9320( 3) - 01/08/02 14:55 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9320 Version: 3 Check-in Date: 08-Jan-2002 14:55:11 1.Proposal Title: Constraining the highly eccentric orbit of the companio of the binary TNO 1998 WW31 by observations at its pericenter ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO/DD 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Christian Veillet Canada-France-Hawaii Telescope Corporation CoI: Joel Parker Southwest Research Institute N CoI: Ian Griffin Space Telescope Science Institute 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). 1998 WW31 has been observed on three HST orbits, thanks to an allocation of DD time. The combination of all the ground based obse rvations and these three high precision HST positions allowed a first determination of the motion of the faint component with resp ect to the primary body. Instead of the circular orbit assumed before the HST observations, we found a highly eccentric orbit whose eccentricity, ~0.7, is poorly constrained by the observations, mainly made far from the pericenter. Some models could even accommod ate an eccentricity as high as 0.9. These results will be presented a the AAS DPS meeting on Nov 27 and a paper is being submitted to Nature. A normal proposal has been made for the next cycle, but we now know that the companion will pass at the pericenter betw een January and March of 2002, and the next occurrence will be only in September 2003 (+/- a couple of months with the current uncer tainties). With a separation of the two components at pericenter close to 0.15", there is no way it can be observed from the ground with any sufficient accuracy. Hubble's unparalleled resolution will enable us to assess the ellipticity of the orbit in a definite way, providing an important constraint to the models proposed for the creation of such a binary system. It is our intent, as soon as our Nature paper is published, to implement an outreach site showing the evolution of our knowledge of the system with the acqu isition of new data from HST and from the ground, as a "case study" demonstrating the "prediction-correction" scheme widely used in science, with the advantage of simple basic physics (Keplerian motion, simple assumptions on physical characteristics like density o r albedo) easily accessible to young students, but still bringing important conclusions on the nature of the objects themselves. ------------------------------------------------------------------------------------ 9320( 3) - 01/08/02 14:55 - [ 2] Observations Description ------------------------ We request 3 orbits in total, the first close to January 1, and the two others following at a 1 month interval. We keep the same scheme as for the previous set of HST observations: WFPC2 observations in three colors on each orbit (F555W, F675W and F814W) to enhance our statistics on the color determination of each component (still weak from our first HST set) with two exposures wit h each filter and exposure times of 230s for F555W and F675W, and 300s for F814W. The astrometry is made using all the images. The S/N ratio as been found good enough to provide a reliable astrometric measurement at the level of 0.01". Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9320( 3) - 01/08/02 14:55 - [ 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=44.97832537,E=0.08427128 | 3,I=6.7761615,O=237.0970217,W=56.4678759 | ,M=114.1895498,EPOCH=18-Oct- | 2001,EQUINOX=J2000 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 23.3 | Orbital elements from MPC \{source: | MPC 12916\} cross-checked with | Horizons as of 2001 Dec 10 | ------------------------------------------------------------------------------------------------------------------------------------ 9320( 3) - 01/08/02 14:55 - [ 4] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 30-Dec-2001 AND 03-Jan-2002 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 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 ------------------------------------------------------------------------------------------------------------------------------------ 9320( 3) - 01/08/02 14:55 - [ 5] Visit: 02 Visit Priority: Visit Requirements: BETWEEN 18-Jan-2002 AND 22-Jan-2002 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 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 ------------------------------------------------------------------------------------------------------------------------------------ 9320( 3) - 01/08/02 14:55 - [ 6] Visit: 03 Visit Priority: Visit Requirements: BETWEEN 21-Feb-2002 AND 28-Feb-2002 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 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 ------------------------------------------------------------------------------------------------------------------------------------ 9320( 3) - 01/08/02 14:55 - [ 7] Summary Form for Proposal 9320 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/DD ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 30-Dec-2001 AND 03-Jan-2002 BETWEEN 18-Jan-2002 AND 22-Jan-2002 BETWEEN 21-Feb-2002 AND 28-Feb-2002 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F675W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names 1998WW31 ------------------------------------------------------------------------------------------------------------------------------------