9287( 10) - 08/04/01 10:32 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9287 Version: 10 Check-in Date: 04-Aug-2001 10:30:53 1.Proposal Title: STIS Ultraviolet Observations of the Death Star in Outburst ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO/DD 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Christian Knigge University of Southampton CoI: Emilios Harlaftis National Observatory Athens N CoI: Luisa Morales Southampton N CoI: Sofia Betancor Southampton N CoI: Thomas Marsh Southampton N CoI: Danny Steeghs Southampton N CoI: Knox Long STScI N CoI: Peter Wheatley Leicester N CoI: Erik Kuulkers SRON Utrecht N CoI: Keith Horne St. Andrews N CoI: Michael Garcia CfA N CoI: Joe Patterson Columbia N CoI: Warren Skidmore St. Andrews N CoI: Jorge Casares IAC Tenerife N ------------------------------------------------------------------------------------ 5. Abstract A few days ago, amateur astronomers have established that the cataclysmic variable star WZ Sge has gone into outburst, 23 years after the last outburst event and about 10 years earlier than expected. The system rose from V=15 to V=8 in the course of a day and is expected to remain in outburst for about 1-2 months. WZ Sge is arguably the most extreme and interesting cataclysmic variable (CV) in the sky. Whereas other dwarf-nova-type CVs undergo 3-5 magnitude eruptions every few weeks or months, WZ Sge's outbursts have an amplitude of 7-8 magnitudes and recur on a time-scale of roughly 33 years. In addition, WZ Sge's 82 minute orbital period is one of the shortest of any CV, its mass ratio of M2/M1 $ simeq$ 0.03 is one of the lowest and its time-averaged absolute magnitude one of the faintest ($M_V simeq 11.5$). All of these facts imply that WZ Sge is a "death star" (Patterson 1998), i.e. a highly evolved cataclysmic binary in which gigayears of mass transfer have converted an initially main sequence secondary star to a 0.02 solar mass brown dwarf. We propose to obtain time-resolved HST/STIS observations of WZ SGE, to be scheduled (near- )simultaneously with the already approved Chandra outburst. ------------------------------------------------------------------------------------ 9287( 10) - 08/04/01 10:32 - [ 2] Observations Description ------------------------ We will observe WZ Sge 3 times, for a total of 12 HST orbits. Four HST orbits per visit are necessary to cover all orbital phases of WZ Sge's binary period in each visit. This is essential to our goal of studying orbital variations and disentangling these from other types of variability on similar time-scales. The first observing epoch should coincide as nearly as possible with a 25 ksec Chandra/HRC-S/LETG observations (scheduled for the week of August 6); the other two should coincide with two 10 ksec Chandra ACIS-S observations (scheduled for the weeks of Aug 6 and 20). The majority of time during each 4 orbit HST visit will be used to obtain high time- and spectral resolution FUV data, using the STIS/FUV-MAMA/E140M set-up in TIME-TAG. We will also obtain one near-UV spectrum in each HST visit, in order to bridge the gap between our FUV and optical data sets. The short NUV exposure will be taken with the STIS/FUV- MAMA/E230M set-up, but in ACCUM mode, since the global count rate is expected to be very close to the upper limit that can be supported in TIME-TAG mode. Since the NUV exposure is very short in any case, we prefer to play it safe and use ACCUM mode for it. For both FUV and NUV exposures, we will use 0.2x0.06 arcsecond slit. We have used IUE spectra obtained during the previous (1978) outburst of WZ Sge to compute appropriate exposure times and to check that MAMA bright limits will not be violated. The spectra we used were obtained approximately 2 weeks into the 1978 outburst, comparable to the timing of the observations proposed here. More specifically, the IUE spectra we used in the exposure time calculations (SWP03592 and LWR03169) were obtained on Dec 14, 1978, thirteen days after the start of the outburst on Dec 1, 1978. The first possible HST observations would be on August 6, 2001, fourteen days after the beginning of the present outburst on July 23, 2001. IUE observations suggest that the UV flux declined relatively steadily over the course of the last outburst, so that the IUE spectra should be reasonable for determining instrument safety. The online exposure time calculator suggest that, with our FUV set-up, we should expect to reach S/N=10 per resolution element at 1500 A in about 160 s. The peak local count rate is 0.23 c/s/p; the global count rate is 18, 000 c/s. Both numbers are well below the MAMA bright limits. In the NUV, the online ETC suggests that we should reach S/N=10 per resolution element at 2500 A in about 26 s. The peak local count rate is 0.98 c/s/p; the global count rate is 41, 000 c/s. Again, both numbers are well below the MAMA bright limits. For the estimated global count rate in the FUV, the appropriate BUFFER-TIME is roughly 2e6/1.8e4 = 111 s, and the maximum exposure duration that can be sustained in TIME-TAG mode is 6e7/1.8e4 = 3333 s. To be conservative, we will use a slightly shorter BUFFER-TIME of 100 s. The maximum exposure duration is then 30x100s = 3000 s. The observing strategy will be simple: we will use all but two minutes of the time available for scientific exposures to obtain successive 3000 s (or shorter) TIME-TAGged FUV exposures. During the last orbit of each visit, we will also obtain a two minute NUV ACCUM spectrum, which will yield a S/N of about 20 per resolution element at 2500 A. WE FINALLY STRESS THAT WE HAVE FUSE OBSERVATIONS SCHEDULED FOR JULY 30, WHICH WILL ALLOW US CHECK FIRST-HAND WHETHER OUR UV FLUX ESTIMATES BASED ON THE PREVIOUS OUTBURST ARE VALID AND TO ADJUST OUR OBSERVING STRATEGY, IF NECESSARY. Real Time Justification ----------------------- A few days ago, amateur astronomers have established that the cataclysmic variable star WZ Sge has gone into outburst, 23 years after the last outburst event. Since the present outburst occurred about 10 years earlier than expected, no TOO observations were submitted to the most recent TAC. The proposal cannot wait wait until the next TAC, since the outburst is expected to last only 1-2 months and will be well over before the start of Cycle 11. We are asking for three visits consisting of 4 HST orbits each in the early stages of the WZ Sge outburst. Four HST orbits per visit are necessary to cover all orbital phases of WZ Sge's binary period in each visit. In order to maximise scientific output of the data, scheduling simultaneous with planned Chandra visits is strongly requested. Given our current knowledge of planned Chandra dates, we ask for the first visit to be (near) simultaneous with a 25 ksec Chandra/HRC-S/LETG observations scheduled for the week of August 6; the other two should coincide with two 10 ksec Chandra ACIS-S observations scheduled for the weeks of Aug 6 and 20. If scheduling simultaneous with Chandra turns out to be an impossibility, we request the three visits to be scheduled within the first 5-6 weeks of the outburst (before mid september) in order to make sure observations are acquired before the outburst maximum is over. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9287( 10) - 08/04/01 10:32 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 WZSGE STAR, DWARF NOVA RA=20H 7M 36.4S +/- 0.1S, J2000 V = 8 DEC=17D 42' 15.4" +/- 0.1" Coordinate Source: OTHER_SOURCE 9287( 10) - 08/04/01 10:32 - [ 4] Visit: 11 Visit Priority: Visit Requirements: 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 WZSGE STIS/C ACQ F28X50O MIRROR 1 1.1 S CD II ------------------------------------------------------------------------------------------------------------------------------------ 2 WZSGE STIS/C ACQ/PEA 0.2X0.0 G430M 4194 1 10 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 3 WZSGE STIS/N ACCUM 0.2X0.0 E230M 1978 1 120 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 4 WZSGE STIS/N ACCUM 0.2X0.0 E230M 2707 1 120 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 10 WZSGE STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=99 1 600 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 20 WZSGE STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=99 1 2850 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9287( 10) - 08/04/01 10:32 - [ 5] Visit: 12 Visit Priority: Visit Requirements: 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 WZSGE STIS/C ACQ F28X50O MIRROR 1 1.1 S CD II ------------------------------------------------------------------------------------------------------------------------------------ 2 WZSGE STIS/C ACQ/PEA 0.2X0.0 G430M 4194 1 10 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 3 WZSGE STIS/N ACCUM 0.2X0.0 E230M 1978 1 120 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 4 WZSGE STIS/N ACCUM 0.2X0.0 E230M 2707 1 120 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 10 WZSGE STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=99 1 600 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 20 WZSGE STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=99 1 2850 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9287( 10) - 08/04/01 10:32 - [ 6] Visit: 13 Visit Priority: Visit Requirements: SCHED 90% 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 WZSGE STIS/C ACQ F28X50O MIRROR 1 1.1 S CD II ------------------------------------------------------------------------------------------------------------------------------------ 2 WZSGE STIS/C ACQ/PEA 0.2X0.0 G430M 4194 1 10 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 3 WZSGE STIS/N ACCUM 0.2X0.0 E230M 1978 1 120 S MAX DUR UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 4 WZSGE STIS/N ACCUM 0.2X0.0 E230M 2707 1 120 S MAX DUR UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 10 WZSGE STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=99 1 480 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 20 WZSGE STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=99 1 2730 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9287( 10) - 08/04/01 10:32 - [ 7] Visit: 14 Visit Priority: Visit Requirements: SCHED 90% AFTER 13 BY 2.5H TO 3.5H 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 WZSGE STIS/C ACQ F28X50O MIRROR 1 1.1 S CD II ------------------------------------------------------------------------------------------------------------------------------------ 2 WZSGE STIS/C ACQ/PEA 0.2X0.0 G430M 4194 1 10 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 3 WZSGE STIS/N ACCUM 0.2X0.0 E230M 1978 1 120 S MAX DUR UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 4 WZSGE STIS/N ACCUM 0.2X0.0 E230M 2707 1 120 S MAX DUR UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 10 WZSGE STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=99 1 480 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 20 WZSGE STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=99 1 2730 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9287( 10) - 08/04/01 10:32 - [ 8] Visit: 23 Visit Priority: Visit Requirements: SCHED 90% 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 WZSGE STIS/C ACQ F28X50O MIRROR 1 2.5 S CD II ------------------------------------------------------------------------------------------------------------------------------------ 3 WZSGE STIS/N ACCUM 0.2X0.2 E230M 1978 1 120 S MAX DUR UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 4 WZSGE STIS/N ACCUM 0.2X0.2 E230M 2707 1 120 S MAX DUR UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 10 WZSGE STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=99 1 1180 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 20 WZSGE STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=99 1 2730 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9287( 10) - 08/04/01 10:32 - [ 9] Visit: 24 Visit Priority: Visit Requirements: SCHED 90% AFTER 23 BY 2.5H TO 3.5H 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 WZSGE STIS/C ACQ F28X50O MIRROR 1 2.5 S CD II ------------------------------------------------------------------------------------------------------------------------------------ 3 WZSGE STIS/N ACCUM 0.2X0.2 E230M 1978 1 120 S MAX DUR UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 4 WZSGE STIS/N ACCUM 0.2X0.2 E230M 2707 1 120 S MAX DUR UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 10 WZSGE STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=99 1 1180 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 20 WZSGE STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=99 1 2730 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9287( 10) - 08/04/01 10:32 - [ 10] Visit: 25 Visit Priority: Visit Requirements: SCHED 90% BETWEEN 20-AUG-2001 AND 27-AUG-2001 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 WZSGE STIS/C ACQ F28X50O MIRROR 1 2.5 S CD II ------------------------------------------------------------------------------------------------------------------------------------ 3 WZSGE STIS/N ACCUM 0.2X0.2 E230M 1978 1 120 S MAX DUR UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 4 WZSGE STIS/N ACCUM 0.2X0.2 E230M 2707 1 120 S MAX DUR UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 10 WZSGE STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=99 1 1180 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 20 WZSGE STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=99 1 2730 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9287( 10) - 08/04/01 10:32 - [ 11] Visit: 26 Visit Priority: Visit Requirements: SCHED 90% AFTER 25 BY 2.5H TO 3.5H 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 WZSGE STIS/C ACQ F28X50O MIRROR 1 2.5 S CD II ------------------------------------------------------------------------------------------------------------------------------------ 3 WZSGE STIS/N ACCUM 0.2X0.2 E230M 1978 1 120 S MAX DUR UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 4 WZSGE STIS/N ACCUM 0.2X0.2 E230M 2707 1 120 S MAX DUR UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 10 WZSGE STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=99 1 1180 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 20 WZSGE STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=99 1 2730 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9287( 10) - 08/04/01 10:32 - [ 12] Summary Form for Proposal 9287 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50OII 0.2X0.06 0.2X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=99 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/DD ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SCHED 90% MAX DUR SCHED 90% AFTER 13 BY 2.5H TO 3.5H SCHED 90% AFTER 23 BY 2.5H TO 3.5H SCHED 90% BETWEEN 20-AUG-2001 AND 27-AUG-2001 SCHED 90% AFTER 25 BY 2.5H TO 3.5H ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G430M E230M E140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names WZSGE ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 4194 1978 2707 1425 ------------------------------------------------------------------------------------------------------------------------------------