Proposal_Information ! Section 4 Title: The periodic UV spectral variations in the Intermediate Polar FO Aqr Proposal_Category: GO Scientific_Category: Hot Stars Cycle: 5 Investigators PI_name: Domitilla de Martino PI_Institution: IUE Observatory VILSPA European Space Agency CoI_Name: Martine Mouchet CoI_Institution: DAEC Observatoire de Paris Meudon Contact: ! Y or N (designate at most one contact) CoI_Name: Simon Rosen CoI_Institution: University of Leicester Contact: ! Y or N (designate at most one contact) CoI_Name: David Buckley CoI_Institution: South African Astronomical Observatory Contact: ! Y or N (designate at most one contact) CoI_Name: Koji Mukai CoI_Institution: Goddard Space Flight Center NASA/USRA Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) Spectral periodic variations in Intermediate Polars (IPs) are a powerful tool to investigate the accretion geometry in these X-ray binaries. The asynchronous rotation (spin) of the accreting magnetized white dwarf is such that IPs mainly display periodicities at the orbital, spin and beat frequencies. The UV behaviour of both continuum and emission lines at the spin and beat periods is mostly unexplored for these systems. While orbital variations have been observed with IUE, the unknown relative proportion in this range of the shorter period variations makes difficult to also ascertain the intrinsic UV orbital modulated component. This is an avenue of investigation newly opened by HST since there are no other instruments capable of studying such rapid variabilities. We propose to observe the so-called "king" of IPs, FO Aqr, which is known to show strong optical variations at the three periods. The UV observations will allow us to test a scenario we proposed for this system where accretion takes place in a more complex way than what current disc-less or disced accretion theories predict. Questions ! Free format text (please update) Observing_Description: We propose to use the FOS/BL+G160L configuration to cover the spectral range 1150-2500 Angstrom at a resolution of ~ 1000 km/s. This would provide the far-UV emission coverage where the variable components are expected to dominate. Our strategy is to acquire FO AQR with the ACQ/PEAK mode and with FOS/BL+G270H configuration, through the 4.3, the 1.0-PAIR and 0.5-PAIR apertures. The upper square apertures (A) of the 1.0-PAIR and 0.5-PAIR will be used. The ACQ/PEAK mode will allow to precisely center the target in the 1.0-PAIR-A science aperture. The choice of using one of the pair apertures has been dictated by the presence of a flat-field feature in the 1.0 circular aperture in the region of 1500-1550A, as we aim to observe flux variations of C IV (1550A) line with a precision better than 20percent. We propose to acquire spectra of FO Aqr with the 1.0-PAIR-A aperture with FOS/BL+G160L in RAPID mode with 20sec resolution in order to sample both spin 21mins and beat 23mins periods and to detect rapid non-periodic variations. FO Aqr is relatively bright in the UV with a relativley flat continuum at about 3.3E-14 erg/cm2/s/A. We expect to reach a flux ranging from 1.1 counts/s/diode (at 1250A) to 13.9 counts/s/diode (at 2400A). The 20sec min exposures will give a S/N ranging from 5 to 16 at these end wavelengths and integrating over 1200-2400A range about 8035 counts per 20 sec exposure spectrum will be achieved as a light curve flux. This will allow to detect rapid UV flux variations. Binning the spectra in time with a 1 min interval a S/N ranging from 8 to 28 will be obtained in the continuum at the end wavelengths. Furthermore a S/N of 30 in the CIV emission line will be obtained. With this binning we will obtain 21 and 23 bins per spin and beat cycles respectively which will allow to study the spectral behaviour at these periods. Real_Time_Justification: We will observe for 7 consecutive HST orbits in order to avoid a second target visit. The target acquisition will take about 46mins and therefore the first orbit cannot be used for science observations. In the remaining 6 consecutive orbits the effective time on source is about 43mins for each HST visibility period per orbit. This will allow to cover 2 spin and 1.9 beat periods leading to a total coverage of 12 spin and 11 beat periods respectively. As the source orbital period (4.85hrs) is about 3 time the HST orbit, with an orbital phase shift of 0.01 every 3 HST orbit, we will sample about the same orbital phases. This will allow to detect cycle to cycle variations. Each orbital phase will be obtained by sampling 21 spin spectra to average out the expected strong spin UV pulsation. This will lead to about 4 bins in each orbital phase interval covered during the HST visibility periods. We note that the beat period between the HST orbit and the source orbital period is 2.4hrs, about half the target orbital period, and this will be taken into account in our analysis. Also, since IPs are variable at different timescales we plan ground-based spectroscopic and photometric observations in the optical as well as in the near-IR at SAAO Observatory and ESO in the period August-October 1995. These observations will give a completed knowledge of the state of the source. Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: FO-AQR Alternate_Names: H2215-086,GSC5804.00775 Description: STAR,INTERMEDIATE POLAR,INTERACTING BINARY Position: RA=22H 17M 55.43S +/- 0.02S, DEC=-08D 21' 4.7" +/- 0.4", PLATE-ID=015K Equinox: J2000 Epoch: 1983.70 Annual_Parallax: 0.0 Flux: V=13.59 +/- 0.6 B-V=0.11 +/- 0.04 E(B-V)=0.0 F-CONT(1550)=3.3 +/- 0.5 E-14 F-CONT(2400)=3.1 +/- 0.5 E-14 F-LINE(1550)=2.6 +/- 0.3 E-13 W-LINE(1550)=9.1 +/- 0.1 F-LINE(1640)=9.4 +/- 0.9 E-14 W-LINE(1640)=8.9 +/- 0.1 Visits Visit_Number: 1 Visit_Requirements: BETWEEN 06-AUG-95 AND 31-OCT-95 Exposure_Number: 1 Target_Name: FO-AQR Config: FOS/BL Opmode: ACQ/PEAK Aperture: 4.3 Sp_Element: G270H Optional_Parameters: SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 SCAN-STEP-Y=1.204 Number_of_Iterations: 1 Time_Per_Exposure: 4S Special_Requirements: ONBOARD ACQ FOR 2 Exposure_Number: 2 Target_Name: FO-AQR Config: FOS/BL Opmode: ACQ/PEAK Aperture: 1.0-PAIR-A Sp_Element: G270H Optional_Parameters: SEARCH-SIZE-X=6 SEARCH-SIZE-Y=2 SCAN-STEP-Y=0.602 SCAN-STEP-X=0.602 Number_of_Iterations: 1 Time_Per_Exposure: 4S Special_Requirements: ONBOARD ACQ FOR 3 Exposure_Number: 3 Target_Name: FO-AQR Config: FOS/BL Opmode: ACQ/PEAK Aperture: 0.5-PAIR-A Sp_Element: G270H Optional_Parameters: SEARCH-SIZE-X=3 SEARCH-SIZE-Y=3 SCAN-STEP-Y=0.29 SCAN-STEP-X=0.29 Number_of_Iterations: 1 Time_Per_Exposure: 4S Special_Requirements: ONBOARD ACQ FOR 4 Exposure_Number: 4 Target_Name: FO-AQR Config: FOS/BL Opmode: ACQ/PEAK Aperture: 0.25-PAIR-A Sp_Element: G270H Optional_Parameters: SEARCH-SIZE-X=3 SEARCH-SIZE-Y=3 SCAN-STEP-Y=0.17 SCAN-STEP-X=0.17 Number_of_Iterations: 1 Time_Per_Exposure: 4S Special_Requirements: ONBOARD ACQ FOR 5 Exposure_Number: 5 Target_Name: FO-AQR Config: FOS/BL Opmode: RAPID Aperture: 1.0-PAIR-A Sp_Element: G160L Optional_Parameters: STEP-PATT=SINGLE READ-TIME=20 Number_of_Iterations: 1 Time_Per_Exposure: 259M Data_Distribution Medium: 8MM ! 8MM or 6250BPI or 1600BPI Blocking_Factor: 10 ! 10 or 1 Ship_To: PI_Address ! STSCI or PI_Address or Ship_Via: UPS ! UPS (2-day) or OVERNIGHT