Abstract
MB. O. R. WALKEY has investigated the distance of Canopus (α Carinee) by a new line of approach (J. Brit. Ast. Assoc., 58, No. 6 ; 1948). The results obtained for this star vary considerably, some of the derived parallaxes being more than five times those of others. Mr. Walkey approaches the problem from the secular parallax of the star, a star's proper motion being frequently a fair criterion of its distance, and the radial velocity of Canopus provides a clue in the present case. Accepting results he has obtained for the apex of the solar motion (Man. Not. Roy. Ast. Soc., 106, No. 4 ; 1946) and also for the velocity of the sun, the antapex of this motion, R.A. 90·2°, Dec. –28·7°, is just 24° north of Canopus, and as the recessional radial velocity of the star is 20·8 km./sec., we may regard it as stationary within the velocity framework. The proper motion of Canopus in R.A. is given as 0·0020s ± 0·0012s in G.C., and the large probable error in R.A. should, Mr. Walkey thinks, warrant the simplicity of considering the motion in declination alone in the investigation. This is 0·017" ± 0· 0015" towards the solar antapex, and applying the correction for galactic rotation it becomes 0-0126" ± 0-0015". If this represents the crosswise reflex of the sun's motion from the antapex, the absolute parallax of Canopus is 0·0071" ± 0·00009". Adopting a final parallax of 0·007" or a distance of 460 light-years, the absolute magnitude of the star is –6·6. It is significant that this distance finds confirmation in Charlier's determination of the distance of the centre of the brighter B-type stars lying in Carina (Medd. Lund., Series ii, 14 ; 1916. 34; 1926). The revised and higher luminosity basis, of one magnitude brighter than that used by Charlier for the given B stars, places their centre at a distance represented by a parallax of 0·0072".
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Distance of Canopus. Nature 162, 989 (1948). https://doi.org/10.1038/162989d0
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DOI: https://doi.org/10.1038/162989d0