9678( 8) - 08/15/02 11:17 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9678 Version: 8 Check-in Date: 15-Aug-2002 11:16:58 1.Proposal Title: Direct Measurement of the Size of the Largest Kuiper Belt Object ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO/DD 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Michael Brown California Institute of Technology ------------------------------------------------------------------------------------ 5. Abstract We have recently discovered a Kuiper belt object with the potential to be larger than Pluto. The largest public impact of the announcement of the existence of this object will come if we can simultaneously announce the true size (particularly if it really is larger than Pluto), rather than size based on speculation about an unknown albedo. A proposal for the next cycle would delay the measurement by more than a year and would significantly decrease the impact of the measurement. ------------------------------------------------------------------------------------ 9678( 8) - 08/15/02 11:17 - [ 2] Observations Description ------------------------ Object X will be observed using the F330W filter on the HRC as a trade-off between maximum resolution and maximum sensitivity. We will fill the orbit with a sequence of ~16 60-second exposures tracking at the sidereal rate and letting the object drift across the field (50 mas per exposure). We have used this observing mode extensively in our extremely successful KBO binary search and find that it allows highly accurate subtraction of background stars (which are copious in this field in the galactic plane) and excellent instantaneous calibration of the PSF (which is critical for these observations). We will measure the size of Object X in a single direction perpendicular to the direction of motion, to avoid having to model the effects of movement. We have found in the past that this method allows a more accurate and reliable measurement of the width of this moving source than any method where an attempt is made to track the object and let the stars drift. Sixty second exposures on the R=18.5 object (with an approximately solar spectrum) should give S/N ~ 40. Extensively modeling of point sources and resolved sources with this S/N suggests that the diameter of a Pluto-sized object will be measureable to an accuracy of ~7% and that the size of a 1400 km object will be measureable to an accuracy of ~20%. If Object X has an unexpectedly high albedo of 30% (higher even than Charon) we will only be able to put an upper limit to the size of ~800km. Quaoar will be observed using the F430W filter on the HRC as a trade- off between maximum resolution and maximum sensitivity. We will fill the orbit with a sequence of 16 ~120-second exposures tracking at the sidereal rate and letting the object drift across the field (50 mas per exposure). Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9678( 8) - 08/15/02 11:17 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 2 QUAUAR SOLAR SYSTEM, ASTEROID, RA=16H 34M 49.446S +/- 1", DEC=- J2000 R = 18.6+/-0.1 SOLAR SYSTEM, PLANET 14D 47' 34.5" +/- 1" TYPE=G3V Coordinate Source: OTHER_SOURCE Comments: QUAUAR will be near this position from 2002-Jul-29- 0:00 until 2002-Jul-29-6:00 9678( 8) - 08/15/02 11:17 - [ 4] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: OBJECTX ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: ASTEROID Kuiper belt object ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | TYPE=COMET,Q=29.7258,E=.89208,I=7.70595, | O=184.792,W=133.41922,T = 18-Nov- | 2030:19:27:51.0,EQUINOX=J2000,EPOCH=13- | Jun-2002:07:39:22.0 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | R = 18.6+/-0.1 | | Ephemeris Uncertainty: 8 S | Acquisition Uncertainty: 20 " | ------------------------------------------------------------------------------------------------------------------------------------ 9678( 8) - 08/15/02 11:17 - [ 5] Visit: 01 Visit Priority: Visit Requirements: NOTRACK BETWEEN 01-Jul-2002 AND 08-Jul-2002 On Hold Comments: Additional Comments: Track on background stars, not target Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 OBJECTX ACS/HR ACCUM HRC F330W CR-SPLIT=NO 16 110 S REQ EPHEM CORR OBJECT C Comments: Disable parallax correction ------------------------------------------------------------------------------------------------------------------------------------ 9678( 8) - 08/15/02 11:17 - [ 6] Visit: 02 Visit Priority: Visit Requirements: BETWEEN 28-Jul-2002:15:00:00.0 AND 29-Jul-2002:06:00:00.0 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 QUAUAR ACS/HR ACCUM HRC F435W CR-SPLIT=NO 16 120 S C Comments: QUAOAR will be within the HRC during the BETWEEN period, as will a bright PSF star. ------------------------------------------------------------------------------------------------------------------------------------ 9678( 8) - 08/15/02 11:17 - [ 7] Summary Form for Proposal 9678 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures HRC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/HRC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/DD ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements NOTRACK BETWEEN 01-Jul-2002 AND 08-Jul-2002 REQ EPHEM CORR OBJECT BETWEEN 28-Jul-2002 15 00 00.0 AND 29-Jul-2002 06 00 00.0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F330W F435W ------------------------------------------------------------------------------------------------------------------------------------ Target Names OBJECTX QUAUAR ------------------------------------------------------------------------------------------------------------------------------------