Alert Notice 399: Nightly monitoring of AG Dra in support of HST calibration observations

July 27, 2009

Edward Smith (STScI) has requested nightly photometric monitoring of the symbiotic star AG Draconis during the period 2009 August 2, and tentatively scheduled to continue through mid-September 2009. They are specifically requesting nightly B and V-band monitoring, with B-band observations strongly encouraged; the onset of activity will result in larger changes in the B-band than in V and will provide the clearest and earliest evidence of activity in AG Dra.  However, all observers, both visual and instrumental, are encouraged to observe during this time. Intensive time-series are not required.

Smith and STScI staff will be observing this bright symbiotic using the Cosmic Origins Spectrograph on the Hubble Space Telescope during this time period. Their observations are intended to test and calibrate this newly-installed instrument. Observations of the system in quiescence rather than outburst are needed, and so observers are asked to report quickly any observations significantly above quiescence to the AAVSO via WebObs. According to Smith, they want to observe narrow ultraviolet spectral lines typical of quiescence, rather than the broad lines observed in outburst. He also notes that bright outbursts may overwhelm and damage the instrument, and so your observations will also serve to safeguard the spacecraft.

The estimated time of first observation is August 17, 2009, with further observations tentatively scheduled two and four weeks later. They request that monitoring begin by August 2 to provide a 1-2 week baseline of photometry with which to estimate the current state of the system. The AAVSO light curve will then be continually monitored through the end of observations. Monitoring is requested to continue through at least mid-September 2009; exact dates may be announced in a subsequent AAVSO Special Notice.

For more information on this HST observing program, please visit the proposal information pages at the following URL:

where the relevant proposal IDs for these observations are 11480 and 11490.

AG Draconis is located at the following (J2000) coordinates:

RA: 16 01 41.00 , Dec: +66 48 10.0

Customized charts for AG Dra may be created with AAVSO VSP:

Please submit all data promptly to the AAVSO via WebObs, using the name "AG DRA".

This AAVSO Alert Notice was prepared by M. Templeton.



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