8620( 3) - 11/17/00 12:12 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8620 Version: 3 Check-in Date: 17-Nov-2000 12:12:10 1.Proposal Title: Taking a glance at the beating heart of 4 Draconis ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Boris Gaensicke Universitats-Sternwarte Gottingen CoI: Prof. Klaus Beuermann Universitaets-Sternwarte Goettingen N CoI: Mr. Jens Kube Universitaets-Sternwarte Goettingen N CoI: Dr. Axel Schwope Astrophysikalisches Institut Potsdam N ------------------------------------------------------------------------------------ 5. Abstract 4 Dra is a unique triple system containing a magnetic cataclysmic variable (AM Her- type) and an M3 III giant. Even though the M-giant completely dominates the optical emission of the system, we can learn much from 4 Dra about the accretion physics in and the evolution of AM Her stars, because: (a) 4 Dra is the second brightest AM Her star in the ultraviolet, (b) 4 Dra is one of the very few cataclysmic variables with a good HIPPARCOS parallax (d~180 pc), and, in addition, (c) 4 Dra is so far the only bright CV for which an estimate of the age, ~10^8 yrs could be derived. We propose an in-depth HST/STIS echelle study of the AM Her star in 4 Dra. Our scientific goals are twofold. (1) We will derive the fundamental properties of the accreting magnetic white dwarf, such as its photospheric temperature, the temperature and the size (lateral extent) of the accretion-heated pole cap, and the chemical composition of the accretion-enriched atmosphere. (2) We will use the HST/STIS echelle spectra for Doppler mapping of the UV line emission. The HST maps of LineCIV1550 and LineHeII1640 emission will probe the velocity field and ionization structure in the complete accretion flow, including the irradiated face of the donor star, the ballistic gas stream from that star to the white dwarf magnetosphere, the threading region between the stream and magnetosphere, the magnetically controlled flow down to the standoff shock, and the surrounding heated regions at the white dwarf surface. ------------------------------------------------------------------------------------ 8620( 3) - 11/17/00 12:12 - [ 2] Observations Description ------------------------ HST will be used to obtain orbital phase-resolved UV spectroscopy of the cataclysmic variable in 4 Dra. Instrument setup: In the optical, the M3 III giant completely dominates the emission of 4 Dra (V~5.1), the target should be acquired using the F28x50OII filter. The spectroscopic observation will be done with the E140M grating and the 0.2arcsecx0.2" slit. This setup covers the 1150- -1700 Angstrom\ region simultaneously, where the cataclysmic variable is the dominant source of continuum and line emission, with a resolution of ~45 000. All data will be taken in the time-tagged mode, allowing for an arbitrary temporal binning of the spectra during the analysis. Scheduling: The Doppler tomography analysis of the STIS spectra outlined above requires that a full binary orbit (\Porb~4 h) is covered in one continous visit. As 4 Dra lies in the northern Continous Viewing Zone, 3 CVZ HST orbits are sufficient to obtain the desired data set. Accounting for guide star acquisition, target acquisition, and instrument overheads, the estimated on-target time is ~268 min. S/N simulation and bright object limit: We estimate the signal- to-noise ratio (S/N) of the proposed STIS observations using the existing IUE spectrum of 4 Dra (Fig. 1) as input for the Exposure Time Calculator. For the Doppler tomography analysis, the time-tagged photon stream will be binned into 600 sec exposures, which yields 26 individual E140M spectra with an orbital phase resolution of DeltaPhi~0.04. The spectra will be rebinned in wavelength by a factor of 10, corresponding to a spectral resolution of R~4500, i.e. ~65 kms. The resulting S/N is ~12 and ~24 in the continuum and in the lines, respectively. The continuum variation will be analysed extracting light curves from emission-line free regions at a temporal resolution of ~1 min. A detailed study of the interstellar -- and possibly photospheric white dwarf-- absorption line spectrum will be conducted on E140M spectra integrated over 1 hr at the full spectral resolution, whith an expected S/N of ~8-15 in the continuum. In the FUV, the emission of 4 Dra is dominated by the cataclysmic variable. With the described instrument configuration, we expect a peak count rate of 0.03 \cts\ and a global count rate of 1700 \cts, which is far below all MAMA safety limits. A total of <~3*10^7 counts will be accumulated during the whole 3-orbit visit, which is more than a factor 2 below the integrated counts constraint (HST/STIS Handbook, p. 211). Real Time Justification ----------------------- We request that the observations are scheduled during a CVZ window, as the Doppler tomography analysis of the E140M echelle requires the continous observation of a full binary orbit. None Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8620( 3) - 11/17/00 12:12 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD108907 STAR, POLAR, M III-I, RA=12H 30M 6.69S +/- 0.1", J2000 V = 4.9+/-0.1 INTERACTING BINARY DEC=69D 12' 4" +/- 0.1" B = 6.57+/-0.05 F-CONT(1300)=3+/-1e-13 F-CONT(1800)=2+/-0.8e-13 Coordinate Source: HIPPARCOS_INPUT_CATALOGUE 8620( 3) - 11/17/00 12:12 - [ 4] Visit: 01 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 HD108907 STIS/C ACQ F28X50O MIRROR 1 0.5 S SEQ 10-40 NON-INT CD II Comments: Target acquisition for exposure 20 ------------------------------------------------------------------------------------------------------------------------------------ 20 HD108907 STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=350 1 5300 S SEQ 10-40 NON-INT UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 30 HD108907 STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=350 1 5300 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 40 HD108907 STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=350 1 4550 S SEQ 10-40 NON-INT UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8620( 3) - 11/17/00 12:12 - [ 5] Summary Form for Proposal 8620 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50OII 0.2X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=350 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ SEQ 10-40 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD108907 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 ------------------------------------------------------------------------------------------------------------------------------------