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Special Notice #330: Next HST/COS targets are IR Com and BB Dor

February 2, 2013:  Further to AAVSO Alert Notice 471 (, the next HST/COS target is the SU UMa-type dwarf nova IR Com. HST/COS observations are scheduled for:

     IR Com   2013 February 8 00:38:46 through 05:57:49 UT

IR Com is an eclipsing SU UMa-type dwarf nova. According to observations in the AAVSO International Database, it reaches V magnitude 18-19 at minimum. IR Com can be as bright as 13.5 V at maximum.

Your observations are crucial, particularly in the 2-3 days prior to the date above, as the HST planners will decide whether to observe IR Com based on your observations. They will need to know whether the system is in quiescence, as if it is too bright it will damage the instrumentation and the observations will be cancelled. They will likely make their decision early on February 7.

As instructed in AAVSO Alert Notice 471, for CCD observers, simultaneous photometry [shortly before, during, and after the HST observations] would be ideal. For the magnitude estimates, a nightly V measurement from now through the HST observations and a day beyond would be best. At 18-19 V at minimum, IR Com is likely too faint for positive visual observations at minimum. If positive visual observations are possible, however, they are welcome, as are visual fainter-than observations fainter than magnitude 15.0.

Coordinates for IR Com: R.A. 12 39 32.02  Dec. +21 08 06.4 (2000.0)

The target after IR Com will be the novalike (VY Scl) cataclysmic variable BB Dor. HST COS observations are scheduled for:

    BB Dor   2013 February 13 20:57:03 through 23:53:50 UT    

Observations in the AAVSO International Database show that BB Dor dropped from its high state (V~15) to its low state in December 2012 and is currently at V magnitude 18.908 (HKEB, Kevin Hills, Hartford, England). Southern observers are asked by Dr. Boris Gaensicke, coordinating PI, to obtain nightly V snapshot observations for the next two weeks.

Coordinates for BB Dor: R.A. 05 29 28.59  Dec. -58 54 46.3 (2000.0)

Charts for both stars may be created using the AAVSO Variable Star Plotter (

Please report observations as soon as possible to the AAVSO International Database using the names IR Com and BB Dor, respectively. If an outburst of IR Com is detected or if BB Dor returns to its high state, please report observations immediately.  Many thanks!

This AAVSO Special Notice was compiled by Elizabeth O. Waagen.


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