248 



NATURE 



[April 21, 192 1 



The New Star of 1912— Nova Geminorum 



By Major William J. S. Lockyer. 



II. 



THOUGH new stars are of comparatively rare 

 occurrence, several have appeared during 

 the past few years, and much attention has been 

 devoted to their study. Many observatories which 

 have now taken up the spectroscopic examination of 

 celestial objects, and are therefore equipped with 

 spectroscopic apparatus of various kinds, have together 

 secured a great amount of material which was lacking 

 for the study of the earlier novae. 



Such was the case with the new star which was 

 discovered by Enebo in Norway on the evening of 

 March 12, 191 2. This star appeared in the constella- 

 tion of Gemini and is known as Nova Geminorum H., 

 since it is the second nova that has shown itself in 

 that constellation. 



The star was, fortunately, discovered before it had 

 attained its greatest brilliancy, as was also the case 

 with the most recent new star, Nova Cygni III. 

 (1920). On March 10, 1912, Nova Geminorum was 

 less than a star of the eleventh magnitude, and it 

 attained its maximum on March 14, being then of 

 magnitude 337. After that it faded very rapidly, 

 diminishing with fluctuations which were irregulg^r in 

 both period and amount. 



The Solar Physics Observatory at Cambridge was 

 fortunate enough to sepure a very fine series of photo- 

 graphs taken by Mr. Stratton during the months of 

 March and April, 1912 — ^so good a series, in fact, that 

 it required only a few photographs from other observa- 

 tories to fill up the gaps. Most of these were supplied 

 from the Allegheny and Bonn Observatories. Other 

 photographs were taken of the later stages of the 

 nova's career, but longer intervals between these onlv 

 were required, as the spectral changes were slow. 

 The measurement of all the photographs was com- 

 pleted in 19 14, but owing to the outbreak of war the 

 work of discussion could not be taken up until Mr. 

 Stratton 's return to the observatorv in February, 19 19. 

 •His discovery of the identification of many lines in 

 the nova's spectrum with nitrogen, oxygen, and 

 helium lines, which were greatly displaced from their 

 normal positions, facilitated the Work. 



A discussion of all these photographs has now 

 been published, and Mr. Stratton, who undertook it, 

 has presented us with a work which gives a valuable 

 insight into the nature of the changes which the 

 spectrum of this nova underwent. The volume 

 will thus greatly assist other workers who are dis- 

 cussing their observations of later novae, and will 

 possibly give them clues as to what kind of changes 

 may be expected or how to look for them. 



Since the spectrum of a nova is changing constantly, 

 and sometimes with very considerable rapiditv, 

 especially about the time of maximum brilliancy, every 

 photograph of its spectrum, wherever taken, mav 

 prove useful in the elucidation of the nova problem'. 

 Since the puzzling changes in the spectra are much 

 more likely to be understood if the time interval 

 between successive spectrograms can be greatly 

 reduced, the author puts forward the view that for 

 a complete elucidation of the problems involved all 

 the spectra secured for any one nova should be placed 

 at the disposal of a single" investigator. There should 

 be no diflRculty in carrying out such a suggestion, 

 provided that each observatorv which takes some of 

 the photographs and wishes to discuss them mav do 

 so prior to handing them over for the final inquiry. 



<<iu'^"J^'^°^"^'= ^"''*'' PhvsicB Observatory. Cambridee. Vol. iv. parti • 

 I he Snectrum of Nova Geminorum IT." By F. J. M. Stratton. ' Under 

 the d,rect.pn of Prof. H. F. Newall. Pp. viii + y.+ii plates. Cambri5ge : 

 At the University Press, 1920.) * 



NO. 2686, VOL. IO7I 



One marked feature of this research is that it 

 deals with photographs of the nova taken with instru- 

 ments giving both large- and small-scale spectra. As 

 the spectra of novae at some stages consist of a mix- 

 ture of broad, dirfuse bands, togetner with very sharply 

 defined lines, the former are seen and measured at 

 their best in the small-scale spectra, while the latter 

 are practically seen only in the large-scale spectra. 



The discussion of the observations has led the author 

 to dirterentiate between seven different stages in the 

 spectrum of this nova. One cannot do better than 

 quote from p. 9 the summary he gives of the different 

 stages, as space forbids one to elaborate the informa- 

 tion : 



'■(i) An absorption spectrum of type A5 displaced, 

 with weak radiations undisplaced (1912 March 13). 



"(2) An absorption spectrum of type A2/) (o Cygni) 

 displaced, with radiation spectrum undisplaced and 

 with many absorptions doubled (1912 March 15-21). 



■' (3) Superposed absorption spectra of types A2^ 

 (o Cygni) and B2 (7 Orionis) displaced by separate 

 amounts, together with an a Cygni radiation spectrum 

 undisplaced. The y Orionis absorption spectrum in- 

 creases in strength compared with the a Cygni absorp- 

 tion spectrum, and accompanying bright bands of 

 7 Orionis type gradually appear and increase in 

 strength (1912 March 22-31). 



"(4) a Cygni and 7 Orionis radiation spectra undis- 

 placed (19 1 2 April 8). 



"(5) y Orionis and nebular radiation spectra undis- 

 placed (1912 April 22). 



"(6) Nebular radiation spectrum (1912 December 6). 

 "(7) Nebular and Wolf-Rayet radiation spectra 

 (1914 February 22)." 



The author enters fully into the method he adopted 

 for differentiating between the types of spectra referred 

 to in Nos. (i) to (3) above, and shows how by em- 

 ploying a displacement factor from known lines he 

 was able to tie up lines of other elements, the dis- 

 placement factor varying according to the date of the 

 photograph examined. Thus, to take one instance, 

 out of 108 strong lines in a Cygni, 79, according to 

 this method, appeared displaced in the nova on 

 March 15 ; reasons are given for the absence of many 

 of the remaining lines. 



As to the cause of the outburst of the new star, 

 based on the spectroscopic evidence here brought 

 together, the author does not commit himself, for he 

 says that a final theory of novae cannot yet be written. 

 With regard to the most hopeful theory at present put 

 forward, suggesting the collision of a star with a 

 dark nebula and the consequent terrific action causing 

 a tremendous outstreaming of glowing gases from the 

 central body and the final formation of a planetary 

 nebula with a W^olf-Rayet star as nucleus, the author 

 says we " must await modification as further facts 

 come to light." 



In his preface Prof. Newall states that this 

 vol. iv. of the Annals will be followed by memoirs 

 on Nova Persei (1901) and on Nova Aquilae III. 

 (1918). The latter star, he says, "seems likely to 

 afford more insight into the nature of the outburst 

 of a nova than all the other new stars that have 

 bepn studied with the help of the spectroscope." 



While reference has onlv briefiv been made to some 

 of the main points in this volume on Nova Geminorum 

 II., there are many other features in the nova's spec- 

 trum which Mr. Stratton has discussed very minutely, 

 such as the undisplaced calcium lines, the structure of 

 bright bands, etc. Two plates accompan\^ the volume 

 illustrating the spectra both as a whole and in parts. 



