9635( 3) - 06/13/02 10:15 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9635 Version: 3 Check-in Date: 13-Jun-2002 10:14:41 1.Proposal Title: UV Zeeman spectroscopy of AM Herculis ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO/DD 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Francis Fekel Tennessee State University CoI: Dr. Knox Long Space Telescope Science Institute N ------------------------------------------------------------------------------------ 5. Abstract AM Herculis, the brightest strongly magnetic cataclysmic variable, entered in December 2001 an extended state of low accretion activity. During such low states, the magnetic white dwarf totally dominates the ultraviolet emission of the system, and only then an in-depth study of its photospheric properties becomes feasible. We propose to obtain an exploratory HST/STIS observation of the magnetic white dwarf in AM Herculis. We will use these data to measure for the first time the Zeeman splittings of metal (C, N, O, Si) resonance lines in a magnetic field that is far beyond the reach of any terrestrial laboratory (B=14MG). These observations will provide fundamental experimental input that should enable significant progress of our understanding of the behaviour of matter in strong magnetic fields. Four HST orbits will be sufficient to map both the abundance and temperature variation over the surface of the WD. ------------------------------------------------------------------------------------ 9635( 3) - 06/13/02 10:15 - [ 2] Observations Description ------------------------ Since we want to be able to reconstruct the spectra as a function of position on the WD surface and since we want to be sensitive to the possibility of rapid time variability, we will use the high-time resolution mode (TIME-TAG) and the G140L grating for the observations. In addition to Lyman alpha, this grating provides access to the prominent resonance lines of CII, III, and IV, NII, NIV, NV, Si II, III, III which have been used to establish abundances of these species in WDs in DNe. As an indication of the quality of the spectra we expect to obtain, we have used the ETC and a model spectrum of a 20000K WD star renormalized to the average low state flux of 7x10**-14 erg/cm**2/s/AA at 1400A observed in quiescence by Gaensicke et al. (1995). With this choice of grating, the 52"x0.2" slit and a 200 second exposure, the S/N per resolution elements exceeds 10 over the entire spectral range, and exceeds 20 from 1300-1500A. Thus we would expect to obtain high quality spectra in less than 1/50 of the orbital period, which is ample for the deconvolutions that must be undertaken. The global count rate of ~1000 cts/s will also facilitate studies of short term temporal variability in the feeble accretion flow. The resolution of the G140L grating (~1200) is ample to resolve not only the lines in the spectrum but also the Zeeman splittings of the lines, which given the magnetic field are expected to be of order 10A. The requested 4 HST orbits will provide near complete (>90%) phase coverage of AM Her. This is needed both for the Zeeman splitting measurements and so that the temperature and abundance distribution on the WD surface can be reconstructed in a unbiased, model-independent way. Because the orbital period of AM Her is nearly twice that of the HST orbit, the observation will be carried out in two two-orbit segments spaced about one day apart. A similar strategy was successfully executed for the high-state GHRS observations of AM Her (Gaensicke et al. 1998, A&A 338, 933). Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9635( 3) - 06/13/02 10:15 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 AM-HER STAR, POLAR RA=18H 16M 13.33S +/- 0.1", J2000 V = 14+/-1.5 DEC=49D 52' 4.1" +/- 0.1", PLATE B-V = 0.0+/-0.2 -ID=00TB E(B-V) = 0.00+/-0.01 F-CONT(1300)=3.0+/-2.0e-13 Coordinate Source: GSC_SURVEY_PLATE Comments: PERIOD 1.857H AND ZERO-PHASE JD=2443014.76614, AM Her is an HST Guide Star (Star ID 1105, Plate 00TB) 9635( 3) - 06/13/02 10:15 - [ 4] Visit: 01 Visit Priority: Visit Requirements: BEFORE 01-Aug-2002 On Hold Comments: Additional Comments: Schedule as early as possible Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 AM-HER STIS/C ACQ F28X50L MIRROR 1 1 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 AM-HER STIS/F TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=200 1 2450 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 30 AM-HER STIS/F TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=200 1 3050 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9635( 3) - 06/13/02 10:15 - [ 5] Visit: 02 Visit Priority: Visit Requirements: AFTER 01 BY 15 Orbits TO 17 Orbits 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 AM-HER STIS/C ACQ F28X50L MIRROR 1 1 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 AM-HER STIS/F TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=200 1 2450 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 30 AM-HER STIS/F TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=200 1 3030 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9635( 3) - 06/13/02 10:15 - [ 6] Summary Form for Proposal 9635 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=200 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/DD ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 01-Aug-2002 AFTER 01 BY 15 Orbits TO 17 Orbits ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names AM-HER ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 ------------------------------------------------------------------------------------------------------------------------------------