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AAVSO Alert Notice 433

Request for observations of GW Lib in support of HST observations

March 20, 2011: Dr. Paula Szkody, University of Washington, has requested our help in monitoring the cataclysmic variable GW Lib for upcoming Hubble Space Telescope observations, scheduled to be made during the week of 2011 April 7-11 UT. Dr. Szkody also observed this object with HST in March 2010 (see AAVSO Alert Notice 417).

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. At the end of March the schedulers will give Dr. Szkody the exact date of the HST observations, and an AAVSO Special Notice will be issued.

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.

Coordinates: RA: 15 19 55.45 , Dec: -25 00 25.30 (J2000.0)

GW Lib is a cataclysmic variable part of a larger study of pulsating white dwarf primaries in cataclysmic variables. (Successful HST observations were made this month on another cataclysmic in the study, SDSS074545.) 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.

GW Lib is faint at quiescence, magnitude ~16.8 visual/unfiltered. It is also an observing challenge because of its -25o declination and because, at RA 15 hr, it is a late-night object. Visual observers should report any "fainter-than" estimates using the faintest comparison star magnitude you can reach if unable to detect GW Lib 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=16.8 in reasonable time, but please use sufficient exposure to detect at least the V=143 comparison star (AUID 000-BBW-012; RA 15:19:39.54  Dec. -25:00:31.8) or V=147 (000-BBW-026; RA 15:20:01.73 Dec. -24:58:37.7) with a S/N of 10 and report the observation as a "fainter-than" observation.

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 GW LIB. In the event of an outburst, please contact the AAVSO immediately.

Charts for GW Lib (AUID 000-BBW-023) may be plotted using the AAVSO Variable Star Plotter:   http://www.aavso.org/vsp

Thank you for your observing efforts and valuable observations!

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