The Discovery of the Companion of Sirius and its Aftermath

The extreme subluminous nature of white dwarfs first came to the attention of H. N. Russell in 1910, when he learned of the ‘A’ spectral type of the faint companion to 40 Eri (see H. N. Russell, “Notes of white dwarfs and small companions”, Astronomical journal, li (1944), 1944–17, p. 13). It is 40 Eri B that is the conspicuously isolated outlier in the lower left-hand corner of Russell's 1913 ‘Russell Diagram’ (H. N. Russell, “Relations between the spectra and other characteristics of the stars”, Popular astronomy, xxii (1914), 1914–351, p. 285). This star was soon joined by Sirius B in 1915 when W. S. Adams at Mt Wilson succeeded obtaining a spectrum of Sirius B and pronounced it an ‘A’ star (W. S. Adams, “The spectrum of the companion of Sirius”, Publications of the Astronomical Society of the Pacific, xxvii (1915), 1915–7). At that point it became clear that 40 Eri B was not an isolated fluke, but along with Sirius B, was a nearby representative of a totally new class of star.

The suggestion of measuring the gravitational redshift of Sirius B was made by Arthur Eddington in a 1924 letter to W. S. Adams (Vibert A. Douglas, The life of Arthur Stanley Eddington (London, 1957), 75). Adams published his measurements in 1925 (W. S. Adams, “The relativity displacement of spectral lines in the companion of Sirius”, Proceedings of the National Academy of Sciences, xi (1925), 1925–7). Although long regarded as a third conformational test of General Relativity, it is now known that both Eddington's theoretical calculations of size of the redshift and Adams's measurement of it, were too low by a factor of four. (For a discussion of this issue see Hetherington Norris , “Sirius B and the gravitational redshift: An historical review”, Quarterly journal of the Royal Astronomical Society, xxi (1980), 1980–52).

Up until the late 1930s Sirius B was the only white dwarf for which a reliable mass was known. Eddington first called attention to the extreme density of Sirius B in 1924 (A. Eddington, “On the relation between the masses and luminosities of the stars”, Monthly notices of the Royal Astronomical Society, lxxxvi (1924), 1924–32, p. 322) and attributed the high density and small radius of the star to the complete ionization of the interior matter. He also noted such stars were thermodynamically problematic. The white dwarf problem was apparently resolved in 1926 when Ralph Fowler (R. H. Fowler, “On dense matter”, Monthly notices of the Royal Astronomical Society, lxxxvii (1926), 1926–22) published his equation of state for nonrelativistic degenerate matter. However, Chandrasekhar's 1930 relativistic equation of state, and the resulting Chandrasekhar limit, reopened the problem of the stability of white dwarfs' having masses above a certain limit. The relativistic equation of state and the limiting mass are at the origin of the dispute between Eddington and Chandrasekhar that came to a head in 1935 (see K. C. Wali, Chandra: A biography of S. Chandrasekhar (Chicago, 1991)).

Bessel Friedrich Wilhelm , “On the variation of proper motions of Procyon and Sirius”, Monthly notices of the Royal Astronomy Society, vi (1844), 136–44.

Peters Christian A. F. , “Ueber die eigene Bewegung des Sirius”, Astronomische Nachrichten, xxxii (1851), cols 1–58.

Safford Truman Henry , “On the proper motions of Sirius in declination”, Astronomical notices, xxviii (1862), 25–32.

Safford Truman Henry , “On the proper motions of Sirius in declination”, Monthly notices of the Royal Astronomical Society, xxii (1862), 1862–7.

Auwers Arthur , “On the irregularities of the proper motion of Sirius”, Monthly notices of the Royal Astronomical Society, xxii (1862), 1862–50.

Deborah Jean Warner and Robert B. Arial, Alvan Clark & Sons, artists in optics, 2nd edn (Richmond, VA, 1995).

At the time the world's largest refractors were the two 15-inch telescopes constructed by the Metz & Mahler firm of Munich for the Pulkovo Observatory near St Petersburg, and the ‘Great Refractor’ at Harvard College Observatory. The American Civil War effectively ended the plans of the University of Mississippi for the 181/2-inch. The completed telescope was acquired by the Chicago Astronomical Society in 1863. The lens is still in service at the Dearborn Observatory in Evanston, Illinois, while the original wooden telescope tube is on display at the Adler Planetarium in Chicago.

Newcomb Simon , “The story of a telescope”, Scribners monthly, November 1873, 44–55, p. 47.

“Log book for 1862 (no. 199) of the 15-inch Equatorial”, Harvard College Observatory.

“Log book for 1862” (ref. 12), 18 Feb. 1862.

Bond George P. , “On the companion of Sirius”, American journal of science, xxxiii (1862), 286–7.

Bond George P. , “On the companion of Sirius”, Astronomische Nachrichten, lvii (1862), cols 131–4. Bond published a second paper in the summer of 1862 including all of his observations of Sirius's companion, among them the initial 7 February confirmation observation. Bond George P. , “Letter to Editor”, Astronomische Nachrichten, lviii (1862), cols 85–90.

Rutherfurd Lewis , “Companion to Sirius”, American journal of science, xxxiv (1862), 294–5.

Moigno Abbé , Cosmos, 28 March 1862, 377: “Le compagnon de Sirius? M. Péters nous écrit qu'il n'accepte pas l'identité du compagnon qui vient d'être découvert, avec celui qu'il a calculé”.

Chacornac J. , “Schreiben des Herrn Chacornac an den Herausgeber”, Astronomische Nachrichten, lvii (1862), cols 175–6.

Ibid., col. 176: “… ist es darnach allerdings möglich, dass in dem letztern der Bessel'sche Begleiter aufgefunden ist”.

Galignani's Messenger, 1–2 April 1862, 2.

Lassel W. , “Schreiben des Herrn W. Lassell an den Herausgeber”, Astronomische Nachrichten, lvii (1862), cols 251–2.

Burnham Sherwood W. , “Double stars discovered by Mr. Alvan G. Clark”, American journal of science, xvii (1879), 283–9.

Schaeberle J. M. , “Discovery of the companion to Procyon”, Publications of the Astronomical Society of the Pacific, viii (1896), 314.

Flammarion Camille , Popular astronomy: A general description of the heavens, transl. by Gore J. E. (London, 1894), 466.

Tobin William , “Foucault's invention of the silvered-glass reflecting telescope and the history of his 80-cm reflector at the Observatoire de Marseille”, Vistas in astronomy, xx (1987), 153–84.

Chacornac's log books for the period are bound together in a small volume (approximately 4 × 6 inches). Most of the entries, probably made at the telescope, are written in pencil in a difficult-to-read scrawl. Many words remain hard to decipher. Some annotations in ink are easier to read and appear to have been made by Chacornac later, in good lighting. The log books are held in the Bibliothèque de l'Observatoire de Paris, call number F14.

Le Verrier U.-J. , “Rapport sur l'Observatoire Impérial de Paris et projet d'organisation”, Annales de l'Observatoire Impérial de Paris, i (1855), 1–68, p. 7. Here, the companion is described not as a star but as a large (but faint) planet in orbit around the Sirius sun.

Moigno , op. cit. (ref. 17), 391.

Moigno , op. cit. (ref. 17), 392.

Chacornac , op. cit. (ref. 26): “27 janvier 62. examine Sirius avec le No. 2, 3 et 4. Le No. 2 et 3 sont garnis d'une barre. L.V. dit voir un compagnon à gauche à 5 ou 6″. Je ne vois rien que des rayons courts, une étoile au dessous de 11^e grandeur est seule visible.” The bar mentioned here is part of a micrometer system that permits the measurement of angular distances and dimensions.

Chacornac , op. cit. (ref. 26), 14 March 1862.

Moigno , op. cit. (ref. 17), 392.

Chacornac , op. cit. (ref. 26), 20 March 1862.

Chacornac , op. cit. (ref. 26), 21 March 1862.

Chacornac , op. cit. (ref. 26), 24 March 1862.

Chacornac , op. cit. (ref. 18).

Chacornac , op. cit. (ref. 26), 24 March 1862.

“Prix d'Astronomie”, Compte rendu des séances de l'Académie des Sciences, lv (1862), 936–7.

The members of the Lalande Foundation astronomy prize committee for 1862 were: Charles Delaunay, Joseph Liouville, Louis Mathieu, Ernest Laugier and Hervé Faye. It is unlikely that Delaunay was on very good terms with Le Verrier in 1862, following their earlier acrimonious debate on the secular variations in the mean motion of the Moon (see, e.g., Compte rendu des séances de l'Académie des Sciences, l (1860), 510–31). Furthermore, only Laugier and Faye could be considered observational astronomers.

Moigno , op. cit. (ref. 17), 392.

Chacornac , op. cit. (ref. 26), 9 March 1862.

Chacornac , op. cit. (ref. 26), 10 March 1862.

Le Verrier consistently defended the position, first outlined in 1862, that observations of faint objects and of objects that required a combination of a large telescope and a high magnification should be carried out under more favourable skies. In the course of the later debate (1867–68) on the wisdom of relocating the observatory in the Seine river valley, Le Verrier argued against such a move given that the observation of the most “delicate phenomena” had already been moved to Marseille (see, e.g., Compte rendu des séances de l'Académie des Sciences, lxv (1867), 1867–81; lxvi (1868), 21–29 and 68–76, p. 76).