TypeGW Lib/UGWZ/ZZClick for lightcurveGW Librae stars, subtype of ZZ Ceti stars, non-radially pulsating white dwarfs in cataclysmic systems, see ZZ/GWLIB.WZ Sagittae type subclass of UGSU dwarf novae in which the interval between super-outbursts is unusually long (that is due to a very low mass-transfer rate), measured in decades, while normal outbursts are few and far between. They show re-brightenings. Orbital periods range from 0.05 to 0.08 d.ZZ Ceti variables. These are non-radially pulsating white dwarfs that change their brightnesses with periods from 30 s. to 25 min. and amplitudes from 0.001 to 0.2 mag. in V. They usually show several close period values. Flares of 1 mag. are sometimes observed; however, these may be explained by the presence of close UV Ceti companions.AAVSO Alert Notice 667, 20 May 2019V386 Ser to be observed with HSTMay 20, 2019: Dr. Paula Szkody (University of Washington) has requested AAVSO assistance in monitoring the cataclysmic variable V386 Ser in support of observations scheduled with the Hubble Space Telecope for 2019 May 30 - 2019 June 1 UT.Nightly snapshots are requested beginning immediately and continuing through June 7. Intensive monitoring is requested May 27 through June 2; this period of intensive monitoring may be adjusted when the exact time of the HST observations is known. When the exact time is known, it will be posted to the AAVSO forum thread on this campaign (see below) and this Alert Notice will be updated online. During the period of intensive observations, prompt submission of observations will be critical.AAVSO observations are essential to know the state of the V386 Ser system in order to ensure that the system is NOT in outburst when observed with HST. AAVSO observations made 24 hours before the HST observing time will be used to make a go/no-go decision; AAVSO data will be used in the analysis of the resulting HST data.V386 Ser (UGWZ+ZZ/GWLIB = WZ Sge type with a non-radially pulsating white dwarf) is faint at quiescence (V~19.2). It had an outburst in January 2019, and on 2019 May 18.1018 UT had declined to V=18.407 +-0.012 (B. Harris, New Smyrna Beach, FL). There is a V=17.757 star to the NW of the variable (178 in the AAVSO comparison star sequence; R.A. 16 10 33.15 Dec. -01 02 14.2); knowing whether the variable is fainter than, comparable to, or brighter than it will be very useful.If visual observers are unable to detect V836 Ser, 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 is preferred. Detection of the variable itself is not required unless you can reach V=18.4 in reasonable time, but please use sufficient exposure to detect at least the 178 comparison star with a S/N of 10 and report the observation as a ""fainter-than"" observation. V386 Ser may be as bright as V=10.4 in outburst.