Letters of Intent received in 2013

LoI 2015-185
Focus Meeting: Statistics and Exoplanets

Topics

Planetary signal extraction, periodicity detection
Multiplanet model selection
Planetary populations (eta-Earth)
Challenging planetary transit analyses
High contrast imaging

+ theoretical & observational introductory overviews
+ concluding panel of senior commentators (including statistician)

Rationale

The IAU Working Group in Astrostatistics and Astroinformatics (IAU/WGAA) was formed at the 2012 IAU GA to facilitate the use of advanced statistical and computational methodology in astronomical research. The discovery and characterization of exoplanets requires both superbly accurate instrumentation and sophisticated statistical methodologies to extract the extremely weak planetary signals from the dominant starlight or very large samples. Spectroscopic radial velocity, photometric transit, direct imaging, and microlensing planet detection are all technically difficult and benefit from new analysis methodologies. Modeling the recovered signal, often from noisy and irregularly spaced data, often raises significant mathematical challenges.

We outline here a tentative program for a 2.5-3 day FM covering five topics on the interface between exoplanetary research and astrostatistics.

1. Planetary signal extraction and periodicity detection
While the Fourier transform has been known for two centuries, it is not designed for finding periodic signals in sparse, irregularly-spaced data with non-sinusoidal variations. A modified Fourier method, the Lomb-Scargle periodogram is in common use, but it has various deficiencies and the significance of its spectral peaks are difficult to quantify. Studies from Russia, Austria, South Africa, United States, Poland, Germany and Italy have wrestled with this problem in the recent astronomical literature. Non-Fourier methods are also widely used, but again their statistical properties are often not well-established. Presentation and discussion by the expert community is sorely needed on this topic.

2. Multiplanet model selection
Five hundred years ago, Johannes Kepler struggled for years to construct a multiplanet model of the Solar System from irregularly spaced, noisy positional data. Today, we struggle with similar problems in hundreds of planetary systems using radial velocity and/or transit data. Here the question is whether the signal is produced by two, three or more planets. Subtle transit time variations are often present to assist in the modeling. In statistical parlance, this is called a nested model selection problem, and advanced techniques are available to address the issue. The problem is often best approached through Bayesian inference, and some leading Bayesian statisticians have been working with exoplanetary astronomers to shape the methodology. Bayesian computations for high-dimensional models (i.e. several planets) can be very demanding, so that sophisticated algorithmic approaches and GPU computers can be brought to the task.

3. Planetary populations (eta-Earth)
To the public, the primary questions in this field is: Are there other Earths? Can we visit? Are they inhabited? Astronomers are definitely answering the first of these questions affirmatively: the latest estimates are 10^8-10^9 Earth-like planets in Habitable Zones in the Galaxy, with the nearest only parsecs away. But answering this question (known to professionals as estimation of the fraction eta-Earth) requires extrapolation from the available data, where Earth-like planets can today only be found in very small orbits inside the Habitable Zone. However, quantitative estimates of eta-Earth range over nearly a factor of 100. The techniques for this extrapolation, and the fusion of surveys with different selection effects, need to be discussed by scholars to assist the community in achieving greater consensus on the value of eta-Earth.

4. Challenging planetary transit analyses
Planetary transits have recently become the richest resource for planet detection, particularly with the superb photometry of ~160,000 stars over several years by NASA's Kepler mission. We envision a session that discusses some exciting innovations in the analysis of Kepler data: the sophisticated Kepler pipeline; transit timing variations from multiplanet interactions; the photoeccentric effect; Doppler boosted emission; detecting moons. Ground-based telescopes also allow detection of planetary thermal emission and planetary atmospheric absorption. All of these problems involve the extraction of very faint signals from time series with complicated, poorly known behaviors.

5. High contrast imaging
Imaging surveys are discovering a growing number of young gas-giant exoplanets, using specialized high-contrast instruments designed to correct atmospheric changes and efficiently suppress the starlight. Sophisticated signal processing methods have been developed for analyzing these datasets, in order to extract faint planet signals and obtain reliable photometry and spectroscopy. In concert, statistical analyses of results from direct imaging surveys provide strong constraints on the distribution of planet masses and orbital separations.

A FM on Statistics and Exoplanets should have considerable impact at the 2015 GA. The meeting will likely draw many U.S. attendees; 1/3 of papers at recent Amer Astro Soc meetings concern exoplanets. These (mostly young) researchers will benefit from talks on the most advanced statistical methodologies, with pitfalls and advantages of various approaches discussed by leading experts. The FM will also be essential for the vanguard methodologists: never before have they gathered specifically to discuss and compare statistical approaches to various problems. The talks, posters and discussions will be presented to the public on the IAU/WGAA Web site, the Astrostatistics & Astroinformatics Portal (http://asaip.psu.edu) in addition to the published proceedings. The entire worldwide exoplanetary and astrostatistical community will thus quickly benefit from the FM in Hawaii.

We have constructed a hypothetical scientific program for a 2.5-3 day FM to see whether high quality scientists from diverse nations could be found for speakers and panelists. We had no difficulty constructing a program with speakers from eleven nations on four continents, including three women. The S.O.C. will seek out the best and most diverse speakers. We will also ask the International Astrostatistics Association, affiliated with the International Statistical Institute (sister organization to the IAU), to support one or two senior statisticians to attend the meeting.

The proposed co-Chairs of the FM are Eric Feigelson (Chair of the IAU/WGAA) and Suzanne Aigrain (Oxford UK) with Michael Liu (Hawaii USA) leading the L.O.C. This FM proposal has been discussed with the following IAU leaders, all with positive comments. Letters of support are expected from Division B, Division F, and Commission 5. Very little overlap is seen with a FM proposal led by Commission 53 on multiplanetary dynamics.
- David Silva, President of Division B (Facilities, Technologies and Data Science)
- Robert Hanisch, President of Commission 5 (Documentation & Astronomical Data)
- Giovanni Valsecchi, President of Division F ({Planetary Systems and Bioastronomy)
- Alessandro Morbidelli, President of Commission 53 (Extrasolar Planets)