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Alert Notice 195: Symbiotic stars AND Cataclysmic variables AND 1510+83 Z Ursae Minoris

THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
25 Birch Street, Cambridge, MA 02138 USA
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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. 

Chart links are obsolete; 11/2013 create charts using VSP at http://www.aavso.org/vsp

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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