Call for Exo-Zodiacal Dust Survey Key Project Teams
NASA is
soliciting proposals for Key Science teams to use the Keck
Interferometer Nuller to study exo-zodiacal dust around main sequence
stars. This call is being administered by the Michelson Science Center
(MSC). These proposals will be evaluated by a specially-convened NASA
Keck Time Allocation Committee which will make recommendations to the
MSC Executive Director. We expect that a few teams will be selected in
response to this call.
The KI Nuller (KIN) provides a unique observing capability
specifically designed to detect faint material near a central star by
nulling out the central region with an angular resolution of the
fringe pattern of 25 milliarseconds (mas) within a field of view of
approximately 600 mas (FWHM). The Nuller operates across the 8-13 micron
spectral band (N band) with a spectral resolution of 40.
For a single calibrated measurement, the 1-sigma uncertainty in the
flux with the interferometer at null is approximately 0.5% of the flux
at peak when averaged over the spectral channels weighted by flux,
which emphasizes the shorter wavelengths. Note that for an extended
object, only 1/2 of the flux passes through the interferometer fringe
pattern as compared to a compact object. The validation tests
completed to date indicate good repeatability of the null leakage
performance at the 0.5% uncertainty level for single target/calibrator
pairs during a 3 hr block on targets with an N band flux of 2 to 3 Jy.
The compilation of the validation tests completed to date indicate a
bias of approximately -0.5% in the final calibrated leakage. It is
most likely that this bias is attributable to intensity differences
between the target and its calibrators in the tests to date. A
specific experiment performed in August supports that this bias is
tied to the flux level, but the underlying origin of the bias is not
yet understood. Achieving sqrt(N) improvements in accuracy with
repeated 3-hour blocks will require addressing this bias through
either modeling or experiment design.
For a G2V star the sensitivity in a 3-hour block corresponds to a
limit of Ldust/Lstar = 3x10-5 (3
sigma) or roughly 300 times the level of emission of our solar
system's zodiacal cloud. We expect that the quoted KIN uncertainty can
be improved as the square root of the number of observing blocks.
The fringe tracking limit of the Nuller is 2.0
Jy in the N band, which sets a floor to the faintest stars that can be
studied with KIN. Unlike the photometric or spectroscopic methods
applied most recently using the Spitzer Space Telescope, measurements
using the KIN remove the photospheric signal spatially and thus do not
rely on precise absolute photometry or depend on the spectrum of the
excess being different from that of the central star. Details of the
observing parameters and sensitivities are available at
http://msc.caltech.edu/software/KISupport/nulling/index.html.
Science Goals
The proposals should address two fundamental questions:
What are
the physical and evolutionary properties of exo-zodiacal disks, with a
particular focus on studying warm (~300 K) material located in
regions analogous to the zodiacal dust and asteroid belt of our solar
system? Is material found within 1 AU by KIN a continuation of
material seen at longer wavelengths by Spitzer? Are there excesses
from hot material not previously identified in Spitzer surveys due to
limitations on absolute photometric accuracy, and whose presence is
hinted at by shorter-wavelength interferometric observations
(e.g. Vega; Ciardi et al 2001; Absil et al, 2006)? Can spectroscopic
information in the KIN band reveal mineralogical species not
detectable in lower-spatial resolution observations? Does the
presence of one or more planets affect the incidence or physical
properties of the exo-zodiacal emission?
What is the level of warm
(~300 K) material in the exo-zodiacal disks around specific nearby
main sequence stars which will be the prime targets for future planet
finding missions such as TPF and Darwin. Studies at Spitzer
sensitivity levels reveal that approximately 1% of main sequence stars show an
excess at ~10 microns. How does this number increase with improved
sensitivity? Is there a population of very small, hot dust grains
(>500 K) that might have been missed by Spitzer's photometric or
spectroscopic observations?
Observing Scenario and Available Time
During the 2008A and B semesters (Feb 2008 - Jan 2009) NASA is
allocating the majority of its Keck observing time to this
project. The proposed total Key Science allocation (for all teams) is
16 interferometer nights per semester. Proposals should assume a
1-year duration for the Key Science and describe a program which can
be completed within that time frame, although an extension to future
years with a lower number of nights may be possible for follow-up of
interesting sources. All observations will be made in roughly 3-hour
blocks. The observing time will be grouped into runs of 3-4 nights
with 4 runs spread throughout the observing semester. Accounting for
instrument setup overheads and weather losses, we expect to make ~40
of these block measurements in the 2008 observing year. Each observing
block will typically include 3 calibrated scans with the performance
described above.
To maximize observing efficiency and to ensure
uniformity of the final dataset for future archival use, all
observations in this program will be queue-scheduled in these roughly 3-hour
blocks and be carried out in a service observing mode to be conducted
by the MSC and Keck Observatory.
After the team(s) are selected, they will be asked to produce a
prioritized list of targets in both science categories, i.e. disk
science and TPF target survey. In the case of overlapping targets
between multiple teams, objects will be assigned to only one team on
the basis of the ranked lists. i.e. the team proposing the higher
ranking for a particular source will be given the observations for
that source. For each observing run, the MSC will request a
prioritized list of targets (after the assignments above) for each
team. The observing will be scheduled by the MSC in 3-hour blocks
using these priorities while also striving to maximize the use of
telescope time. In the case of multiple teams, the observing time
allocated to each team will be divided in accord with TAC
recommendations as averaged over a few runs. The list of successfully
completed observations will be made available to all selected teams.
Data processing and Proprietary Period
All data will be processed through a standard pipeline by the MSC.
The MSC will provide instrument-calibrated null leakages (Level 1) and
sky-calibrated null leakages (Level 2) for all objects, as well as
the Level 2 processing program. The MSC will also provide support in
calibrating these observations. The data proprietary period will be
18 months from the day the data are taken. Each team will have access
to data from its own targets and to all calibrator data. The MSC
will also provide a visibility modeling tool which will include the
basic properties of the nuller transmission pattern and the relevant
KI parameters.
Evaluation Criteria
The proposals will be evaluated on the following criteria:
Demonstrated understanding of the scientific context and theoretical
background of the two science goals of the program:
Improved
scientific understanding of the debris disk phenomenon possible using
the improved sensitivity and angular/spectral resolution of the KIN
instrument.
Characterizing exo-zodiacal emission in the context
of the long term NASA goals for the detection and characterization
of potentially habitable planets around solar-type stars.
Detailed plan for source selection and observing time allocation
within the bounds specified above (1 year, observing block
allocations from 15 to 45 blocks). Note that there are no reserved objects for this call.
Plan for data modeling and
interpretation to include such topics as:
Incorporating the
interferometer response function in the measured excess.
How
measured excess relates to spatial structure and composition of the
emitting material.
How the statistics of detections and upper
limits of the KIN survey relate to evolution of zodiacal clouds.
How the statistics of the survey relate to NASA goals for planet
detection.
Proposal Specifications
The proposal should contain the following sections and be formatted
with 12-point font and 1-inch margins:
Title page (1 page):
Proposal title, PI (one only) and co-I names and affiliations, contact
author identified with address, email, and fax.
Scientific
justification (5 pages, text only): Should include how the team will
address the specified science goals.
Source selection and
interpretation plan (2 pages, including tables): Should include plan
for source selection in queue observing mode
References and
figures (2 pages).
No budget information is requested at this
time.
The total proposal length must not exceed 10 pages. All
proposals should be submitted online at
http://msc.caltech.edu/missions/KeckSolicitation/
by no later than 5 pm PDT on September 24, 2007. The opportunity to
propose as a Principal Investigator for NASA time on the Keck
Telescopes is open to all U.S.-based astronomers having their
principal affiliation at a U.S. institution. Contingent on available
resources, limited funding may be available for data
reduction and analysis through the Keck PI data award program.
If you have questions not addressed in this material,
contact R. Akeson at rla@ipac.caltech.edu. A list of all questions and
answers is available here.
