! Proposal 6688, submission 1 ! PI: Thomas Marsh ! Received Mon Feb 12 14:48:12 EST 1996 ! From: trm@astro.soton.ac.uk ! +====================+ ! | PED OUTPUT PRODUCT | ! +====================+ ! ! /pool7/trm/hst_phaseII/6688.prop ! Generated by PREPROCESSOR, version 6.0e ! Date: Mon Feb 12 18:23:29 GMT 1996 Proposal_Information Title: The accretion disk and white dwarf in the dwarf nova HS1804+6753 Proposal_Category: GO Scientific_Category: BINARIES AND STAR FORMATION Cycle: 6 Investigators PI_Name: Thomas Marsh PI_Institution: Southampton University CoI_Name: Keith Horne CoI_Institution: St. Andrews University Contact: 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. Questions Observing_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: Fixed_Targets Target_Number: 1 Target_Name: HS1804+6753 Alternate_Names: GSC4429.01070 Description: STAR,DWARF NOVA,INTERACTING BINARY, Position: RA=18H 04M 14.11S +/- 0.4",DEC=67D 54' 12.2" +/- 0.4",PLATE-ID=00T0 Equinox: J2000 RV_or_Z: RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: V = 14.0+/-1.0 B-V = 0.2+/-0.2 E(B-V) = 0.0+/-0.05 U-B = -1.0+/-0.3 Comments: Eclipsing binary, rapidly variable. Solar_System_Targets Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: CVZ; PERIOD 0.2099372667D AND ZERO-PHASE JD2448398.45250 On_Hold_Comments: Visit_Comments: Exposure_Number: 10 Target_Name: HS1804+6753 Config: FOS/BL Opmode: ACQ/PEAK Aperture: 4.3 Sp_Element: MIRROR Wavelength: Optional_Parameters: SEARCH-SIZE-X=1,SEARCH-SIZE-Y=3,SCAN-STEP-Y=1.23 Number_of_Iterations: 1 Time_Per_Exposure: 5S Special_Requirements: ONBOARD ACQ FOR 20; PHASE 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. Exposure_Number: 20 Target_Name: HS1804+6753 Config: FOS/BL Opmode: ACQ/PEAK Aperture: 1.0-PAIR-A Sp_Element: MIRROR Wavelength: Optional_Parameters: SEARCH-SIZE-X=6,SEARCH-SIZE-Y=2,SCAN-STEP-X=0.61,SCAN-STEP-Y=0.61 Number_of_Iterations: 1 Time_Per_Exposure: 6S Special_Requirements: ONBOARD ACQ FOR 30 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. Exposure_Number: 30 Target_Name: HS1804+6753 Config: FOS/BL Opmode: ACQ/PEAK Aperture: 0.5-PAIR-A Sp_Element: MIRROR Wavelength: Optional_Parameters: SCAN-STEP-X=0.29,SCAN-STEP-Y=0.29,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 Number_of_Iterations: 1 Time_Per_Exposure: 6S Special_Requirements: ONBOARD ACQ FOR 40 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. Exposure_Number: 40 Target_Name: HS1804+6753 Config: FOS/BL Opmode: ACQ/PEAK Aperture: 0.25-PAIR-A Sp_Element: MIRROR Wavelength: Optional_Parameters: SCAN-STEP-X=0.11,SEARCH-SIZE-X=4,SEARCH-SIZE-Y=4,SCAN-STEP-Y=0.11 Number_of_Iterations: 1 Time_Per_Exposure: 6S Special_Requirements: ONBOARD ACQ FOR 100 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. Exposure_Number: 100 Target_Name: HS1804+6753 Config: FOS/BL Opmode: RAPID Aperture: 1.0-PAIR-A Sp_Element: G160L Wavelength: Optional_Parameters: READ-TIME=4,SUB-STEP=2,STEP-PATT=SINGLE Number_of_Iterations: 1 Time_Per_Exposure: 10.0H Special_Requirements: NO SPLIT Comments: READ-TIME must be kept at 4 seconds; SUB-STEP=2 for low telemetry. Exposure_Number: 200 Target_Name: HS1804+6753 Config: FOS/BL Opmode: RAPID Aperture: 1.0-PAIR-A Sp_Element: G160L Wavelength: Optional_Parameters: READ-TIME=4,SUB-STEP=2,STEP-PATT=SINGLE Number_of_Iterations: 1 Time_Per_Exposure: 1.57H Special_Requirements: NO SPLIT Comments: READ-TIME must be kept at 4 seconds; SUB-STEP=2 for low telemetry. Data_Distribution ! Defaults indicated; change if desired Medium: 8MM Blocking_Factor: 10 Ship_To: PI_Address Ship_Via: UPS Recipient_Email: ! Let us know what you think of this template and software! ! Please send a list of your likes and dislikes to your Program Coordinator