9175( 10) - 05/02/01 13:09 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9175 Version: 10 Check-in Date: 02-May-2001 13:08:32 1.Proposal Title: The Best Brown Dwarf Yet?: FGS Astrometry of the Companion to the Hyades Eclipsing Binary V471 Tau ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Edward Guinan Villanova University CoI: Dr. Ignasi Ribas Villanova University N CoI: Dr. Alfred Schultz Computer Sciences Corporation N CoI: Dr. John Hershey Computer Sciences Corporation N CoI: Dr. Frederic Arenou Observatoire de Paris N ------------------------------------------------------------------------------------ 5. Abstract The analysis of over 30 yr of 161 eclipse timings of the Hyades eclipsing binary V471 Tauri shows the presence of a low mass tertiary companion. A third body was found from periodic variations in the observed arrival times of the eclipses - known as the ``light time'' effect. The light time effect occurs as the relative distance (and light travel time) changes as the eclipsing binary moves around the barycenter of the triple system. Our analysis yields an orbital period of P_3=30.5+/-1.6 yr, e_3=0.31+/-0.04, a semi-major axis of a_3=11.2+/-0.4 AU, and a tertiary mass M_3 sin i_3 =0.039+/- 0.004 Mo. For orbital inclinations >35 degrees the mass of the third body would be below the stable hydrogen burning limit of M~0.07 Mo and thus would be a brown dwarf. We propose HST/FGS observations of V471 Tau over the next 3 years (2 HST orbits/year) to determine its astrometric orbit. These HST observations, when combined with Hipparcos astrometry and the light time orbit, will unambiguously yield the orbital inclination and the mass of the third body. The identification of a brown dwarf in V471 Tau will provide the first direct dynamical mass determination of a brown dwarf with a known age (tau(Hyades)=625 Myr), chemical composition, and distance. In a few years (near maximum elongation), it should be feasible to obtain IR images and spectra of this object that will provide crucial tests of brown dwarf models. ------------------------------------------------------------------------------------ 9175( 10) - 05/02/01 13:09 - [ 2] Observations Description ------------------------ A star and its companion (BD or more massive) orbit a common center of mass. The presence of an unseen companion can be inferred from the motion of the central star about the center of mass, astrometrically, photometrically (light time), and with radial velocity techniques. Besides being unfeasible because of the long period and the expected small reflex radial velocity amplitude of the binary pair, the information provided by the radial velocity method is redundant since it yields essentially the same information as the light-time orbit, but not the much needed value of i_3. The astrometric wobble of a star on the plane of the sky due to a companion can be determined by measuring the position of the star over time relative to fixed, background stars. A frame of reference is set up and all measurements of the target are relative to this reference frame. FGS astrometry is obtained by using two FGSs for guiding while the third FGS determines the positions of selected target stars within its field of view. Long and intensive series of FGS observations of this type have been done on Proxima Centauri and Barnard's star (Benedict et al. 1998). We have extracted an image of V471 Tau from the GSSS plate scans and there are four good close reference stars that could be used for astrometry. The position on the sky of V471 Tau will be measured relative to these reference stars. An observation set will consist of FGS POS mode observations of V471 Tau (beginning, middle, and end as a drift check star) and with at least two passes through the reference frame of stars. The necessity of a drift check star has arisen from the experience of all previous FGS POS mode programs. The sequence will be repeated as many times as possible to fill an entire orbit. Real Time Justification ----------------------- We need to observe V471 Tau at minimum parallax factor, which occurs in November. Thus, we request observing time during the time interval November 21 to November 24 each cycle. Observing at these time intervals has the bonus of minimizing the effects of any inaccuracy in the Hipparcos parallax determination. V471 Tau is a close binary with a 12.5-hr period and at optical wavelengths the white dwarf contributes less than 1% of the light. The orbital wobble of the photocenter is thus insignificantly small and there is no requirement of phasing the FGS observations with the orbital motion of the close binary. Even though coordinated photometric observations to determine further eclipse arrival times will be carried out with ground-based facilities during Cycle 10, these will not affect HST scheduling. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9175( 10) - 05/02/01 13:09 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 V471-TAU STAR, K V-IV RA=3H 50M 24.848S +/- 0.01S, J2000 V = 9.45+/-0.09 DEC=17D 14' 47.73" +/- 0.1" B-V = +0.60+/-0.32 Coordinate Source: HIPPARCOS_INPUT_CATALOGUE Comments: coordinates from Hipparcos Input Catalogue, proper motion and parallax from Hipparcos Output Catalogue. sp type = K0V Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0.00908 -0.02330 0.02137 2 HD24040 STAR, G V-IV RA=3H 50M 22.962S +/- 0.01S, J2000 V = 7.512+/-0.005 DEC=17D 28' 34.91" +/- 0.1" B-V = +0.653+/-0.003 Coordinate Source: HIPPARCOS_INPUT_CATALOGUE Comments: coordinates from Hipparcos Input Catalogue, proper motion and parallax from Hipparcos Output Catalogue. sp type = G0 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0.00798 -0.25231 0.02150 3 V471-REF-1 STAR RA=3H 50M 27.78S +/- 1", DEC=17D J2000 V = 12.21+/-0.3 27' 22.3" +/- 1", PLATE-ID=00FH Coordinate Source: GUIDE_STAR_CATALOG Comments: coordinates from Guide Star Catalogue 4 V471-REF-2 STAR RA=3H 50M 18.29S +/- 1", DEC=17D J2000 V = 13.58+/-0.3 25' 49.4" +/- 1", PLATE-ID=00FH Coordinate Source: GUIDE_STAR_CATALOG Comments: coordinates from Guide Star Catalogue 5 V471-REF-3 STAR RA=3H 50M 13.32S +/- 1", DEC=17D J2000 V = 13.21+/-0.3 26' 19.4" +/- 1", PLATE-ID=00FH Coordinate Source: GUIDE_STAR_CATALOG Comments: coordinates from Guide Star Catalogue 6 V471-REF-4 STAR RA=3H 50M 17.18S +/- 1", DEC=17D J2000 V = 15.15+/-0.3 22' 39.9" +/- 1", PLATE-ID=00FH Coordinate Source: GUIDE_STAR_CATALOG Comments: coordinates from Guide Star Catalogue 7 V471-REF-5 STAR RA=3H 50M 6.95S +/- 1", DEC=17D J2000 V = 13.37+/-0.3 21' 39.0" +/- 1", PLATE-ID=00FH Coordinate Source: GUIDE_STAR_CATALOG Comments: coordinates from Guide Star Catalogue 8 V471-REF-6 STAR RA=3H 50M 16.02S +/- 1", DEC=17D J2000 V = 14.42+/-0.3 17' 43.8" +/- 1", PLATE-ID=00FH Coordinate Source: GUIDE_STAR_CATALOG Comments: coordinates from Guide Star Catalogue 9 V471-REF-7 STAR RA=3H 50M 15.48S +/- 1", DEC=17D J2000 V = 14.15+/-0.3 16' 41.3" +/- 1", PLATE-ID=00FH Coordinate Source: GUIDE_STAR_CATALOG Comments: coordinates from Guide Star Catalogue 9175( 10) - 05/02/01 13:09 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 358.0D TO 359.5D Between 21-Nov-2001 and 22-Nov-2001 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 V471-TAU FGS POS 1 F583W 1 18 S GS ACQ SCENARIO SINGLE POS TARG 400,-150 SEQ 10-200 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 20 V471-REF-4 FGS POS 1 F583W 1 21 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 30 V471-REF-5 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 40 V471-REF-6 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 50 V471-REF-7 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 60 V471-TAU FGS POS 1 F583W 1 18 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 70 HD24040 FGS POS 1 F550W 1 18 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 80 V471-REF-1 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 90 V471-REF-2 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 100 V471-REF-3 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 110 V471-REF-4 FGS POS 1 F583W 1 21 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 120 V471-TAU FGS POS 1 F583W 1 18 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 130 V471-REF-5 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 140 V471-REF-6 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 150 V471-REF-7 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 160 V471-TAU FGS POS 1 F583W 1 18 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 170 HD24040 FGS POS 1 F550W 1 18 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 180 V471-REF-1 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 190 V471-REF-2 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 200 V471-REF-3 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 9175( 10) - 05/02/01 13:09 - [ 5] Visit: 02 Visit Priority: Visit Requirements: SAME ORIENT AS 01 AFTER 01 BY 5 Orbits TO 10 Orbits 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 V471-TAU FGS POS 1 F583W 1 18 S GS ACQ SCENARIO SINGLE POS TARG 400,-150 SEQ 10-200 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 20 V471-REF-4 FGS POS 1 F583W 1 21 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 30 V471-REF-5 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 40 V471-REF-6 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 50 V471-REF-7 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 60 V471-TAU FGS POS 1 F583W 1 18 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 70 HD24040 FGS POS 1 F550W 1 18 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 80 V471-REF-1 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 90 V471-REF-2 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 100 V471-REF-3 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 110 V471-REF-4 FGS POS 1 F583W 1 21 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 120 V471-TAU FGS POS 1 F583W 1 18 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 130 V471-REF-5 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 140 V471-REF-6 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 150 V471-REF-7 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 160 V471-TAU FGS POS 1 F583W 1 18 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 170 HD24040 FGS POS 1 F550W 1 18 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 180 V471-REF-1 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 190 V471-REF-2 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 200 V471-REF-3 FGS POS 1 F583W 1 20 S SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ 9175( 10) - 05/02/01 13:09 - [ 6] Summary Form for Proposal 9175 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations FGS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes POS ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 358.0D TO 359.5D Between 21-Nov-2001 and 22-Nov-2001 GS ACQ SCENARIO SINGLE POS TARG 400,-150 SEQ 10-200 NON-INT SAME POS AS 10 SAME ORIENT AS 01 AFTER 01 BY 5 Orbits TO 10 Orbits ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F583W F550W ------------------------------------------------------------------------------------------------------------------------------------ Target Names V471-TAU V471-REF-4 V471-REF-5 V471-REF-6 V471-REF-7 HD24040 V471-REF-1 V471-REF-2 V471-REF-3 ------------------------------------------------------------------------------------------------------------------------------------