254 
IONISATION, DIFFUSION, ROTATION 
The adoption of a mean value must necessarily be a matter of judgment. 
Having regard to the rarity of the elements heavier than Ag and the 
cosmical abundance of Fe and some lighter elements we have adopted 21. 
We do not think this is likely to be in error by as much as 0-2. 
177. We next seek to obtain an idea of the variation of ¡/^ in stars of 
different mass and spectral type. Since 
/xT 3 = 35K (1 - j8) 
P ~ afi 
we have from (174*2) 
0-4343 fa/RT = 14*1182 - log /8/(1 - /3) - ■§ log T. 
For stars of the main series the central temperature is approximately 
40 million degrees. We shall calculate the ionisation conditions at a point 
where the temperature is 26 million degrees in accordance with § 94. 
Making use of Table 23 the results are— 
Table 31 a. 
Ionisation in Stars of the Main Series. 
1-/3 
Mass 
T, 
'I'JRT 
Ax 
Examples 
•002 
•182 
2600 
0-69 
8-0 
Faintest red dwarfs 
•004 
•258 
3200 
1-40 
3-9 
Krueger 60 
•015 
•512 
4600 
2-72 
2-0 
•05 
1-00 
6300 
3-96 
1-4 
Sun 
•10 
1-58 
8200 
4-71 
1-2 
Procyon 
•18 
2-56 
10500 
5-40 
1-0 
Sirius 
•30 
•50 
4-53 
11-46 
13300 
17500 
6-07 
6-92 
0-9 
0-8 
| Eclipsing variables 
•80 
90-6 
26000 
8-31 
0-7 
Plaskett’s star 
Table 31 b contains some examples of giant stars also calculated for 
a point where the temperature is § of the central temperature. 
Table 31 b. 
Ionisation in Giant Stars. 
1-/8 
Mass 
T e 
10-6 y 
HRT 
Ax 
Examples 
•283 
4-18 
5200 
6-06 
8-17 
2-9 
Capella 
•283 
4-18 
3000 
2-51 
9-49 
6-0 
•50 
11-46 
5200 
3-73 
9-84 
3-9 
Cepheids 
•50 
11-46 
3000 
1-55 
11-16 
8-3 
•75 
56-15 
3000 
0-92 
13-03 
11-9 
Betelgeuse 
The stars given under the heading “Examples” do not accurately 
correspond to the data of mass and T e but will call to mind the kind of 
star to which the tabulated results relate.