March 18, 2015: 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 window 2015 April 22-25 UT. Dr. Szkody also observed this object with HST in March 2011 and March 2010 (see AAVSO Alert Notices 433 and 417, respectively).
AAVSO observations are needed to ensure that the object is NOT in outburst when observed with HST. AAVSO observations made April 21-24 will be used to make a go/no go decision, and will also be used in the analysis of the resulting data. In mid-April 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 beginning now, intensive monitoring April 21-25, and nightly observations through May 2.
Coordinates: RA: 15 19 55.45 , Dec: -25 00 25.30 (J2000.0)
GW Lib is a cataclysmic variable that is 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.
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. If visual observers are unable to detect GW Lib, please report any "fainter-than" estimates using the magnitude of the faintest comparison star magnitude seen. 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 (RA 15:19:39.54 Dec. -25:00:31.8) or V=147 (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 now, 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 International Database using the name GW LIB. During the nights of April 20-21, 21-22, 22-23, and 23-24 prompt submission of your observations will be critical. In the event of an outburst, please contact the AAVSO immediately.
Charts for GW Lib may be plotted using the AAVSO Variable Star Plotter (VSP, 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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