! Date generated: Thu Sept 6, 2001 ! Proposal_Information Prop_ID: 9298 !AC13 Title: Kuiper Belt Objects Search Proposal_Category: GTO/ACS Cycle: 11 avail_ok: YES Investigators PI_Name: Holland Ford PI_Institution: Johns Hopkins University CoI_Name: Paul Feldman CoI_Institution: Johns Hopkins University Contact: Y CoI_Name: Bob Brown CoI_Institution: Space Telescope Science Institute Abstract: Over the past several years ground-based observations have revealed more than 200 bodies in orbit beyond Neptune in what is referred to as the Kuiper Belt. These Trans-Neptunian Objects (TNOs) are mainly at 30 to 50 AU, and with a detection threshold magnitude m_R = 22.5, correspond to bodies with diameters D>100 km. Even with a small sample there is evidence that TNOs belong to three distinct dynamical classes. The diameters of the detected TNOs are considerably larger than those of the known short-period comets implying that there must exist a large population of such objects with diameters similar to that of comet Halley (~10 km) and smaller. An attempt to detect Halley size TNOs using the WFPC2 to a limiting m_V~28 resulted only in a statistical detection that has been strongly criticized. The ACS Wide-Field Camera can significantly improve upon the WFPC2 survey by virtue of its greatly enhanced discovery potential. Our strategy will be to choose fields such that the HRC will contain a known, relatively bright TNO, so that the search algorithm can be internally verified. In addition, this will enable the search for cometary activity in the form of a faint dust coma around the brightest (and largest) TNOs. We estimate that in a single HST orbit, an object at a limiting magnitude of m_R = 28 can be detected with a signal to noise of >6. Extrapolation of the cumulative luminosity function predicts three such TNOs will be found, on average, in each WFC frame. Questions ! Free format text Observing_Description: On the first visit, a known TNO will be placed at the center of the HRC field and the search for faint TNO's will be done with WFC auto-parallel exposures. In a given orbit, the known TNO will not be tracked. On the second visit, the same TNO will be placed at WFC and five orbits of short exposures will be used for a deeper search. Real_Time_Justification: We require that the motion of a TNO on the sky will be such that it will move about 2 WFC pixels (0.1 arc-sec) in each exposure so that we can utilize the technique of stacking and shifting several short exposures (~5-10 minutes) per HST orbit to identify the moving objects in the WFC field. This requires that the TNO selected for the HRC be observed near its stationary point, which gives us a two-week window every six months for a given TNO. In addition, the TNO selected for the HRC must have a well constrained orbit, be bright (for a TNO) and that its orbit parameters must include heliocentric distance around 40 AU, low inclination, and high galactic latitude. For the first observation of this program, we have selected 1992 QB1 (since given the IAU designation 15760), the very first TNO discovered, since it satisfies the above constraints. The observing window is from December 14, 2002 to December 20, 2002. Calibration_Justification: None Additional_Comments: Solar_System_Targets Target_Number: 1 Target_Name: 1992-QB1 Description: ASTEROID Kuiper belt object Level_1: TYPE=ASTEROID,A=44.0920028,E=0.0722316,I=2.19092,O=359.44889,W=5.81856, M=6.50735,EPOCH=18-Oct-2001,EQUINOX=J2000 Level_2: Level_3: Window: A_VEL 1992-QB1 FROM EARTH LT 0.00020, A_VEL 1992-QB1 FROM EARTH GT 0.00010 Ephem_Uncert: 0.0 S Acq_Uncert: 0.5 " Flux: V = 23.5+/-0.03 Comments: This object is a placeholder. The exact target will be specified at a later date. Visits Visit_Number: 1 Visit_Requirements: ON HOLD ! SEQ 1-2 WITHIN 6H On_Hold_Comments: ON HOLD Visit_Comments: Visit 1 is designed to use HRC (F555W) as prime and WFC (F606W) in parallel. Multiple short exposures are taken to combine later. DO NOT TRACK the target. Exposure_Number: 11 Target_Name: 1992-QB1 Config: ACS/HRC Opmode: ACCUM Aperture: HRC SP_Element: F555W Wavelength: Optional_Parameters: PAREXP=MULTIPLE,CR-SPLIT=4,GAIN=1 Number_of_Iterations: 1 Time_Per_Exposure: 2400.0S Special_Requirements: Comments: Visit_Number: 2 Visit_Requirements: ON HOLD On_Hold_Comments: ON HOLD Visit_Comments: Visit 2 is designed to use WFC (F606W). Multiple short exposures are taken to combine later. DO NOT TRACK the target. Exposure_Number: 21 Target_Name: 1992-QB1 Config: ACS/WFC Opmode: ACCUM Aperture: WFC SP_Element: F606W Wavelength: Optional_Parameters: CR-SPLIT=4,GAIN=1 Number_of_Iterations: 1 Time_Per_Exposure: 2100.0S Special_Requirements: Comments: Exposure_Number: 31 Target_Name: 1992-QB1 Config: ACS/WFC Opmode: ACCUM Aperture: WFC SP_Element: F606W Wavelength: Optional_Parameters: CR-SPLIT=4,GAIN=1 Number_of_Iterations: 1 Time_Per_Exposure: 2200.0S Special_Requirements: Comments: Exposure_Number: 41 Target_Name: 1992-QB1 Config: ACS/WFC Opmode: ACCUM Aperture: WFC SP_Element: F606W Wavelength: Optional_Parameters: CR-SPLIT=4,GAIN=1 Number_of_Iterations: 1 Time_Per_Exposure: 2200.0S Special_Requirements: Comments: Exposure_Number: 51 Target_Name: 1992-QB1 Config: ACS/WFC Opmode: ACCUM Aperture: WFC SP_Element: F606W Wavelength: Optional_Parameters: CR-SPLIT=4,GAIN=1 Number_of_Iterations: 1 Time_Per_Exposure: 2200.0S Special_Requirements: Comments: Exposure_Number: 61 Target_Name: 1992-QB1 Config: ACS/WFC Opmode: ACCUM Aperture: WFC SP_Element: F606W Wavelength: Optional_Parameters: CR-SPLIT=4,GAIN=1 Number_of_Iterations: 1 Time_Per_Exposure: 2200.0S Special_Requirements: Comments: