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AAVSO Alert Notice 431

Request to monitor SDSS074545 for HST Observations

February 25, 2011: Dr. Paula Szkody (University of Washington) has requested our help in monitoring the cataclysmic variable SDSS074545 (SDSS J074531.91+453829.5) for upcoming Hubble Space Telescope observations. The HST observations are scheduled to be made during the week of 2011 March 7-14. Dr. Szkody also observed this object with HST in October-November 2007 (see AAVSO Alert Notice 359).

AAVSO observations are needed to ensure that the object is not in outburst when observed with HST, as it could damage the instrument if it were to go into outburst. AAVSO observations will be used to make a go/no go decision when the observing window opens, and will also be used in the analysis of the resulting data. According to Dr. Szkody, "currently the plan is to have the hold take place Mar 7-11 and the actual observations Mar 10-14. This means they will likely schedule Mar 10 or 11 - if it's the 10th, the critical night for ground confirmation will be the 9th. They will tell us the exact date and time at the end of Feb."

Dr. Szkody requests nightly monitoring of this object from now until the observing window opens, intensive monitoring during the 24-48 hour period during which observations will be made, and nightly observations for the week following the HST observations. An AAVSO Special Notice will be issued when HST ground controllers inform us the observing window is officially open.

Coordinates: R.A. 07:45:31.92 , Dec +45:38:29.5 (J2000)

SDSS074545 is a cataclysmic variable part of a larger study of pulsating white dwarf primaries in cataclysmic variables. In particular, Szkody and collaborators are investigating the effects that higher temperatures and larger rotation velocities caused by accretion have on the pulsation behavior. In these HST observations, they want to measure the temperature of the white dwarf at minimum.

This object is very faint at quiescence, with V=19.1. Visual observers should report any "fainter than" estimates using the faintest comparison star magnitude you can reach if unable to detect SDSS074545 itself. CCD observers are asked to use filters during observations if available; V filter is preferred, but B,Rc, and Ic may also be used. Detection of the variable itself is not required unless you can reach V=19 in reasonable time, but please use sufficient exposure to detect at least the V=15.8 comparison star (AUID 000-BCY-392; RA 07:45:35.45 Dec +45:38:47.6) with a S/N of 10 and report the observation as a "fainter-than" measure.

Beginning today, please observe this object as often as possible according to the schedule and using the observing procedure outlined above, and submit data as soon as possible to the AAVSO using the name SDSS074545. In the event of an outburst, please contact the AAVSO immediately.

Charts for SDSS074545 (000-BCY-351) may be plotted using the AAVSO Variable Star Plotter:

Thank you for your observing efforts and valuable observations!

This AAVSO Alert Notice was prepared by Elizabeth O. Waagen.


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