9955(  1) - 04/04/03 10:36  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      9955
                                                       Version: 1
                                                       Check-in Date: 04-Apr-2003
                                                                      10:35:41

1.Proposal Title:
All-Sky Archival Zodiacal Background Measurements: Constraints to Kuiper Belt
Objects at R=28-60 mag.
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2. Proposal For  3. Cycle
AR               11
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4. Investigators
                                                                                     Contact?
    PI: Rogier Windhorst                  Arizona State University
   CoI: Dr. Scott Kenyon                  Smithsonian Institution Astrophysical         N
                                          Observatory
   CoI: Dr. Larry Petro                   Space Telescope Science Institute             N

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5. Abstract

More than 95% of all photons in the HST Archive come from distances 3-50 AU. Yet, no
precise all-sky measurements of the optical Zodiacal background exist. We show that
such a measurement will significantly constrain the faint counts of Kuiper Belt
Objects (KBOs) at R=28-60 mag (i.e., sizes =1 km-1 mm). The optical luminosity
function (LF) of KBOs is predicted to be very steep. We recently applied simple
estimates of the on-orbit Zodiacal background in the Ecliptic plane to resolve
Olbers Paradox as posed by KBOs, i.e. their apparently diverging sky-brightness
integral (Kenyon & Windhorst 2001), and conclude that KBOs with sizes r= 1mm-1km
must have a size distribution n(r)=r^-a with a<3. We propose to make accurate
differential Zodiacal background measurements versus Ecliptic coordinates in V
(F606W) and I (F814W) from 6, 600 Archival WFPC2 exposures taken in orbital dark-
time all over the sky. With careful attention to WFPC2 and foreground systematics,
this will allow us to: (1) Study the variance in the Zodiacal background in the
Ecliptic plane due to comet trails; (2) Set tighter upper limits to KBO-counts in
the range R=28- 60 mag; (3) Measure the KBO integral as a small but significant
excess on top of the Zodiacal background as interpolated to Lat=0 deg; (4) Detect
the unresolved Plutino population as a Zodi enhancement at certain Longitudes; and
(5) Make a direct estimate of the albedo, temperature, and size distribution for
small KBOs in the outer solar system.
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                                                9955(  1) - 04/04/03 10:36  - [  2]

            Summary Form for Proposal  9955

  Item                         Used in this proposal
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  Proposal Category            AR
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