Abstract
DOUBLE STARS.—In Gilliss's catalogue of 290 double stars formed from observations made at Santiago, Chile, during the U.S. Astronomical Expedition in the years 1850-52, the conspicuous star a Eridani (Achernar), is reported to have been seen double, the companion being of the seventh magnitude, faint blue, and preceding, 3″south. We look in vain for mention of this companion-star in the observations of Herschel, Jacob, and Powell, and it is especially strange that it should not have been detected by the former during his sweeps with the 2O-feet reflector at the Cape. The well-known binary p Eridani is less than 2° distant, consisting of two nearly equal components of between the sixth and seventh magnitude, and at first sight it might be inferred that by a typographical error the name of the star is wrongly given by Gilliss. His position, however, is that of a Eridani, and further we happen to possess measures of p Eridani by Jacob, at the precise epoch of the Santiago observation 1850.79, giving for the angle 268°.7, and distance 4″.32; the comes therefore could hardly be described as preceding, 3″ south, but might rather be said to precede on the parallel. This would indicate that the star intended is really Achernar, and it must be left for further observation to decide upon the accuracy or otherwise of the statement made by Gilliss. If the companion exists it would be of interest to know its present position; the proper motion of the principal star is very insignificant, and marked difference from Gilliss's description would be suspicious as showingabinary character. Still it is to be observed that there are considerable discordances between the angles and distances of many of the stars in the Santiago catalogue and those in Her-schel's Cape volume. The former are not the results of actual micrometrical measures. It is stated that the catalogue was formed by plotting, on a large scale, the differences of right ascension and declination of the components of the double-stars observed with the transit-circle (4½ inches aperture), and then measuring from the drawings the angles of position and distances. In most cases the right ascensions and declinations observed are given in the preceding catalogue of 1,963 stars, and the results of the graphical process can be verified by calculation. In looking through the list of double-stars the reader will note differences from Herschel's data, which are not always easily explained by possible motion, though, as some of the stars have not been properly measured since Herschel's epoch, there will remain a doubt as to the cause of these differences. As instances in point, we may mention the following numbers of the Cape catalogue:—3860, 3966, 4119, 4281, 4538, 4667, and 4770. Probably Mr. Ellery at Melbourne, or Mr. Todd at Adelaide—both of whom are understood to be partially occupied with measures of the southern double-stars—may eventually clear up the uncertainties which characterise the results published by Gilliss.
Article PDF
Rights and permissions
About this article
Cite this article
OUR ASTRONOMICAL COLUMN . Nature 18, 334–335 (1878). https://doi.org/10.1038/018334b0
Issue Date:
DOI: https://doi.org/10.1038/018334b0