March 14 igoi] 



NA TURE 



467 



FURTHER 



OBSERVATIONS 

 PERSEI.' 



ON NOVA 



SINCE the preliminary note on this star was communi- 

 cated to the Royal Society on February 28, observa- 

 tions have been possible on the nights of February 28, 

 March i, 3 and 5, and twenty-four photographs of the 

 spectrum have been taken with the instruments before 

 •detailed. 



It may be stated generally that the light is slowly 

 waning. On February 28 the star was only slightly 

 brighter than a Persei. On March i it was estimated 

 as about equal to a Persei i.e. about 20 magnitude. 

 When it was again visible, on the evening of March 3, 

 it was distinctly less bright than ^ Persei, and its mag- 

 nitude probably near 2"5. On the 5th its estimated 

 magnitude was 27. 



The above refers to the visual brightness. A photo^ 

 graph of the region occupied by the Nova on March 3 

 showed it to be photographically brighter than a Persei. 



General Description of the Spectrum. 



The photographs show that the bright hydrogen lines 

 are successively feebler as the ultra-violet is approached, 

 and the whole of the series of hydrogen lines have, during 

 the past week, become relatively brighter with respect 

 to the remaining lines and the continuous spectrum. The 

 spectrum extends far into the ultra-violet. 



Among the changes which have taken place in the 

 visible part of the spectrum, it may be mentioned that, 

 while the lines of hydrogen have become relatively 

 brighter during the past week, the remaining lines, with 

 the possible exception of the prominent one at X 5169, 

 have become distinctly dimmer. There has also been a 

 •diminution of the intensity of the continuous spectrum. 

 The line in the yellow, the identity of which has not yet 

 been definitely determined, has gradually decreased in 

 intensity with the diminution of brightness of the star. 

 The bright green-blue F line of hydrogen has become 

 more conspicuous as the neighbouring green lines 

 have become fainter, and the bright C line is intensely 

 "brilliant. 



From all these causes, which give us blue light on 

 the one hand and red on the other, the star should 

 present to us the precise quality of red which has been 

 •observed. 



Colour. 



At discovery the star was described as bluish-white. 

 No observations on its variation in hue during its bright- 

 ening were possible, owing to unfavourable weather con- 

 ditions. The observations during the period of decline 

 have indicated a change to the present colour of a decided 

 claret-red. In comparison with this it is interesting to 

 note that in the case of the Nova which appeared in 1604, 

 Kepler alludes to purple and red tints assumed by the 

 star. 



Changes in the Photographic Spectrum. 



Between February 25 and March 5, to take the extreme 

 ■diflference of dates on which photographs were obtained, 

 it has been noted that while some of the dark lines were 

 absent on the later date, either new lines had come in or 

 previously feeble lines had become intensified. There 

 has not yet been time to determine accurately the posi- 

 tions of these lines. The appearance of the bright lines 

 of hydrogen, which I described as being reversed on 

 February 25, had very materially changed by March 3. 



In inspecting the dark band representing the bright 

 hydrogen at He, two darker fine lines are seen nearly 

 ■coincident in position with the edges of He in the 

 spectrum of a Persei photographed on the same plate. 



The appearance in the case of the "F" line (H/^), is 

 seen by the accompanying light curve (Fig. i). 



1 Abridged from a paper read at the Royal Society on March 7, by 

 Sir Norman Lockyer, K.C.B., F.R.S. 



NO. 1637, VOL. 63] 



No doubt the diflferences in the appearances are due to 

 a fact that at He we are dealing with the lines both of H 

 and Ca. 



Rough measuiements on the bright line H^ show that 

 the interval between the centres of the two extreme 

 maxima shown in the light curve corresponds to about 

 25 tenth-metres. This would give a differential velocity 

 of 960 miles per second between the different sets of 

 hydrogen atoms in the bright line swarm itself. 



It may be, then, that the appearances described as 

 reversals of the hydrogen lines on February 25 were but 

 the beginning of the subsequent changes. 



The comparisons with stars which have been taken 

 with the slit-spectroscope on each evening of observation, 

 indicate that no great change in the velocity of the dark 

 line component has occurred. So much, however, cannot 



Blue 



Red 



Fig. 1. 



be said of the bright lines in which a change has been 

 observed. 



In addition to the hydrogen lines, the strong lines in 

 the green already ascribed to iron appear to be double 

 in the photographs most recently obtained. 



Comparison with a Cygni. 



The view of the apparent similarity between the spectra 

 of Nova Persei and Nova Aurigae, to which I drew 

 attention in my previous paper, has been strengthened 

 by the comparisons which have since been made. 



The bright lines in the spectrum of Nova Persei are so 

 broad, especially in the blue and violet, that accurate 

 determinations of their wave-lengths are difficult to 

 obtain. The lines less refrangible than F, however, 

 besides being more isolated, are narrower than those 

 in the more refrangible part of the spectrum. A direct 

 comparison of these with the lines in the spectrum of a 

 star which is known to contain the enhanced lines of 

 iron, &c., has been considered a better niethod of arriving 

 at some definite conclusion as to the connection between 

 the Nova lines and the enhanced lines than that of 

 determining the wave lengths of the broad lines and 

 comparing the results with the known wave-lengths of 

 the enhanced lines. 



The best star for this purpose is n Cygni, but, unfor- 

 tunately, no good photograph has been obtained at Ken- 

 sington of the green portion of the spectrum of that star. 

 The star most nearly approaching a Cygni in relation to 

 enhanced lines is a Canis Majoris, which, in the Ken- 

 sington classification, has been placed nearly on a level 

 with, the former star, but on the descending side of the 

 temperature curve. In the spectrum of this star the 



enhanced lines of iron at XX4924-I, 50186, wj5q°' 



and 53i6'9 occur as well-marked lines This spectrum 

 has been directly compared with that of Nova Persei, 

 taken with the same instrument, and the fact that all 

 the lines apparently coincide affords good evidence that 

 the connection is a real one, and that the first four strong 

 Nova lines beyond F on the less refrangible side are the 

 representatives of the enhanced lines of iron. These 

 are the only enhanced lines whicli occur, in that part of 



