6558( 11) - 10/22/96 14:16 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6558 Version: 11 Check-in Date: 22-Oct-1996 14:13:32 1.Proposal Title: The Accreting Magnetic White Dwarf in AM Her. Heating, Chemical Composition and Mass ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle BINARIES AND STAR FOR GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: KLAUS BEUERMANN UNIVERSITAETS-STERNWARTE GOETTINGEN CoI: Boris T. Gaensicke Universitaets-Sternwarte Goettingen Y CoI: Edward Sion Villanova University N CoI: Paula Szkody University of Washington N ------------------------------------------------------------------------------------ 6. Abstract AM Herculis is the UV-brightest object of its class and, therefore, offers a unique possibility to probe the physics of accretion onto magnetic compact objects with unprecedented detail. Using the sensitivity, velocity, and time resolution of the GHRS, we will (a) determine the fractional area of the accretion region on the white dwarf and the thermal response of the white dwarf to accretion-induced heating (e.g. the lateral and vertical (depth) extent of the heating); (b) determine metal abundances in the accretion-enriched white- dwarf atmosphere for the first time; (c) measure the white- dwarf mass from the radial-velocity curve; and (d) reconstruct the accretion-stream geometry from the radial velocities of the high-excitation emission lines. The proposed HST observations are cornerstones of a major HST/ROSAT/IUE/optical campaign devoted to AM Herculis which lasts from February to October 1996. ------------------------------------------------------------------------------------ Observations Description ------------------------ A) Instrumentation. AM Herculis will be observed with the GHRS using the G140L grating and the LSA aperture, covering the region from 1150 to 1435 Angstrom with a resolution of ~ 0.7 Angstrom. This wavelength region encompasses numerous resonance and subordinate transitions of C, N, O and Si as well as the Lyman-alpha wings (cf. Fig.1). This combination allows a much more efficient (factor ~4 in Lyman-alpha: Leitherer & Kinney 1994) usage of spacecraft time over what can be achieved with the FOS/G130H instrumentation. We plan several visits of AM Her, scheduled as described below. Based on the known IUE fluxes (7x10^-14 ergs/cm2/s/AA in low-state faint phase to 2.2x10^-13ergs/cm2/s/AA in high-state bright phase) the expected GHRS count rates are 1.0 to 4.0 cts/s in the red wing of Lyman-alpha, thus a S/N of 20 can be obtained by integrating over 7 and 2 minutes in the low and the high state, respectively, resulting in an orbital phase resolution of Dphi=0.01- 0.04. We will use the standard ONBOARD/ACQ which leaves 9 minutes for science exposures in the first orbit and 50 minutes in the consecutive one. Additional WAVECALS will preceed the ACCUM exposures to correct for zero-point drifts of the wavelength calibration. The geocoronal emission covers eight diodes, resulting roughly in a FWHM of 4 Angstrom comparable to the results using the FOS with the 1.0" aperture (see Fig.1). The observations will be carried out in the ACCUM mode, choosing FP- SPLIT=NO, COMB=2, STEP- TIME=0.2, STEP-PATT=5; resulting in a time resolution of 13.6 sec. Binning the spectra in 50 Angstrom steps we will obtain UV light curves at 6 wavelengths with a S/N of 10-20, used to detect UV flaring activity. B) Scheduling. Complete orbital-phase coverage is needed to determine the mass of the white dwarf and the chemical/temperature distribution over its surface. This will be achieved in observation set 1 (visit 1&2) as follows: two consecutive HST/GHRS orbits cover two slots of 0.13 orbital phase (9 min, visit 1) and 0.25 orbital phase (50 min, visit 2) of AM Her, respectively. Considering the orbital period of 185.6 minutes of AM Her, 15 HST orbits later two more consecutive HST/GHRS orbits will cover the missing parts of the orbital phase. Summerized: Orbit 01,02=Visit 1, orbit 03-15=Nothing, orbit 16,17=Visit 2. Note that this type of scheduling guarantees full orbital coverage without being time or phase-critical. This first set (visit 1&2) should be scheduled as early in Cycle 6 (or possibly even before). A second such four-orbit set (visit 3&4) will cover AM Her in a different accretion state. This set 2 be scheduled in the same way as set 1 as a TOO. Real Time Justification ----------------------- We have obtained 27 ksec ROSAT/HRI time and 148 hours of IUE time (PI: Gaensicke) for a major campaign on long-term variability of the mass accretion rate in AM Herculis lasting from February 1996 to mid-October 1996. We will use the institutional facilities of the University of Washington (0.76 m telescope at MRO and 3.5 m telescope at APO) to monitor the state of the system via optical photometry and spectroscopy. Additional ground-based optical spectroscopy and photometry will be applied for at the McDonald Observatory (University of Texas) and Calar Alto (Spain/MPG). The visual brightness of AM Her is routinely monitored by the AAVSO/AFOEV. Calibration Justification ------------------------- Real_Time_Justification Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6558( 11) - 10/22/96 14:16 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 AM-HER STAR,POLAR,INTERACTING RA=18H 16M 13.3S +/- 0.2", J2000 V = 14+/-1.5 BINARY DEC=49D 52' 04.1" +/-0.2", PLATE B-V = 0.0+/-0.2 -ID=00TB E(B-V) = 0.00+/-0.01 F-CONT(1300)=3.0+/-2.0e-13 Comments: PERIOD 1.857H AND ZERO-PHASE JD=2443014.76614, AM Her is an HST Guide Star (Star ID 1105, Plate 00TB) 6558( 11) - 10/22/96 14:16 - [ 2] Visit: 01 Visit Requirements: BETWEEN 4-JUL-96 AND 26-JUL-96 On Hold Comments: Additional Comments: Schedule as early as possible in Cycle 6 (July window) Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 AM-HER HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,SEARCH-SIZE=3 1 45 S ONBOARD ACQ FOR 2-3 Comments: STEP-TIME=5.0 sec., 200 counts expected ------------------------------------------------------------------------------------------------------------------------------------ 2 WAVE HRS ACCUM SC2 G140L 1292 SPYBAL=YES 1 54.4 S Comments: Wavelength calibration for Exp. 3 ------------------------------------------------------------------------------------------------------------------------------------ 3 AM-HER HRS ACCUM 2.0 G140L 1292 FP-SPLIT=NO,COMB=FOUR, 134 27.2 S STEP-TIME=0.2,STEP-PATT=5 Comments: Covers phase intervals 0.172-0.302 and 0.555-0.819, time resolution 27.6sec ------------------------------------------------------------------------------------------------------------------------------------ 6558( 11) - 10/22/96 14:16 - [ 3] Visit: 02 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 4 AM-HER HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,SEARCH-SIZE=3 1 45 S ONBOARD ACQ FOR 5-6 Comments: STEP-TIME=5.0 sec., 200 counts expected ------------------------------------------------------------------------------------------------------------------------------------ 5 WAVE HRS ACCUM SC2 G140L 1292 SPYBAL=YES 1 54.4 S Comments: Wavelength calibration for Exp. 6 ------------------------------------------------------------------------------------------------------------------------------------ 6 AM-HER HRS ACCUM 2.0 G140L 1292 FP-SPLIT=NO,COMB=FOUR, 134 27.2 S STEP-TIME=0.2,STEP-PATT=5 Comments: Covers phase intervals 0.928-1.058 and 0.311-0.575, time resolution 27.2S ------------------------------------------------------------------------------------------------------------------------------------ 6558( 11) - 10/22/96 14:16 - [ 4] Visit: 03 Visit Requirements: CVZ 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 ------------------------------------------------------------------------------------------------------------------------------------ 7 AM-HER HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,SEARCH-SIZE=3 1 45 S ONBOARD ACQ FOR 8-9 Comments: STEP-TIME=5.0 sec., 200 counts expected ------------------------------------------------------------------------------------------------------------------------------------ 8 WAVE HRS ACCUM SC2 G140L 1292 SPYBAL=YES 1 54.4 S Comments: Wavelength calibration for Exp. 9 ------------------------------------------------------------------------------------------------------------------------------------ 9 AM-HER HRS ACCUM 2.0 G140L 1292 FP-SPLIT=NO,COMB=FOUR, 215 27.2 S STEP-TIME=0.2,STEP-PATT=5 ------------------------------------------------------------------------------------------------------------------------------------ 11 WAVE HRS ACCUM SC2 G140L 1292 SPYBAL=YES 1 54.4 S Comments: Wavelength calibration for Exp. 12 ------------------------------------------------------------------------------------------------------------------------------------ 12 AM-HER HRS ACCUM 2.0 G140L 1292 FP-SPLIT=NO,COMB=FOUR, 200 27.2 S STEP-TIME=0.2,STEP-PATT=5 ------------------------------------------------------------------------------------------------------------------------------------ 6558( 11) - 10/22/96 14:16 - [ 5] Summary Form for Proposal 6558 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN SEARCH-SIZE=3 SPYBAL=YES STEP-PATT=5 STEP-TIME=0.2 COMB=FOUR FP-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category BINARIES AND STAR FORMATION ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 4-JUL-96 AND 26-JUL-96 ONBOARD ACQ FOR 2-3 ONBOARD ACQ FOR 5-6 CVZ ONBOARD ACQ FOR 8-9 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N1 G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names AM-HER WAVE ------------------------------------------------------------------------------------------------------------------------------------