Proposal 11106 (STScI Edit Number: 1, Created: Thursday, January 17, 2008 7:08:34 PM EST) - Overview
11106 - Target of Opportunity Imaging of an Unusual Cloud Feature on Uranus
Cycle: 16, Proposal Category: GO
(Availability Mode: SUPPORTED)
INVESTIGATORS
Name
Dr. Heidi B. Hammel (PI)
Dr. G. Wes Lockwood (CoI)
Dr. Kathy Rages (CoI)
Dr. Imke de Pater (CoI)
Institution
Space Science Institute
Lowell Observatory
SETI Institute
University of California - Berkeley
E-Mail
hbh@alum.mit.edu
gwl@lowell.edu
krages@mail.arc.nasa.gov
imke@astron.berkeley.edu
VISITS
Visit Targets used in Visit
Configurations used in Visit
Orbits Used Last Orbit Planner Run
01
(1) URANUS
WFPC2
1
17-Jan-2008 19:08:20.0
OP Current
with Visit?
yes
02
(1) URANUS
WFPC2
1
17-Jan-2008 19:08:26.0
yes
03
(1) URANUS
WFPC2
1
17-Jan-2008 19:08:31.0
yes
3 Total Orbits Used
ABSTRACT
The planet Uranus is demonstrating increased atmospheric activity as it approaches its 2007 equinox, perhaps in response to extreme insolation
change. Convective sites in the planet's southern hemisphere reached unprecedented altitudes in 2003 (Hammel et al. 2005, Icarus 175, 284); a bright
northern feature showed the highest contrast yet detected in an outer planet atmosphere (Sromovsky et al. 2007, Icarus, submitted); and a dark
atmospheric feature was detected by HST for the first time (Hammel et al. 2007, in preparation). The historical record makes references to discrete
Proposal 11106 (STScI Edit Number: 1, Created: Thursday, January 17, 2008 7:08:34 PM EST) - Overview
structures (both bright and dark) on Uranus during previous equinoctial apparitions (the last equinox occurred in 1965). The best amateur facilities
are now just able to resolve the disk of Uranus and detect such activity if it is very large or has very high contrast. Amateurs also have access to a
great many nights of telescope time. If a discrete cloud feature on Uranus is reported through the amateur network, we propose to obtain follow-up
images with HST's WFPC2. The proposed TOO images will permit determination of detailed structure of the feature at visible wavelengths, and will
provide vertical and horizontal constraints on the feature's scattering properties. HST is the only facility that can provide such information at visible
wavelengths.
OBSERVING DESCRIPTION
Camera and Filter Selection: We request three orbits of WFPC2 imaging in Cycle 16. Our filter selection and observing strategy are designed to
elucidate the vertical structure and temporal variability of the anomalous feature. Each orbit will consist of exposures in the Planetary Camera (PC1;
high spatial resolution required) in a suite of filters, with choices based on our past experience with HST. Similar filter choices with ACS yielded
detection of extended faint material seen in association with the brighter uranian features; whether WFPC2 has similar success depends on the
contrast of these time-variable features.
Timing: Each of the three orbits should have the feature as close as possible to the central meridian to permit optimal imaging of detailed structure.
The first orbit should be as soon as possible after discovery. A 48-hour turnaround from the time of initial feature confirmation would be optimal but
not critical. The convective episode reported by Hammel et al. (2005a) lasted at least 4 days, perhaps as long as a month. Since the triggering event
would necessarily have higher contrast than that observed by Keck, we estimate the TOO feature would have a similar if not longer lifetime.
The second orbit should occur about ~35 hours (two rotations of Uranus, or 22 HST orbits) after the first orbit, and the third should follow about ~35
hours after that. The function of these two additional orbits is to characterize the horizontal and vertical evolution of the feature in much the same
manner as was done for Saturn?s great White Spot. Evolution was seen on this time scale for the bright uranian feature seen with Keck in 2004
(Fig.2; Hammel et al. 2005b).
The specific interval between orbits 1 and 2, and orbits 2 and 3, would be driven by the rotation period of the feature, which will be determined prior
2
Proposal 11106 (STScI Edit Number: 1, Created: Thursday, January 17, 2008 7:08:34 PM EST) - Overview
to execution of the TOO. The feature will likely have a rotation period between ~16 to ~17.5 hours, based on past HST and Keck imaging
(Karkoschka 1998; de Pater et al. 2002; Hammel et al. 2001, 2005b).
REAL TIME JUSTIFICATION
We request a Target of Opportunity (TOO) observation of an anticipated anomalous discrete feature on Uranus. The observations will be timecritical, with execution to occur as soon as possible after reports are confirmed of an anomalous feature on Uranus. The feature must be large enough
to be confirmed by multiple ground-based facilities, and its rotation period must already be known. We specify timing with respect to the first orbit;
we could also specify timing from one orbit to the next, if that makes scheduling more flexible. If the SAA interferes with the temporal sampling
between the three requested orbits, other sampling schemes can produce the requisite longitudinal coverage.
Required turn-around time: A short turn-around from feature confirmation is desirable but not critical. The Keck observations of the anomalous
atmospheric event in 2004 exhibited a feature lifetime of ?4 days, with the feature fading over those four days (Hammel et al. 2005a). However,
since we propose to execute this TOO only for a feature with much more contrast (whether bright or dark) than that observed by Keck or by HST, we
estimate that the feature?s lifetime would be at least 4 days, if not longer. Thus a turn-around time as long as 5 days can be tolerated if necessary,
though of course shorter would be better. We would be satisfied with a 3- or even 4-day turnaround time. Thus, the 15-orbit penalty for "ultra-rapid"
turn-around should NOT be assessed against this program.
Bright-object checking: Bright-object checking is moot if we are triggering for a dark feature. For a bright feature, the TOO will be triggered only if
ground-based data are obtained, thus we will know a priori the feature's brightness (as a check, co-I Lockwood can produce well-calibrated Uranus
photometry at several visible wavelengths with a resident facility at Lowell Observatory). We will assume a bright feature is a point source to obtain
an upper limit of the brightness per pixel, and use this to determine the maximum exposure time (typically we shorten exposures when taking
planetary images, sacrificing S/N for more filters, since wavelength coverage produces better atmospheric vertical sampling). Only exposure times
need adjusting upon TOO triggering.
3
Solar System Targets
Visit
Proposal 11106 - Visit 01 - Target of Opportunity Imaging of an Unusual Cloud Feature on Uranus
Proposal 11106, Visit 01
Diagnostic Status: No Diagnostics
Scientific Instruments: WFPC2
Special Requirements: ON HOLD
On Hold Comments: On hold because this is a Target of Opportunity observation. Slight adjustments to exposure times and orbit separations may be required prior to execution.
#
Name
Level 1
Level 2
Level 3
Window
(1)
URANUS
STD=URANUS
Exposures
#
1
Label
Target
(1) URANUS
Config,Mode,Aperture
WFPC2, IMAGE, FQCH4P15
Opt. Params.
WFPC2, IMAGE, PC1
Spectral Els.
FQCH4P15
8929.0 A
F953N
2
(1) URANUS
3
(1) URANUS
WFPC2, IMAGE, PC1
F850LP
ATD-GAIN=15
4
(1) URANUS
WFPC2, IMAGE, PC1
F791W
ATD-GAIN=15
5
(1) URANUS
WFPC2, IMAGE, PC1
F673N
ATD-GAIN=15
6
(1) URANUS
WFPC2, IMAGE, PC1
F336W
ATD-GAIN=15
7
(1) URANUS
WFPC2, IMAGE, PC1
F439W
ATD-GAIN=15
8
(1) URANUS
WFPC2, IMAGE, PC1
F631N
ATD-GAIN=15
9
(1) URANUS
WFPC2, IMAGE, FQCH4N15
FQCH4N15
6193.0 A
4
Special Reqs.
Groups
Fri Jan 18 00:08:35 GMT 2008
Exp. Time/[Actual Dur.]
160.0 Secs
[==>]
160.0 Secs
[==>]
100.0 Secs
[==>]
35.0 Secs
[==>]
100.0 Secs
[==>]
160.0 Secs
[==>]
30.0 Secs
[==>]
160.0 Secs
[==>]
160.0 Secs
[==>]
Ephem Center
EARTH
Orbit
[1]
[1]
[1]
[1]
[1]
[1]
[1]
[1]
[1]
Orbit Structure
Proposal 11106 - Visit 01 - Target of Opportunity Imaging of an Unusual Cloud Feature on Uranus
5
Solar System Targets
Visit
Proposal 11106 - Visit 02 - Target of Opportunity Imaging of an Unusual Cloud Feature on Uranus
Proposal 11106, Visit 02
Diagnostic Status: No Diagnostics
Scientific Instruments: WFPC2
Special Requirements: AFTER 01 BY 34.0 H TO 36.0 H
#
Name
Level 1
(1)
URANUS
STD=URANUS
Exposures
#
1
Label
Target
(1) URANUS
Config,Mode,Aperture
WFPC2, IMAGE, FQCH4P15
2
(1) URANUS
3
Fri Jan 18 00:08:36 GMT 2008
Level 2
Level 3
Opt. Params.
WFPC2, IMAGE, PC1
Spectral Els.
FQCH4P15
8929.0 A
F953N
(1) URANUS
WFPC2, IMAGE, PC1
F850LP
ATD-GAIN=15
4
(1) URANUS
WFPC2, IMAGE, PC1
F791W
ATD-GAIN=15
5
(1) URANUS
WFPC2, IMAGE, PC1
F673N
ATD-GAIN=15
6
(1) URANUS
WFPC2, IMAGE, PC1
F336W
ATD-GAIN=15
7
(1) URANUS
WFPC2, IMAGE, PC1
F439W
ATD-GAIN=15
8
(1) URANUS
WFPC2, IMAGE, PC1
F631N
ATD-GAIN=15
9
(1) URANUS
WFPC2, IMAGE, FQCH4N15
FQCH4N15
6193.0 A
6
Window
Special Reqs.
Groups
Ephem Center
EARTH
Exp. Time/[Actual Dur.]
160.0 Secs
[==>]
160.0 Secs
[==>]
100.0 Secs
[==>]
35.0 Secs
[==>]
100.0 Secs
[==>]
160.0 Secs
[==>]
30.0 Secs
[==>]
160.0 Secs
[==>]
160.0 Secs
[==>]
Orbit
[1]
[1]
[1]
[1]
[1]
[1]
[1]
[1]
[1]
Orbit Structure
Proposal 11106 - Visit 02 - Target of Opportunity Imaging of an Unusual Cloud Feature on Uranus
7
Solar System Targets
Visit
Proposal 11106 - Visit 03 - Target of Opportunity Imaging of an Unusual Cloud Feature on Uranus
Proposal 11106, Visit 03
Diagnostic Status: No Diagnostics
Scientific Instruments: WFPC2
Special Requirements: AFTER 02 BY 34.0 H TO 36.0 H
#
Name
Level 1
(1)
URANUS
STD=URANUS
Exposures
#
1
Label
Target
(1) URANUS
Config,Mode,Aperture
WFPC2, IMAGE, FQCH4P15
2
(1) URANUS
3
Fri Jan 18 00:08:37 GMT 2008
Level 2
Level 3
Opt. Params.
WFPC2, IMAGE, PC1
Spectral Els.
FQCH4P15
8929.0 A
F953N
(1) URANUS
WFPC2, IMAGE, PC1
F850LP
ATD-GAIN=15
4
(1) URANUS
WFPC2, IMAGE, PC1
F791W
ATD-GAIN=15
5
(1) URANUS
WFPC2, IMAGE, PC1
F673N
ATD-GAIN=15
6
(1) URANUS
WFPC2, IMAGE, PC1
F336W
ATD-GAIN=15
7
(1) URANUS
WFPC2, IMAGE, PC1
F439W
ATD-GAIN=15
8
(1) URANUS
WFPC2, IMAGE, PC1
F631N
ATD-GAIN=15
9
(1) URANUS
WFPC2, IMAGE, FQCH4N15
FQCH4N15
6193.0 A
8
Window
Special Reqs.
Groups
Ephem Center
EARTH
Exp. Time/[Actual Dur.]
160.0 Secs
[==>]
160.0 Secs
[==>]
100.0 Secs
[==>]
35.0 Secs
[==>]
100.0 Secs
[==>]
160.0 Secs
[==>]
30.0 Secs
[==>]
160.0 Secs
[==>]
160.0 Secs
[==>]
Orbit
[1]
[1]
[1]
[1]
[1]
[1]
[1]
[1]
[1]
Orbit Structure
Proposal 11106 - Visit 03 - Target of Opportunity Imaging of an Unusual Cloud Feature on Uranus
9