Spectral Evolution of Nova V 1500 Cyg (1975) from September 1975 to May 1976

Abstract

Spectroscopic observations of Nova V 1500 Cyg have been carried out at Asiago after the first announcement of its discovery from August 30 to the present time.The photoelectric observations discussed by P.TEMPESTI prove’. that the epoch of maximum was August 30.7 (JD 244 2655.2) with visual magnitude 1.7.The times employed by the nova to drop of 2 and 3 magnitudes were t₂= 2.5; t₃= 3.9.The spectrum near maximum and during the first decline was characterized by the presence of wide emission bands,shortward accompanied by broad diffuse absorption features with mean radial velocities increasing from −1700 to −4200 km/s on Sep 23 when the absorption disappeared.The emission bands were very broad and many of them overlapped.The expansion velocity derived by the halfwidth of the bright bands increased from 860 to 1500 km/s on Sep 3,then remaining sensibly constant.The emission bands were saddle-shaped with two symmetric peaks at each side of the central minimum.At first,the strongest bands in the spectrum were due to H,CaII (H and K),NaI,FeII.In the infrared the Pasbhensseries, 0I-NI and particularly OI 8446,were outstanding.The nova entered in the nebular stage between Sep 9 and 12.