COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3613

                                              Konkoly Observatory
                                              Budapest
                                              4 June 1991

                                              HU ISSN 0374 - 0676


    HN CYGNI : THE STAR ERRONEOUSLY CLASSIFIED AS A DWARF NOVA


The variability of HN Cyg (294.1929 Cyg) was discovered by Hoffmeister (1930).
Wachmann (1966) published four moments of the maxima, and the star was
classified in GCVS as UG:. Bruch et al. (1987) reported two additional
outbursts. However, Munari et al. (1990) derived the spectral type of M 6.5
and reclassified the object as the Mira.

The star was observed among the UG-type variables on 232 archive plates of
Sternberg State Astronomical Institute (Andronov and Sidorova, in press),
using the comparison stars of Wachmann (1966). The histogram (Fig. 1) is not
characteristic for Dwarf Novae, nor is the light curve. The brightness changed
from 14.8m to 16.5m (pg), its mean value <m>=15.75m and the mean-squared
deviation sigma_m=0.33m.


                              [FIGURE 1]

 Fig. 1. The histogram of the brightness of HN Cyg. The distribution of 
 magnitude is nearly symmetrical.


To find the possible period, the brightness was fitted by

       m(t_1) = a_0 + a_1 sin(2 pi t_1/P) + a_2 cos(2 pi t_1/P).

As the test function, we used the function

     S(1/P) = sigma_c^2(1/P) / sigma_o^2 = 1 - sigma_o-c^2(1/P) / sigma_o^2

Two prominent peaks were found at the periodogram (Fig. 2a), corresponding to
the periods P_1=72.73d and P_2=820d. From the nonlinear two-frequency
least-squares fit we obtained P_1=72.84 +-0.04d and P_2=828+-6d with the
corresponding amplitudes 0.26+- 0.023m and 0.23+-0.025m and moments of 
maxima at T_1=2440280+-1d and T_2=2440376+-13d.

The periodogram for the residuals (O-C) shows no significant peaks (Fig. 2b).
No periodic waves were found from the periodogram analysis of separate
seasons for P>0.1d.


                                 [FIGURE 2]

 Fig. 2. The periodograms for the observations of HN Cyg (up) and for the 
 residuals from the two-frequency fit (down).



                                I. L. ANDRONOV
               Department of Astronomy, Odessa State University
                               Odessa 270014 USSR

References

Bruch, A., Fischer, F.-J., Wilmsen, U.: 1987.-As. Ap. Suppl.
  70, 481. [BIBCODE 1987A&AS...70..481B ]
Hoffmeister, C.: 1930, Sonn. Mitt. No. 17
Munari, U., Claudi, R., Bianchini, A.: 1990, IBVS No. 3496
Wachmann, A.A.: 1966, Bergd. Abh. 6, No. 4, 283