A New Eclipsing Variable of Large Mass.
Sergei I. Gaposchkin · The Astrophysical Journal · 1939
More than a thousand photographic observations of the new eclipsing variable HD 163181 = IIV 7868 = Boss 4520 have been secured from Harvard plates. The light-curve shows slight indications of effipticity; the minima are well defined, and both are of greater depth than O~4, so that the photometric relative elements may be regarded as of considerable precision. The velocity-curve published in 1928 by Humason and Nicholson refers to the star that is in front during the primary minimum: it is slightly the larger, slightly the brighter, and slightly the more massive of the two components. There is an indication of a slow apsidal motion. A photovisual light-curve based on 87 observations confirms the variability and the range. The star is much redder than would be expected from its spectrum (Harvard, Oe; Mount Wilson, Bie; Lick, Bo); the mean color excess is +°~57. The principal results obtained are as follows: P = I2~0o42; i = 88~4; k2,1 = O.917 = 5.710; 72 = 5.230; JJ.i = 44.380; ~2 = 40.820; p~ = 0.230; P2 0.280; L1 = 0.54; 7 = i.o~; b/a = 0.985. The star is unique in that its mass is of the same order as that of AO Cassiopeiae or UW Canis Majoris, but the radii are much smaller, being similar to those of the com- ponents of Y Cygni. The spectra of all four stars are practically the same. The mass of the heavier component of HD 163181 is about equal to that of the red supergiant component of VV Cephei (44.50), but the radius is 420 times smaller than the radius of that star