
| 6583 | [N II] | Forbidden emission line of singly ionised nitrogen. Seen in some of our stars. |
| 6631 | CN | |
| 6716 | [S II] | Forbidden emission line of singly ionised sulphur. Seen in some of our stars. |
| 6731 | [S II] | As above. |
| 6867 | O2B-band | Fraunhofer B-line. A telluric absorption feature. |
| 6908 | CaH | Discussed with CaH (6946 Å) below. |
| 6925 | CN | |
| 6933 | ZrO | Seen in S-type stars. Clearly visible by mid-S. |
| 6946 | CaH | Strongest in early M-type dwarfs. Bands of CaH serve to widen and deepen the TiO bands in this region. |
| Blended with the O2B-band. | ||
| 6988 | ZrO | Seen in S-type stars. Clearly visible by mid-S. |
| 7054 | TiO | Clearly visible at K5; bandhead degrading redward. |
| 7088 | CN | |
| 7186 | H2O | Telluric band. Degrading redward. |
| 7198 | TiO | Distinct from M1. |
| 7219 | TiO | Distinct from M1. |
| 7259 | CN | |
| 7269 | TiO | Distinct from M1. Combined with TiO bands at 7198 and 7219 Å creates a distinctive triple dip feature. |
| 7334 | VO | Several bands of VO beginning at 7334 Å and increasing in strength from late M-type stars. |
| 7437 | CN | |
| 7590 | TiO | Blended into the O2 A-band. |
| 7594 | O2 A-band | Fraunhofer A-line. A telluric absorption feature. |
| 7628 | TiO | Several TiO bands follow on from 7666 Å, creating a wide depression in the region immediately following the telluric. |
| O2 feature. Seen in M-type stars of all luminosities. First seen around M2 becoming very pronounced by mid-M. | ||
| 7861 | TiO | |
| 7876 | CN | Several CN bands follow on from 7876 Å. Obvious in supergiants, weaker in giants; not seen in dwarfs. |
| 8026 | CN | Several CN bands follow on from 8026 Å. Obvious in supergiants, weaker in giants; not seen in dwarfs. |
| 8183 | Na I | Strong in dwarf stars. |
| 8195 | Na I | As above. |
| 8227 | H2O | Weak telluric feature. Degraded to the red. |
| 8498 | Ca II | Strongest in late K-type through mid M-type stars; strongest in giants and super giants; weaker in dwarfs. |
| 8542 | Ca II | As above. |
| 8662 | Ca II | As above. |
Notes. The wavelengths of some of the major telluric features seen in our spectra are also listed. The most important of these features have been marked on the spectra. Comments are included, where relevant, from the work of Turnshek et al. (1985), Kirkpatrick et al. (1991) and our own observations. Also included are the wavelengths of some important emission lines seen in some of our spectra.
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