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


                 AAVSO ALERT NOTICE 222 (June 25, 1996)


EXTREME FADING OF 1921+50 CH CYGNI

The brightest Z And-type symbiotic star known, CH Cyg, is undergoing a
significant fading as indicated by the following observations:

May 3.4743 UT, 9.4, P. Collins, Scottsdale, AZ; 21.85, 9.6, R. Fidrich,
Rakoczi, Hungary; 23.1, 9.4, J. Bortle, Stormville, NY; 24.800, 9.7, Fidrich;
26.321, 9.4, S. O'Connor, Quebec, Canada; 28.98, 9.2, E. Schweitzer, Strasbourg,
France; Jun 3.4722 UT, 9.7, Collins; 4.96, 9.5, Schweitzer; 5.2132, 9.9, T.
Burrows, Novato, CA; 6.1542, 9.9, Bortle; 6.1708, 9.7, C. Scovil, Stamford, CT;
6.9, 9.7, Fidrich; 7.184, 9.77 CCDV, R. Zissell, South Hadley, MA; 7.9, 9.8,
Fidrich; 8.124, 9.69 CCDV, Zissell; 8.3056, 9.8:, G. Hanson, Cave Creek, AZ;
8.9, 9.9, Fidrich; 10.3069, 9.9, Burrows; 10.9, 9.9, Fidrich; 14.87, 9.9,
Fidrich; 14.933, 9.8:, P. Skalak, Karlovy Vary, Czech Republic; 15.196, 9.93
CCDV, Zissell; 15.3146, 9.9, Burrows; 15.9, 10.0, Fidrich; 16.2500, 10.2:, W.
Dillon, Missouri City, TX; 20.2958, 10.4:, Hanson; 22.2722, 10.4:, Hanson;
25.2347, 10.3: Hanson.

The current fading is unprecedented for CH Cyg.  The above observations
indicate that it is the faintest it has been going back to 1929 (Muciek, M.,
and Mikolajewski, M. 1989, Acta Astronomica, 39, 165; and AAVSO observations
since 1948). The long term activity of the star is shown in the accompanying
light curve of 10-day means calculated from the observations in the AAVSO
International Database.

Observers with photoelectric photometers and/or CCD's are strongly encouraged
to carry out multicolor photometry during this extreme fading of CH Cyg.

Accompanying is the AAVSO 'b' scale chart for TZ Cyg; the field of CH Cyg
appears on this chart.  Observers are encouraged to use the TZ Cyg sequence to
make estimates while CH Cyg is faint, as CH Cyg's sequence is not faint enough
to cover the present brightness of CH Cyg.  Please monitor this system closely,
and inform us by phone, fax, or email of its behavior.  Be sure to indicate
which comparison stars you are using for each estimate, and from which star's
sequence they come.


REMINDER - REQUEST TO MONITOR 2138+43 SS CYGNI FOR OBSERVATIONS WITH HST,
EUVE, AND XTE

Observers are reminded to keep a very close eye on SS Cyg and inform us
immediately when it begins to brighten, i.e., becomes brighter than magnitude
11.5, so that we may immediately inform astronomers with whom we are
collaborating in the observation of SS Cyg with the Hubble Space Telescope
(HST), Extreme Ultraviolet Explorer (EUVE), and X-ray Timing Explorer (XTE)
(see AAVSO Alert Notice 221).

Once SS Cyg goes into outburst, please report your observations daily, so we
may inform our colleagues regarding the behavior of SS Cyg  for the scheduling
of observations with satellites.


CHARTS AVAILABLE ON AAVSO FTP SITE AND AAVSO WEB SITE HOME PAGE

Electronic copies of the AAVSO chart of CH Cyg and the light curve of CH Cyg
mentioned in this Alert Notice are available from our FTP site:

              ftp.aavso.org (198.116.78.2), in /pub/alert222

The chart and the light curve have also been placed on our Web site at the
following address:

                         http://www.aavso.org


The answering machine at AAVSO Headquarters is on nights and weekends for your
convenience.  Please call our charge-free number (800-642-3883) to report your
observations.  **If you are cut off when you telephone in your observations,
please wait a few minutes and call back to complete your call.  We have learned
that if someone calls to leave observations on the answering machine and while
they are speaking someone else calls, the first person may be cut off.**  We
also encourage observers to send observations by fax to 617-354-0665 or by
e-mail through the Internet to observations@aavso.org.  We would appreciate it
very much if you would report your observations in Universal Time.


Many thanks for your valuable astronomical contributions and your efforts.

Good observing!

Janet A. Mattei
Director