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AAVSO Special Notice #16

Possible AG Dra Brightening
(July 19, 2006)

Editor's Note: In the original e-mail, CBET #577 was incorrectly identified as IAUC #577.

U. Munari (Istituto Nazionale di Astrofisica, Astronomical
Observatory, Padova) has asked AAVSO observers to monitor AG
Dra until the end of its current outburst period.

According to AAVSO observations, AG Dra may be rapidly
rising to one of its more significant outbursts, the last of
which occurred in 1991 when AG Dra reached visual magnitude
~8.1.  Munari has obtained spectra that suggests this could
be the beginning of a very active outburst. In CBET 
#577, he states, "This [spectra] is reminiscent of a
currently intermediate state between the opposite types of
cool and hot outbursts described for AG Dra by Viotti et al.
(2005, Ap. Space Sci. 296, 435)" He adds that current
photometry may signify "...one of the most active [states] of
the last few decades."

AG Dra is a symbiotic binary likely containing a cool giant
and a white dwarf. The system goes through both active and
quiescent stages. Last July it reached ~magnitude 9 and
remained there for approximately two months. If this is a
major outburst, it could last into early 2007.

AAVSO visual observers are asked to monitor the star
nightly.  CCD observers are asked to obtain UBVRcIc
photometry once a night until the outburst peaks and then
once every few nights until it fades back to quiescence.

An AAVSO visual observing chart exists for AG Dra. However,
Munari has specifically requested that CCD observers
use a chart and photometry he made available to us. We placed
it online at this URL:

http://www.aavso.org/news/AG_DRA.pdf

The chart comes from a paper by Henden and Munari currently
in press(*). Use "Munari" in the chart field of your
observation report.

AG Dra is located at 16:01:41.00 +66:48:10.0 (J2000).

Munari adds, "The AAVSO monitoring will be quite important
when discussing how this active phase compares to the long
term evolution, given the extremely tight monitoring the
AAVSO memebrs have performed in the past on this object."

(*) A.Henden and U.Munari
"UBVRI photometric sequences for symbiotic stars. III"
Astron.Astrophys. 2006, in press

This special notice was compiled by: Aaron Price
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