COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2434

                                       Konkoly Observatory
                                       Budapest
                                       25 November 1983

                                       HU ISSN 0374-0676





        ANOTHER SEMI-REGULAR VARIABLE IN CYGNUS


 A reinspection of photometric data obtained for the investigation of
galactic structure in selected regions in Cygnus (Hartl 1975) led us
to the detection of on obviously new variable star. Besides 9 U and
8 V values, we derived altogether 63 B values, mainly by using the
plate archives of the observatories in Asiago and Heidelberg, supplemented
by a few plates recently taken in Innsbruck. The star is located
at alpha= 21h14m06s, delta =+46d49'51"; +-10" (1950.0). A finding chart is 
shown in Figure 1.


                          [FIGURE 1]

 Fig. 1: Finding chart reproduced from a B-plate (103a-O + GG13),
 obtained with the 90-65-cm Schmidt of the Asiago Observatory.


 In Figure 2, all data are given except two B values (14.90m +- 0.2m in
1952-07-19 and 14.62m +- 0.2m in 1958-09-05). The variability of the star is
evident especially in Figure 2b; Figure 2c demonstrates its long-term
behaviour.


                          [FIGURE 2]

 Figures 2a-c. Light curve of 3 periods. In Figures 2a,c each point 
 represents one observation. The large symbols in Figure 2b are the mean 
 of up to 5 values, with errors of 0.02m to 0.1m (Triangle: m_V, +:m_U), 
 the residual data in Figure 2b are accurate to <= 0.2m.


 On objective prism plates of the Asiago archives, the star could be
classified as M4 - M6. In addition, we found it in a list of cool stars
(Nandy and Smriglio 1970), where it is classified as M5.
 The luminosity class can be determined indirectly by employing Hartl's
(1975) colour excess vs. distance diagram and the extinction in the
line-of-sight to the object: For several nights, we have U-B and B-V
values at hand derived from plates taken within a few hours; the mean
is U-B = 1.29m and B-V = 1.95m, respectively. U-B is a rather uncertain
quantity for evaluating the extinction for the spectral type we are
interested in: e.q., (U-B)_0 = 1.58m for M5III, but 1.16m for M6III according
to Landolt-Bornstein. The usage of B-V gives E(B-V) ~ 0.2m for an M5 or M6
star, provided it is a giant; this assumption is strongly suggested by
Hartl's (1975) absorption model - according to it, a super-giant should
suffer from a much higher obscuration. The observed colours also argue
against a main-sequence star.
 The light curve, spectral type, and luminosity class point to a variable 
star of semi-regular type (SRa or SRb), though we cannot rule out
that it is of irregular type. Since Cygnus is one of the best studied
regions of the sky and the star is moderately faint, it might be contained 
on a number of other plates, particularly because the famous nova
Cygni 1975 is only 1.4d distant.

 We are grateful for the permission to use the plate archives of the
Osservatorio Astrofisico in Asiago and of the Landessternwarte in Heidelberg.
This work was supported by the Austrian Fonds zur Forderung der
wissenschaftlichen Forschung under project no. 4128.




           G. AUNER, H. HARTL AND R. WEINBERGER

       Institut fur Astronomie der Universitat Innsbruck
                Universitatsstr. 4
                A-6020 Innsbruck





References:
Hartl, H.; 1975, Astron. Astrophys. 41, 321 [BIBCODE 1975A&A....41..321H ]
Nandy, K., and Smriglio, F.: 1970, Publ. R. Obs., Edin., 7, no. 1, 1-18 [BIBCODE 1970PROE....7....1N ]