44 



KNUT LUNDMARK, GLOBULAR CLUSTERS AND SPIRAL NEBULA. 



By measuring X e ff. of nebula? it has been possible considerably to advance our 

 spectral knovvledge of these objects. To obtain a spectrogram admitting a determina- 

 tion of the spectral type has formerly been possible only for a few of the greatest 

 spiral nebula? with the aid of very powerful instruments and especially long exposu- 

 res, while with our method spectral types and colour-indices will be attainable even 

 for fainter objects with rather small instruments and relatively short exposures. 

 The 44 objects, nebulse and dusters, examined by us, ha ve been measured on plates 

 taken with the Upsala 6-inch twin telescope (/ = 150 cm.) with a total exposure of 

 157 hours. As, however, the same object is sometimes occurring on more than one 

 plate and with several exposures, the average exposure-time for the objects that 

 can be reached with our instrument need not be put higher than 3 hours. Our ca- 

 talogue of objects, the X eff . of which ought to be attainable with the instrument, 

 bölds about 500 objects, most of them certainly spirals. 



The objects yet measured show that the effective wave-length of planetary 

 nebulse is <416 wl and as an average, X ef f =413"". The spirals give wave-lengths 

 between 420"" and 436"", and in the average, X eff . = 429'"" (spectral type G 2 ). This 

 gives a method of determining whether a small nebula without a distinct structure 

 belongs to the planetary or spiral nebula?, and it seems not improbable that the method 

 will also prove useful for distinguishing different types among the spiral nebula?. 



Lundmark and Lindblad have thus measured 12 nebula?, whose nebular type 

 is unknown but which certainly are to be included among the spirals on account of 

 the high values of their X e ff. 



TabU XI. 



N. G. C. 



Xeff. 



Spectrurn 

 inferred 



Colour-index 

 inferred 



Magnitude 



(Holetschek) 



Deseription according 

 to N. G. C. 



3077 



424'"'" 



i\ 



■m 

 f 0,42 



m 

 10,2 



c B, cL, mbM, R with ray 



3377 



433 



K a 



+ 1,00 



9,8 



vB, cL, IE, svmbMBN 



3379 



432 



Os 



+ 0,91 



9,1 



v B, cL, B, psbM, r 



3384 



428 



G 



+ 0,56 



9,5 



vB, L, R, psmbM, 2nd of 3 



3412 



427 



Fa 



+ 0,53 



9,5 



B, S, IE 135°±, smbMN 



3613 



429 



K t 



+ 1,20 



10,5 



vB, cL, mE 305°, smbMN 



3619 



439 



A' 6 



+ 1,20 



11,0 



cB, cL, R, vgmbM 



4278 



424 



F* 



+ 0,42 



9,6 



vB, pL, R, mbM, r, 1st of 3 



4494 



428 



o a 



+ 0,56 



9,2 



vB, pL, R, vsmbMN 



5471 



431 



G 6 



+ 0,82 



— 



F, S, R, *12l3p 



5473 



429 



G* 



+ 0,G4 



10,7 



pB, S, R, gbM 



5485 



430''" 



G t 



+ 0,74 



11,0 



cB, R, vgbMf of 2 



For further details concerning the measures and reduction of X e ff. for nebula?, see 

 Aph. J. 46,205 1917 and 50 (in press). 



