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Kepler Guest Observer Program

Cycle 1 (2008) Participating Scientist Programs

Derek Buzasi
US Air Force Academy

The primary noise sources for the Kepler mission include photon noise, CCD and other instrumental noise, and "noise" intrinsic to the targets themselves: stellar activity, oscillations, and granulation. Presently, the granulation contribution is estimated based on the solar case, which means that it typically accounts for 10% of the noise contribution at frequencies of interest for planet detection. However, for high metallicity stars, recent models suggest that granulation noise could be an order of magnitude higher than the solar case would lead one to expect. Not only will this lead to fewer planet detections, it also constitutes a selection bias which will hinder the statistical description of the frequency of planets around different types of host stars. The proposed effort involves using Kepler data to construct an improved granulation model as a function of fundamental stellar parameters, including mass, effective temperature, activity level, and metallicity. This model can then be used to minimize the granulation signature in the time series.

Laurance Doyle
SETI Institute

About 350 eclipsing binary stars may be found in the NASA Kepler Mission field of view (FOV). We have developed two methods for the discovery of planets around eclipsing binaries -- a matching filter to look at quasi-periodic transit features indicative of a planet in transit across the two moving stars in the background, and a second method using timing of the stellar eclipse minima themselves to see if the stars are being offset by giant planets farther out around a binary-planet barycenter. This last method does not require planetary orbits to be in the line-of-sight orbital plane, and non-detections mean that circum-binary planets of a certain minimum mass are not present. One must know the spectral type and luminosity class of the stars for a determination of the size of the planets (transiting) or their projected mass (eclipsing timing). We will use ground-based Stromvil photometry to spectrally classify each eclipsing binary star system, following this with the application of the Wilson-Devinny (WD) eclipsing binary code to determine the exact parameters of the star systems. We have been guaranteed observing time on the 0.9-meter Crossley telescope at Lick Observatory for these observations. We will then apply a well tested matching filter program correlating light curves of the photometric data with generated models of planetary orbits and sizes in order to detect close-in transiting planets at a quantifiable confidence limit. Over a long term we shall then apply the WD code to see if any changes in binary eclipse epochs have shifted in a periodic way, indicative of larger-orbit circum-binary planets. We estimate that hundreds of additional planets may be discovered in the Kepler FOV in this way and that such circum-binary planets will be of significant interest to our understanding of planet formation processes in close binary star systems.

Eric Ford
University of Florida

The discovery of over 200 extrasolar planets with the radial velocity technique has revealed that many giant planets have large eccentricities, in striking contrast with most of the planets in the solar system and prior theories of planet formation. The realization that many giant planets have large eccentricities raises a fundamental question: ``Do terrestrial-size planets of other stars typically have significantly eccentric orbits or nearly circular orbits like the Earth?'' Theorists have proposed numerous mechanisms that could excite orbital eccentricities. If the mechanism(s) exciting eccentricities of the known giant planets also affect terrestrial planets, then it may be that Earth-mass planets on nearly circular orbits are quite rare. On the other hand, if large eccentricities are only common in systems with massive giant planets and/or very massive disks, then there may be an abundance of planetary systems with terrestrial planets on low eccentricity orbits. On one hand, the idea that our solar system is special appears to fly in the face of the Copernican principle. On the other hand, most of the known giant planets zones of FGK stars have sizable eccentricities, and these eccentric giant planets would inevitably perturb the orbits of any nearby terrestrial planets. We propose to use Kepler data (and follow-up observations when available) to characterize the orbital eccentricities of transiting planets found by Kepler. This research would contribute to understanding the origin and history of solar systems, and particularly terrestrial planets. Since a significant eccentricity will cause the incident stellar flux to vary, a planet's eccentricity affects its climate and potentially its habitability. Thus, this research would contribute to NASA's goal of searching for Earth-like planets and the results could influence the design of future space missions that will attempt to characterize Earth-like planets and search for signs of life.

Jonathan Fortney
NASA Ames Research Center

The most readily predictable science return from the Kepler Mission will be a greatly enhanced understanding of the structure, composition, and atmospheres of giant planets. Here, PI Jonathan Fortney, an expert in both the atmospheres and interiors of giant planets, proposes to join the Kepler science team. His work will be essential to the interpretation of giant planet radii, density, albedo, and light curve measurements to enable the maximum science return from the mission. PI Fortney will compute models of the structure, evolution, and contraction of planets in the Neptune to super-Jupiter mass range to aid in the interpretation of Kepler's initial planet detections. Trends in composition and core mass discerned by comparing measured radii to model radii in different planetary systems will allow us to better understand formation processes. He will also investigate the reflected flux from the close-in hot Jupiter planets that will be observed as a function of orbital phase. State-of- the-art spectral models of these atmospheres will be necessary to interpret albedo observations of these planets as both visible thermal emission and reflected stellar flux will be present in the Kepler band. For the most highly irradiated planets day/night temperature contrasts may be determined. Selected observations of some planets at high time cadence at particular orbital phases may allow for the characterization of condensates in these atmospheres. PI Fortney proposes to joint the Kepler science team to interpret and model the data on atmospheres, interiors, structure, and evolution of the giant planets that will be discovered by the Kepler Mission. These investigations will have implications for the formation of giant planets and solar systems, as well as comparative planetary atmospheres. NASA's 2007 publication Science Plan for NASA's Science Mission Directorate extensively highlights exoplanet research within Astrophysics. These areas include: "Understanding the Diversity and Frequency of Other Worlds" and performing "Comparative Planetology." The 2006 NASA Strategic Plan lists several strategic goals. A key science question of Section 3D that we address is: "How do planets, stars, galaxies, and cosmic structure come into being?" A research objective with 3D that this project will help achieve is: "Progress in creating a census of extrasolar planets and measuring their properties." Here we seek to understand properties of giant planet interiors and atmospheres. The Kepler Mission Participating Scientists (PS) "Description of the Opportunity" lists "Characterization of Discovered Planets" as a Kepler Science Team activity. PI Fortney's proposed work will enable characterization of discovered giant planets both by revealing their interior structure and enabling determination of their atmospheric albedos and scattering properties.

Matthew Holman
Smithsonian Astrophysical Observatory

Measuring the masses of many of the Kepler planets will present significant challenges. Most of the target stars will be faint; many of the planets will have low masses; and, some of the planets will have distant orbits. Although high-precision spectrographs on large aperture telescopes on which ample amounts of observing time are available will be able measure the masses of some of these planets, an alternative means of estimating the masses of Kepler planets and, in some cases, confirming their terrestrial nature is highly desirable. The variations in the time interval between transits, produced by gravitational interactions with additional planets, allow for the detection of those perturbing planets. And, perhaps more importantly, the variations allow the orbital period and mass of the additional planets to be determined from transit observations alone (Holman & Murray 2005, Agol et al. 2005). This suggests a promising means of detecting and measuring the masses of additional planets with Kepler photometry. I propose to contribute to the theoretical and analytical interpretation the photometry from the Kepler mission. The specific scientific objectives of this proposal are: (1) to develop the transiting timing variations (TTV) method for application to Kepler and (2) to detect additional nontransiting planets with Kepler using the TTV method.

Sara Seager
Massachusetts Institute of Technology

The existence of extrasolar planets is now firmly established with over 200 planets known to orbit nearby Sun-like stars. The next important advances in this field are characterizing the physical properties of exoplanets, specifically their densities and atmospheres. Indeed, hot Jupiter exoplanet atmospheres are now routinely measured with the Spitzer Space Telescope. Spitzer has found that hot Jupiter exoplanets are hot and likely dark. But how dark and how hot globally remains unknown. An important missing piece of information for the hot Jupiter class as a whole is their albedos: how much of the incident stellar energy is reflected and how much is absorbed? Measured albedos or upper limits across the whole visible wavelength range would tell us about the planet's energy balance, equilibrium effective temperature, and possible planet atmosphere composition. The energy balance plays a critical role in atmospheric circulation and in governing the partition of molecular species that we try to observe in the planet atmosphere. We propose to interpret the Kepler albedos and reflected light phase curves of hot Jupiter exoplanets using our existing suite of model atmosphere codes.

Jason Steffen

Each transiting planet identified by Kepler brings an opportunity to discover additional, nontransiting planets in that system. This is accomplished by identifying and analyzing variations in the time between transits---variations caused by planet-planet interactions. These transit timing variations are particularly large near mean-motion resonances and are capable for probing for planets with masses less than the mass of the Earth; as shown in the only published analyzes of this effect for TrES-1 (Steffen & Agol 2005) and HD 209458 (Agol & Steffen 2007). This proposal addresses: 1) developing the software necessary to analyze the transit times of Kepler planets in effort to detect additional planets in those systems and to infer their orbital elements; 2) testing that software on simulated data to determine how efficiently one can identify secondary planets in the system; and 3) work with the Kepler science team to implement that software and to analyze Kepler data when they are available. Some advantages that the proposed work brings to the Kepler mission include: 1) detecting nontransiting, terrestrial planets in the habitable zone by analyzing the transits of planets that are interior to the habitable zone; 2) identifying planetary and stellar masses and radii from the transit times of doubly transiting systems (see proposal by Eric Agol); 3) providing information that constrains planet formation theories which make predictions regarding the number and distribution of planets that are too small to detect by other means; and 4) constraining the evolution of planetary systems by identifying the orbital elements (including inclinations) of multi-planet systems.

William Welsh
San Diego State University

The Kepler Mission will provide ultra high quality photometric observations that will allow a rich and detailed investigation of extrasolar planets and their host stars. The primary goal of the Mission is reconnaissance: to gather statistics and characteristics such as frequencies, sizes, and orbital distributions of Earth-size extrasolar planets and determine correlations with the properties of their host stars. The PI proposes to analyze a subset of the Kepler observations -- the short-period systems -- at a level that is impossible to do for a large set of systems. These short-period systems will be scrutinized with painstaking attention to detail. This narrow focus adds a strong complement to the broader Kepler Mission objectives. In particular, the set of products that will be generated include: (1) precise transit timings (to be used by the Kepler Science Team to detect other bodies for example); (2) accurate system parameters for the planet and host star (e.g. relative radii); and (3) characterization of photospheric "texture" and its effect on the transit light curves (i.e. mapping photospheric features). The PI of this proposal is well--versed in skills relevant to this research, including periodic and aperiodic time series analysis, binary star research, high--speed photometry, and in particular, extrasolar planet transit modelling. Along with Fourier, auto-regressive, correlation, and other similar general tools, the eclipse modelling software ``ELC'' will be the primary tool employed by the PI. ELC will be improved to take full advantage of the unprecedented level of precision of the Kepler light curves. Thus a fourth product will be generated: (4) the enhanced ELC code will be made available to all Kepler Science Team members. Through the Kepler Participating Scientist Program the PI will become a member of the Kepler Science Team, enabling him to add his expertise and directly contribute to the Kepler Mission.

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