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35. The M Stars

Discussion of the M dwarfs is outside the range of the present Atlas. Since no stars have been observed intermediate between M dwarfs and giants, the latter can be considered separately.

Plate 51. The M Giant Sequence
Plate 51
High resolution image

The titanium oxide bands in the photographic region increase smoothly in intensity with decreasing temperature, and spectral classification from the intensity of the bands is a temperature classification (Pl.52). The four stars illustrated in Plate 51 as standards of the M-giant sequence are on the Mount Wilson system. We are greatly indebted to Dr. Joy for checking our types at Mount Wilson. He has noted that some M stars probably vary slightly in spectral type, so that some of the standards illustrated may have a slightly different appearance at times.

Plate 52. The M Sequence as a Temperature Sequence
Plate 52
High resolution image

The absolute magnitudes of some of the giant M stars have been discussed recently by Keenan, (1) and the details of the luminosity classification are given there. Keenan's spectral types require systematic corrections to reduce them to the Mount Wilson system. Some luminosity effects in the early M giants are illustrated in Plate 53.

Table 30 gives a selection of stars whose luminosity classes have been taken from Keenan`s paper. The spectral types are from the Mount Wilson catalogue of spectroscopic parallaxes. Luminosity line ratios are lambda 4045: lambda 4077, lambda 4215: lambda 4250, lambda 4376: lambda 4383 and lambda 4383: lambda 4390.


Star MKK a delta m HD Notes

RW Cep . M0: Ia 22:19 +55°27' 6.2-7.6* Ma 1
µ Cep .... M2 Ia 21:40 +58 19 4.4* Ma
SU Per ... M4 Ia-Ib 02:15 +56 09 7.3* Ma
a Ori ...... M2 Ib 05:49 +07 23 0.9* Ma
a Sco ...... M1 Ib 16:23 -26 13 1.2 Ma
5 Lac ...... M0 II 22:25 +47 12 4.6 K0
pi Aur ..... M3 II 05:52 +45 56 4.6 Ma
beta Peg ..... M2 II-III 22:58 +27 32 2.6* Ma
chi Peg ..... M2 III 00:09 +19 39 4.9 Ma
beta And .... M0 III 01:04 +35 05 2.4 Ma
eta Gem .... M3 III 06:08 +22 32 3.7* Ma

1. The spectrum indicates that the absolute magnitude is brighter than µ Cep. Spectral type by Keenan.
* Light variable.

Plate 54. A Carbon Star and a Long Period Variable
Plate 54
High resolution image

Plate 55. The Banded Stars in the Visual Region
Plate 55
High resolution image

1 Ap. J., 95, 461, 1942. Back.

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