7397( 9) - 09/02/98 16:23 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7397 Version: 9 Check-in Date: 02-Sep-1998 16:22:24 1.Proposal Title: Probing the 230 MG Accreting Magnetic White Dwarf in AR Ursae Majoris ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Gary D. Schmidt University of Arizona CoI: Paula Szkody Astronomy Department, University of N Washington CoI: H.S. Stockman Space Telescope Science Institute N CoI: Boris Gaensicke Universitaet-Sternwarte, Goettingen N ------------------------------------------------------------------------------------ 5. Abstract During the past year we identified the luminous X-ray source AR UMa to be the first ``high-field'' (B > 100 MG) AM Her- type magnetic accretion binary. Evidence for a strong magnetic field on the primary star comes from several lines of evidence, however the quantitative estimate of B~230 MG is based on the identification of the photospheric LyAlpha Sigma+ Zeeman component with an absorption feature in the low- state IUE spectrum, which itself is of limited S/N and offers no binary phase resolution. We propose to place this discovery on a firmer observational footing through low- resolution, phase-resolved FUV and NUV spectroscopy with STIS. Two detector/grating combinations will 1) examine the position and shape of the LyAlpha Sigma+ feature at high S/N throughout the orbital cycle; 2) enable a search for the LyAlpha PI component, which is expected to appear just shortward of the geocoronal line at this field strength; 3) evaluate the reality of other Zeeman features suggested by the current data; and 4) allow the emitted energy distribution to be compared to lower-field AM Her systems being studied with HST. Already, the peculiar properties of AR UMa suggest that the dyamics and radiation physics of accreted material in high-field binaries are qualitatively different from the standard AM Her systems, and therefore that study of high-field objects will lend new insight into the general phenomenon of accretion in strong magnetic fields. ------------------------------------------------------------------------------------ 7397( 9) - 09/02/98 16:23 - [ 2] Observations Description ------------------------ The proposed observational sequence is straightforward and thus well-suited for STIS during its initial Cycle of use. AR UMa is a V=16.5 source when in the low accretion state and up to 2.5 mag brighter in the high state. Acquisition will consist of a normal guide-star acquisition, target acquisition, and point- source peak-up into the 0.2 arcsec- wide slit. For these, we allow a total of 27 min of the first orbit. We propose to fill the visibility window of that orbit and an additional 3.5 orbits with TIMETAG exposures using the G140L grating and FUV-MAMA (LambdaLambda1150-1736). This is the minimum number of consecutive spacecraft orbits for which it is possible to achieve full coverage of the binary phases. Including the target reacquisitions, 60 sec overhead per exposure, and automatic wavecals, this strategy obtains more than 150 minutes of exposure over 4 binary cycles. Though our top priority -- phase analysis of the spectral features -- will require binning to intervals of DeltaPhi~0.05, TIMETAG mode has been chosen in the event that we catch the system in an active state when it will be possible to inspect for flickering due to the anticipated ``blobby'' accretion. From the STIS exposure time calculator, the expected count rate in the active state is only ~700 Hz, far below the TIMETAG limits. Limiting individual exposures to ~8 mins will ensure that we do not overrun the TIMETAG total count limitation, even if the source is 5* brighter than measured by IUE in the high state. The remainder of the 5th orbit will utilize the G230L grating and NUV-MAMA to examine the longer-wavelength UV region (LambdaLambda1570-3180) for the reality of a possible Zeeman feature near 1680 Angstrom and for extension of the energy distribution toward the ground-based optical. Note that the line flux for CIVLambda1550 specified in the "Flux Data" section of this proposal is the flux INTEGRATED across the line, and so is in units of erg/cm**2/s. Typical line widths are ~1000 km/s = 20 Angstroms. Real Time Justification ----------------------- Because IUE has shown that the UV continuum level does not vary appreciably with changes in accretion state, TOO scheduling is not required. AR UMa is not within the CVZ. Ground-based polarimetry, spectropolarimetry, and spectroscopy of AR UMa will be obtained throughout 1996-97 in our continuing investigation of this important system. Szkody has received a TOO allocation with the EUVE satellite and has submitted a TOO proposal for ASCA to examine the X- ray spectrum of the source when it next enters a high accretion state. We are also collaborators on an XTE proposal (R. M. Wagner, PI) to search for correlated X- ray/optical fluctuations which would be indicative of the ``blobby'' accretion predicted by our interpretation. None of these supporting observations require coordination with the HST observations requested here. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7397( 9) - 09/02/98 16:23 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7397( 9) - 09/02/98 16:23 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ARUMA STAR, POLAR RA=11H 15M 44.68S +/- .3", J2000 V = 15.5+/-1.0 DEC=42D 58' 22.50" +/- .3", F-CONT(1500)=2+/-1e-14 PLATE-ID=01QX F-LINE(1550)=3+/-1e-12 7397( 9) - 09/02/98 16:23 - [ 5] Visit: 01 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 ARUMA STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 3 S ONBOARD ACQ FOR 30-60 CD P ------------------------------------------------------------------------------------------------------------------------------------ 30 ARUMA STIS/F TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=500 1 39.5 M UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 40 ARUMA STIS/F TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=500 1 2730 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 42 ARUMA STIS/F TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=500 1 2730 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 44 ARUMA STIS/F TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=500 1 2730 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 50 ARUMA STIS/F TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=500 1 1320 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 60 ARUMA STIS/N TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=500 1 1200 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 7397( 9) - 09/02/98 16:23 - [ 6] Summary Form for Proposal 7397 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT BUFFER-TIME=500 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 30-60 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L G230L ------------------------------------------------------------------------------------------------------------------------------------ Target Names ARUMA ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 2376 ------------------------------------------------------------------------------------------------------------------------------------