82 



KNOWLEDGE & SCIENTIFIC NEWS. 



[April, 1905. 



0.5102, or a total surface of 0.7126. Now the mass of 

 Sirius being 2.36, its relative surface would be— if of 

 the same density as Castor — 1.7726. Hence the sur- 

 face of Sirius would be 2.487 times that of the com- 

 bined surfaces of Castor's lucid components. But 

 Sirius is 3.16 magnitudes {i.5Si-i.5Sj brighter than 

 Castor. From these data I find that the parallax of 

 Castor would be about o'/. 136, which docs not differ 

 widely from the result found by Johnson. The brighter 

 component of this interesting pair has recently been 

 found at the Lick Observatory to be also a spectro- 

 scopic binary, but the period lias not yet been deter- 

 mined. The fact that bolh components are spectro- 

 scopic binaries makes Castor one of the most 

 remarkable objects in the heavens. 



For * Equulei, a binary star with the very short 

 period of 5.7 years, Hussey finds from spectroscopic 

 measures a parallax of ©".O/i, and a combined mass of 

 1.89 times the sun's mass. He says, " The com- 

 ponents of the pair are slightly unequal in brightness, 

 and, perhaps, also in mass. One may be as massive 

 as the sun, but it cannot much exceed it."* The 

 parallax found by Hussey would, I find, reduce the 

 sun to a star of 5.81 magnitude, and as the photo- 

 metric magnitude of * Equulei is 4.61, we have the 

 star 1.20 magnitude, or three times brighter than the 

 sun. Assuming that the masses of the components are 

 1. 00 and 0.89 (as suggested by Hussey), I find that if 

 the surface luminosity of each were equal to that of 

 the sun, the combined light of the two components 

 would be 1.9247, or nearly twice the sun's light. The 

 star's spectrum is of the type F, probably indicating a 

 somewhat brighter sun than ours. The difference in 

 the results found above is, therefore, not inconsistent 

 with the parallax found by Hussey. A comparison with 

 Procyon is also confirmatory of Hussey's result. 



Let us now consider the case of the bright star 

 Procyon, which has a spectrum F 5 G, or intermediate 

 between that or Equulei and the sun. The parallax 

 is about o''.32s, and the mass of the system is, there- 

 fore, from Dr. See's orbit of the satellite, 3. 627 times 

 the sun's mass, that of the bright star being about 

 three times the mass of the sun. At the distance 

 indicated by the parallax the sun would, I find, be 

 reduced to a star of 2.51 magnitude, and as the magni- 

 tude of Procyon is 0.48, we have the star 2.03 magni- 

 tude, or 6.487 times brighter than the sun. As, 

 however, the mass of Procyon is three times the sun's 

 mass, the star should be— if of the same densitv and 

 surface luminosity, 2.08 times brighter than the' sun. 

 Hence it follows that Procyon is really ';',"' or 3.1 

 times brighter than our sun in proportion to its mass. 

 This may be due either to a larger size, and, there- 

 fore, less density than the sun, or to a greater 

 luminosity of surface per unit of area. Probably both 

 causes combine to produce the increased brilliancy, 

 and the result seems to agree well with the star's 

 spectrum, which probably indicates a slightly more 

 luminous sun than ours. 



fhc binary star 70 Ophiuchi has a spectrum inter- 

 mediate between the .second and third types (K, Picker- 

 ing), probably indicating a rather fainter bodv than our 

 sun. An orbit computed by f)r. See, combined with a 

 parallax of oH.ift found by Schur, gives a combined 

 ma.ss of 2.94 times the sun's mass. This parallax 

 would reduce the sun to a star of about 4.05 magni- 

 tude, and as the photometric magnitude of 70 

 Ophiuchi is 4.07, the star is about equal to the sun in 



'Aslr,:hliv:ii-,il /..,/im,i/ |i>nf. ,,.^, 



brightness. But as the star's mass is 2.94 times the 

 sun's mass, the star should be, if exactly comparable 

 with the sun, about twice as bright. Hence it would 

 follow that the surface luminosity of the star is less 

 than that of the sun — about one-half, and the spectrum 

 indicates that this is probably the case. 



Let us now consider the case of the " Algol vari- 

 ables." r'or .Mgol itself, \'ogel found from spectro- 

 scopic observations the diameter of the bright star to 

 be 1,074,000 miles, with a mass of 4-9ths of the sun's 

 mass, and for the " dark " companion a diameter of 

 840,600 miles and a mass of 2-9ths of the solar mass. 

 This result was obtained on the assumption that both 

 components are of equal density — about one-third that 

 of water. But that a dark body of such large size 

 should have the same density as a bright body, like 

 Algol itself, seems highly improbable. The density of 

 the planet Jupiter — which has some inherent heat of its 

 own — is about 1.30, and that of Saturn about 0.68. 

 We should, therefore, expect that a large body, like 

 the companion of Algol, would have a considerable 

 amount of inherent light, or surface luminosity. Let 

 us see what brightness it could have without sensibly 

 affecting the obser\ed light variation of .Algol. That 

 is, what is the maximum brightness which the com- 

 panion might have without producing a secondary 

 minimum of light when hidden behind the disc of the 

 bright star? Chandler finds for Algol a parallax of 

 o'i.o-,. The sun placed at the distance indicated by this 

 small parallax would be reduced to the light of a star 

 of 5.84 magnitude, and the photometric magnitude of 

 Algol being 2.31, it would be 3.53 magnitude, or nearly 

 26 times brighter than the sun. Let us assume that 

 the companion has this magnitude of 5.84 — which it 

 might have without the spectroscope showing it. Then 

 when in the course of its orbital revolution round Algol 

 it is hidden behind the bright star, the normal light of 

 .\lgol would be reduced by its 27th part. This means 

 that the light of Algol would be diminished by about 

 0.04 magnitude, or from 2.31 to 2.35, a difference 

 which would not be perceptible to the naked eye, and 

 could hardly be detected with certainty by even the 

 most delicate photometer. The spectrum of Algol is, 

 according to Pickering, B 8 .\, that of Sirius being A. 

 Comparing the two stars, and assuming the surface 

 luminosity to be the same, I find a parallax of o'.'. 1 1 for 

 Algol. This would reduce the sun to a star of 4.84 

 magnitude, and if we suppose the companion to have 

 this brightness, then .Mgol would be about 10 times 

 brighter than its companion, and when the latter is 

 hidden behind the brighter star, the light of Algol 

 would be reduced from about 2.31 to 2.41, and even 

 this difference could hardly be determined with cer- 

 tainty. It would seem probable, therefore, that the 

 companion of Algol has some inherent light of its own, 

 and is not quite a " dark body." -Assuming a parallax 

 'of o".o7, I find that the surface luminosity of Algol 

 itself would be 17 times that of the sun. 



In the Algol system the components are separated 

 by a distance of o\er two millions of miles (between 

 their surfaces), but in some of the " Algol variables " 

 the components revolve in contact, or nearly so. .Some 

 have both components bright. Examples of this type 

 of variation are P Lyr;c, U Pegasi, V Puppis, X 

 Carinae, and RR Centauri. The characteristics of 

 the light fluctuations are, according to Dr. A. W. 



• It has been recently found thai a difference in brighlncss of 

 two maRniludes between the components of a spectroscopic 

 binary is sufficient to obliterate the spectrum of tlic fainter 

 component. 



