6605( 6) - 07/16/96 10:12 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6605 Version: 6 Check-in Date: 15-Jul-1996 18:22:45 1.Proposal Title: Ultraviolet Pulsations in WZ Sagittae ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle BINARIES AND STAR FOR GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: JOE PATTERSON COLUMBIA UNIVERSITY CoI: Carole Haswell Columbia University Y CoI: Fu Hua Cheng University of Maryland N ------------------------------------------------------------------------------------ 6. Abstract WZ Sagittae is one of the most famous and extensively studied cataclysmic variables. High-speed photometry at quiescence shows 28 s pulsations, whose origin is still unknown. Also puzzling is the high X-ray luminosity at quiescence; after photospheric light is subtracted, the star remains with L_x/L_opt~30, a surprisingly high ratio for any plausible accretion theory. An elegant solution to both problems would be achieved if the white dwarf is predominantly a `propellor' in quiescence, with the X-rays generated not in an accretion shock, but in the tangled, field- entrained plasma at the magnetospheric boundary. High-speed spectrophotometry in the UV can specify the origin of the pulsations by measuring the pulse fraction in continuum and lines, and can perhaps measure the photospheric magnetic field by `freezing' the Zeeman-split spectral features of the white dwarf as a function of rotational phase. ------------------------------------------------------------------------------------ 6605( 6) - 07/16/96 10:12 - [ 2] Observations Description ------------------------ We plan one visit to WZ Sge to perform high time resolution UV spectroscopy and simultaneous optical photometry using FOS with the G160L grating. This capability for simultaneous optical photometry and fast spectroscopy between 1140 - 2508 Angstrom is unique to FOS, and will be lost after cycle 6. While it is theoretically possible to obtain simultaneous optical photometric coverage from the ground, in practise weather and scheduling considerations often disrupt such plans. (The pulse amplitude varies by a factor of 2 on a timescale of hours, so simultaneity is needed.) The visibility window for WZ Sge is 52 minutes. We will operate in RAPID mode, with READ- TIME=6.18s, SUB-STEP=4. This gives us 4.51 spectra over the 27.9 s pulsation period. In `integral' photometry the amplitude is reduced by a factor sinc(PI fdt), so this will only diminish the measured amplitude by 7\\%. WZ Sge has an orbital period of 82 minutes. Thus, in each HST visibility window we will obtain coverage of just over half the binary orbital phase. We require four consecutive HST visibility windows to cover all phases of WZ Sge's orbit. A fifth consecutive HST visibility window provides coverage of almost all binary phases three times. Therefore we request a total of 6 HST orbits: one for target acquisition, and five for our exposures. This gives us a total of 230 minutes of exposure, almost uniformly distributed in binary orbital phase. Hence we will discriminate between random variability and features which repeat each orbit. WZ Sge is slightly brighter than AE Aqr in the relevant UV continuum. Thus we studied the AE Aqr observation of Eracleous et al. (1994) to estimate detection limits. Over ~600 Angstrom of continuum we estimate that we can measure a pulse amplitude of 2\\% with an `unbiased' search procedure (requirement of independent demonstration of periodicity), or ~1\\% with the period assumed known. This meets every need of the science program. Real Time Justification ----------------------- No special requirements. We have been observing the star for 19 years, so will certainly continue watching it with high-speed photometry at visual wavelengths. In 1996/7 we will emphasize multicolor observations, to extend the UV baseline to longer wavelengths (though without simultaneity of course). Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6605( 6) - 07/16/96 10:12 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 WZ-SGE STAR, INTERACTING RA=20H 7M 36.41S +/- 0.4", 2000 V = 15.3 BINARY, DWARF NOVA DEC=+17D 42' 15.4" +/- 0.4", E(B-V) = 0.0+/-0.05 PLATE-ID=02UQ B-V = 0.0+/-0.2 U-B = -1.0+/-0.3 Comments: ECLIPSING BINARY, RAPID VARIABLE Copied above from GO6019 6605( 6) - 07/16/96 10:12 - [ 4] Visit: 01 Visit Requirements: PERIOD 0.0566878455D AND ZERO-PHASE JD2437547.72845 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WZ-SGE FOS/BL ACQ/BIN 4.3 MIRROR 1 13.2 S ONBOARD ACQ FOR 2; PHASE ARY 0.15 TO 0.85 Comments: ACQ/BIN should be OK for this star (shallow eclipse). Computed the exposure time for ACQ/BIN using B-V and V, following table 2-5 in FOS manual. Assumes A1V spectral type. Checked with Tony Keyes. ------------------------------------------------------------------------------------------------------------------------------------ 2 WZ-SGE FOS/BL RAPID 1.0-PAI G160L READ-TIME=3.50,SUB-STEP=2, 1 14955.5 R-A STEP-PATT=SINGLE Comments: Sub-Step = 2 for speed. Read-time =3.5 for 80% duty cycle ------------------------------------------------------------------------------------------------------------------------------------ 6605( 6) - 07/16/96 10:12 - [ 5] Summary Form for Proposal 6605 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/BINARY RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters READ-TIME=3.50 SUB-STEP=2 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category BINARIES AND STAR FORMATION ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PERIOD 0.0566878455D AND ZERO-PHASE JD2437547.72845 ONBOARD ACQ FOR 2; PHASE 0.15 TO 0.85 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G160L ------------------------------------------------------------------------------------------------------------------------------------ Target Names WZ-SGE ------------------------------------------------------------------------------------------------------------------------------------