58 
The Light from the Stars [ch. ii 
and 155 radii of the sun, and the distance between their centres being 40T 
radii of the sun, so that their closest points are only 0'8 radii of the sun apart. 
V Puppis. This is a spectroscopic and eclipsing binary whose elements 
are well determined. Both components have spectral type B 1, and Plaskett 
assigns an effective temperature 22,000 degrees to both. The masses are 19*2 
and 17‘9 times the mass of the sun, and the absolute bolometric magnitudes 
are - 5’26 and — 505, so that the emission of radiation of the two components 
are 11,000 and 9100 times that of the sun respectively. 
Sirius (a Canis Majoris), the brightest star in the sky, is a visual binary 
with a period of 49‘3 years. 
Its brighter component is of spectral type A 0; Sampson and Abbott have 
determined effective temperatures of 12,800 and 11,000 respectively, while 
its colour-index indicates an effective temperature of 11,200. Assuming an 
effective temperature of 11,200, its absolute bolometric magnitude is 0’9. Its 
diameter is then T58 times that of the sun, its mass being 245 times that 
of the sun, so that its mean density is 0 - 9. 
The faint companion is of absolute visual magnitude 11*3. Moore finds its 
spectral type to be A 5, or possibly A 3 or A 4. Its mass is about 0 85 times the 
mass of the sun. The ratio of mass to radius, as determined by the Einstein 
shift of spectral lines, fixes its radius as 0030 times that of the sun; hence 
its mean density must be about 50,000. Its bolometric absolute magnitude 
must be approximately the same as its absolute visual magnitude, and its 
total emission of radiation must be 0‘0028 times that of the sun. Com 
bining this with its known size, we can deduce an effective temperature 
of 8000°. This corresponds to a spectral type of about A 7, in agreement 
with Adams’ determination. 
Kruger 60 This is a visual binary of period 54’9 years. Its two com 
ponents are the least massive of all stars whose masses are known with fair 
accuracy. 
The brighter component has a mass equal to 025 times that of the sun. 
Its spectral type M3 corresponds to an effective temperature of about 3200. 
This gives it an absolute bolometric magnitude of 100, so that its emission 
of radiation is 0‘009 times that of the sun. Its radius must accordingly be 
one-third of that of the sun, and its mean density about 10 . 
The fainter component has a mass equal to 020 times that of the sun, 
its spectral type and effective temperature being approximately the same as 
those of its companion. Its absolute bolometric magnitude is 1T5, so that it 
has an emission of radiation equal to 0‘002 times that of the sun, and a radius 
equal to one-sixth that of the sun. Its mean density is accordingly about 60. 
The foregoing data, together with some others, estimated and calculated 
by similar methods, are collected in the following table: 
* Aitken, Lick Observ. Bull. 365 (1925).