9283( 2) - 08/13/01 09:17 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9283 Version: 2 Check-in Date: 13-Aug-2001 09:16:40 1.Proposal Title: Probing the Gas in the V471 Tau System with Absorption Spectroscopy ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Frederick Walter State University of New York at Stony Brook ------------------------------------------------------------------------------------ 5. Abstract The eclipsing dA+K2V binary V471 Tau afford an opportunity to use X-ray absorption to probe the spatial extent of the chromosphere/corona of an active dwarf star. HST observations have shown chromospheric and transition region species (O I through N V) in absorption at radial extents of up to 2 K star radii on one side of the star, but not on the other. X-ray observations have revealed large absorption dips, primarily but not exclusively from gas near the inner Lagrangian points of the system. Chandra can probe the neutral gas, by observing the time-variability of the neutral Hydrogen absorption column, and by observing the variations of the depths of absorption edges. The white dwarf photosphere provides a bright, soft continuous spectrum against which to observe these changes. ------------------------------------------------------------------------------------ 9283( 2) - 08/13/01 09:17 - [ 2] Observations Description ------------------------ We will observe V471 Tau for 4 consecutive spacecraft orbits while the white dwarf is viewed though the atmosphere of the K star. The observations will use the STIS E140M is TTAG mode. The acquisition in the STIS must be started between orbital phases 0.73 and 0.81 (a 60 minute long window), so that we obtain data between orbital phases 0.75 and 1.25, when the white dwarf is located behind the K star. All uncertainties in the ephemeris (e.g., the heliocentric correction) is accoiunted for within this starting time window. Acquisition parameters are identical to those we used in Program 7735. The exposure times were (re)verified using the STIS ETC. Instrument parameters are identical to those used in Program 7735. If necessary, then lengths of exposures 12-15 can be adjusted to fill the orbit. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- This program should be scheduled simultaneously with a 90 ksec CHANDRA observation. The HST observation is phase-critical, and will be more difficult to schedule (the CHANDRA observation spans two complete orbital phases, and so has no phase constraints). ------------------------------------------------------------------------------------ 9283( 2) - 08/13/01 09:17 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 V471-TAU STAR, DA, K V-IV, RA=3H 50M 24.79S +/- .2", J2000 V=+35 V = 9.50+/-0.2 INTERACTING BINARY DEC=17D 14' 47.8" +/- .2", PLATE B-V = 0.92+/-0.1 -ID=00FH F-CONT(1300)=1.5+/-0.1e-12 Coordinate Source: GUIDE_STAR_CATALOG Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1982.959 0.0091 -0.023 0.021 9283( 2) - 08/13/01 09:17 - [ 4] Visit: 01 Visit Priority: Visit Requirements: PERIOD 0.52118334D AND ZERO-PHASE JD2440610.06413 On Hold Comments: Additional Comments: Exposures 12-12 may be expanded (or contracted) to fill the available orbit. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 V471-TAU STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 2.0 S PHASE 0.73 TO 0.81 CD III ------------------------------------------------------------------------------------------------------------------------------------ 11 V471-TAU STIS/C ACQ/PEA 0.2X0.0 G750M 7283 1 4.0 S CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 12 V471-TAU STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=240 1 27.5 M UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 13 V471-TAU STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=240 1 48.25 M UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 14 V471-TAU STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=240 1 48.25 M UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 15 V471-TAU STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=240 1 48.25 M UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 9283( 2) - 08/13/01 09:17 - [ 5] Summary Form for Proposal 9283 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50OIII 0.2X0.06 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT BUFFER-TIME=240 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PERIOD 0.52118334D AND ZERO-PHASE JD2440610.06413 PHASE 0.73 TO 0.81 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G750M E140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names V471-TAU ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 7283 1425 ------------------------------------------------------------------------------------------------------------------------------------