9259( 3) - 06/01/01 07:34 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9259 Version: 3 Check-in Date: 01-Jun-2001 07:33:47 1.Proposal Title: Astrometry and Photometry of the binary TNO 1998 WW31 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO/DD 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Christian Veillet Canada-France-Hawaii Telescope Corporation CoI: Ian Griffin Space Telescope Science Institute N CoI: Joel Parker Southwest Research Institute N CoI: Marc Buie Lowell Observatory N CoI: Alain Doressoundiram Observatoire de Paris N CoI: Matthew Holman Harvard-Smithsonian Center for N Astrophysics CoI: Brian Marsden Harvard-Smithsonian Center for N Astrophysics CoI: David Tholen Institute for Astronomy N ------------------------------------------------------------------------------------ 5. Abstract The discovery that the Trans Neptunian Object (TNO) 1998 WW31 has a satellite was announced on IAU Circular 7610 (16th April 2001). HST observations of this object would be of immense public interest. Combining images taken at separate epochs would afford an opportunity to demonstrate the immense power of Hubble in deriving the orbit and physical parameters of this system. DD time is being requested to get an initial look, and additional observations to resolve possible mirror-image ambiguities would be proposed in subsequent cycles. Since we don't yet know the optimum sampling interval to get a decent orbital solution, the DD time would enable us to prepare a better Cycle 11 proposal. We really need to get a crude orbital period first, then we will be in a good position to propose a more thorough strategy in future cycles. Hence observations made in July, August and September will greatly assist the determination of the orbital parameters and physical characteristics of this important new object. Hubble's unparalleled resolution will enable the physical characteristics of this system to be derived significantly earlier and to far better precision than using ground based observations alone. We note that this object is not a target of any accepted program for the coming cycle and that the observations we wish to perform (observations at a few epochs for refining the orbit, and at least at one epoch a good multicolor photometry for comparing the two components of the system) is not the goal of any of the programs presently accepted for Cycle 10. ------------------------------------------------------------------------------------ 9259( 3) - 06/01/01 07:34 - [ 2] Observations Description ------------------------ Studies of the Kuiper Belt have proved to be amongst the most exciting in Planetary science. The Kuiper Belt offers clues to the nature of the early solar system, and studies of it might also give insight into the processes behind the formation and growth of planets during the early history of the solar system. Observations exist of only a few hundred Trans Neptunian Objects (and colors exist for no more than 50 objects) and there is great interest in binary asteroids (origin and stability) and this distant object is an important addition to the very few cases discovered so far in the asteroid belt. Since they are too distant to be resolved (even by HST), and their albedoes are unknown, TNO properties have generally been estimated using thermal models similar to those used for main belt asteroids. Hence, to date only model dependant estimates of mass and density have been inferred from observations of TNO's. The unique nature of 1998 WW31 will enable us to derive precise physical information for both components of the 1998 WW31 system using astrometric and photometric observations. As the first binary TNO (with the exception of Pluto) this object is very important for TNO studies. Deriving an orbit for this object using HST astrometry, and combining this with a size derived from photometry will eventually allow determination of the systems mass and density. Obtaining high resolution Hubble data at an early epoch is thus extremely important. A calculation from the observed position angles as given by Christian Veillet (private communication) on 2451512.8, 2451550.8 and 2451901.5, and assuming that the orbit is circular and that the last observation was made at the maximum elongation, Marsden (private communication) finds a revolution period of about 405 days and suggest that the orbit is inclined at about 27 degrees to the plane of the sky. The resulting predicted ephemeris (the chosen dates at 100-day intervals--actually being near the extremes in position angle) is: Date p.a. sep. deg 2001 Apr 1 345.7 0.54 2001 Jul 10 244.9 1.20 2001 Oct 18 116.5 0.54 2002 Jan 26 51.1 1.20 An HST observation in July should get the object near its other maximum elongation. HST observations in August and September would be very useful, because the small separation would directly give us the inclination, which may in fact be greater than suggested. HST colors of both objects would help tie down the physical characteristics of the system. Of course, the above orbit could be wrong, and is another argument for HST observations. We request 3 orbits in total. 1 in July for Astrometry and Photometry, with single orbit follow up in August and September to improve the astrometric orbit. Although we would like the observations to occur as early as possible in July, the precise date is not important. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- We request that initial observations be made in July, as soon as can be conveniently scheduled possible once the target leaves the solar avoidance Zone. Follow up astrometric observations should be made in August and September. ------------------------------------------------------------------------------------ 9259( 3) - 06/01/01 07:34 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: 1998WW31 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: ASTEROID binary trans-neptunian object ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | TYPE=ASTEROID,A=45.0160969,E=0.0845787,I | =6.77412,O=237.09738,W=57.19907,M=112.71 | 141,EPOCH=01-Apr-2001,EQUINOX=J2000 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 23.3 | Orbital elements from MPC cross- | checked with Horizons \{source: | E2001H21\} as of 2001 May 30 | ------------------------------------------------------------------------------------------------------------------------------------ 9259( 3) - 06/01/01 07:34 - [ 4] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 09-Jul-2001 AND 14-Jul-2001 On Hold Comments: Additional Comments: We would like visits 01, 02, and 03 to be scheduled a month apart, starting in July as soon as possible (i.e., as soon as the target's elongation is out of the sun avoidance angle). The target should be available sometime around/after July 8th, so our optimal dates would be July 12, August 12, and September 12, all with a tolerance of +/-3 days. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 1998WW31 WFPC2 IMAGE PC1 F555W 2 230 S ------------------------------------------------------------------------------------------------------------------------------------ 20 1998WW31 WFPC2 IMAGE PC1 F675W 2 230 S ------------------------------------------------------------------------------------------------------------------------------------ 30 1998WW31 WFPC2 IMAGE PC1 F814W 2 300 S ------------------------------------------------------------------------------------------------------------------------------------ 9259( 3) - 06/01/01 07:34 - [ 5] Visit: 02 Visit Priority: Visit Requirements: BETWEEN 09-Aug-2001 AND 14-Aug-2001 On Hold Comments: Additional Comments: We would like visits 01, 02, and 03 to be scheduled a month apart, starting in July as soon as possible (i.e., as soon as the target's elongation is out of the sun avoidance angle). The target should be available sometime around/after July 8th, so our optimal dates would be July 12, August 12, and September 12, all with a tolerance of +/-3 days. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 1998WW31 WFPC2 IMAGE PC1 F555W 2 230 S ------------------------------------------------------------------------------------------------------------------------------------ 20 1998WW31 WFPC2 IMAGE PC1 F675W 2 230 S ------------------------------------------------------------------------------------------------------------------------------------ 30 1998WW31 WFPC2 IMAGE PC1 F814W 2 300 S ------------------------------------------------------------------------------------------------------------------------------------ 9259( 3) - 06/01/01 07:34 - [ 6] Visit: 03 Visit Priority: Visit Requirements: BETWEEN 09-Sep-2001 AND 14-Sep-2001 On Hold Comments: Additional Comments: We would like visits 01, 02, and 03 to be scheduled a month apart, starting in July as soon as possible (i.e., as soon as the target's elongation is out of the sun avoidance angle). The target should be available sometime around/after July 8th, so our optimal dates would be July 12, August 12, and September 12, all with a tolerance of +/-3 days. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 1998WW31 WFPC2 IMAGE PC1 F555W 2 230 S ------------------------------------------------------------------------------------------------------------------------------------ 20 1998WW31 WFPC2 IMAGE PC1 F675W 2 230 S ------------------------------------------------------------------------------------------------------------------------------------ 30 1998WW31 WFPC2 IMAGE PC1 F814W 2 300 S ------------------------------------------------------------------------------------------------------------------------------------ 9259( 3) - 06/01/01 07:34 - [ 7] Summary Form for Proposal 9259 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/DD ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 09-Jul-2001 AND 14-Jul-2001 BETWEEN 09-Aug-2001 AND 14-Aug-2001 BETWEEN 09-Sep-2001 AND 14-Sep-2001 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F675W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names 1998WW31 ------------------------------------------------------------------------------------------------------------------------------------