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          THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
               25 Birch Street, Cambridge, MA 02138 USA
                BITNET:  aavso@cfa     SPAN:  cfa::aavso
                    INTERNET:  aavso@cfa.harvard.edu
               Tel. 617-354-0484       FAX 617-354-0665


                AAVSO ALERT NOTICE 195 (November 23, 1994)


SYMBIOTIC STARS

Several symbiotic stars have been of interest to astronomers, particularly 
those observing with satellites.  Below is the status of these stars.  Most 
of them are quite bright and are suitable for observing with binoculars or 
small telescopes.  The accompanying light curves of these stars are 10-day 
means of the observations in the AAVSO International Database.

1601+67 AG Draconis
This symbiotic star had an outburst that started in late May 1994, during 
which it brightened from its usual mean magnitude of 9.9, reaching 8.3 by 
mid-summer 1994.  It has been observed quite extensively with the IUE
satellite during this outburst.  It is now fading slowly, and is around 9.2, 
as indicated by the following observations:  Nov 2.98 UT,  9.2 (J. Bortle, 
Stormville, NY); 5.69, 9.0 (G. Zajacz, Debrecen, Hungary); 5.7, 9.0 (L. Kiss, 
Szeged, Hungary); 8.12, 9.5 (T. Burrows, Novato, CA); 20.09, 9.5 (Burrows); 
20.68, 9.1 (Zajacz).

Accompanying is the light curve of 10-day means of AAVSO observations of AG 
Dra from March 1992 to the present.  Observers are encouraged to monitor 
this star and are urged to indicate the source of the finder chart and the 
comparison stars used when reporting their observations.

1921+50 CH Cygni
This symbiotic star with multiperiodic variations has recently faded
significantly, as indicated by the following observations:  Nov 5.74, 8.6 
(G. Zajacz, Debrecen, Hungary); 7.15, 8.8 (P. Collins, Scottsdale, AZ); 9.16, 
8.9 (Collins); 13.12, 9.1 (Collins).

The accompanying light curve of 10-day means of AAVSO observations of CH Cyg 
from July 1987 to date shows well the multiperiodic nature of this variable.  
Observers are urged to report the source of the chart, and the magnitudes of 
the comparison stars used in making their estimates.  

2016+21 PU Vulpeculae
This interesting symbiotic variable had a deep minimum, fading from its mean 
magnitude of 8.7 to 13.6 between March 1980 and June 1981.  It then recovered 
and was at maximum until mid-1987, when it started to fade again.  H. 
Nussbaumer and M. Vogel, Institute of Astronomy, Zurich (IAU Circular 5960), 
reported PU Vul was undergoing an eclipse during its faded phase, and recently 
P. Garnavich, Harvard-Smithsonian Center for Astrophysics, and S. Trammell, 
University of Chicago, have reported (IAU Circular 6089) that the eclipse has 
ended.  Observations reported by telephone and email since October are as 
follow:  Oct 3.88 UT, 11.7 (G. Poyner, Birmingham, England); 4.82, 11.7 
(Poyner); 25.05, 11.6 (J. Bortle, Stormville, NY).

The accompanying light curve of 10-day means of AAVSO observations of PU Vul 
from October 1984 to date shows this interesting behavior.  Observers are 
encouraged to observe PU Vul as much as possible as it brightens slowly.

1810+20 YY Herculis
This symbiotic star, which has a mean magnitude of 13.0, started to brighten 
in May 1993, reaching 11.6 by July 1993.  It then slowly faded, reaching 13.6 
by June 1994.  The following recent observations reported by John Bortle 
indicate that YY Her may be brightening again:  Oct 1.0 UT, 13.0 (J. Bortle, 
Stormville, NY); 3.83, 13.3 (G. Poyner, Birmingham, England); 4.80, 13.1
(Poyner); 7.0, 12.9 (Bortle); 13.0, 12.9 (Bortle); 25.0, 12.7 (Bortle); 25.04, 
12.7 (Bortle); Nov 3.0, 12.6 (Bortle); 3.01, 12.6 (Bortle); 8.00, 12.5 
(Bortle); 8.0, 12.5 (Bortle). 

The accompanying light curve of 10-day means of AAVSO observations of YY Her 
from April 1990 to date shows its behavior.  Observers are encouraged to keep 
an eye on this interesting symbiotic variable.


CATACLYSMIC VARIABLES

We have standing requests to monitor 0749+22 U Geminorum and 0409-71 VW Hydri
for the forthcoming observations of these stars with various satellites, 
including Hubble Space Telescope (HST), Extreme Ultraviolet Explorer (EUVE), 
and ASTRO-2 (to be flown from the space shuttle in late February 1995).  Some 
astronomers are interested in observing these stars when they are at maximum, 
and some when they are at minimum.  Therefore, please monitor these stars 
closely and call in your observations when either of them starts to brighten.  

We have been informed by D. Overbeek and S. Dominguez that VW Hyi is presently 
undergoing an outburst, as indicated by the following observations:  
Nov 19.053, 8.8 (D. Overbeek, Edenvale, South Africa); 19.735, 8.8 (Overbeek);
19.977 8.6 (Overbeek); 20.052 8.8 (J. Smit, Waverly, South Africa); 20.744 
8.6 (Smit); 20.967 8.8 (Overbeek); 22.080 8.8 (S. Dominguez, Buenos Aires, 
Argentina).


1510+83 Z URSAE MINORIS

This star, initially classified in the General Catalogue of Variable Stars 
as a possible Mira variable, has recently been discovered through both CCD 
photometry and spectroscopy to be an R Coronae Borealis star (Benson, P. J., 
Clayton, G. C., Garnavich, P., and Szkody, P., Astronomical Journal, 108, 247, 
1994).  Benson et al. report Z UMi to vary between a mean maximum magnitude of 
about 10.8 and 16.7.  

Z UMi is presently around maximum, as reported by J. Bortle (Stormville, NY) 
at about 12.0 magnitude on Nov 20.01 UT, and by C. Scovil (Stamford, CT) at 
about 11.5 on Nov 22.34.  

Accompanying is a finder chart drawn by C. Scovil, using a Stamford 
Observatory photovisual plate and the identification chart published by Benson 
et al. (1994).  The magnitudes from the Guide Star Catalog (GSC) which 
correspond to the letter sequence on the accompanying chart are as follows:
Comparison star a (10.9), b (11.1), c (12.5), d (12.9), e (143), and f (14.4).
Magnitudes given in the GSC often do not match visual magnitudes.  Thus, 
please use the letter sequence until a good comparison star sequence that has 
been well evaluated by observers is established. 

Note to observers: Z UMi is mis-identified in the finder chart published in 
La Gazette d'Etoiles Variables, Number 138, November-December 1994.  Z UMi 
is the comparison star indicated as 11.2 on that chart.  

Observers are encouraged to monitor this star and report their observations in 
letter sequence.  Comments are welcomed on the GSC magnitudes given above. 

Many thanks to all the observers who have contributed observations for the 
accompanying light curves.  We very much appreciate and acknowledge with 
thanks your continued efforts and valuable astronomical contributions.  The 
AAVSO staff and I wish you and your loved ones a very happy holiday season.

Good observing!

Janet A. Mattei
Director


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AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484