COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1153

                                Konkoly Observatory
                                Budapest
                                1976 July 14

         Hbeta OBSERVATIONS OF NOVA CYGNI 1975


    Hbeta photoelectric observations of Nova Cygni 1975 were made
at Villanova University Observatory during the period 8 September 
1975 to 7 December 1975. The observing instrumentation 
consisted of the 38 cm telescope and photoelectric photometer 
equipped with an uncooled EMI 9558 QB photomultiplier tube. The
sensitivity of the system was monitored by observations of an 
internal Sr 90 Cerenkov light source. Interference filters, of both
narrow and intermediate bandpass, centered near the wavelength
of the Hbeta line, were used for the observations. The characteristics 
of these filters have been tabulated by Guinan and McCook
(1979). Note that the Hbeta filter is similar to that utilized by
Crawford (1960) to define the Hbeta system.
    BD +47d3292 (m_v =4.6) was chosen as the comparison star,
while BD +47d3348 (m_v =6.3) served as the check star to monitor
the constancy of the comparison star. For observations made after
7 October 1975, this situation was reversed, with BD +47d3348
acting as the comparison, and BD +47d3292 acting as the check.
This was necessitated by the large decrease in magnitude of the
nova during the observation period. On several nights, differential 
magnitudes were obtained for the two reference stars in both
filters and the appropriate correction applied to the post 7 
October 1975 observations, thus referencing all (v-c) calculations
to BD+47d3292. The effects of atmospheric extinction were removed
from all observations. No significant variations were noted 
between the reference stars.
    Figure 1 presents the nightly mean differential magnitudes,
computed as (v-c) = (Nova Cygni 1975 - BD +47d3292), obtained
with the Hbeta narrow (Hbeta n) and the Hbeta intermediate (Hbeta w) filters,
plotted against Julian Date. The change in magnitude during the
period plotted (9 September 1975 to 11 November 1975) amounted
to a decline of 2.88m in the Hbeta w filter and 3.86m in the Hbeta n
filter. Figure 2 is a plot of the nightly mean Hbeta index versus
Julian Date. This index is expressed in magnitudes and is 
computed in sense:

              Hbeta index = Hbeta n - Hbeta w

    The author wishes to acknowledge J. Buckley, L. Casswell,
P. Miskinis, K. Rahlfs, and D. Routsis for their observations
of Nova Cygni 1975, and Dr. George P. McCook, under whose 
direction this project was conducted.


                             JOHN A. BANGERT
                           Villanova University
                           Astronomy Department
                           Villanova, Pa. 19085



References:

Crawford, D.L. 1960, Ap. J., 132, 66. [BIBCODE 1960ApJ...132...66C ]
Guinan, E.F. and McCook, G.P. 1974, P.A.S.P., 86, 947. [BIBCODE 1974PASP...86..947G ]

                       [FIGURE 1]

 Fig.1. Nightly mean differential magnitudes (v-c) vs. Julian
Date, for both Hbeta n and Hbeta w filters.

                       [FIGURE 2]

 Fig.2. Nightly mean Hbeta index vs. Julian Date. Note that the index
is expressed in magnitudes and Hbeta emission decreases as index
becomes more positive. This index is computed as Hbeta index =
Hbeta n - Hbeta w, and due to the 180 A half-bandwidth of the Hbeta w
filter, also reflects changes in the continuum around the Hbeta line, as
well as changes in the line itself.