Proposal_Information ! Section 4 Title: The Accreting Magnetic White Dwarf in AM Her. Heating, Chemical Composition and Mass Proposal_Category: GO Scientific_Category: BINARIES AND STAR FORMATION Cycle: 6 Investigators PI_name: Klaus Beuermann PI_Institution: Universitaets-Sternwarte Goettingen CoI_Name: Boris T. Gaensicke CoI_Institution: Universitaets-Sternwarte Goettingen Contact: Y CoI_Name: Edward Sion CoI_Institution: Villanova University Contact: N CoI_Name: Paula Szkody CoI_Institution: University of Washington Contact: N 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. Questions ! Free format text (please update) Observing_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: Fixed_Targets Target_Number: 1 Target_Name: AM-HER Alternate_Names: Description: STAR,POLAR,INTERACTING BINARY Position: RA=18H 16M 13.3S +/- 0.2", DEC=49D 52' 04.1" +/-0.2", PLATE-ID=00TB Equinox: J2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: V = 14 +/- 1.5 B-V = 0.0 +/- 0.2 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) Visits Visit_Number: 1 Visit_Requirements: BETWEEN 4-JUL-96 AND 26-JUL-96 On_Hold_Comments: Visit_Comments: Schedule as early as possible in Cycle 6 (July window) Exposure_Number: 1 Target_Name: AM-HER Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N1 Wavelength: Optional_Parameters: BRIGHT=RETURN, SEARCH-SIZE=3 Number_of_Iterations: 1 Time_Per_Exposure: 45S Special_Requirements: ONBOARD ACQ FOR 2-3 Comments: STEP-TIME=5.0 sec., 200 counts expected Exposure_Number: 2 Target_Name: WAVE Config: HRS Opmode: ACCUM Aperture: SC2 Sp_Element: G140L Wavelength: 1292 Optional_Parameters: SPYBAL=YES Number_of_Iterations: 1 Time_Per_Exposure: 54.4S Special_Requirements: Comments: Wavelength calibration for Exp. 3 Exposure_Number: 3 Target_Name: AM-HER Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1292 Optional_Parameters: FP-SPLIT=NO, COMB=FOUR, STEP-TIME=0.2, STEP-PATT=5 Number_of_Iterations: 134 Time_Per_Exposure: 27.2S Special_Requirements: Comments: Covers phase intervals 0.172-0.302 and 0.555-0.819, time resolution 27.6sec Visit_Number: 2 Visit_Requirements: On_Hold_Comments: Visit_Comments: Exposure_Number: 4 Target_Name: AM-HER Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N1 Wavelength: Optional_Parameters: BRIGHT=RETURN, SEARCH-SIZE=3 Number_of_Iterations: 1 Time_Per_Exposure: 45S Special_Requirements: ONBOARD ACQ FOR 5-6 Comments: STEP-TIME=5.0 sec., 200 counts expected Exposure_Number: 5 Target_Name: WAVE Config: HRS Opmode: ACCUM Aperture: SC2 Sp_Element: G140L Wavelength: 1292 Optional_Parameters: SPYBAL=YES Number_of_Iterations: 1 Time_Per_Exposure: 54.4S Special_Requirements: Comments: Wavelength calibration for Exp. 6 Exposure_Number: 6 Target_Name: AM-HER Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1292 Optional_Parameters: FP-SPLIT=NO, COMB=FOUR, STEP-TIME=0.2, STEP-PATT=5 Number_of_Iterations: 134 Time_Per_Exposure: 27.2S Special_Requirements: Comments: Covers phase intervals 0.928-1.058 and 0.311-0.575, time resolution 27.2S Visit_Number: 3 Visit_Requirements: CVZ On_Hold_Comments: Visit_Comments: Exposure_Number: 7 Target_Name: AM-HER Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N1 Wavelength: Optional_Parameters: BRIGHT=RETURN, SEARCH-SIZE=3 Number_of_Iterations: 1 Time_Per_Exposure: 45S Special_Requirements: ONBOARD ACQ FOR 8-9 Comments: STEP-TIME=5.0 sec., 200 counts expected Exposure_Number: 8 Target_Name: WAVE Config: HRS Opmode: ACCUM Aperture: SC2 Sp_Element: G140L Wavelength: 1292 Optional_Parameters: SPYBAL=YES Number_of_Iterations: 1 Time_Per_Exposure: 54.4S Special_Requirements: Comments: Wavelength calibration for Exp. 9 Exposure_Number: 9 Target_Name: AM-HER Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1292 Optional_Parameters: FP-SPLIT=NO, COMB=FOUR, STEP-TIME=0.2, STEP-PATT=5 Number_of_Iterations: 215 Time_Per_Exposure: 27.2S Special_Requirements: Comments: Exposure_Number: 11 Target_Name: WAVE Config: HRS Opmode: ACCUM Aperture: SC2 Sp_Element: G140L Wavelength: 1292 Optional_Parameters: SPYBAL=YES Number_of_Iterations: 1 Time_Per_Exposure: 54.4S Special_Requirements: Comments: Wavelength calibration for Exp. 12 Exposure_Number: 12 Target_Name: AM-HER Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1292 Optional_Parameters: FP-SPLIT=NO, COMB=FOUR, STEP-TIME=0.2, STEP-PATT=5 Number_of_Iterations: 200 Time_Per_Exposure: 27.2S Special_Requirements: Comments: Data_Distribution ! 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