The Spectrum of Nova Cygni 1942.

Changes in the light and spectrum of Nova Cygni 1942 from September 15 to December 17, 1942, are briefly outlined. Emission lines-While the nova was bright, emission lines of hydrogen were outstanding; those of Ca ii and Na i were prominent; and many others were present, including lines of Fe II, Ti ii, 0 I, 0 ii, and N ii. After the nova began its rapid decline in magnitude, its continuous spectrum weakened, ab- sorption detail was meager, and emission lines of hydrogen remained prominent. Those of [Fe ii] ap- peared and, with those of Fe ii, gained in strength relative to the hydrogen emission, [Fe ii] faster than Fell. On November 27 the nova, increasing in brightness, had lost its Feii and [Fe ii] lines, retained the hydrogen, and showed many of the well-known nebular emissions, some of them in great strength. Absorption lines-Several sets of absorption lines accompanied the emission lines on their violet sides. These were especially marked for hydrogen. Data for them are in Table 2 and Figure 1. A sharp set of lines giving a constant radial velocity of -509 km/sec is the most persistent. The other strong absorp- tion set had very wide lines and a displacement of -1185 km/sec when first observed. This increased to -1400 km/sec in five days and remained constant thereafter. Two weaker sets of lines had displace- ments of -900 to -700 km/sec and about -270 km/sec, respectively. Interstellar lines-The mean radial velocity from the interstellar lines is -11.8 ± 0.9 km/sec. The equivalent width of interstellar K is 0.59 A. These two data give an absolute magnitude at maximum of about -4, appreciably less than that of the average nova. Comparison with Nova Herculis 1934.-The general behavior of Nova Cygni 1942 is quite similar to that of Nova Herculis in respect to variations both in light and in spectrum