! File: 3820C.PROP ! Database: PEPDB ! Date: 19-FEB-1994:20:38:02 coverpage: title_1: INSTABILITIES IN ACCRETION DISCS AND THE OUTBURSTS OF DWARF title_2: NOVAE RETAKE OF SAFING sci_cat: STELLAR ASTROPHYSICS sci_subcat: ERUPTIVE BINARIES proposal_for: GO targ_of_opp: X cont_id: 2380 pi_title: DR. pi_fname: KEITH pi_lname: HORNE pi_inst: STSCI pi_country: USA pi_phone: 3013384964 keywords_1: WHITE DWARF DWARF NOVA ACCRETION BOUNDARY LAYER INTER- keywords_2: ACTING BINARY hours_pri: 6.80 num_pri: 1 fos: X time_crit: X funds_amount: 24494 funds_length: 12 funds_date: MAR-90 off_fname: H.S off_lname: STOCKMAN off_title: DEPUTY DIRECTOR off_inst: SPACE TELESCOPE off_addr_1: 3700 SAN MARTIN DRIVE off_city: BALTIMORE off_state: MD off_zip: 21218 off_country: USA ! end of coverpage abstract: line_1: We will use the HST with the FOS to observe eclipses of a dwarf nova at 5 line_2: epochs in the quiescent period between outbursts. From the eclipse data we will line_3: determine the secular evolution of the white dwarf, the accretion disc, and the line_4: bright spot. This evidence will be a clean test of the two competing theories line_5: for the instability which triggers dwarf nova outbursts. In the disc line_6: instability model the transition of the disc from a cool to hot state triggers line_7: the outburst, whereas in the red star instability model the cool binary line_8: companion transfers a short burst of material into the disc which then becomes line_9: brighter. During quiescence the disc instability model predicts an increasing line_10: accretion rate and hence an increasing ultraviolet flux, whereas the red star line_11: model predicts a decreasing accretion rate and ultraviolet flux. Therefore the line_12: variation of the ultraviolet flux with time will distinguish which of the two line_13: current models is correct. line_15: Only the HST is able to resolve the rapid variations seen in an eclipsing dwarf line_16: nova, and therefore determine the ultraviolet flux from the accretion disc. The line_17: observations that we propose will also probe the nature of the boundary layer line_18: between the disc and the white dwarf, a region too small and hot to be well line_19: constrained by any previous observations. In particular, we will measure the line_20: extent of heating of the white dwarf by the boundary layer, and the cooling ! ! end of abstract general_form_proposers: lname: HORNE fname: KEITH title: P.I. inst: STSCI country: USA ! lname: MARSH fname: TOM inst: STSCI country: USA ! ! end of general_form_proposers block general_form_text: question: 3 section: 1 line_1: We will take time-resolved FOS spectra of OY Car, covering a series line_2: of eclipses during the quiescent phase between two outbursts. We line_3: request Target of Opportunity status so that the observations can line_4: start several days after an outburst is reported by variable star line_5: observers of the RASNZ. Our priorities are to measure the relative line_6: contributions of the white dwarf, disc and bright spot to the line_7: ultraviolet flux and to see how they change during the quiescent line_8: period. To do this we must cover the eclipse of each component and line_9: so our exposure times are driven by orbital phase coverage NOT signal line_10: to noise ratio. To ensure that a long timebase is used we have line_11: put the exposures into five groups with defined periods in between. line_12: Other arrangements are possible, for example uniform coverage but line_13: it is not possible to specify in a simple manner. An example of an line_14: unacceptable arrangement is for all the eclipses to be observed line_15: in less than three groups. Our exact specification is designed to line_16: cover two timescales of around 8 days and 40 days. ! question: 4 section: 1 line_1: The HST is the only telescope in existence that can observe at space line_2: ultraviolet wavelengths with sufficient sensitivity to time-resolve line_3: the sharp eclipse features. line_4: Analysis of optical photometry has established a coherent set of line_5: parameters for OY Car, with the orbital inclination accurate to better line_6: than a degree and the mass ratio to 3 percent, and it has led to the line_7: developement of techniques that will be needed to decompose the line_8: ultraviolet light curves. This work provides a firm base for our study line_9: but it does not answer the problems that we wish to investigate. IUE line_10: observations demonstrate a secular decrease in ultraviolet flux during line_11: quiescence, but IUE cannot distinguish between a cooling white dwarf line_12: and a decreasing accretion rate. line_13: The fraction of flux contributed by different sources can only be line_14: measured with the HST. OY Car has been detected by IUE during line_15: quiescence at a flux level of 0.5 mJy at 2400 A, anf therefore the line_16: experiment proposed will work. ! question: 5 section: 1 line_1: For each eclipse, we need to cover all the contact points, and get line_2: a sufficient range outside eclipse to establish baselines for flux line_3: measurements. This requires a minimum of 24 (??) around mid-eclipse. line_4: The dates of our observations are chosen to cover two time-scales. line_5: IUE observations have shown a decrease over 8 days after an outburst. line_6: If this is white dwarf cooling, we can expect the same time-scale for line_7: OY Car. Three epochs is the minimum needed to detect and confirm any line_8: secular trend. Therefore the groups of eclipses at 3, 6 and 10 days line_9: after outburst are designed to detect this post-outburst cooling. We line_10: must also measure trends over the whole of the quiescent period, line_11: which typically lasts 40 to 70 days. The eclipse samples at 10, 25 and line_12: 40 days are sensitive to this long time-scale. The main source of line_13: noise will be the random flickering characteristic of cataclysmic line_14: variables, and in order to reduce and calibrate this, we will observe line_15: three eclipses at each epoch. ! question: 6 section: 1 line_1: Time-critical, uninterrupted observations are needed for two reasons. line_2: First, each exposure must cover all the eclipse contacts of a given line_3: eclipse (therefore time-critical). Since these all occur within 15 line_4: minutes of each other, the exposure must be continuous. line_5: Second, we must cover longer 8 and 40 day timescales of variation. line_6: Many arrangements of the 14 eclipses are possible, however the line_7: limited variety of specifications available has limited our selection. line_8: In words, 8 eclipses should be spread from 3 to 10 days after outburst line_9: and the remaining 6 should cover 15 to 40 days. Finally, to ensure line_10: full coverage of a quiescent period, the observations should start line_11: within 5 days of the detection of an outburst. Note that although line_12: the outbursts are only predictable to within about 30 days, the line_13: the eclipse ephemerides are known precisely. ! question: 7 section: 1 line_1: The data will initially be reduced with the standard software at line_2: STScI. The data analysis techniques that we have developed for line_3: optical eclipse dta will then be deployed. The first priority in line_4: the analysis will be to produce light curves for each eclipse for line_5: three sections of continuum covering the full range of wavelengths line_6: observed. The resulting light curves will then be decomposed to line_7: measure the fluxes from the white dwarf, disc and bright spot as in line_8: figure 2. We will also produce light curves of the Lyman-alpha line_9: absorption and any emission lines detected. line_10: These analyses will give us the white dwarf and disc fluxes at three line_11: wavelengths and also the strength of Lyman-alpha absorption as a line_12: function of time since the outburst. At this stage we will be able to line_13: determine which outburst model is supported by the data. The data will line_14: be further analysed with model atmospheres to deduce the temperature line_15: and size of the emission region on the white dwarf. Emission lines line_16: will be studied to determine their distribution in the system, in line_17: particular to see if there is any evidence for a wind from the disc line_18: during quiescence. ! !end of general form text general_form_address: lname: HORNE fname: KEITH title: DR. category: PI inst: SPACE TELESCOPE SCIENCE INSTITUTE addr_1: 3700 SAN MARTIN DRIVE city: BALTIMORE state: MD zip: 21218 country: USA ! ! end of general_form_address records fixed_targets: targnum: 1 name_1: OY-CAR descr_1: STAR; ECLIPSING BINARY; DWARF NOVA; descr_2: VARIABLE; INTERACTING BINARY; CV; descr_3: ACCRETION DISK; WHITE DWARF pos_1: RA = 10H 6M 22.47S +/- 0.5", pos_2: DEC = -70D 14' 4.9" +/- 0.5", pos_3: PLATE-ID=0196 equinox: 2000 comment_1: VARIABLE STAR. V MAGNITUDE GIVEN comment_2: CORRESPONDS TO FULL RANGE FROM comment_3: QUIESCENCE TO OUTBURST AWAY FROM comment_4: THE ECLIPSE. UV FLUXES SPECIFIED comment_5: FOR QUIESCENCE ONLY. fluxnum_1: 1 fluxval_1: V = 14.0 +/- 2.0, E(B-V) = 0.0 fluxnum_2: 2 fluxval_2: F(1500) = 6 +/- 3 E-15 fluxnum_3: 3 fluxval_3: F(2500) = 6 +/- 3 E-15 ! ! end of fixed targets ! No solar system records found ! No generic target records found exposure_logsheet: linenum: 1.000 sequence_1: DEFINE sequence_2: ECLPS targname: OY-CAR config: FOS/BL opmode: ACQ/BINARY aperture: 4.3 sp_element: MIRROR num_exp: 1 time_per_exp: 3S priority: 1 param_1: FAINT=1800, BRIGHT=720000 req_1: ONBOARD ACQ FOR 2 ; req_2: CYCLE 1 / 1-16 comment_1: BRIGHT AND FAINT SET VERY WIDE BECAUSE comment_2: FIELD IS SIMPLE BUT OBJECT IS LIKELY comment_3: TO CHANGE BRIGHTNESS DURING THE COURSE comment_4: OF THE OBSERVATIONS. ! linenum: 2.000 sequence_1: DEFINE sequence_2: ECLPS targname: OY-CAR config: FOS/BL opmode: RAPID aperture: 1.0 sp_element: G160L wavelength: 1500 num_exp: 1 time_per_exp: 39M priority: 1 param_1: READ-TIME=6.18 req_1: NON-INT ; req_2: ZERO-PHASE JD2443993.55321 +/- 1S ; req_3: PERIOD 0.0631209239D +/- 0.0000000005D ; req_4: PHASE 0.829 +/- 0.03 comment_1: THE EXPOSURE TIME IS DETERMINED BY comment_2: PHASE COVERAGE, NOT SIGNAL-TO-NOISE. comment_3: AT WORST MUST COVER PHASES 0.95 TO comment_4: 0.10 ! linenum: 3.000 sequence_1: USE ECLPS req_1: AT 16-DEC-91 +/- 30D; comment_1: EARLY ECLIPSE TEST;RESCHEDULE comment_2: AS SOON AS POSSIBLE. FIRST TRY comment_3: FAILED DUE TO FOS SAFING. ! linenum: 4.000 sequence_1: USE ECLPS req_1: TARG OF OPP / 4-16 ; req_2: GROUP 4-6 WITHIN 2D comment_1: MUST GET ONTO THE TARGET WITHIN comment_2: 2D +/- 2D OF DETECTION OF OUTBURST comment_3: BY AMATEUR OBSERVERS ! linenum: 5.000 sequence_1: USE ECLPS ! linenum: 6.000 sequence_1: USE ECLPS ! linenum: 7.000 sequence_1: USE ECLPS req_1: AFTER 4 BY 3D +/- 18H ; req_2: GROUP 7-8 WITHIN 2D ! linenum: 8.000 sequence_1: USE ECLPS ! linenum: 9.000 sequence_1: USE ECLPS req_1: AFTER 7 BY 4D +/- 1D ; req_2: GROUP 9-11 WITHIN 3D ! linenum: 10.000 sequence_1: USE ECLPS ! linenum: 11.000 sequence_1: USE ECLPS ! linenum: 12.000 sequence_1: USE ECLPS req_1: AFTER 10 BY 15D +/- 4D ; req_2: GROUP 12-13 WITHIN 4D ! linenum: 13.000 sequence_1: USE ECLPS ! linenum: 14.000 sequence_1: USE ECLPS req_1: AFTER 12 BY 15D +/- 4D ; req_2: GROUP 14-16 WITHIN 5D ! linenum: 15.000 sequence_1: USE ECLPS ! linenum: 16.000 sequence_1: USE ECLPS ! ! end of exposure logsheet ! No scan data records found