+--------------+----------+-------------+ | Star |Luminosity|Diameter (in | | | |terms of sun)| +--------------+----------+-------------+ |Sirius _A_ | 26·3 | 1·58 | |Procyon _A_ | 5·5 | 1·80 | |α Centauri _A_| 1·12 | 1·07 | |Sun | 1·00 | 1·00 | |α Centauri _B_| 0·32 | 1·22 | |τ Ceti | 0·32 | 0·95 | |ε Indi | 0·15 | 0·82 | |Kruger 60 _A_ | 0·0026 | 0·33 | | ” _B_ | 0·0007 | 0·17 | |Wolf 359 | 0·00002 | 0·03 | +--------------+----------+-------------+ This table shews clearly how stellar luminosity and diameter decrease together as we pass down the main-sequence. The remaining group of stars in fig. 22, those in the bottom left-hand corner, are generally known as “white dwarfs.” Their position in the diagram shews that their diameters must be excessively small. The vicinity of the sun provides three examples of this class of star, as shewn in the following table: +-------------------+-------------+-----------------+ | Star | Luminosity | Diameter (in | | | | terms of sun) | +-------------------+-------------+-----------------+ | Sirius _B_ | 0·0026 | 0·03 | | ο₂ Eridani _B_ | 0·0031 | 0·018 | | van Maanen’s star | 0·00016 | 0·009 | +-------------------+-------------+-----------------+ In addition to these, the faint companion of ο Ceti is certainly a white dwarf, while Procyon _B_ may be. These are the only known examples of white dwarfs, but the extreme faintness of these stars makes them very difficult of detection, so that it is quite likely that they are fairly frequent objects in space. In the table on p. 279, the main-sequence stars were intended to be arranged in the order of luminosity, but this happens also to be the order of weights. The weights of three of the stars are unknown; those of the remainder are as follows: +-------------------+-------------+-----------------+ | Star | Luminosity | Weight (in | | | | terms of sun) | +-------------------+-------------+-----------------+ | Sirius _A_ | 26·3 | 2·45 | | Procyon _A_ | 5·5 | 1·24 | | α Centauri _A_ | 1·12 | 1·14 | | Sun | 1·00 | 1·00 | | α Centauri _B_ | 0·32 | 0·97 | | Kruger 60 _A_ | 0·0026 | 0·25 | | ” _B_ | 0·0007 | 0·20 | +-------------------+-------------+-----------------+ Like the luminosities, the weights fall off steadily as we pass down the main-sequence, although, as already remarked, weight falls far less rapidly than luminosity.