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Alert Notice 614 : Monitoring of GW Lib to support XMM-Newton observation

February 12, 2018: Dr. Koji Mukai (NASA Goddard Space Flight Center) and colleagues have requested AAVSO observations of the WZ Sge type dwarf nova GW Lib in support of observations with the ESA XMM-Newton spaceobservatory scheduled for

2018 February 17  05:46:41 - 21:36:41 UT

In addition to being a WZ Sge variable that had a remarkable outburst in 2007, GW Lib is the prototype of dwarf novae in which the white dwarf is seen to be pulsating. Dr. Mukai writes: "The purpose of the XMM-Newton observation is twofold: (1) To take a deep X-ray look at GW Lib, 11 years after the outburst; (2) To use the optical monitor on-board XMM-Newton in fast mode to study the white dwarf pulsation in the UV."

GW Lib was the target of three HST observations in 2017 led by Dr. Boris Gaensicke (Warwick University) (see AAVSO Alert Notices 591, 595, 596, 597). Dr. Mukai is collaborating with Dr. Gaensicke and his collaborators in the current campaign, and the HST data will be utilized in the pulsation study.

Nightly monitoring of GW Lib is requested beginning now, changing to intensive monitoring on February 17, and then stepping down to nightly observations again through 2018 February 23. The XMM-Newton observations are not constrained by the brightness of GW Lib at the time of the observations, but it is important to know the optical brightness of the system before, during, and after for the current study.

GW Lib is faint at quiescence, magnitude ~16.8 visual/unfiltered, and may be as bright as V=8.2 in outburst. 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 preferred if 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.

Coordinates (2000.0):  R.A. 15 19 55.41   Dec.  -25 00 25.1

Charts with a comparison star sequence for GW Lib may be plotted using the AAVSO Variable Star Plotter (VSP).

Please submit observations to the AAVSO International Database using the name GW LIB.

This observing campaign is being followed on the AAVSO Campaigns and Observing Reports online forum at

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

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