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Special Notice #297: HST COS observations of SDSS J164248.52+134751.4 scheduled

October 5, 2012:  Following on AAVSO Alert Notice 471 (Gaensicke, Patterson, and Henden,, the HST COS (Cosmic Origins Spectrograph) far ultraviolet observations of the cataclysmic variable SDSS J164248.52+134751.4 have been scheduled for 2012 October 12 from 01:03:27 to 06:21:43 UT. Extensive coverage in the 48 hours preceding the HST window is crucial, as the HST scheduling team will make a go/no-go decision in the 24 hours preceding the 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.

Positive observations, if at all possible, are preferred to fainter-thans so as to know the actual magnitude of the system. During quiescence SDSS J164248.52+134751.4 is around magnitude V=18.6.

Coordinates:  R.A. 16 42 48.51     Dec. +13 47 51.5  (2000.0)

As instructed in Alert Notice 471, for CCD observers, simultaneous photometry [shortly before, during, and after the HST observations] would be ideal. B filter would be best for a light curve, although for the magnitude estimates, a V measurement would be best. An uninterrupted light curve would be better than cycling between filters. This target is likely too faint for positive visual observations, but if possible they are welcome, as are visual fainter-than observations fainter than magnitude 15.0.

Charts for SDSS J164248.52+134751.4 may be created using VSP (

Please report observations promptly to the AAVSO International Database using the name SDSS J164248.52+134751.4. If you see the target in outburst, please contact the AAVSO immediately and post a message to the Observations and Campaigns & Observations Reports forum (

Your observations will be crucial to the success of these observations and are greatly appreciated. Many thanks!

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


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