6084( 27) - 11/22/95 14:52 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6084 Version: 27 Check-in Date: ********** 1.Proposal Title: The Rotation, Masses and Chemical Abundances of the White Dwarfs in WZ Sagittae and VW Hydri ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Hot Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr.Edward Sion Villanova University CoI: Dr. Min Huang Villanova University N CoI: Dr. Paula Szkody University of Washington N CoI: Dr. Ivan Hubeny NASA GSFC N ------------------------------------------------------------------------------------ 6. Abstract The central accreting object in compact binaries and other accreting systems is usually hidden from direct observation, enshrouded by optically thick accretion disks which are opaque to the radiation emitted by the central object as it accretes matter. In the dwarf novae WZ Sagittae and VW Hydri the underlying white dwarf accreter is clearly exposed in the far UV during quiescence. Orbital phase-resolved GHRS spectra near the quadratures (0.25 and 0.75) of their orbits during quiescence will deliver the following fundamental information: (1) the white dwarf rotation rates, yielding critical information on the boundary layer temperature/structure and spinup of the white dwarfs by accretion; (2) the orbital velocity semi-amplitudes and hence white dwarf masses, independent of disk emission line velocities; (3) delineation by profile shape and velocity,of lower temperature line formation regions associated with the rotating photosphere of the white dwarf from line formation region(s) of higher temperature ion species associated with a boundary layer/accretion belt (or putative hot corona?) still present surrounding the white dwarf; (4) detection of weak metal line profiles and variations versus phase in WZ Sagittae to test accretion versus dredgeup for the origin of carbon, and test physical mechanisms that control the flow of accreted elements and hence abundance changes (diffusion, mixing, dilution, dredeup and ongoing accretion during quiescence). ------------------------------------------------------------------------------------ 6084( 27) - 11/22/95 14:52 - [ 2] Observations Description ------------------------ For WZ Sagittae we need high quality far UV spectra of absorption line features with accurate velocities, orbital phase-resolved and detailed profiles for modelling line shapes, determining the rotational velocity and obtaining GHRS observations centered near orbital phases 0.25 and 0.75 to determine the radial velocity amplitude of the white dwarf by standard cross-correlation techniques of the spectra against each other. Therefore we will use the GHRS side 1 with G140L in (1237-1567 Angstrom), two sets of observations centered at orbital phases 0. 25 and 0.75. From IUE, the flux at 1400Angstrom for WZ Sge is 3* 10^- 14. With the G140L disperser we get 0.57Angstrom/diode and can centroid the lines to 0.1 of 0.57Angstrom or 0.06Angstrom. In 8 minutes (giving a phase resolution of 0.1 orbit) we expect 115 c/s/diode and a S/N = 10. We will use the still reliable (Patterson 1994) eclipse ephemeris of Robinson, Nather and Patterson (1978); viz., T = JD2437547.72845+ 0.0566878455E For VW Hyi (a CVZ target spectra of the line region encompassing the strongest ion absorption features, detected for the first time with our FOS observation of cycle 2. In order to obtain the fully- resolved line profiles, the radial velocity amplitude of the white dwarf, determine the rotational velocity of the white dwarf and delineate different line forming regions, we will use the G160M disperser in the ACCUM operating mode to observe VW Hyi near phases 0.25 and 0.75. Our detailed line profile fitting with TLUSTY and SYNSPEC (Hubeny 1988) utilizes a grid of theoretical profiles broadened by values of vsin i from 0 to several thousand km/s, including composite profiles produced by combining the model fluxes due to a hot differentially rotating accretion belt of adjustable width with synthetic profiles from cooler more slowly rotating higher latitudes of the white dwarf. For VW Hyi during quiescence: Our GHRS, G160M (LSA 1235-1270Angstrom) exposures have count rates of 0.084 cts/sec/diode for VW Hyi requiring 44.5 minutes to reach S/N = 15/diode =60/Angstrom resolution = 0.07 Angstrom/diode (covering high and low temperature species and strongest features (Si II 1260, 1264) in the FOS spectrum; N V (1238, 1242); C III 1247; red wing (turnover) of Lyman Alpha; We will split exposures to obtain a spectrum every 9 minutes. Essentially the same instrumental setup and procedure was used for our successful determination of the velocity amplitude (mass= 0.82 M_\odot) and rotation rate (V_rot = 150 km/s) of the white dwarf in U Gem (Sion et al. 1994). Real Time Justification ----------------------- We need time critical observations for VW Hyi in the sense of obtaining spectra during its quiescence between outbursts (duration 25~50 days) and normal outbursts of 2$~3 days duration. An observation has a 90\ unlikely event of a spectrum during an outburst, it is still of great interest to us. The count rate would not be too large for the GHRS and G160M. The outbursts are statistically very well- characterized by AAVSO and normally quite predictable. The AAVSO and its Director Dr. Janet Mattei have cooperated closely and enthusiastically with us during cycles 2, 3 and 4. Janet Mattei will provide us with VW Hyi normal and superoutburst predictions as she accurately did for cycle 2. Indeed through a scheduling error due to STScI, SPSS operations, one of our FOS spectra was mistakenly rescheduled during a superoutburst avoidance interval, which had been predicted by Dr. Mattei, and specified as a scheduling avoidance interval in our phase II proposal. As a result, the STScI Director approved a cycle 4 carryover to obtain another FOS spectrum of VW Hyi in quiescence. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6084( 27) - 11/22/95 14:52 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6084( 27) - 11/22/95 14:52 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 WZ-SGE STAR, DWARF NOVA, RA=20H 7M 36.416S +/- 0.15S, 2000.0 V=15.0 +/- 0.1 INTERACTING BINARY DEC=+17D 42' 15.39" +/- 0.20" B-V=+0.1+/-0.05 E(B-V)=0.0+/-0.1 F-CONT(1400) = 1.5 +/- 1 E-14 2 VW-HYI STAR, DWARF NOVA, RA=04H 09M 11.300S +/- 0.15S, 2000.0 V=13.6+/-0.1 INTERACTING BINARY DEC=-71D 17' 42.00" +/- 0.15" B-V=+0.0+/-0.1 E(B-V)=0.0+/-0.1 F-CONT(1400) = 8.0 +/- 1 E-14 6084( 27) - 11/22/95 14:52 - [ 5] Visit: 01 Visit Requirements: PERIOD 1.36H AND ZERO-PHASE JD2437547.72845 On Hold Comments: Additional Comments: CENTER EXPOSURES ON PHASES 0.25 AND 0.75 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 HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN, 1 25S ONBOARD ACQ FOR 2 SEARCH-SIZE=5 ------------------------------------------------------------------------------------------------------------------------------------ 2 WZ-SGE HRS RAPID 2.0 G160M 1465 SAMPLE-TIME=1.0 1 1500S ------------------------------------------------------------------------------------------------------------------------------------ 3 WZ-SGE HRS RAPID 2.0 G140L 1381 SAMPLE-TIME=1.0 1 2600S PHASE 0.18 TO 0.21 Comments: PHASE CHOOSEN TO INCLUDE BOTH 0.25 AND 0.75 IN EXPOSURE ------------------------------------------------------------------------------------------------------------------------------------ 6084( 27) - 11/22/95 14:52 - [ 6] Visit: 02 Visit Requirements: CVZ On Hold Comments: Additional Comments: BETWEEN 24-JUN-95 AND 17-DEC-95 BETWEEN 15-JAN-96 AND 8-JUL-96 SCHEDULE ONLY BETWEEN ABOVE DATES TO AVOID SUPERMAXIMA Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 4 VW-HYI HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN, 1 25S ONBOARD ACQ FOR 5; SEARCH-SIZE=5 ------------------------------------------------------------------------------------------------------------------------------------ 5 VW-HYI HRS RAPID 2.0 G160M 1253 SAMPLE-TIME=1.0 1 9800S ------------------------------------------------------------------------------------------------------------------------------------ 6084( 27) - 11/22/95 14:52 - [ 7] Summary Form for Proposal 6084 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN SEARCH-SIZE=5 SAMPLE-TIME=1.0 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Hot Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PERIOD 1.36H AND ZERO-PHASE JD2437547.72845 ONBOARD ACQ FOR 2 PHASE 0.18 TO 0.21 CVZ ONBOARD ACQ FOR 5; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names WZ-SGE VW-HYI ------------------------------------------------------------------------------------------------------------------------------------