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HST/COS Obs CANCELLED for SDSS J154453.60+255348.8

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HST/COS Obs CANCELLED for SDSS J154453.60+255348.8

HST/COS observations of SDSS J154453.60+255348.8 scheduled for 2013 May 1 UT have been CANCELLED. Please continue to observe this system nightly until the current outburst is over. AAVSO Special Notice #349 has the details.

Good observing  -  Elizabeth Waagen, AAVSO HQ

Yes, yesterday, it happened:

Yes, yesterday, it happened: we had to cancel the HST observation of SDSS1544+2553 ... your monitoring of this star was as usual vital for keeping the detectors on HST safe. While this is frustrating for all of us, it had to happen sooner or later as  CV are unpredictable beasts. 

But, let me stress here again that it is thanks to your support that we managed to observe the first 25 targets safely!

A bit more background on yesterdays problem.  SDSS1544+2553 is a long-period (6h) eclipsing CV (Skinner et al. 2011PASP..123..259S) and the M1.5V companion shows nicely up in quiescence (g~16.9). Our expectation was to get a spectrum of the WD with HST, just as we did for HS0218+3229 last December. Given that, in quiescence, the star is quite faint in the UV, we had to use an imaging strategy to acquire the target into the COS aperture ... which leaves little headroom for brightening. However, the last few days saw the system brightening up to V~15.9, and also the eclipse depth increased, unambiguously showing that the accretion disk got brighter.  Without a reliable prediction of the temperature of the disk, the UV flux that HST would have seen in the acquisition image was uncertain, and there was a real probability that it would be too bright - which called for the decision to abort the observations.

Fingers crossed that the next systems behave better.

Best wishes,


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