Spectroscopy of the nova FH Serpentis (1970) during the early decl early decline stage

Eleven spectrograms obtained between February 21 and March 30, 1970 in the spectral region from 480 to 660 nm with an original dispersion of 1.0 to 1.5 nm.mm-1 were used for line identification and spectral development study of the nova FH Ser in the early decline stage. Two systems of the principal absorption spectrum and two systems of the diffuse enhanced spectrum were resolved by measuring the radial velocities of the H, Fe II, [O I] and Si II lines. For three systems the almost linear increase of the radial velocity during one month after the maximum could be explained by the same constant acceleration a of the expanding clouds: a=0.02 m.s-2; the value is very similar to the acceleration found recently for the nova LV Vul by Grygar et al. (1981). The splitting of the diffuse enhanced spectrum into two systems which occurred on February 27, 1970 may most readily be explained by the assumption that the slower cloud was ejected earlier while the faster cloud initially displayed an extremely steep increase in radial velocity. Finally, the variations of the strengths of the emission peaks of the lines of H#betta# and Fe II (multiplet No. 42) were found and the distance of the nova, r=900 pc, was derived. (author)