COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       NUMBER 878

                               Konkoly Observatory
                               Budapest
                               1974 March 22


     ON THE SPECTRAL VARIATIONS OF P CYGNI IN 1973



   Irregular spectral variations of P Cyg in the last 30 years
have been reported by Luud (Soviet Astr. 11, 211, 1967), Astafyev,
Hollandsky and Kopylov (Izv.Krym. 40, 46, 1969), and de Groot (BAN
20, 225, 1969). These variations are in general of rather small
amplitude, but recently Stephenson (IAU Circ. 2562, 1973) claimed
a remarkable weakening of the violet-displaced P Cyg-absorption
lines, as well as of the circumstellar H and K lines of CaII: his
observations are based on a 130 A mm^-1 spectrogram obtained on
July 17, 1973. A blue spectrum of P Cyg (W5752) was taken on March
23, 1973 at the Coude focus of the 193 cm telescope of the Obsevatoire 
de Haute-Provence with a reciprocal dispersion of 9.7 A mm^-1.
After Stephenson's communication a second plate of the star (W5837)
was secured with the same equipment on September 11 of the same
year. The Figure reproduces the intensity spectrum of P Cyg, 
normalized to the continuum, near lambdalambda3933 and 3970. Small intensity
variations of the hydrogen lines and of the H_8+HeI 3888 blend have
been observed. We have measured on the tracings the differences
V_E-V_A of the radial velocities of the emission and absorption
components for the lines given in Table 1.
               
                        [FIGURE 1]
         

                        Table 1.
 
        V_E-V_A (km s^-1)              V_E-V_A (km s^-1)
Line                              Line
         W5752    W5837                 W5752    W5837
H11       175      120        HeI 3819    90      135
H10       200      115            3964   110      120
H9        185      125            4026   120      130
H8+HeI    185      150            4388    85:     115:
Hepsilon  195      185            4471   125      120
Hdelta    180      180      NII   3995    80       95
Hgamma    185      170     FeIII  4395   100       90
CaII K                            4419   100       90
a_1-a_2   105       95            
a_1-a_3   180:     180 


Only for H11 to H8 we have observed a remarkable variation of
the radial velocities.
The CaII K-line displays two absorption components: a sharp 
interstellar line and a broad and shallow violet-displaced feature
(Figure). The latter one is originated in the outermost parts of
the expanding envelope of P Cyg and is probably formed by two or
more distinct components of variable intensities. The presence of 
multiple components of this line has been noticed by Underhill
(The Early Type Stars, p. 220, 1966), and a similar feature is also
shown by the NaI yellow doublet (Beals, Publ. Victoria 9, 1, 1950).
In conclusion, the large spectral change of P Cyg reported by
Stephenson is not confirmed by our spectra, unless it lasted for less
than 2 months. The observed spectral variations are of rather small
amplitude and take origin in the external parts of the star's 
atmosphere.

March 14, 1974

				ROBERTO VIOTTI and ROBERTO NESCI
				Laboratorio di Astrofisica Spaziale
				00044 Frascati, Italy.