A very remarkable variable star has been recently discovered in the constellation Auriga. Prof. Hartwig found it of the 9th magnitude on March 6, 1908, the star “having increased four magnitudes in one day, whilst within eight days it was less than the 14th magnitude.”[324] In other words its light increased at least one-hundredfold in eight days!
The period of the well-known variable star β Lyræ seems to be slowly increasing. This Dr. Roberts (of South Africa) considers to be due to the component stars slowly receding from each other. He finds that “a very slight increase of one-thousandth part of the radius of the orbit would account for the augmentation in time, 30m in a century.” According to the theory of stellar evolution the lengthening of the period of revolution of a binary star would be due to the “drag” caused by the tides formed by each component on the other.[325]
M. Sebastian Albrecht finds that in the short-period variable star known as T Vulpeculæ (and other variables of this class, such as Y Ophiuchi), there can be no eclipse to explain the variation of light (as in the case of Algol). The star is a spectroscopic binary, it is true, but the maximum of light coincides with the greatest velocity of approach in the line of sight, and the minimum with the greatest velocity of recession. Thus the light curve and the spectroscopic velocity curve are very similar in shape, but one is like the other turned upside down. “That is, the two curves have a very close correspondence in phase in addition to correspondence of shape and period.”[326]
The star now known as W Ursæ Majoris (the variability of which was discovered by Müller and Kempf in 1902), and which lies between the stars θ and υ of that constellation, has the marvellously short period of 4 hours (from maximum to maximum). Messrs. Jordan and Parkhurst (U.S.A.), find from photographic plates that the star varies from 7·24 to 8·17 magnitude.[327] The light at maximum is, therefore, more than double the light at minimum. A sun which loses more than half its light and recovers it again in the short period of 4 hours is certainly a curious and wonderful object.
In contrast with the above, the same astronomers have discovered a star in Perseus which seems to vary from about the 6th to the 7th magnitude in the very long period of 7½ years! It is now known as X Persei, and its position for 1900 is R.A. 3h 49m 8s, Dec. N. 30° 46′, or about one degree south-east of the star ζ Persei. It seems to be a variable of the Algol type, as the star remained constant in light at about the 6th magnitude from 1887 to 1891. It then began to fade, and on December 1, 1897, it was reduced to about the 7th magnitude.
On the night of August 20, 1886, Prof. Colbert, of Chicago, noticed that the star ζ Cassiopeiæ increased in brightness “by quite half a magnitude, and about half an hour afterwards began to return to its normal magnitude.”[328] This curious outburst of light in a star usually constant in brightness is (if true) a very unusual phenomenon. But a somewhat similar fluctuation of light is recorded by the famous German astronomer Heis. On September 26, 1850, he noted that the star “ζ Lyræ became, for a moment, very bright, and then again faint.” (The words in his original observing book are: “ζ Lyræ wurde einen Moment sehr hell und hierauf wieder dunkel.”) As Heis was a remarkably accurate observer of star brightness, the above remark deserves the highest confidence.[329]
The variable star known as the V Delphini was found to be invisible in the great 40-inch telescope of the Yerkes Observatory on July 20, 1900. Its magnitude was, therefore, below the 17th. At its maximum brightness it is about 7½, or easily visible in an ordinary opera-glass, so that its range of variation is nearly, or quite, ten magnitudes. That is, its light at maximum is about 10,000 times its light at minimum. That a sun should vary in light to this enormous extent is certainly a wonderful fact. A variable discovered by Ceraski (and numbered 7579 in Chandlers’ Catalogue) “had passed below the limit of the 40-inch in June, 1900, and was, therefore, not brighter than 17 mag.”[330]
The late Sir C. E. Peck and his assistant, Mr. Grover, made many valuable observations of variable stars at the Rousden Observatory during many years past. Among other interesting things noted, Peck sometimes saw faint stars in the field of view of his telescope which were at other times invisible for many months, and he suggested that these are faint variable stars with a range of brightness from the 13th to the 20th magnitude. He adds, “Here there is a practically unemployed field for the largest telescopes.” Considering the enormous number of faint stars visible on stellar photographs the number of undiscovered variable stars must be very large.
Admiral Smyth describes a small star near β Leonis, about 5′ distant, of about 8th magnitude, and dull red. In 1864 Mr. Knott measured a faint star close to Smyth’s position, but estimated it only 11·6 magnitude. The Admiral’s star would thereupon seem to be variable.[331]
The famous variable star η Argus, which Sir John Herschel, when at the Cape of Good Hope in 1838, saw involved in dense nebulosity, was in April, 1869, “seen on the bare sky,” with the great Melbourne telescope, “the nebula having disappeared for some distance round it.” Other changes were noticed in this remarkable nebula. The Melbourne observers saw “three times as many stars as were seen by Herschel.” But of course their telescope is much larger—48 inches aperture, compared with Herschel’s 20 inches.