6688( 8) - 08/21/96 09:32 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6688 Version: 8 Check-in Date: 21-Aug-1996 09:30:14 1.Proposal Title: The accretion disk and white dwarf in the dwarf nova HS1804+6753 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle BINARIES AND STAR FOR GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: THOMAS MARSH SOUTHAMPTON UNIVERSITY CoI: Keith Horne St. Andrews University N ------------------------------------------------------------------------------------ 6. Abstract We will take high-speed UV spectroscopy of the dwarf nova HS1804+6753 to find and measure the role of supersonic turbulence in its outer accretion disk. With HST observations of the eclipsing dwarf nova OY Car we have discovered a sensitive probe of physical conditions in its accretion disk. This is based upon model atmosphere fits to strong veiling of the white dwarf by a mass of FeII lines at ultraviolet wavelengths. Suprisingly we found supersonic microturblence at Mach ~ 6 in the absorbing gas. While this would normally be expected to dissipate in shocks, recent theoretical work suggests that the disk can become strongly magnetic in which case it is the Alfven rather than sound speed which is relevant. The result needs to be confirmed on other targets. Other systems are also needed to study vertical stratification in the disk as a single object only gives us one line of sight. Eclipsing dwarf novae are of particular interest as the eclipse allows the component spectra to be separated and because the line-of-sight is likely to pass through the disk. Therefore we propose to observe a newly discovered and relatively bright eclipsing dwarf nova named HS1804+6753. At 5 hours HS1804+6753 has a much longer period than any other suitable target and there are signs that it has a particularly high inclination and therefore it will provide an extreme test of our model. ------------------------------------------------------------------------------------ Observations Description ------------------------ The absorption curtain occurs over a wide range of wavelengths from Ly-alpha up to around 3000 Angstrom, and therefore as we have used on OY Car we will use the G160L (1140 to 2510 Angstrom) which has the important benefit of providing zeroth order light weighted to longer and less obscured wavelengths. We need high time resolution, because the ingress and egress of the white dwarf take only 40 seconds. To fully resolve this we need to observe with the FOS RAPID mode with READ-TIME=4. At the same time continuous coverage of the eclipses is vital as dwarf novae do not repeat precisely from cycle to cycle. This requires long exposures and therefore the low telemetry rate. Therefore we have chosen SUB-STEP=2; the mild under-sampling incurred with the use of SUB-STEP=2 is of no significance to our program. The orbital period of HS 1804+6753 is 5.038 hours and so to obtain continuous coverage of entire orbits we need CVZ scheduling. After a 4-stage peak-up into the 1.0-PAIR-A aperture we can observe for 11.75 hour within the 8 orbit uninterrupted period. This covers more than 2 whole orbits of HS1804+6753 and therefore guarantees coverage of at least 2 eclipses without a phase constraint. If possible, the exposure should be started 30-60 minutes before an eclipse to give coverage of 3 eclipses. However we have not required this in order not to constrain the program any more than already implied by the CVZ restriction. HS1804+6753 is variable so we will use ACQ/PEAK. We have lengthened the acquisition exposures to allow for the eclipses (1.7 mags deep from the usual magnitude around 15), and we have also used a 4-stage peak-up so that even if variability during an eclipse causes the wrong peak to be selected, the star will not be too far from the centre of the aperture. However, if possible, the acquisition exposures should avoid phases within +/-0.08 of the eclipses; again we have not enforced this for flexibility. Real Time Justification ----------------------- Continuous coverage is most important scientifically as pieces of different eclipses cannot be spliced together. Therefore we have requested CVZ scheduling. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6688( 8) - 08/21/96 09:32 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HS1804+6753 STAR,DWARF RA=18H 04M 14.11S +/- J2000 V = 14.0+/-1.0 NOVA,INTERACTING 0.4",DEC=67D 54' 12.2" +/- B-V = 0.2+/-0.2 BINARY, 0.4",PLATE-ID=00T0 E(B-V) = 0.0+/-0.05 U-B = -1.0+/-0.3 Comments: Eclipsing binary, rapidly variable. 6688( 8) - 08/21/96 09:32 - [ 2] Visit: 01 Visit Requirements: CVZ; PERIOD 0.2099372667D AND ZERO-PHASE JD2448398.45250 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 HS1804+6753 FOS/BL ACQ/PEA 4.3 MIRROR SEARCH-SIZE-X=1,SEARCH-SIZE-Y=3, 1 5 S ONBOARD ACQ FOR 20; PHASE K SCAN-STEP-Y=1.23 0.09 TO 0.60 Comments: HS1804+6753 shows eclipses on the HELIOCENTRIC ephemeris HJD = 2448398.45250 + 0.2099372667 E. Acquisition preferable in phase range 0.08 to 0.92. ------------------------------------------------------------------------------------------------------------------------------------ 20 HS1804+6753 FOS/BL ACQ/PEA 1.0-PAI MIRROR SEARCH-SIZE-X=6,SEARCH-SIZE-Y=2, 1 6 S ONBOARD ACQ FOR 30 K R-A SCAN-STEP-X=0.61,SCAN-STEP-Y=0.61 Comments: HS1804+6753 shows eclipses on the HELIOCENTRIC ephemeris HJD = 2448398.45250 + 0.2099372667 E. Acquisition preferable in phase range 0.08 to 0.92. ------------------------------------------------------------------------------------------------------------------------------------ 30 HS1804+6753 FOS/BL ACQ/PEA 0.5-PAI MIRROR SCAN-STEP-X=0.29,SCAN-STEP-Y=0.29 1 6 S ONBOARD ACQ FOR 40 K R-A ,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 Comments: HS1804+6753 shows eclipses on the HELIOCENTRIC ephemeris HJD = 2448398.45250 + 0.2099372667 E. Acquisition preferable in phase range 0.08 to 0.92. ------------------------------------------------------------------------------------------------------------------------------------ 40 HS1804+6753 FOS/BL ACQ/PEA 0.25-PA MIRROR SCAN-STEP-X=0.11,SEARCH-SIZE-X=4, 1 6 S ONBOARD ACQ FOR 100 K IR-A SEARCH-SIZE-Y=4,SCAN-STEP-Y=0.11 Comments: HS1804+6753 shows eclipses on the HELIOCENTRIC ephemeris HJD = 2448398.45250 + 0.2099372667 E. Acquisition preferable in phase range 0.08 to 0.92. ------------------------------------------------------------------------------------------------------------------------------------ 100 HS1804+6753 FOS/BL RAPID 1.0-PAI G160L READ-TIME=4,SUB-STEP=2, 1 10.0 H NO SPLIT R-A STEP-PATT=SINGLE Comments: READ-TIME must be kept at 4 seconds; SUB-STEP=2 for low telemetry. ------------------------------------------------------------------------------------------------------------------------------------ 200 HS1804+6753 FOS/BL RAPID 1.0-PAI G160L READ-TIME=4,SUB-STEP=2, 1 1.57 H NO SPLIT R-A STEP-PATT=SINGLE Comments: READ-TIME must be kept at 4 seconds; SUB-STEP=2 for low telemetry. ------------------------------------------------------------------------------------------------------------------------------------ 6688( 8) - 08/21/96 09:32 - [ 3] Summary Form for Proposal 6688 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 SCAN-STEP-Y=1.23 SCAN-STEP-Y=0.61 SEARCH-SIZE-X=3 SCAN-STEP-Y=0.11 STEP-PATT=SINGLE SUB-STEP=2 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category BINARIES AND STAR FORMATION ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ; PERIOD 0.2099372667D AND ZERO-PHASE JD2448398.45250 ONBOARD ACQ FOR 20; PHASE 0.09 TO 0.60 ONBOARD ACQ FOR 30 ONBOARD ACQ FOR 40 ONBOARD ACQ FOR 100 NO SPLIT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G160L ------------------------------------------------------------------------------------------------------------------------------------ Target Names HS1804+6753 ------------------------------------------------------------------------------------------------------------------------------------