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Kepler Guest Observer Program

White Papers Responding to Call for Two-Wheel Science Opportunities

White papers will be combined by the Kepler Project Office into a report to NASA HQ on the potential of two-wheel operations by Sep 27, 2013.

S. Aigrain
University of Oxford
+white paper

We outline a proposal to use the Kepler spacecraft in two-wheel mode to monitor a handful of young associations and open clusters, for a few weeks each. Judging from the experience of similar projects using ground-based telescopes and the CoRoT spacecraft, this program would transform our understanding of early stellar evolution through the study of pulsations, rotation, activity, the detection and characterisation of eclipsing binaries, and the possible detection of transiting exoplanets. Importantly, Kepler’s wide field-of-view would enable key spatially extended, nearby regions to be monitored in their entirety for the first time, and the proposed observations would exploit unique synergies with the GAIA ESO spectroscopic survey and, in the longer term, the GAIA mission itself. We also outline possible strategies for optimising the photometric performance of Kepler in two-wheel mode by modelling pixel sensitivity variations and other systematics.

Conny Aerts
University of Leuven
+white paper

Our goal is to perform in-depth ensemble asteroseismology of the young (age less than 6 million years) open cluster NGC 2244 with the 2-wheel Kepler mission. While the nominal Kepler mission already implied a revolution in stellar physics for solar-type stars and red giants, it was not possible to perform asteroseismic studies of massive OB stars because such targets were carefully avoided in the FoV in order not to disturb the exoplanet hunting. Now is an excellent time to fill this hole in mission capacity and to focus on the metal factories of the Universe, for which stellar evolution theory is least adequate. Our white paper aims to remedy major shortcomings in the theory of stellar structure and evolution of the most massive stars by focusing on a large ensemble of stars in a carefully selected young open cluster. Cluster asteroseismology of very young stars such as those of NGC 2244 has the major advantage that all cluster stars have similar age, distance and initial chemical composition, implying drastic restrictions for the stellar modeling compared to asteroseismology of single isolated stars with very different ages and metallicities. Our study requires long-term photometric measurements of stars with visual magnitude ranging from 6.5 to 15 in a large FoV with a precision better than ~30 ppm for the brightest cluster members (magnitude below 9) up to ~500 ppm for the fainter ones, which is well achievable with the 2-Wheel Kepler mission, in combination with high-precision high-resolution spectroscopy and spectro-polarimetry of the brightest pulsating cluster members. These ground-based spectroscopic data will be assembled with the HERMES and CORALIE spectrographs attached to the twin 1.2 m Mercator and Euler telescopes at the Observatories of La Palma, Canary Islands and La Silla, Chile, respectively, as well as with the spectro-polarimetric NARVAL instrument attached to the 2 m Bernard Lyot Telescope at the Pic du Midi in the French Pyrenees, to which the scientists in the present consortium have guaranteed access.

Charles Beichman
+white paper

This White Paper calls for the use of Kepler to conduct a survey in the ecliptic plane to search for planet transits around stars at high galactic latitudes and to study star forming regions to investigate physics of very young stars not studied by Kepler in its prime mission. Recent analysis by the Kepler project indicates that the spacecraft's best pointing will be possible in the ecliptic plane. We propose a 3 year program to survey between 5 and 10% of the sky located near the ecliptic plane (where pointing drifts are minimal) and at high galactic latitudes, |b|> 45 degree (where confusion effects are minimized). The proposed survey could examine roughly 20 fields (ecliptic latitude<±5 deg) for 60 days each or 40 fields (ecliptic latitude<±15 deg) for 30 days each. The survey could yield hundreds of gas and ice giants orbiting host FGK stars and hundreds of ice giants and rocky (radius < 2 Re) Super Earths orbiting mid‐ to late M stars.

Yuly Billig
Carleton University
+white paper

Spatial orientation of a solid body is parametrized by the group SO3 of rotations of a sphere. If we are given two types of control, that is we are able to rotate the body around two given axes, then we can achieve an arbitrary orientation of this body. In this paper we discuss how to perform this operation in the optimal way, minimizing the sum of the angles of rotation. We hope that our methods and results can be applied to improve control of the Kepler spacecraft using two reaction wheels.

W. J. Borucki
NASA Ames Research Center
+white paper

It is recommended that the Kepler Mission continue the observation of Kepler-Objects of Interest (KOI) in the current field-of-view to obtain a reliable estimate of eta-Earth. Currently no Earth-size planes in the HZ of a solar-analog have been found. Although the analysis of the four years of data already in hand, but not yet fully analyzed is expected to show one or more such planets, additional discoveries of planets with orbits at least as long as those associated with the habitable zone (HZ) are needed to increase the reliability of eta-Earth. The degradation of the photometric precision because of the loss of two reaction wheels is likely to prevent the discovery of Earth-size planets in the HZ of G dwarfs, but it is possible that the precision will be sufficient to detect larger planets with long orbital periods. It is proposed to use an interpolation techniques that incorporates a full range of planet sizes, orbital periods, and stellar properties is one of several methods that could provide a useful estimate of eta-Earth and its uncertainties.

Douglas Caldwell
SETI Institute
+white paper

We propose to continue and extend the Kepler Mission’s exoplanet survey by observing 8 to 12 fields in the Ecliptic plane for 2 to 3 months each over the next two years. Kepler is optimized for precise photometry and stable long-duration observations of many thousands of targets. By taking advantage of the pointing stability available for ecliptic plane fields we can retain much of the precision and stability. Continuing the exoplanet survey but concentrating on small cool stars will allow Kepler 2.0 to meet several key science goals: to determine the habitable zone planet occurrence rate for cool stars, to identify a number of planets orbiting bright small stars amenable for characterization with JWST, to link the planet statistics of the prime mission with those of the TESS survey of nearby stars, to help quantify the background false-positive rate in the TESS results, to enhance TESS target selection by identifying giants in the TESS input catalog, and to identify planets for long-baseline TTV follow-up by TESS. By continuing observations in a manner very similar to the Kepler prime mission, Kepler 2.0 will provide the most technically feasible and lowest-cost way to leverage the experience of the engineering, operations, and analysis teams, as well as the data processing pipeline, in order to provide light curves, planet candidates, and diagnostic products for tens of thousands of cool stars.

Michael Carini
Western Kentucky University
+white paper

A two-wheel operation scenario for the Kepler spacecraft is proposed, with blazar astrophysics as a primary science driver. In addition to blazar astrophysics, this scenario will enable a wide variety of other astrophysics to continue to be accomplished with the Kepler spacecraft. The operations scenario is comprised of two elements: a monitoring element and a target of opportunity element. In the monitoring element, the spacecraft cycles through multiple fields providing high precision, regularly sampled light curves of blazars. In the target of opportunity element the spacecraft responds to flaring blazars providing high time resolution, high precision photometry of blazars during flaring events. Studies of blazars are aligned with the 2010 NASA science plan for astrophysics.

W. J Chaplin
University of Birmingham
+white paper

This document is a response to the Kepler Project Call for White Papers. In it, we comment on the potential for continuing asteroseismology of solar-type and red-giant stars in a 2-wheel Kepler Mission. These stars show rich spectra of solar-like oscillations. Our main conclusion is that by targeting stars in the ecliptic it should be possible to perform high-quality asteroseismology, as long as favorable scenarios for 2-wheel pointing performance are met. Targeting the ecliptic would potentially facilitate unique science that was not possible in the nominal Mission, notably from the study of clusters that are significantly brighter than those in the Kepler field. Our conclusions are based on predictions of 2-wheel observations made by a space photometry simulator, with information provided by the Kepler Project used as input to describe the degraded pointing scenarios. We find that elevated levels of frequency-dependent noise, consistent with the above scenarios, would have a significant negative impact on our ability to continue asteroseismic studies of solar-like oscillators in the Kepler field. However, the situation may be much more optimistic for observations in the ecliptic, provided that pointing resets of the spacecraft during regular desaturations of the two functioning reaction wheels are accurate at the ≤ 1 arcsec level. This would make it possible to apply a post-hoc analysis that would recover most of the lost photometric precision. Without this post-hoc correction—and the accurate re-pointing it requires—the performance would probably be as poor as in the Kepler-field case. Critical to our conclusions for both fields is the assumed level of pointing noise (in the short-term jitter and the longer-term drift). We suggest that further tests will be needed to clarify our results once more detail and data on the expected pointing performance becomes available, and we offer our assistance in this work.

Joseph M. Clay
Spacedesign Corporation
+white paper

Spacedesign Corporation’s submission involves rotating the spacecraft to reduce the pointing accuracy to a single axis, subdividing the detector into two linear strip arrays (one named MAX and one named BLUE), and using a statistical two factors averaging technique to sense possible planet crossings with the MAX array while capturing precise elemental data with the trailing BLUE array. It is also suggested that transmitting data at a higher data rate may be possible using multiple input multiple output (MIMO) layered space-time communication architecture like that used by modern cell phone networks. Given these changes to the operation of the spacecraft the same science mission may be performed to achieve more or equivalent planetary candidate detection, albeit over a larger investigated area. General details are given and it is expected that the detailed operations would be worked out with the spacecraft stakeholders.

Brice-Olivier Demory
Massachusetts Institute of Technology
+white paper

We propose to use Kepler in 2-wheel mode to conduct a detailed search for Earth- sized planets orbiting ultra-cool stars and brown dwarfs (spectral types from M7 to L3). This population of objects presents several advantages for exoplanet surveys. First, ultra-cool stars and brown dwarfs are small and thus result in favorable planet- to-star area ratios. Second, because of their low effective temperature, the inner edge of their habitable zone is extremely close (2 to 3 days only). Third, our targets are bright at infrared wavelengths, which will enable detailed follow-up studies. Our program therefore represents a unique opportunity to find a transiting Earth-size exoplanet for which atmospheric features (including biosignatures) could be detected with near-to-come facilities such as JWST. Such exoplanet has not been discovered yet. Kepler in 2-wheel mode is the only facility that provides the required stability and photometric precision to make this survey successful. Our initial target sample includes 60 ultra-cool stars and brown dwarfs from which we expect to detect at least one transiting planet. We propose to monitor each source for 4 days, resulting in a total program duration of ∼240 days.

Saurav Dhital
Embry-Riddle Aeronautical University
+white paper

Even with the diminished precision possible with only two reaction wheels, the Kepler spacecraft can obtain mmag level, time-resolved photometry of tens of thousands of sources. The presence of such a rich, large data set could be transformative for stellar astronomy. In this white paper, we discuss how rotation periods for a large ensemble of single and binary main- sequence dwarfs can yield a quantitative understanding of the evolution of stellar spin-down over time. This will allow us to calibrate rotation-based ages beyond ∼1 Gyr, which is the oldest benchmark that exists today apart from the Sun. Measurement of rotation periods of M dwarfs past the fully-convective boundary will enable extension of gyrochronology to the end of the stellar main-sequence, yielding precise ages (σ ∼10%) for the vast majority of nearby stars. It will also help set constraints on the angular momentum evolution and magnetic field generation in these stars. Our Kepler-based study would be supported by a suite of ongoing and future ground-based observations. Finally, we briefly discuss two ancillary science cases, detection of long-period low-mass eclipsing binaries and microvariability in white dwarfs and hot subdwarf B stars that the Kepler Two-Wheels Program would facilitate.

Niklas J. T. Edberg
Swedish Institute of Space Physics
+white paper

We propose to use the Kepler telescope as a comet tail monitor during a 5-months interval in 2014-2015 while at the same time the Rosetta spacecraft will be performing in situ measurements in the near comet environment. The ESA corner stone mission Rosetta will arrive at comet 67P/Churyumov- Gerasimenko after a 10-year cruise phase in the solar system. While in orbit around the comet the extensive instrument package onboard will monitor the comet nucleus, coma and tail, and study their evolution as the comet approaches the Sun. We can at the same time make us of Kepler remote observations to gain a global view of the entire coma and tail. The science topics we anticipate to do within this kind of campaign include:

  • Monitor the evolution of the cometary coma and tail as the comet approaches the Sun
  • Study the structure and dynamics of the tail and coma caused by solar wind variability
  • Remotely observe comet tail disconnection events
  • The total dust brightness from Kepler will be useful to monitor the overall production from the comet.
  • Combine Kepler observations with earth-based remote measurements to get a stereo view of the tail structure of the comet
  • The 0.5 AU Kepler–Earth distance implies that Kepler can observe the comet when Earth-based observations are obscured by the Sun

R. Edelson
+white paper

We present a strategy to identify and gather light curves for dozens of AGN concurrent with the main observations of a repurposed Kepler mission. These parallel observations only require modest telemetry resources and will not affect where the telescope is pointed. Thus the repurposed mission will continue to gather light curves that probe AGN variability on shorter timescales than any other telescope, enhancing our picture of the physical conditions close to the supermassive black hole.

Mohamed Salah Elghamry
+white paper

In a response for NASA call for white papers I decided to share this proposal solution for Kepler’s Mission.

  1. A Kepler simulator: the work of this simulator is to take the current position of Kepler in the orbit and converts it to the right measurements of the gyroscopes with a help from the two running gyroscopes.
  2. Get the error percentage in the Kepler’s images: This can be done by comparing an old image from Kepler and a new image for the same place, this will help to calculate the exact drifting and the wrong pixels in the Field of View.
  3. Developing a subsystem or filtering layer for the current earth-station system which takes the measurements from the last two parts and apply them to the image which coming from Kepler.

Martin Elvis
Harvard-Smithsonian Center for Astrophysics
+white paper

We propose to use a modest fraction of the re-purposed Kepler mission time and apertures to greatly increase the quantity and quality of our knowledge of near-Earth asteroids (NEAs) rotation and shape. NEAs are important for understanding the origins of the Solar System, for selecting targets for robotic and human visits, and for hazardous object deflection. While NEAs are being discovered at a rate of 1000/year, only a ~75/year have well-measured rotation periods and shapes. Not only can the Kepler mission greatly increase the numbers of well-determined NEA rotation periods (to ≥1000 in 5 years), but may do so with order-of-magnitude greater precision than is routinely achieved from the ground. This will enable 3-D tomographic maps to be produced for the ~250 of the brighter NEAs. A multi-year science program would enable improved data quality checks, larger samples and additional types of science. All these numbers are preliminary. We list a number of issues to be resolved before this program can be properly assessed.

Daniel C. Fabrycky
University of Chicago
+white paper

We propose a scientific program to complete a census of planets, characterizing their masses, orbital properties, and dynamical histories using continued observations of the Kepler field of view with the Kepler spacecraft in a two reaction wheel mission (subsequently referred to as Kepler-II). Even with a significantly reduced photometric precision, extending time-domain observations of this field is uniquely capable of pursuing several critical science goals: 1) measuring the architectures of planetary systems by identifying non-transiting planets interleaved among known transiting planets, 2) establishing the mass-radius relationship for planets in the important transition region between small, gas-rich sub-Neptune planets and large, rocky super-Earths, and 3) uncovering dynamical evidence of the formation and evolution of the inner regions of planetary systems. To meet these objectives, the unique multi-object observing capabilities of Kepler will be used in a set of concurrent campaigns with specific motivations. These campaigns focus largely on the ability to interpret Transit Timing Variations (TTVs) that result from dynamical interactions among planets in a system and include: 1) observations of systems that exhibit large TTVs and are particularly rich in dynamical information, 2) observations of systems where additional transit times will yield mass measurements of the constituent planets, 3) observations of systems where the TTV signal evolves over very long timescales, and 4) observations of systems with long-period planet candidates where additional transits will remove orbital period ambiguities caused by gaps in the original Kepler data.

Mark Giampapa
+white paper

We propose a Kepler program to obtain a unique data set consisting of observations of short-term, transient activity and longer-term cycle-related, magnetic activity and associated irradiance variability in solar-type members of open clusters with ages from ~ 10 Myr – 400 Myr. We also discuss a new data collection mode for Kepler with broad applicability and minimal operations and cost impact. The results will significantly advance our understanding of the potential range of variability in solar- type stars on both short and evolutionary time scales, from the very young Sun to the contemporary Sun. The data can then be utilized as input for realistic models of planetary atmospheres from early to contemporary phases of evolution. In essence, we will delineate the nature and range of the joint variability of luminosity and activity experienced by planetary systems bathed in the ambient and variable radiation fields of their parent suns at all astrobiologically relevant time scales.

John E. Gizis
University of Delaware
+white paper

I discuss the possibilities for "ultracool" (late-M and L ) dwarf science using a two-wheel Kepler Mission. There is approximately one nearby ultracool dwarf per Kepler pointing, allowing this science to serve as an “add-on” to a variety of possible missions. The results will include characterization of rotation peri- ods, condensate cloud weather, stellar radius, starspots, flare activity, and even transiting planets in the habitable zone.

Andrew Gould
Ohio State University
+white paper

In its first 4 years, Kepler discovered thousands of hot planets, including many small ones, that transit their host stars. With 2 reaction wheels, Kepler can no longer deliver the μmag photometry required for transit surveys, but rather mmag photometry over its 115 deg2 field of view. By pointing toward Baade’s window, Kepler can observe hundreds of Galactic Bulge microlensing event lightcurves simultaneously, with near-continuous coverage and from a perspective displaced from the Earth by 0.15-0.4 AU (projected). Kepler will then see microlens lightcurves offset in time and in peak magnification relative to those from Earth, determining the distance and mass of the lens stars and their planets. Kepler’s lightcurves also probe for planets along different image trajectories on the lens plane, potentially more than doubling the number of detectable microlens planets. Pointing constraints, as we understand them, limit Kepler’s coverage to two 14- day windows in Spring and two more in Fall of each year. We show that microlens parallaxes can still be uniquely measured for of order 300 events that peak near one of the two Spring windows.

Joyce A. Guzik
Los Alamos National Laboratory
+white paper

We propose to observe with Kepler an age sequence of nearby uncrowded open clusters. The current Kepler field contains very few (only 4) somewhat distant and/or old clusters. Nearby open clusters are already well characterized from ground- and many space-based observations. Our proposal focuses on mid and upper main-sequence variables (main sequence and pre-main sequence gamma Dor or delta Scuti stars, SPB/beta Cep stars, Cepheids, or yellow supergiants), having periods of hours to days accessible by longer-cadence observations. Asteroseismology for these objects to date is limited by the number of modes observable from the ground, difficulty in obtaining spectroscopic or photometric mode ID for the fainter targets that have been observed by Kepler, uncertainties in interior and initial abundances, especially for stars with abundance anomalies, uncertainties in distance/luminosity, and lack of knowledge of prior evolution history. The additional constraints of common age, distance and initial abundances in clusters will place these variables in their evolutionary context, and help unlock some of the science and reduce uncertainties for understanding star formation and stellar evolution.

David W. Hogg
New York University
+white paper

(1) The primary recommendation of this white paper is image modeling, that is, fitting to the pixel values downlinked from the Kepler satellite a quantitative description of pixel sensitivities (flat-field), point-spread function (PSF), and sky, bias, and dark signals, all as a function of focal-plane position. This kind of modeling has not been required for Kepler so far because its aperture-photometry precision has been maintained through pointing stability. The degraded pointing precision in two-wheel operations will be a blessing as well as a curse: It reduces the precision of aperture photometry, but it provides diversity that permits inference of the detector sensitivity map and PSF. We propose developing a probabilistic generative model of the Kepler pixels. We argue that this may per- mit continuance of photometry at 10-ppm-level precision. We demonstrate some baby steps towards precise models along both data-driven (flexible) and physics-driven (interpretably parameterized) directions. We demonstrate that the expected drift or jitter in positions in the two-weel era will help enormously with constraining calibration parameters. In particular, we show that we can infer the device flat-field at higher than pixel resolution; that is, we can infer pixel-to-pixel variations in intra-pixel sensitivity. These results are relevant to almost any scientific goal for the repurposed mission; image modeling ought to play a role no matter what. We have several secondary recommendations:
(2) It will be imperative to operate the spacecraft with modifications to tables or software: Either the pointing will need to be adjusted frequently using the two operational wheels and some propellant; or else the telemetered focal-plane apertures will have to be enlarged; or else the apertures will have to be adapted in real time to follow drifting stars.
(3) It will be wise to perform deliberate focus pulls, dithers, and integration-time adjustments; these will provide much more data support for hard-to-constrain calibration parameters. These calibration observations will improve any two-wheel data but will also improve the precision of the extant Kepler data that we expect contains many undiscovered signals.
(4) It is our view that Kepler ought to continue work on what many of the present authors consider its key scientific goal, which is to continue to find Earth-like planets on year-ish orbits around Sun-like stars. With a multi-pronged image-modeling effort and a bit of good luck (with respect to assumptions about spacecraft hardware and data- modeling software), it is our view that in the next few years Kepler can do even more than it already has on this deep and important mission. That said, what’s written in this white paper is fundamentally agnostic about the scientific program in the two-wheel era.

Mark A. Huebner
+white paper

While the Kepler Spacecraft is being stabilized by the remaining two momentum wheels a high power laser is scanned across the nearby solar system area within the gaze of the Kepler telescope. The laser could be an infra-red wavelength capable of passing through the atmosphere and be shone through a telescope optic (for example the 60 inch Hale telescope on Mt. Wilson in California) and scanned (using a piezoelectric actuator) across an area that the Kepler telescope was looking at. The Kepler telescope would then be able to use it’s sensitive brightness change discriminating CCD array to detect an increase in brightness from the beam striking an asteroid or cometary debris object.

Brian Jackson
Carnegie Institution for Science
+white paper

A re-purposed Kepler mission could continue the search for ∼Earth-sized planets in very short-period (≤ 1 day) orbits. Recent surveys of the Kepler data already available have revealed at least a dozen such planetary candidates, and a more complete and focused survey is likely to reveal more. Given the planets’ short orbital periods, building the requisite signal-to-noise to detect the candidates by stacking multiple transits requires a much shorter observational baseline than for longer-period planets, and the transits are likely more robust against the much larger instrumental variations anticipated for the modified Kepler pointing capabilities. Searching for these unusual planets will also leverage the Kepler mission’s already considerable expertise in planetary transit detection and analysis. These candidates may represent an entirely new class of planet. They may also provide unprecedented insights into planet formation and evolution and sensitive probes for planet-star interactions and the stellar wind. Whatever their origins and natures, such planets would be particularly amenable to discovery by the planned TESS mission, and a preliminary survey by Kepler could pave the way for such TESS discoveries.

Mukremin Kilic
University of Oklahoma
+white paper

A large fraction of white dwarfs (WDs) may host planets in their habitable zones. These planets may provide our best chance to detect bio-markers on a transiting ex- oplanet, thanks to the diminished contrast ratio between the Earth-sized WD and its Earth-sized planets. The James Webb Space Telescope is capable of obtaining the first spectroscopic measurements of such planets, yet there are no known planets around WDs. Here we propose to take advantage of the unique capability of the Kepler space- craft in the 2-Wheels mode to perform a transit survey that is capable of identifying the first planets in the habitable zone (P = 4-30 h) of a WD. We propose to obtain Kepler time-series photometry of 104 WDs in the Sloan Digital Sky Survey imaging area to search for planets in the habitable zone. Thanks to the large field of view of Kepler, for the first time in history, a large number of WDs can be observed at the same time, which is essential for discovering transits. Our proposed survey requires a total of 200 days of observing time, and will find up to 100 planets in the WD habitable zone. This survey will maintain Kepler’s spirit of searching for habitable Earths, but near new hosts. With few-day observations and minute-cadences per field, it will also open up a completely unexplored discovery space. In addition to planets, this survey is sensitive to pulsating WDs, as well as eclipsing short period stellar and sub- stellar companions. These have important implications for constraining the double WD merger rate and their contribution to Type Ia supernovae and the gravitational wave foreground. Given the relatively low number density of our targets, this program can be combined with other projects that would benefit from high cadence and ‘many-fields’ observations with Kepler, e.g. a transit survey of a magnitude-limited, complete sample of nearby M dwarfs or asteroseismology of variable stars (e.g. RR Lyrae) in the same fields.

K. E. Kraemer
Boston College
+white paper

Continued periodic monitoring of the original Kepler field, or monitoring a new field in a different part of the Milky Way Disk, would provide an unbiased census of long-period variables (LPVs) in the Galactic Disk. While other variability surveys of the Magellanic Clouds and the Galactic Bulge (e.g. OGLE and MACHO) have enabled accurate counts and characterizations of LPVs in those environments, no such sample exists for the Disk, despite the fact that this is where most of the stars in our Galaxy reside. The material shed by these stars, enriched by the nucleosynthetic products created deep within each star’s core, will be recycled into the interstellar medium to form the next generation of stars and planets, thus changing the chemical composition of the Galaxy over time. Although the two-wheel mission is expected to have degraded sensitivity and a smeared point spread function, with this project as part of the extended mission, Kepler is still fully capable of providing important information on the life cycle of stars, the enrichment of the interstellar medium, and the chemical evolution of galaxies.

Charles F. Lillie
+white paper

Although the Kepler spacecraft has only two operational reaction wheels there should be, in principal, a spacecraft orientation in which the attitude disturbance torque due to solar radiation pressure is minimized, and the remaining reaction wheels have sufficient control authority to provide high pointing accuracy for 10 to 30 days at a time. This white paper describes this optimum orientation (or “Sweet Spot”) relative to the sun, an observing strategy and potential targets to be investigated during alternate science investigations by the Kepler Spacecraft.

James P. Lloyd
Cornell University
+white paper

This white paper discusses a repurposed mission for the Kepler spacecraft that fo- cusses on solving outstanding problems in planet formation and evolution by targeting the study of the hot Jupiter population of young stars. This mission can solve the ques- tion of the mode of migration of hot Jupiters, address the problem of whether Jupiters form by hot-start (gravitational instability) or cold-start (core accretion) mechanisms, and provide a wealth of data on the early stages of planetary system evolution during the active phases of stars which impact planetary habitability. In one year of observa- tions of three weeks dwell time per field, Kepler would increase by more than an order of magnitude the number of known hot Jupiters, which can be followed up with fast cadence observations to to search for transit timing variations and to perform aster- oseismological characterization of the host stars. This mission scenario continues to operate Kepler in the photometric monitoring mode for which it was designed, and is generally flexible with regards to field selection enabling prioritization of fuel usage and attitude control constraints.

Mark Marley
NASA Ames Research Center
+white paper

This white paper suggests a potentially high-reward secondary science target that may be appropriate to include during a revised Kepler planet search. If Kepler is to be repurposed to observe a field on or near the ecliptic plane we suggest that Neptune be included in the field of view. Assuming an appropriate field is chosen there should be few additional resources required to observe this planet. A longterm (three months or longer) photometric series taken of Neptune could potentially detect internal oscillation modes of the planet and open a new window to probing the interior structure of an ice giant. Kepler has demonstrated both that ice giants are common in the galaxy and the exceptional value of continuous photometric monitoring for detecting and interpreting stellar oscillations. A Kepler observation of Neptune would appropriately combine these two successes to perhaps similarly dissect the interior structure of one of our own ice giants.

Eduardo L. Martin
University of Florida
+white paper

It is argued here that Kepler is still the best observatory to search for planet transits around nearby very low-mass (VLM) stars. This white paper lies out a plan to reveal transits of potentially habitable rocky planets around VLM dwarfs using the Kepler spacecraft. It is widely accepted in the scientific community that an unambiguous signature of the existence of life in the universe would be to find planets similar in size to the Earth, and to detect atmospheric signatures in their atmosphere that resemble that of the current Earth. Transits around nearby tiny dwarfs will provide candidates for infrared radial velocity follow-up, and for the characterization of the atmospheric constituents of potentially habitable planets by means of transmission spectroscopy with existing or planned telescopic facilities such as the James Webb Space Telescope or the new generation of extremely large ground-based telescopes.

P. R. McCullough
+white paper

In response to the call for white papers for alternative science to be performed with the Kepler spacecraft, we convened approximately a dozen astronomers of STScI and JHU to “brain storm” on possibilities. The most compelling ideas to us were the following:

  • Monitoring Kepler Exoplanetary Candidates
  • Microlensing parallaxes
  • Augmenting the data quality of the original Kepler mission
  • All-sky variability survey

In a second tier were the following:

  • Transit search of open clusters
  • Search for transits of known RV planets
  • Look back at Earth, other planets

Ames Research Center, Code DL
+white paper

This paper proposes the use of the Kepler spacecraft to enhance mitigation capabilities for protecting government and commercial spacecraft from orbital debris.

L. Molnar
+white paper

As a response to the Kepler white paper call, we propose to keep Kepler pointing to its current field of view and continue observing thousands of large amplitude variables (Cepheid, RR Lyrae and delta Scuti stars among others) with high cadence in the Kep-Cont Mission. The degraded pointing stability will still allow observation of these stars with reasonable (better than millimag) precision. The Kep- Cont mission will allow studying the nonradial modes in Blazhko-modulated and first overtone RR Lyrae stars and will give a better view on the period jitter of the only Kepler Cepheid in the field. With continued continuous observation of the Kepler RR Lyrae sample we may get closer to the origin of the century-old Blazhko problem. Longer time-span may also uncover new dynamical effects like apsidal motion in eclipsing binaries. A continued mission will have the advantage of providing unprecedented, many-years-long homogeneous and continuous photometric data of the same targets. We investigate the pragmatic details of such a mission and find a number of advantages, especially the minimal need of reprogramming of the flight software. Another undeniable advantage of the current field of view is the completed, ongoing and planned ground-based follow-up observations and allocated telescope times focusing on the current field. We emphasize that while we propose this continuation as an independent mission, we can easily share slots with e.g. planetary mission with a strong belief that both (or more) communities can still benefit from Kepler’s current capabilities.

Benjamin T. Montet
California Institute of Technology
+white paper

Primary Recommendation: In Paper I (Hogg et al.) we propose image modeling tech- niques to maintain 10-ppm-level precision photometry in Kepler data with only two working reaction wheels. While these results are relevant to many scientific goals for the repurposed mission, all modeling efforts so far have used a toy model of the Kepler telescope. Because the two-wheel performance of Kepler remains to be determined, we advocate for the consideration of an alternate strategy for a > 1 year program that maximizes the science return from the “low-torque” fields across the ecliptic plane. There are considerable benefits of such a strategy which make this design a viable approach for Kepler in any scenario, but especially one in which, for any reason, the field analyzed in the primary mission cannot be used moving forward.
By an analysis of planetary candidates previously detected by Kepler, if we can achieve photometry equal to that of the primary mission we conservatively expect to detect 800 new planetary candidates (after a thorough vetting for false positives). Even if our photometry is degraded by a factor of two from the primary mission, our conservative estimate decreases only to 400 new planetary candidates.
The first scientific goal1 of Kepler is to determine the frequency of terrestrial and larger planets in or near the habitable zone of a wide variety of spectral types of stars. Not only does this recommendation not detract from this strategy, it may provide the best chance to answer this question moving forward.
In Hogg et al. we argue for a shorter target list. By culling the target list such that we are limiting ourselves to bright stars, the Kepler long cadence integrations of 29.4 minutes can also be shortened, which has the benefit of allowing for more sensitive observations of transit timing and transit duration variations. These stars will be later observed by the Transiting Exoplanet Survey Satellite (TESS Brown & Latham 2008), but only for 30 days; there will not be enough transits observed in this mission to detect variations due to planet-planet interactions. Therefore, by observing bright stars that can be followed up by TESS, this will enable dynamical studies that could not be undertaken with either telescope alone.
Similarly, shorter integrations may allow for asteroseismic studies of more stars. Most asteroseismic targets have been giant stars, for which the period of oscillations are long enough to be observed in long cadence data (Chaplin & Miglio 2013). By decreasing the integration time, solar-type oscillations can be observed on subgiants and other stars nearer the main sequence. On these stars, asteroseismic signals are smaller, but by focusing on bright stars we expect the signals to be observable on stars nearer the main sequence.
Bright stars are also advantageous in that they allow radial velocity follow-up observations to be carried out. By selecting brighter stars, we assure interesting objects can be characterized from the ground before the launch of JWST.

Aviv Ofir
+white paper

The Kepler spacecraft is currently unable to hold a steady pointing and it is slowly drifting during observations. We believe that if one has to deal with targets that drift across the CCDs, one should at least be able to track the targets well enough to correct for some – if not most – of the problems caused by this drift. We therefore propose to observe as many stars as possible in short cadance. We propose that at least all currently known planetary candidate host stars will be so observed, with possibly known Kepler eclipsing binaries, astroseismology targets, guest observer targets and new targets in increasingly lower priority. We also outline the modifications needed to flight software in order allow for such observations to take place, aiming to provide ample non-photometric data that should allow post-processing to recover most of the pre-failure photometric performance. In total, the KeSeF Mission will allow Kepler to follow up it’s own previous discoveries in a way that is not otherwise possible. By doing so it will enable to continue pursuing nearly all the science goals that made the original mission choose staring at a single field of view in the first place.

Rob Olling
University of Maryland
+white paper

This white paper is a response to NASA's "Call for White Papers: Soliciting Community Input for Alternate Science Investigations for the Kepler Spacecraft." We describe what the monitoring of small galaxies with Kepler can do for supernova explosions, exotic transients, and Active Galactic Nuclei and other blackhole phenomena. Kepler’s results on extragalactic astrophysics, while less well known than the planetary discoveries are, just as exciting. Early results on active galactic nuclei (AGN) (e.g., Mushotzky et al, 2011, Edeleson et al 2013) have explored AGN variability on a wide variety of timescales from hours to months. Another program, targeting just ~400 galaxies, is not only finding many new AGN (Olling etal 2013b) at much lower levels of activity than have been found heretofore, but has also discovered a number (>4) of likely supernova (SN) candidates, providing, for the first time, constant coverage months before the event, through the rise, and for many months afterwards (Olling etal, 2013a). Extra-galactic science has benefited from the monitoring of a few hundred galaxies with Kepler, and can be revolutionized with the monitoring of thousands of galaxies. A strawman “Kepler Extragalactic Survey,” or KES, would comprise one year of Kepler observations of about 20,000 galaxies and a few hundred normal AGN, perhaps split over 6 or so fields in the sky, with the specific aim of searching for and identifying SNe and low-variability AGN. We propose to monitor bright galaxies (m <19) to search for extra-galactic variability and transients. Given the result from our Kepler GO programs, we expect this study to discover and provide light curves with unprecedented detail of ~140 SNe. In addition, we would identify ~2,000 low-variability AGN candidates and study known AGN in the fields chosen. There are no existing or planned facilities that could observe SN explosions as well as Kepler, even in two gyro mode. Every Kepler transient should be promptly detected by our ground-based survey and follow-up resources can be brought to bear. Thus, we will be able to combine the full value of ground-based surveys: colors, spectra, wide area context, classification, with the exquisite light curves that will be downloaded from Kepler. The combination promises to create a "gold standard", unbiased set of transient sources that can serve many different science projects.

Michael Shao
Jet Propulsion Laboratory
+white paper

This white paper describes the use of sub-pixel calibration techniques to partially recover the photometric accuracy of Kepler, when the spacecraft is operated in the "2 wheel" mode. Its content is based on a brief study conducted after Kepler's third reaction wheel starting showing signs of increased friction. With only 2 wheels, Kepler has one uncontrolled axis of rotation. Solar pressure will cause the spacecraft to rotate about that uncontrolled axis and the pointing of the spacecraft will drift in an "arc." While the pointing is very poor, knowledge of the pointing from the FGS CCDs is quite good. Our brief study suggests that if we calibrate the CCDs and the PSF across the field of view, we could recover photometric accuracy of approximately 70 ppm. For the CCD calibration we would measure the sub-pixel QE variations of the Kepler flight spare CCDs. For the PSF calibration, we would use dithered images of the 100 deg2 FOV from archived data. The anticipated 70 ppm photometric accuracy is to be compared with the ~30 ppm short-term accuracy achieved by Kepler under 3-wheel operations, limited by stellar astrophysical noise (instrument noise was ~20 ppm). This level of recovered accuracy would enable several science investigations, most notably finding longer period exoplanets–possible only for a mission lasting longer than 4 years. Moreover, our proposed approach enables other investigations that were previously inaccessible: while Kepler's short term (~1 day) photometric accuracy was 30 ppm, its long term astrometric and photometric accuracy was much (~50X) poorer. This calibration procedure can now enable long term photometric accuracy at the ~100 ppm level, which can be of benefit to astroseismology science.

Kevin B. Stevenson
University of Chicago
+white paper

The Kepler Mission has been an irrefutable success. In the last 4.5 years, it has monitored 150 confirmed exoplanets in over 75 stellar systems and detected an additional ∼3,300 planet candidates. Using these data, we have learned the size distribution of planets in our galaxy, the likelihood that a star hosts an Earth-sized planet, and the percentage of stars that contain multi- planet systems. The recent failure of a second reaction wheel has ended Kepler’s primary mission; however, its plight is a unique opportunity to make significant advances in another important field, without the time and costs associated with designing, building, and launching another spacecraft. We propose a new Kepler mission, called NEOKepler, that would survey near Earth’s orbit to identify potentially hazardous objects (PHOs). To understand its surveying power, Kepler’s large field of view produces an etendue (AΩ) that is 4.5 times larger than the best survey telescope currently in operation. In this paper, we investigate the feasibility of NEOKepler using a double “fence post” survey pattern that efficiently detects PHOs. In a simulated 12-month survey, we estimate that NEOKepler would detect ∼150 new NEOs with absolute magnitudes of less than 21.5, ∼50 of which would be new PHOs. This would increase the annual PHO discovery rate by at least 50% and improve upon our goal of discovering 90% of PHOs by the end of 2020. Due to its heliocentric orbit, Kepler would also be sensitive to objects inside Earth’s orbit, discovering more objects in its first year than are currently known to exist. Understanding this undersampled sub-population of NEOs will reveal new insights into the actual PHO distribution by further constraining current NEO models. As an alternative science goal, NEOKepler could employ a different observing strategy to discover suitable targets for NASA’s Asteroid Redirect Mission.

R. Szabo
Konkoly Observatory
+white paper

As a response to the Kepler white paper call, we propose to turn Kepler to the South Ecliptic Pole and observe thousands of large amplitude pulsating and eclipsing variables for years with high cadence in the frame of the Kepler-SEP (Kepler - South Ecliptic Pole) Mission. The degraded pointing stability will still allow observing these stars with reasonable (probably better than millimag) accuracy. Long-term continuous monitoring already proved to be extremely helpful to investigate several areas of stellar astrophysics, like the century-old Blazhko-enigma. Space-based photometric missions opened a new window to the intricate dynamics of pulsation in several class of pulsating variable stars and facilitated very detailed studies of eclipsing binaries. The main aim of this mission is to better understand the fascinating dynamics behind various stellar pulsational phenomena (resonances, mode coupling, period-doubling, chaos, mode selection) and interior physics (turbulent convection, opacities). This will also improve the applicability of these astrophysical tools for distance measurements, population and stellar evolution studies. We investigated the pragmatic details of such a mission and found a number of advantages: minimal reprogramming of the flight software, a favorable field of view, access to both galactic and LMC objects. However, the main advantage of the SEP field comes from the largest possible sample of well classified targets, mainly through OGLE. Synergies and significant overlap (spatial, temporal and in brightness) with both ground-based (OGLE, LSST) and space-based missions like GAIA and TESS will greatly enhance the scientific value of the Kepler-SEP mission. GAIA will allow full characterization of the distance indicators (calibration of the zero point of the period- luminosity diagram), by providing distances. TESS will continuously monitor this field for at least one year, and together with the re-purposed Kepler mission provide long time series data that cannot be obtained by other means. If Kepler-SEP program is successful, there is a possibility to place one of the so-called LSST "deep-drilling" fields in this region.

Angelle Tanner
Mississippi State University
+white paper

While the primary science goal for the Kepler mission is the detection and characterization of terrestrial and giant exoplanets through ultra-precision photometry, the telescope is theoretically capable of collecting ~2 milli-arcsecond precision relative astrometric data. This single measurement precision when combined with the few thousand epochs collected by the mission each quarter over its lifetime (> 40000 observations to date), means Kepler should be sensitive to Jupiter-mass planets and brown dwarfs around some of the nearest stars in the input catalog in addition to parallax and proper motions for the closest KOIs. Unfortunately, the Kepler PSF is out of focus and painfully undersampled with each pixel at 3.98 arcseconds/pixel. This combined with instrumental effects such as temperature/focus changes and CCD crosstalk have made it difficult to reach the predicted milli-arcsecond astrometric stability across multiple, continuous Kepler quarters. Even some of the red giant stars, the systematics are ~80 mas and above and repeat annually. This prevents the estimation of parallaxes and planetary orbits but not stellar proper motions. Utilizing the remainder of the Kepler mission in 2-wheel mode we propose to take some time to collect additional dithered images of the Kepler field at all four orientations in order to construct detailed point spread functions as a function of channel and position within a channel.

Stuart F. Taylor
+white paper

By surveying new fields for the shortest-period “big” planets, the Kepler spacecraft could provide the statistics to more clearly measure the occurrence distributions of giant and medium planets. This would allow separate determinations for giant and medium planets of the rela- tionship between the inward rate of tidal migration of planets and the strength of the stellar tidal dissipation (as expressed by the tidal quality factor). We propose a “Hot Big Planets Survey” to find new big planets to better determine the planet occurrence distribution at the shortest period. We refer to the planets that Kepler will be able to find as “big”, for the purpose of comparing the distribution of giant and medium planets above and below 8 earth radii. The distribution of planets from one field has been interpreted to show that the shortest period giant planets are at the end of an ongoing flow of high eccentricity migration, likely from scattering from further out. The numbers of planets at these short periods is still small, leaving uncertainty over the result that the distribution shows the expected power index for inward tidal migration. The current statistics make it hard to say whether the switch between more medium planets at most periods but more giant planets at the shortest periods indicates a greater migration of giant than medium planets. We propose a repurposed Kepler mission to make enough 45-day observations to survey 10 times as many stars as in Kepler’s survey of the original field, to survey for planets with periods of up to fifteen days with at least three transits. This would better measure the occurrence distribution in the period range that will include planets migrating into the star. We seek to measure the relative rate of migration of giant and medium planets at the shortest periods. Results from ground surveys and from surveying the first Kepler field show a dropoff in the distribution that can be attributed to stellar tides causing planets to undergo inward migration into the star, but currently available statistics are still low, producing only very uncertain measurements of the parameters of the innermost distribution. Studying the innermost occurrence distribution will not only allow studying tidal migration, it will allow study of why are many of the short period giants planets inflated. It would find out if planets sometimes become smaller due to atmospheric blowoff. Separating out these three effects requires better statistics than those from one Kepler field. More planets can be found by moving to new fields. Short period planets are found much more rapidly than longer period planets. Only a dedicated space-based survey can provide planet occurrence statistics that do not have the hard-to-quantify biases of ground-based surveys. Surveying many fields for as many planets as possible will provide an important baseline for TESS and other studies.

David E. Trilling
Northern Arizona University
+white paper

We propose a plan to use a repurposed Kepler telescope to search for near Earth objects (NEOs). Kepler-NEO can effectively be used to discover tens to hundreds of thousands of NEOs as small as 10 meters. Kepler-NEO will also be sensitive to asteroids that are generally not observable from the Earth. Over a multi-year mission, Kepler-NEO can be used to retire almost all significant impact risk from NEOs, provide space mission target candidates, and constrain the history of the inner Solar System. This project will require significant software upgrades, but in return will address several of NASA’s strategic goals at a fraction of the price of a new mission.

William Welsh
San Diego State University
+white paper

We show that the Kepler spacecraft in two–reaction wheel mode of operation is very well suited for the study of eclipsing binary star systems. Continued observations of the Kepler field will provide the most enduring and long-term valuable science. It will enable the dis- covery and characterization of eclipsing binaries with periods greater than 1 year – these are the most important, yet least understood binaries for habitable-zone planet background considerations. The continued mission will also enable the investigation of hierarchical multi- ple systems (discovered through eclipse timing variations), and provide drastically improved orbital parameters for circumbinary planetary systems.

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