6088( 8) - 04/10/96 10:36 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6088 Version: 8 Check-in Date: 10-Apr-1996 10:32:19 1.Proposal Title: Ultraviolet Tomography of the Chromosphere of the K2 Dwarf in V471 Tauri ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Cool Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Frederick M. Walter State University of New York CoI: Edward F. Guinan Villanova University N CoI: Jeffery L. Linsky Joint Institute for Laboratory Astrophyics N CoI: Edward M. Sion Villanova University N CoI: Howard E. Bond Space Telescope Science Institute N CoI: Lynn D. Matthews State University of New York N ------------------------------------------------------------------------------------ 6. Abstract The solar atmosphere is composed of structures on scales of the solar radius down to smaller than we can resolve. Presumably, such a wealth of detail exists on other stars, but it is difficult to observe directly. It is important to observe the scale and filling factor of this structure to determine the heating rate and energy balance in the magnetic active regions. We propose to use the passage of the DA white dwarf in the V471 Tau system behind the atmosphere of the K star to probe the atmospheric structure of the active K2 dwarf star. The atmosphere on the line of sight to the DA white dwarf will be observed in absorption; variations in the equivalent widths of the transition region (C IV, Si IV) and chromospheric (O I, C II) lines will yield the run of temperature and density with height integrated along this line of sight. We will use the GHRS in rapid readout mode to obtain 0.5 second time resolution. The white dwarf traverses the distance of its own radius (7*10^8 cm) in 30 seconds, and the radius of the K star in ~24 minutes. We will be able to resolve structures on spatial scales down to 2% of the K dwarf radius. Finally, we be able to study the 555 s rotation of the white dwarf, and use the edge of the K dwarf as a knife-edge during the partial eclipse phases to study the surface brightness variations of the white dwarf. ------------------------------------------------------------------------------------ 6088( 8) - 04/10/96 10:36 - [ 2] Observations Description ------------------------ This observation must be undertaken in the far ultraviolet because essentially all the transition region lines lie in the far ultraviolet, and the continuum flux from the DAWD peaks there. The DAWD has a monochromatic continuum flux of 1.0*10^-12 erg cm^-2/s/A at 1400A (Figure 2). We will use the low resolution grating of the GHRS, centered at 1430 A. At this wavelength setting we are sensitive to lines ranging from the chromospheric O I complex at 1304 A (~8000K) through the 20,000K C II 1335 A multiplet to the 1393,1402 A Si IV and 1548,1551 A C IV lines, formed in the transition region at about 100,000K. All these lines have been detected in IUE spectra of V471 Tau. Our wavelength range also includes the coronal Fe XI (1349 A) and Fe XXI (1354 A) transitions. In the dMe star AD Leo, these lines are seen at about one tenth the flux of the Si IV 1393 A emission line; if this flux ratio is appropriate for V471 Tau, then we will also be able to map the extent of the corona. We used the GHRS team software procedure GHRS_PREDICT to predict the count rates. The monochromatic count rate (counts/diode/s) for the HST/GHRS using G140L ranges from 15 near 1300 A to 5 near 1550 A. We will be able to detect a 2 A equivalent width C IV absorption line in a few seconds. In 30 seconds, corresponding roughly to the time the DAWD moves its own diameter, we detect the 1400 A continuum at 24Sigma, and can detect at 3Sigma a 0.14 A equivalent width absorption feature. Integrating over 5 minutes (~10^10 cm) permits detection at 3Sigma significance of lines with 50mA equivalent widths, corresponding to absorption columns of order 3x10^12 ions cm^-2. We will observe using rapid readout mode, with readouts taken every 0.5 seconds. There will be 4 observations in total, each using one full orbit of spacecraft time. We will observe one ingress, beginning about 21 minutes prior to first contact, and one egress, ending about 21 minutes after fourth contact. Observations at ingress and egress permit sampling of two stellar hemispheres. We will repeat the cycle after an interval of about 3 months. This second sequence will permit searches for changes in the atmospheric structure on timescales of order the spot migration period. Real Time Justification ----------------------- These are phase critical observations. V471 Tau has a period of 0.52118334 days. Total eclipse (centered at Phi=0) lasts 47 minutes. The ephemeris is well known (cf Bois, Lanning, & Mochnacki 1988 AJ 96,157). The O-C variation is well -characterized (Ibanoglu et al 1994 A&A 281, 811), and increases from about 20 to 60 seconds during cycle 5. We have built this into our observing phases. THE TIME OF ZERO-PHASE IS HELIOCENTRIC; A TIMING CORRECTION OF UP TO +/- 500 SECONDS MUST BE APPLIED, DEPENDING ON THE TIME OF YEAR OF THE OBSERVATION. PHASE CONSTRAINTS ARE HELIOCENTRIC, NOT GEOCENTRIC. HELIOCENTRIC CORRECTION IS +500 SECONDS ON MAY 20 (ECLIPSE LATE) AND -500 SECONDS ON NOVEMBER 23 (ECLIPSE EARLY). ******************************************************************* *We expect to discuss the various scheduling constraints and * *options with STScI personnel prior to scheduling. In particular, * *we need to know the exact time of the start of the RAPID * *readouts relative to the end of the GSACQ to compute the * *optimal observing phases. * * * *If the program cannot be scheduled as written, we are amenable to* *modifying exposure times so the program can fit in orbits with * *shorter visibility. * ******************************************************************* We will observe two ingresses and two egresses. We must observe the actual ingress to or egress from totality, in order to establish the absolute location of the DAWD relative to the K dwarf. We seek to maximize the exposure of the uneclipsed DAWD. Because of the rapidity of the eclipse, the scheduling of these observations may be technically challenging. The ingress observations must occur when the visibility window opens at about Phi=0.93. We have built in a +/- 5 minute (0.0067 cycle) tolerance to aid with scheduling. Following 12 minutes of GSACQ and 11 minutes of TA, we obtain 21+/-5 minutes of data with the DAWD visible through the atmosphere of the K dwarf. Second contact (Phi=0.967) occurs 44+/-5 minutes into the observing window, and we obtain 5+/- 5 minutes of data on the K star with the DAWD in eclipse. The egress observations must begin at Phi=0.01 (see observing form for details). The rapid readout begins with the star still in eclipse. Egress (3^rd to 4^th contact) occurs at Phi=0.033, 30+/-5 minutes into the visibility window. We will obtain 21+/-5 minutes of data with the DAWD visible through the atmosphere of the K dwarf. We propose to repeat each ingress and egress after an interval of 90-180 days to search for changes in the chromospheric structures on a timescale comparable to the ~150 day photometric wave period. We will pursue supportive ground-based photometry and spectroscopy, but these will in no way constrain the scheduling of the HST. We will use the Fairborn-Villanova 0.8m APT to obtain UBVRI light curves around the times of the HST observations. These light curves will be used to establish the longitude of the starspots on the surface, their areas, and the spot distributions. Such knowledge is crucial to the interpretation on the HST/GHRS data. Calibration Justification ------------------------- Additional Comments ------------------- THE HELIOCENTRIC CORRECTION MUST BE APPLIED PRIOR TO SCHEDULING. THE MAGNITUDE OF THE CORRECTION (+/- 8.3 MINUTES) EXCEEDS OUR +/- 5 MINUTE TOLERANCE. ------------------------------------------------------------------------------------ 6088( 8) - 04/10/96 10:36 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6088( 8) - 04/10/96 10:36 - [ 4] TARGET LIST a) 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 24.85S +/- .7", J2000 V=+35 V = 9.50+/-0.2 INTERACTING BINARY DEC=17D 14' 47.7" +/- .7", PLATE B-V = 0.92+/-0.1 -ID=00FH F-CONT(1300)=1+/-0.5e-12 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1982 0.0062 -0.014 0.0 6088( 8) - 04/10/96 10:36 - [ 5] Visit: 01 Visit Requirements: PERIOD 0.52118334D AND ZERO-PHASE JD2440610.06413 On Hold Comments: Additional Comments: HELIOCENTRIC CORRECTION MUST BE APPLIED TO ZERO-PHASE, VISIT 1 OF 4 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 HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,S 1 18.0S ONBOARD ACQ FOR 12-24 EARCH-SIZE=3 ------------------------------------------------------------------------------------------------------------------------------------ 12 V471-TAU HRS ACCUM 2.0 G140M 1545 STEP-PATT=5 6 136.0S ------------------------------------------------------------------------------------------------------------------------------------ 14 V471-TAU HRS ACCUM 2.0 G140L 1430 STEP-PATT=5 4 108.8S END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ 22 V471-TAU HRS RAPID 2.0 G140L 1430.0 SAMPLE-TIME=0.5 1 32.5M PHASE 0.9207 TO 0.9340; SEQ 22-24 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 24 V471-TAU HRS ACCUM 2.0 G140L 1430 STEP-PATT=5 3 163.2S ------------------------------------------------------------------------------------------------------------------------------------ 6088( 8) - 04/10/96 10:36 - [ 6] Visit: 02 Visit Requirements: PERIOD 0.52118334D AND ZERO-PHASE JD2440610.06413; On Hold Comments: Additional Comments: HELIOCENTRIC CORRECTION MUST BE APPLIED TO ZERO-PHASE, VISIT 2 OF 4, EGRESS Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 30 V471-TAU HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,S 1 18.0S ONBOARD ACQ FOR 32-42 EARCH-SIZE=3 ------------------------------------------------------------------------------------------------------------------------------------ 32 V471-TAU HRS ACCUM 2.0 G140L 1430 STEP-PATT=5 14 108.8S END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ 40 V471-TAU HRS ACCUM 2.0 G140L 1430 STEP-PATT=5 3 163.2S PHASE 0.9950 to 0.0084; SEQ 40-42 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 42 V471-TAU HRS RAPID 2.0 G140L 1430. SAMPLE-TIME=0.5 1 33.5M Comments: egress, epoch 1 ------------------------------------------------------------------------------------------------------------------------------------ 6088( 8) - 04/10/96 10:36 - [ 7] Visit: 03 Visit Requirements: PERIOD 0.52118334D AND ZERO-PHASE JD2440610.06413; AFTER 5 BY 90D TO 210D On Hold Comments: Additional Comments: HELIOCENTRIC CORRECTION MUST BE APPLIED TO ZERO-PHASE, VISIT 3 OF 4 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 50 V471-TAU HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,S 1 18.0S ONBOARD ACQ FOR 52 EARCH-SIZE=3 ------------------------------------------------------------------------------------------------------------------------------------ 52 V471-TAU HRS RAPID 2.0 G140L 1430.0 SAMPLE-TIME=0.5 1 27.0M PHASE 0.9334 TO 0.9468; NO SPLIT Comments: ingress, epoch2 ------------------------------------------------------------------------------------------------------------------------------------ 6088( 8) - 04/10/96 10:36 - [ 8] Visit: 04 Visit Requirements: PERIOD 0.52118334D AND ZERO-PHASE JD2440610.06413; AFTER 6 BY 90D TO 210D On Hold Comments: Additional Comments: HELIOCENTRIC CORRECTION MUST BE APPLIED TO ZERO-PHASE, VISIT 4 OF 4, EGRESS Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 60 V471-TAU HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,S 1 18.0S ONBOARD ACQ FOR 62-72 EARCH-SIZE=3 ------------------------------------------------------------------------------------------------------------------------------------ 62 V471-TAU HRS ACCUM 2.0 G140L 1430 STEP-PATT=5 14 108.8S END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ 70 V471-TAU HRS ACCUM 2.0 G140L 1430 STEP-PATT=5 3 163.2S PHASE 0.9950 to 0.0084; SEQ 70-72 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 72 V471-TAU HRS RAPID 2.0 G140L 1430. SAMPLE-TIME=0.5 1 33.5M Comments: egress, epoch 2 ------------------------------------------------------------------------------------------------------------------------------------ 6088( 8) - 04/10/96 10:36 - [ 9] Visit: 05 Visit Requirements: PERIOD 0.52118334D AND ZERO-PHASE JD2440610.06413 On Hold Comments: Additional Comments: HELIOCENTRIC CORRECTION MUST BE APPLIED TO ZERO-PHASE, COPY OF VISIT 1 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 HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,S 1 18.0S ONBOARD ACQ FOR 12-24 EARCH-SIZE=3 ------------------------------------------------------------------------------------------------------------------------------------ 12 V471-TAU HRS ACCUM 2.0 G140M 1545 STEP-PATT=5 6 136.0S ------------------------------------------------------------------------------------------------------------------------------------ 14 V471-TAU HRS ACCUM 2.0 G140L 1430 STEP-PATT=5 4 108.8S END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ 22 V471-TAU HRS RAPID 2.0 G140L 1430.0 SAMPLE-TIME=0.5 1 32.5M PHASE 0.9207 TO 0.9340; SEQ 22-24 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 24 V471-TAU HRS ACCUM 2.0 G140L 1430 STEP-PATT=5 3 163.2S ------------------------------------------------------------------------------------------------------------------------------------ 6088( 8) - 04/10/96 10:36 - [ 10] Visit: 06 Visit Requirements: PERIOD 0.52118334D AND ZERO-PHASE JD2440610.06413; On Hold Comments: Additional Comments: HELIOCENTRIC CORRECTION MUST BE APPLIED TO ZERO-PHASE, COPY OF VISIT 2 , EGRESS Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 30 V471-TAU HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,S 1 18.0S ONBOARD ACQ FOR 32-42 EARCH-SIZE=3 ------------------------------------------------------------------------------------------------------------------------------------ 32 V471-TAU HRS ACCUM 2.0 G140L 1430 STEP-PATT=5 14 108.8S END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ 40 V471-TAU HRS ACCUM 2.0 G140L 1430 STEP-PATT=5 3 163.2S PHASE 0.9950 to 0.0084; SEQ 40-42 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 42 V471-TAU HRS RAPID 2.0 G140L 1430. SAMPLE-TIME=0.5 1 33.5M Comments: egress, epoch 1 ------------------------------------------------------------------------------------------------------------------------------------ 6088( 8) - 04/10/96 10:36 - [ 11] Summary Form for Proposal 6088 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN SEARCH-SIZE=3 STEP-PATT=5 SAMPLE-TIME=0.5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Cool Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PERIOD 0.52118334D AND ZERO-PHASE JD2440610.06413 ONBOARD ACQ FOR 12-24 END ORBIT PHASE 0.9207 TO 0.9340; SEQ 22-24 NON-INT PERIOD 0.52118334D AND ZERO-PHASE JD2440610.06413; ONBOARD ACQ FOR 32-42 PHASE 0.9950 to 0.0084; SEQ 40-42 NON-INT PERIOD 0.52118334D AND ZERO-PHASE JD2440610.06413; AFTER 5 BY 90D TO 210D ONBOARD ACQ FOR 52 PHASE 0.9334 TO 0.9468; NO SPLIT PERIOD 0.52118334D AND ZERO-PHASE JD2440610.06413; AFTER 6 BY 90D TO 210D ONBOARD ACQ FOR 62-72 PHASE 0.9950 to 0.0084; SEQ 70-72 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N1 G140M G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names V471-TAU ------------------------------------------------------------------------------------------------------------------------------------