466 MASSES OF VISUAL P.INARV STARS. 



Stars so faint as 9.68 magnitude have been followed up as double 

 Stars. But if this binary was only one of many to be found at 

 varying distances then it has no rejM-esentatives amongst stars 

 brighter than itself. We may therefore conclude that it is an 

 exceptional pair, like other pairs found in proximity to a bright 

 star. (See, for examples, Oo Eridanus and a Bootes in Table i.) 

 It would seem from from these cases, and the faint companions 

 to Sirius and Procyon, that the j^roximity of a bright star in a 

 binar}^ or ternary system has some ])ower of inhibiting the emis- 

 sion of light in its attendants. 



Alderaran.— iWa_i7;;/7//^t^ 1.06. Spcttniiii I\2. 



This bright star has a 13.5 magnitude companion at a dis- 

 tance of 31". 2, which is travelling with it through space with an 

 annual velocity of o".i88 (Auwers), but since 1877, the year of 

 its discovery by Burnham. up to the last measures made there 

 has been no relative change of lueasurable amount. 



According to Elkin, the iiarallax of Aldebaran is o".ii, 

 giving as its radial 9. If we can assume that the companion is at 

 its mean distance, and assume its radius vector is inclined (yo° 

 to the tangent plane, its semiaxis major is of the order of ^zy 

 units. The Sun would compel a body at this distance to revolve 

 around it in about 6,000 years, making an angular change of 

 about i^° in 28 years. It is certain that the companion of 

 Aldebaran has not changed by that amount, and therefore the 

 period of revolution is longer, and consequently the mass of 

 Aldebaran smaller, than that of the Sun. A star with so strong 

 an absorbing atmosphere as is indicated by the spectrum K2, loses 

 probably i .06 magnitudes at least as compared with a solar tyjie 

 star. I,et us consider this assumption for a moment. It would 

 mean that the distance of Aldebaran is only one radial. At such 

 a distance the gravitative power of the Sun would force a planet 

 at the distance of Aldebaran's companion to move over 2° a year, 

 or about 50 degrees in 28 years. As no such change occurs, it is 

 evident that Aldebaran is not similar to the Sun in gravitative 

 power. Besides this, the Sun at 9 radials distance would only 

 shine as a star of the 1.56 magnitude, or ]/> a magnitude fainter 

 than Aldebaran, in spite of the latter having a strongly absorbent 

 atmosphere. 



Again, let us assume that Aldebaran is more distant than its 

 measured parallax indicate. Let us suppose it is 100 radials 

 away. The Sun at such a distance would shine like a loth mag- 

 nitude star. At this distance its gravitative power upon a com- 

 panion so distance as 3] ".2 would be insignificant, and therefore 

 comparable with Aldebaran's. But allowing for absorption, this 

 would mean that Aldebaran has 25,000 times the Sun's mass, 

 and that the comj^anion moves through about 10° in 28 years — 

 so that this assumption must also be dismissed. 



Thus we are involved in contradictions every way, and we 

 can only escape from them by acknowledging that Aldebaran 



