6448( 8) - 10/15/96 08:17 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6448 Version: 8 Check-in Date: 15-Oct-1996 08:13:12 1.Proposal Title: Ultraviolet Mapping of the Unique Polar HU Aqr ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle BINARIES AND STAR FOR GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: AXEL SCHWOPE ASTROPHYSICAL INSTITUTE POTSDAM CoI: Keith Horne University of St.Andrews N ------------------------------------------------------------------------------------ 6. Abstract HU Aqr is a unique eclipsing magnetic cataclysmic variable star offering incredible diagnostic power because in this system all parts of the accretion flow are visible, with eclipses for spatial and emission-line velocity profiles for kinematic information. We will use HST for Doppler and eclipse mapping of the ultraviolet continuum and line radiation. The HST maps of CIV 1550 and HeII 1640 emission combined with our Balmer, He I, and HeII 4686 maps from optical data will probe the velocity field and ionization structure in the complete flow, including the irradiated face of the companion star, the ballistic gas stream from that star to the white dwarf magnetosphere, the threading region between the stream and magnetosphere, the magnetically controlled flow down to the standoff shock, and the surrounding heated regions at the white dwarf surface. ------------------------------------------------------------------------------------ Observations Description ------------------------ To summarize, we request 11 HST orbits, 2 for guide star and target acquisitions, 5 for 9 Angstrom resolution FOS/G160L observations (covering full binary orbit and 2 eclipses) and 4 for 0.7Angstrom\\ resolution GHRS/G140L observations (full binary orbit including 1 eclipse). GHRS/G140L Observations: To accomplish goal (a), Doppler imaging of the C IV and HeII emission lines, we must sample most phases of HU Aqr's 125m binary orbit. Fortunately, this is very simple to arrange because the 96m HST orbit is by chance very close to 3/4 of the 125m binary period. A 35-40m observation in each of 4 consecutive HST orbits neatly covers all binary phases. To obtain sufficient spectral resolution for Doppler imaging of the accretion flow, we will use the GHRS with the G140L grating. This samples the spectrum with 0.57 Angstrom/diode, affording a FWHM resolution of 0.7Angstrom (135 km/s) over 1450--1735 Angstrom, including both C IV and HeII. For these exposures we will use ACCUM mode with COMB=2 and STEPPATT=5, giving a readout every 17.6 seconds, of which 12.8s is exposure and 4.8s is dead time. We request this high time resolution in order to avoid blurring the Doppler map due to rotation of velocity vectors during the exposures, and also to gain information about rapid variations due to accretion rate fluctuations and eclipses. High-state IUE spectra of HU Aqr have a 1600 Angstrom continuum flux of 2-3 * 10^-14erg cm^-2 s^-1 AA^-1, C IV equivalent width 122 Angstrom, and HeII equivalent width 46 Angstrom. Using the appropriate sensitivity from the GHRS Handbook (67* 10^11 counts/s/diode per erg cm^-2s^-1 A^-1), we expect ~ 0.17 counts/s/diode or ~ 0.3 counts/s/Angstrom in the continuum, and ~ 36 counts/s in the C IV emission line. Our total GHRS exposure time (35- 40min in each of 4 HST orbits) is ~ 9000s, so we will detect ~ 3 * 10^5 C IV counts, which should yield a very impressive Doppler image. Note that the total exposure time needed is NOT dictated by count rates, but rather by the need to cover the binary orbit phases. There is a chance that HU Aqr will be in a faint state at the time of the HST observations. The continuum flux may then be 5-20 times less than assumed above. Note that we expect 6-16 * 10^-16 erg cm^-2 s^-1 A^-1 from the white dwarf alone, assuming a temperature of 10-12* 10^3K. For the lines this may be partially offset by higher equivalent widths in fainter states. Thus even if HU Aqr is in a faint state when HST observes, we still expect to detect ~ 3 * 10^4 C IV counts, sufficient to obtain a good Doppler map. FOS/G160L Observations: To accomplish goals (b) - (d) we need to observe orbital variations and at least 2 eclipses, with a wide wavelength range so that we have good sensitivity for measuring temperatures, and a high time resolution so that we can determine sizes and shapes of features from eclipses. We will accomplish this by using the FOS, Blue digicon, and G160L grating. The first-order spectrum covers 1150-2500 Angstrom at 9 Angstrom resolution, and the zero-order gives a simultaneous `white-light' photometric light curve (bandpass centered near 3400 Angstrom width 2000Angstrom). To maximize the information and permit us to know the optical state of the system at the time of the HST observations, we will insert short FOS/PRISM exposures to record at low-resolution the 2000--7000Angstrom\\ spectrum, including MgII, the Balmer continuum, jump, and optical line fluxes. For all the FOS observations we will use RAPID mode with SUB-STEP=2 and READ- TIME=3.1s, providing a spectrum every 3.1s with a duty cycle of over 75. These FOS observations will be made in 5 consecutive HST orbits, and a binary phase constraint will be placed on the first orbit so that the first and fifth HST orbits contain eclipses of HU Aqr. For FOS/G160L, using 10^-15erg cm^-2s^-1 A^- 1 and inverse sensitivities at 1500 Angstrom from the FOS Instrument Handbook, we expect ~0.05 counts/s/Angstrom from the white dwarf. The white dwarf eclipse ingress and egress each last ~ 40s. Binning the data by Delta t in time and DeltaLambda in wavelength yields a light curve with ~ 200 (Delta t/40 s)(DeltaLambda/100Angstrom) counts from the white dwarf. Analysis of the 2 eclipses should define the white dwarf spectrum with S/N~15 per 100Angstrom at 1500 Angstrom, and given the baseline from 1150 to 2500 in first order and to 3400 including order 0, this should suffice to measure the white dwarf temperature to a few hundred degrees. The ingress and egress durations for eclipses of the hot accretion region on the white dwarf may be 3-20s, depending on its size and shape, and the UV flux from this region is also very uncertain (that's what we're trying to measure.). The above calculation indicates that we will have sufficient photons to define the size, shape, and temperature of the accretion spot provided its flux is comparable to or brighter than the white dwarf, as should be the case. We will attempt to make the fullest use of the data by mapping the temperature distribution on the white dwarf surface using a maximum entropy fit to the spectra as a function of phase. COMMENTS on the BRIGHTNESS VARIATIONS of HU Aqr: HU Aqr is a variable star on short (minutes and hours: QPOs, orbital modulation, flares) and long timescales (month: change between high/intermediate/low states of activity). It displays a deep eclipse lasting 584 sec (0.078 phase units) and has a pronounced modulation on its 125 min orbital timescale. Typical brightness values are: High accretion state and bright phase: Vmax = 15 High accretion state and faint phase: Vmax = 15.5 Intermediate state and bright phase: Vmax = 15.4-16 Intermediate state and faint phase: Vmax = 16-16.5-.. Low state: V approx 17.5 - 18 (not well known), little orbital variablity Eclipse: B~19.5 mag (late Mstar spectrum seen then) The data F-CONT and W-LINE at 1500/1550, however, given below in the target description, apply to a mean orbital high state. Also the colors are changing dependent on brightness: High state, faint phase: B-V = 0.24 Low state, faint phase: not well known, but the spectrum is then that of a ~10-12000K white dwarf, hence B-V~0.0 The high state color of 0.25 suggest the spectrum to be similar to a late A star, but the radiation is not of photospheric origin. Unlike photospheric radiation, we have a strong Balmer jump in EMISSION, hence we get much more UV-photons than from a star of that color. ACQUISITION STRATEGY: The problem for aquisition is the high variability of the target. We have to cope with possible high and low states (V between 15 and 18) which makes an ACQ/BIN difficult and we have to cope with short-time scale variability which may easily exceed 10% if an ACQ/PEAK would be the method of choice. Both methods are in danger to fail We have therefore decided to prefer a mixed strategy of an ACQ/BIN centered on the faint phase (were least variability and smallest range in brightness between the different states of accretion is observed, V=15.5 - 18), followed by an ACQ/PEAK. We have to define as bright and faint limits for the ACQ/BIN the complete allowed and useful range (BRIGHT=720000, FAINT=330). This should cover all possible brightness stages the source can be encountered in. Some confusion exists about the allowed spread. The FOS handbook (page 32) sets limits of +-1mag, contact with STSCI revealed limits of +-1.3 mag, but the recommended values for BRIGHT and FAINT in the FOS handbook (pg. 35, 30 times brighter and 13 times fainter than expected) suggest that ACQ/BIN can cope even with a full range of 6.5 magnitudes We have ASSUMED a brightness of V=16.7 and a color B-V=0.01 for the calculation of the exposure time for ACQ/BIN, which becomes then 60 sec. In its low state the target is to faint to be acquired with the HRS. We, therefore, use the reuse_target_offset option for the second visit in order to re- establish the same guide star pattern. I will prepare also a complete rps2- proposal where Tacq is performed via a series of peakups. Should the technical review reveal, that the mixed strategy cannot work, I am prepared to provide on the instant a functioning alternative (disregarding the effect, that the RPS2 software for the FOS produces corrupt first orbits). Deviating from our original plan and related to the scheme of Tacq defined here, we cannot give the first of the RAPIDS in the first visit a phase constraint. That would collide with the phase constraint given already to the ACQ/BIN. We therefore will not be able to cover the eclipse twice as requested in the original proposal (this apllies also, if a 7th orbit is spent in the first visit). We will, therefore, use the first orbit of the second visit for one phase- constrained FOS/G160L observation which covers the eclipse completely Real Time Justification ----------------------- No special requirements needed. Another 450 ksec has been granted to an EUVE proposal for HU Aqr (PI: Axel Schwope). We are trying to influence the schedule of EUVE in order to perform a simultaneous (or near-simultaneous) observation of HU Aqr using both spaceborne observatories. We will also try hard to provide simultaneous ground-based photometry or spectroscopy. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6448( 8) - 10/15/96 08:17 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HU-AQR STAR,POLAR,INTERACTING RA=21H 07M 58.28S +/- 0.3", DEC= J2000 V = 16.5 BINARY -5D 17' 39.4" +/- 0.3", PLATE- E(B-V) = 0 ID=03U3 F-CONT(1500)=3+/-1e-14 W-LINE(1550)=122 Comments: HU Aqr is a variable star on short (minutes and hours) and long timescales (month). It displays a deep eclipse and has a pronounced modulation on its 125 min orbital timescale. FOR FURTHER COMMENTS ON TARGET BRIGHTNESS AND CONSEQUENCES FOR TACQ STRATEGY SEE SECTION 'OBSERVING DESCRIPTION' ABOVE 6448( 8) - 10/15/96 08:17 - [ 2] Visit: 01 Visit Requirements: PERIOD 0.086820446D AND ZERO-PHASE JD2448896.543707 On Hold Comments: Additional Comments: SCHEDULE BETWEEN 8/30/96 and 8/31/96, which is the best period for accompanying ground-based observations, but in any case BETWEEN 1-JUL-1996 AND 31-DEC-1996 were the first date is simply start of cycle 6 and the second just to safeguard against late scheduling, unforeseen events and failure of the complete observation. The visibility window, however, is only open between August 20 and Dec 10, so this is not a real constraint. Start this visit as early as possible after passage of the SAA, since we are interested in an uninterrupted monitoring of the source. It is not important to reach e.g. a specific S/N and therefore integrating a long time, but to establish a 'perfect' time series. The four iterations in exposure 50 which each fill one complete orbit MUST orbits. Only this mode (together with the 125 min orbital period of the binary and the 96.4 min period of the spacecraft) will provide full orbital coverage of the target. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 HU-AQR FOS/BL ACQ/BIN 4.3 MIRROR 1 30 S ONBOARD ACQ FOR 20 PHASE ARY 0.38 TO 0.54 Comments: ACQ/BIN in faint phase seq 10-36 non-int is workaround for fos-software fault related with filling of first orbit ------------------------------------------------------------------------------------------------------------------------------------ 20 HU-AQR FOS/BL ACQ/PEA 0.5-PAI MIRROR SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3, 1 7.2 S ONBOARD ACQ FOR 35-50 K R-A SCAN-STEP-X=0.11,SCAN-STEP-Y=0.11 SAVE OFFSET OFF1 Comments: FOS search pattern C2 with reduced step-size ------------------------------------------------------------------------------------------------------------------------------------ 35 HU-AQR FOS/BL ACCUM 1.0-PAI PRISM 1 3 M R-A ------------------------------------------------------------------------------------------------------------------------------------ 36 HU-AQR FOS/BL RAPID 1.0-PAI G160L READ-TIME=3.1,SUB-STEP=2, 1 306.9 S R-A STEP-PATT=SINGLE Comments: Fill first orbit ------------------------------------------------------------------------------------------------------------------------------------ 40 HU-AQR FOS/BL RAPID 1.0-PAI G160L READ-TIME=3.1,SUB-STEP=2, 1 2687.7 R-A STEP-PATT=SINGLE Comments: Start series of RAPID exposure ------------------------------------------------------------------------------------------------------------------------------------ 50 HU-AQR FOS/BL RAPID 1.0-PAI G160L READ-TIME=3.1,SUB-STEP=2, 4 2687.7 NO SPLIT R-A STEP-PATT=SINGLE Comments: Four RAPID exposures without phase constraint The iterations (each one fills one orbit), MUST be done in consecutive orbits in order to provide full-phase coverage END of VISIT 1 ------------------------------------------------------------------------------------------------------------------------------------ 6448( 8) - 10/15/96 08:17 - [ 3] Visit: 02 Visit Requirements: AFTER 1 BY 4D TO 30D SAME ORIENT AS 1 PERIOD 0.086820446D AND ZERO-PHASE JD2448896.543707 On Hold Comments: Additional Comments: SCHEDULE BETWEEN 9/3/96 AND 9/5/96. Exposures 130-160 MUST NOT be interrupted due to passage of the SAA. The 96.4 min orbit together with the 125 min period of the binary provides the necessary prerequisite to cover all binary phases without gaps if the observations are performed in 4 CONSECUTIVE orbits. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 110 HU-AQR FOS/BL ACQ/PEA 0.5-PAI MIRROR SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3, 1 7.2 S ONBOARD ACQ FOR 120-160 K R-A SCAN-STEP-X=0.11,SCAN-STEP-Y=0.11 USE OFFSET OFF1 Comments: FOS search pattern C2 with reduced step-size ------------------------------------------------------------------------------------------------------------------------------------ 120 HU-AQR FOS/BL RAPID 1.0-PAI G160L READ-TIME=3.1,SUB-STEP=2, 1 1463.2 PHASE 0.872 TO 0.944 USE R-A STEP-PATT=SINGLE OFFSET OFF1 Comments: phase constraint in order to cover eclipse ------------------------------------------------------------------------------------------------------------------------------------ 130 HU-AQR HRS ACCUM 2.0 G140L 1595 FP-SPLIT=NO,COMB=FOUR,STEP-PATT=5 81 27.2 S NO SPLIT ,STEP-TIME=0.2,DOPPLER=ON ------------------------------------------------------------------------------------------------------------------------------------ 140 HU-AQR HRS ACCUM 2.0 G140L 1595 FP-SPLIT=NO,COMB=FOUR,STEP-PATT=5 81 27.2 S NO SPLIT ,STEP-TIME=0.2,DOPPLER=ON ------------------------------------------------------------------------------------------------------------------------------------ 150 HU-AQR HRS ACCUM 2.0 G140L 1595 FP-SPLIT=NO,COMB=FOUR,STEP-PATT=5 81 27.2 S NO SPLIT ,STEP-TIME=0.2,DOPPLER=ON ------------------------------------------------------------------------------------------------------------------------------------ 160 HU-AQR HRS ACCUM 2.0 G140L 1595 FP-SPLIT=NO,COMB=FOUR,STEP-PATT=5 81 27.2 S NO SPLIT ,STEP-TIME=0.2,DOPPLER=ON ------------------------------------------------------------------------------------------------------------------------------------ 6448( 8) - 10/15/96 08:17 - [ 4] Visit: 52 Visit Requirements: PERIOD 0.086820446D AND ZERO-PHASE JD2448896.543707 On Hold Comments: Additional Comments: HOPR Repeat of Visit 2. Exposures 130-160 MUST NOT be interrupted due to passage of the SAA. The 96.4 min orbit together with the 125 min period of the binary provides the necessary prerequisite to cover all binary phases without gaps if the observations are performed in 4 CONSECUTIVE orbits. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 HU-AQR FOS/BL ACQ/BIN 4.3 MIRROR 1 30 S ONBOARD ACQ FOR 20 PHASE ARY 0.38 TO 0.54 Comments: ACQ/BIN in faint phase ------------------------------------------------------------------------------------------------------------------------------------ 20 HU-AQR FOS/BL ACQ/PEA 0.5-PAI MIRROR SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3, 1 7.2 S ONBOARD ACQ FOR 35-160 K R-A SCAN-STEP-X=0.11,SCAN-STEP-Y=0.11 Comments: FOS search pattern C2 with reduced step-size ------------------------------------------------------------------------------------------------------------------------------------ 35 HU-AQR FOS/BL ACCUM 1.0-PAI PRISM 3 150 S R-A ------------------------------------------------------------------------------------------------------------------------------------ 130 HU-AQR HRS ACCUM 2.0 G140L 1595 FP-SPLIT=NO,COMB=FOUR,STEP-PATT=5 81 27.2 S NO SPLIT ,STEP-TIME=0.2,DOPPLER=ON ------------------------------------------------------------------------------------------------------------------------------------ 140 HU-AQR HRS ACCUM 2.0 G140L 1595 FP-SPLIT=NO,COMB=FOUR,STEP-PATT=5 81 27.2 S NO SPLIT ,STEP-TIME=0.2,DOPPLER=ON ------------------------------------------------------------------------------------------------------------------------------------ 150 HU-AQR HRS ACCUM 2.0 G140L 1595 FP-SPLIT=NO,COMB=FOUR,STEP-PATT=5 81 27.2 S NO SPLIT ,STEP-TIME=0.2,DOPPLER=ON ------------------------------------------------------------------------------------------------------------------------------------ 160 HU-AQR HRS ACCUM 2.0 G140L 1595 FP-SPLIT=NO,COMB=FOUR,STEP-PATT=5 81 27.2 S NO SPLIT ,STEP-TIME=0.2,DOPPLER=ON ------------------------------------------------------------------------------------------------------------------------------------ 6448( 8) - 10/15/96 08:17 - [ 5] Summary Form for Proposal 6448 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/BINARY ACQ/PEAK ACCUM RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE-X=3 SEARCH-SIZE-Y=3 SCAN-STEP-X=0.11 SCAN-STEP-Y=0.11 STEP-PATT=SINGLE SUB-STEP=2 READ-TIME=3.1 DOPPLER=ON STEP-TIME=0.2 STEP-PATT=5 COMB=FOUR FP-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category BINARIES AND STAR FORMATION ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PERIOD 0.086820446D AND ZERO-PHASE JD2448896.543707 ONBOARD ACQ FOR 20 PHASE 0.38 TO 0.54 ONBOARD ACQ FOR 35-50 SAVE OFFSET OFF1 NO SPLIT AFTER 1 BY 4D TO 30D SAME ORIENT AS 1 PERIOD 0.086820446D AND ZERO-PHASE JD2448896.543707 ONBOARD ACQ FOR 120-160 USE OFFSET OFF1 PHASE 0.872 TO 0.944 USE OFFSET OFF1 ONBOARD ACQ FOR 35-160 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR PRISM G160L G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names HU-AQR ------------------------------------------------------------------------------------------------------------------------------------