Our Astronomical Column

Abstract

DOUBLE-STARS.—An important series of observations of double-stars has been recently issued from the United States Naval Observatory at Washington. It includes all the measures made by Prof. Hall with the 26-inch refractor from 1875 to 1880, and a few in the year 1863 with the 9.6-inch equatorial. There are observations of double-stars selected by M. Otto Struve for the comparison of micrometrical measurements by different astronomers, which remain for discussion when those of other observers are published. In addition, in order to apply a geometrical test to the observations, Prof. Hall has carefully measured the multiple stars ∑ 2703 and 311, and the stars in the trapezium of Orion. The observations have been made with the filar-micrometer by A. Clark and Sons, which is commonly, used with the large equatorial. Then follow measures of objects chiefly taken from the catalogues of the Struves, with a few others mostly discovered by Mr. Burnham. ∑ 2 was not separated with power 888 in 1879. Of γ2 Andromedæ we find the angle 101°.0 distance 0″.358 for 1878.21; 40 Eridani (B.C.), 125°.0, 3″.515 for 1879.18. A great change is shown in O.∑.82; we have 230°.8, 1″.08 for 1848.67, while Prof. Hall's measures give 182°.25, 0″765 for 1879.16. Mr. Marth's faint companion of Sirius, estimated 13m., was at 114°.9, 7l″.4, at the epoch 1847.47, which, compared with the particulars at p. 38 of Memoirs R.A.S., vol. 36, indicates fixity. Prof. Hall remarks on the supposed companions of Procyon, “I have never been able to see any of these companions that would stand the test of sliding and changing the eyepiece, turning the micrometer, &c., and am therefore doubtful of their existence. This is an interesting star for the powerful telescopes of the future.” Six nights' measures of 25 Canum Venat. give 157°.5, 0″.507 for 1879.49; Dr. Doberck has calculated elements for this star, period 1241/2) years. γ Coronse Borealis was single in 1875–76 and 1879. 72 Ophiuchi was examined in 1876 and 1879, but no close companion was visible: it may be remembered that at the epoch 1859.61 Secchi saw and measured the close star, and recorded it as “bene separata,” and Otto Struve has measures of it in 1842, 1847, 1851, and 1876, those in the latter year corresponding almost precisely to the date of the Washington examinations, which seems to point to optical illusion, unless rapid variability is admitted. At the epoch 1879.77 δ Equulei was thought to be elongated at 150°, but Prof. Hall was not certain of its duplicity. Many of the more interesting binaries are included in this series of measures. The observations of the companion of Sirius made at Washington from 1866 to 1879 are given in a collective form, and we have observations of the faint stars near the annular nebula in Lyra, of which the following results possess value; a is the brightest of these stars and the one near the following end of the nebula; the angles and distances are referred to it except in the case of the companion of the triple star f which are referred to f itself:—