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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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