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.