Engineering topics

Dotson, Jessie L

Publications and source records attributed to Dotson, Jessie L.

4 records

DOE OSTI2010

KEPLER SCIENCE OPERATIONS

Kepler's mission design includes a comprehensive plan for commissioning and science operations. The commissioning phase completed all critical tasks and accomplished all mission objectives within a week of the pre-launch plan. Since the start of science data collection, the nominal timeline has been interrupted by two safe-mode events, several losses of fine point, and some small pointing adjustments. The most important anomalies are understood and mitigated, so Kepler's technical performance has improved significantly over this period, and the prognosis for mission success is excellent. The Kepler data archive is established and hosting data for the science team, guest observers, and the public. The first data to become publicly available include the monthly full-frame images and the light curves for targets that are dropped from the exoplanet program or released after publication. Data are placed in the archive on a quarterly basis; the Kepler Results Catalog will be released annually starting in 2011.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2010

INITIAL CHARACTERISTICS OF KEPLER SHORT CADENCE DATA

The Kepler Mission offers two options for observations-either long cadence (LC) used for the bulk of core mission science, or short cadence (SC) which is used for applications such as asteroseismology of solar-like stars and transit timing measurements of exoplanets where the 1 minute sampling is critical. We discuss the characteristics of SC data obtained in the 33.5 day long Quarter 1 observations with Kepler which completed on 2009 June 15. The truly excellent time series precisions are nearly Poisson limited at 11th magnitude providing per-point measurement errors of 200 parts-per-million per minute. For extremely saturated stars near seventh magnitude precisions of 40 ppm are reached, while for background limited measurements at 17th magnitude precisions of 7 mmag are maintained. We note the presence of two additive artifacts, one that generates regularly spaced peaks in frequency, and one that involves additive offsets in the time domain inversely proportional to stellar brightness. The difference between LC and SC sampling is illustrated for transit observations of TrES-2.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2010

INSTRUMENT PERFORMANCE IN KEPLER's FIRST MONTHS

The Kepler Mission relies on precise differential photometry to detect the 80 parts per million (ppm) signal from an Earth-Sun equivalent transit. Such precision requires superb instrument stability on timescales up to {approx}2 days and systematic error removal to better than 20 ppm. To this end, the spacecraft and photometer underwent 67 days of commissioning, which included several data sets taken to characterize the photometer performance. Because Kepler has no shutter, we took a series of dark images prior to the dust cover ejection, from which we measured the bias levels, dark current, and read noise. These basic detector properties are essentially unchanged from ground-based tests, indicating that the photometer is working as expected. Several image artifacts have proven more complex than when observed during ground testing, as a result of their interactions with starlight and the greater thermal stability in flight, which causes the temperature-dependent artifact variations to be on the timescales of transits. Because of Kepler's unprecedented sensitivity and stability, we have also seen several unexpected systematics that affect photometric precision. We are using the first 43 days of science data to characterize these effects and to develop detection and mitigation methods that will be implemented in the calibration pipeline. Based on early testing, we expect to attain Kepler's planned photometric precision over 80%-90% of the field of view.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2010

THE KEPLER PIXEL RESPONSE FUNCTION

Kepler seeks to detect sequences of transits of Earth-size exoplanets orbiting solar-like stars. Such transit signals are on the order of 100 ppm. The high photometric precision demanded by Kepler requires detailed knowledge of how the Kepler pixels respond to starlight during a nominal observation. This information is provided by the Kepler pixel response function (PRF), defined as the composite of Kepler's optical point-spread function, integrated spacecraft pointing jitter during a nominal cadence and other systematic effects. To provide sub-pixel resolution, the PRF is represented as a piecewise-continuous polynomial on a sub-pixel mesh. This continuous representation allows the prediction of a star's flux value on any pixel given the star's pixel position. The advantages and difficulties of this polynomial representation are discussed, including characterization of spatial variation in the PRF and the smoothing of discontinuities between sub-pixel polynomial patches. On-orbit super-resolution measurements of the PRF across the Kepler field of view are described. Two uses of the PRF are presented: the selection of pixels for each star that maximizes the photometric signal-to-noise ratio for that star, and PRF-fitted centroids which provide robust and accurate stellar positions on the CCD, primarily used for attitude and plate scale tracking. Good knowledge of the PRF has been a critical component for the successful collection of high-precision photometry by Kepler.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗