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Alert Notice 184: Brightening of YY Dra (= DO Dra) AND Requests for monitoring (SS Cyg, EX Hya, VW Hyi, AM Her)

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

AAVSO ALERT NOTICE 184 (May 17, 1994)

BRIGHTENING OF 1137+72 YY DRACONIS (= DO DRACONIS)

We have been informed by Paul Van Cauteren of the Belgian Astronomical Society (V. V. S. - Working
Group on Variable Stars) of the brightening of the dwarf nova YY Dra (also known as DO Dra), as
observed by Tonny Vanmunster, Landen, Belgium, on May 13.932 UT at magnitude 14.1 and confirmed
by Paul Van Cauteren, Aartselaar, Belgium, on May 13.993 at magnitude 14.2.

In recent years, YY Dra has had two bright outbursts, in March 1988 and September 1990, when it
reached magnitudes 10.1 and 9.7 at maximum, respectively. AAVSO data files indicate observers several
times have reported minor brightenings of YY Dra, between magnitudes 14.0 and 14.5.

Observers are urged to monitor this star, using the accompanying AAVSO preliminary chart, and to
report your observations, together with the comparison stars used, to AAVSO Headquarters.

Chart links are obsolete; 01/2014 create charts using VSP at http://www.aavso.org/vsp

REQUESTS FOR AAVSO MONITORING

We have received several requests from astronomers for AAVSO observers to monitor the following
objects and alert them as indicated:

2138+43 SS CYGNI. Several astronomers are interested in observing SS Cyg in outburst with EUVE
and IUE satellites. Please monitor this star, and alert us as soon as you see it go into outburst, i.e., at
magnitude 11.5 or brighter. Continue to monitor SS Cyg throughout its outburst and report your
observations daily to AAVSO Headquarters until it has returned to minimum magnitude, i.e., magnitude
11.7 or fainter.

1247-28 EX HYDRAE. Astronomers at the Center for EUV Astronomy will be observing EX Hya with
the EUVE satellite between May 26 and June 3. Please use the enclosed AAVSO chart to observe this
star and report its status beginning May 23, and continue to monitor it throughout the EUVE observing
interval and inform us of your observations. Please alert us immediately if you see it go into outburst, i.e.,
brighter than magnitude 12.0, and report your observations daily throughout the outburst.

0409-71 VW HYDRI. An astronomer at Lawrence Livermore National Laboratory is interested in
observing VW Hyi in superoutburst with the EUVE satellite between now and mid-November. Please
use the enclosed chart to monitor this star and submit your observations of it at minimum with your
monthly reports. Please alert us at once if you see it go into outburst, i.e., magnitude 13.0 or brighter, and
report your observations daily throughout the outburst. The superoutbursts typically reach around
magnitude 8.6 and last more than 10 days. The normal outbursts are fainter and shorter, lasting only a
few days.

1813+49 AM HERCULIS. Astronomers are interested in observing this magnetic cataclysmic variable
with the Hubble Space Telescope when it is in its "down" state. Please use the enclosed AAVSO chart to
observe AM Her, and alert us when it goes into its down state, i.e., declines to magnitude 14.2 or fainter.

You may telephone your observations to AAVSO Headquarters using the charge-free number (800-
642-3883). The AAVSO answering machine is on nights and weekends for your convenience.

The success of these observing runs is directly affected by your monitoring the targets and alerting us -
your observations are extremely important! Many thanks for your efforts and valuable astronomical
contributions.

Janet A. Mattei
Director
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