NASA Solicitation
To Join the Large Binocular Telescope Interferometer Science Team
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Description of the Opportunity
LBTI Instrument Description
LBTI Exo-zodi Key Science
LBTI Science Team Activities and Roles
Period of Performance and Awards
Proposal Requirements
Contact
References
Previous Exo-zodi Surveys at Similar Wavelengths
FAQs
Description of the Opportunity
The proper design of a future mission to directly detect and spectroscopically characterize exo-Earths around nearby stars, demands a good understanding of the level and morphology of exo-zodiacal dust emission around the target stars1.
A new opportunity to directly address this question is with the Large Binocular Telescope Interferometer (LBTI2,3), an instrument on the Large Binocular Telescope (LBT) on Mount Graham, Arizona. The LBTI is part of NASA's strategic effort to find planets and ultimately life beyond our solar system. NASA funds the LBTI and the key science project to survey the exo-zodi dust levels around a sample of nearby Sun-like stars, prime targets for a future exo-Earth direct imaging mission. NASA hereby solicits proposals for membership on the LBTI Science Team (LBTI-ST). The LBTI-ST will work under the leadership of the LBTI Principal Investigator (Phil Hinz, University of Arizona) in order to most effectively execute this exo-zodi key science program. LBTI-ST members will participate in science deliberations, target selection, LBTI observations, data processing and analysis, follow-up observations, and publication in peer-reviewed journals.
LBTI Instrument Description
The LBTI combines the light from the twin 8.4 m diameter telescopes to make high angular resolution measurements of stars and galaxies and to measure the emission from dust orbiting nearby stars. The common-mount geometry of the LBT, combined with the deformable secondary mirror approach to adaptive optics, results in a low-background system. The spatial resolution of the LBTI is set by the 14.4 meter separation of the centers of the telescope pupils.
This call pertains only to the use of the LBTI instrument for addressing the exo-zodiacal key science.
The LBTI Nulling instrument operates at N-band (8 -14 μm) and it was specifically designed to make measurements of exo-zodiacal dust levels and morphology. The angular resolution is ~ 100 milliarcsecond, corresponding to 1 AU at a distance of 10 pc. Thus, the spatial resolution of the interferometer probes a physically interesting scale for the stars of interest, compared to filled aperture telescopes.
In the following description, we use models of exo-zodi clouds based on empirical fits to observations of the Solar system's zodiacal cloud4, as implemented by the Zodipic5 code. The unit "1 zodi" refers to an exo-zodi disk with the same optical depth at 1 AU and radial density profile as in the Solar System, but with a spectral type dependent dust sublimation radius (1 zodi models have a fractional dust luminosity LDust/LStar ≈ 10-7, the Solar System value).
For a Sun-like star at 10 pc and a 1 zodi dust disk, the dust flux at 10 μm is ≈ 5 x 10-5 that of the star. This provides the challenge of not only resolving the dust, but detecting it at a high contrast ratio. The LBTI Nulling instrument accommodates the required dynamic range via the technique of Nulling Interferometry6. Light from two apertures is interfered out of phase for the starlight in order to eliminate its contribution to the final image. The resolved dust emission is not suppressed by this interference, and can be detected relatively free of contaminating starlight.
The photometric sensitivity of the LBTI at N-band is projected to be 40 μJy (1σ) or better in an hour-long integration. A 1 zodi disk around a Sun-like star at 10 pc produces a 10 μm flux of 100 μJy, of which 2/5 (40 μJy) is transmitted by the LBTI fringe pattern (if the disk is viewed face-on; the transmission is 1/3 for a 60° inclination). Therefore, it is expected that the LBTI will have a photometric 1σ noise equivalent ≈ 1 zodi. Based on simulations of the null stability, including atmospheric seeing and the performance of the LBT adaptive optics systems, it is expected that the null calibration will have 1σ equivalent errors of 3 - 6 zodi. The possible presence of un-modeled calibration biases will be assessed by the team by conducting dedicated observations during commissioning and early key science time, in order to establish optimum observing and/or data calibration strategies.
The LBTI instrument has been built and assembled over the past several years and is now being commissioned. Science observations will begin during the late commissioning phases, and full science capabilities are expected after Summer 2012.
| Telescope diameter | 8.4 m |
| Telescope center-to-center separation | 14.4 m (22.7 m maximum baseline) |
| Wavelength coverage | 8 - 14 μm |
| Throughput | >20% |
| Pixel size | 0.018 arcsecond |
| FOV | 12 arcsecond |
| Minimum Strehl | 95% |
| Spectral resolution | 100 |
| Angular resolution | 100 mas |
| Photometric sensitivity* | 40 μJy (1σ, 1 hour) |
| Exo-zodi sensitivity* | 3 - 6 zodis (1σ) |
| Stellar limiting magnitude* | Kmag = 6 - 7 (limited by fringe sensing unit) |
LBTI Exo-zodi Key Science
The primary goal of this survey is to obtain measurements or upper limits of the exo-zodi dust levels around a sample of 60 - 100 nearby FGKM stars, prime targets for a future exo-Earth direct imaging and spectroscopic mission.
A total of 60 nights will be dedicated to this project, distributed over 5 years (with the majority of the observations taking place during the first 3 years). The data will be archived and publicly distributed by the NASA Exoplanet Science Institute (NExScI).
LBTI Science Team (LBTI-ST) Activities and Roles
The LBTI-ST will be assembled during commissioning of the LBTI instrument. Therefore, selected team members will be involved at an early stage and will be expected to participate in the optimum definition of the exo-zodi key science survey. The activities of the LBTI-ST may include, but are not limited to, the following anticipated areas of needed expertise:
- Optimum survey definitions and selection of targets
- Optimization and calibration of interferometric instrumentation
- Data reduction
- Data modeling and interpretation
- Dust physics and chemistry
Working in coordination with and under the leadership of the LBTI Principal Investigator, the selected LBTI-ST members will be expected to lead the activities in an area of work (such as those in the examples above). The LBTI-ST is expected to publish the results of this survey in a peer-reviewed journal in a timely manner.
Period of Performance and Awards
Investigators could propose for up to five years of support running from August 20, 2012 to September 30, 2017 (contingent on funding availability), which effectively corresponds to the end of the LBTI prime mission.
The total annual budget for the LBTI-ST is approximately $250K per year during the first three years and $200K per year during the last two years. The total yearly budget will be divided equally among the awardees. It is anticipated that 3-4 LBTI-ST members could be selected, and these funds may be used to cover travel to observing runs and team meetings, publications costs, and partial salary for the proposer or students or postdocs. Annual award funding is contingent upon availability of funds and annual assessment of performance and relevance of the research effort to the LBTI and program requirements.
Proposal Requirements
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 additional collaborators and affiliations, contact author identified with address, email, and fax.
Scientific justification (5 pages maximum including figures). The principal criteria will be the proposer's demonstrated ability to enhance the LBTI's contribution to measuring the exo-zodiacal dust emission around nearby stars that may be targets for a future mission to detect and characterize exo-Earths. Proposers should clearly identify his or her areas of expertise and their relevance to the Key Project. In particular, the LBTI-ST would benefit from expertise in the following areas: (a) detailed knowledge of exo-zodi datasets for potential LBTI targets at visible and/or infrared wavelengths; (b) modeling capabilities for the spectral energy distribution of debris disks in the context of physical location, grain size and composition; (c) modeling capabilities for the spatial distribution of debris disks in the context of relevant physical effects, including grain collisions, P-R drag, radiation pressure, and the possible influence of planets; (d) optimization and calibration of interferometric instrumentation; (e) knowledge of suitable stars for direct imaging experiments to assist with target selection.
References (1 page).
No budget information is requested at this time.
One-page biographical sketch for PI and additional collaborators if any.
Applications to the LBTI-ST are open to all U.S.-based astronomers having their principal affiliation at an accredited U.S. institution. Researchers with an affiliation outside the U.S. are welcome to apply, however they will receive no funding.
All proposals should be submitted by no later than 5 pm PDT on April 27, 2012, using the following online submission site:
Proposals will be evaluated by a merit-based process, implemented by an independent peer review of experts from the exo-planet and exo-zodi community.
Contact
If you have questions not addressed in this solicitation, please contact Dr. Rafael Millan-Gabet (NASA-LBTI Project Scientist) at lbti_nexsci@ipac.caltech.edu. Click here for answers to FAQs that have been received to date.
References
- "Impact of exozodiacal dust on exoplanet imaging and sensitivity of current and upcoming facilities to exozodiacal dust", Roberge, A. et. al., 2012. NASA Exoplanet Exploration Program Analysis Group (ExoPAG) report, in preparation, will be available at http://exep.jpl.nasa.gov/exopag/.
- "Detection of debris disks and wide orbit planets with the LBTI", Hinz, P., 2009, AIP Conference Proceedings Vol. 1158, pp. 313-317.
- LBTI web site: http://lbti.as.arizona.edu/LBTI-Main/Project.html
- "The COBE diffuse infrared background experiment: Model of the interplanetary dust could", Kelsall, T. et al., 1998, ApJ, 508, 44.
- http://irsa.ipac.caltech.edu/data/SPITZER/docs/dataanalysistools/tools/contributed/general/zodipic/
- "Imaging circumstellar environments with a nulling interferometer", Hinz, P. et al. 1998, Nature, 395, 251.
Previous Exo-zodi Surveys at Similar Wavelengths
- "Explorations beyond the snow line: Spitzer/IRS spectra of debris disks around Solar-type stars", Lawler, S. et al., 2009, ApJ, 705, 89.
- "Exozodiacal dust levels for nearby main sequence stars: A survey with the Keck Interferometer Nuller", Millan-Gabet, R. et. al., 2011, ApJ, 734, 67.
last updated April 2, 2012