[Paper Review] Characteristics of Kepler Planetary Candidates Based on the First Data Set: The Majority are Found to be Neptune-Size and Smaller

W. J. Borucki|arXiv (Cornell University)|Jun 14, 2010

Stellar, planetary, and galactic studiesPhysics and Astronomy25 references204 citations

TL;DR

This paper analyzes the first quarter of Kepler space telescope data, identifying 306 stars with exoplanet candidates; it finds that the majority of these candidates are Neptune-sized or smaller, with a significant peak in occurrence between 2–5 days, and reports five multi-planet systems, including one with two super-Earth-sized planets in near-resonant orbits.

ABSTRACT

In the spring of 2009, the Kepler Mission commenced high-precision photometry on nearly 156,000 stars to determine the frequency and characteristics of small exoplanets, conduct a guest observer program, and obtain asteroseismic data on a wide variety of stars. On 15 June 2010 the Kepler Mission released data from the first quarter of observations. At the time of this publication, 706 stars from this first data set have exoplanet candidates with sizes from as small as that of the Earth to larger than that of Jupiter. Here we give the identity and characteristics of 306 released stars with planetary candidates. Data for the remaining 400 stars with planetary candidates will be released in February 2011. Over half the candidates on the released list have radii less than half that of Jupiter. The released stars include five possible multi-planet systems. One of these has two Neptune-size (2.3 and 2.5 Earth-radius) candidates with near-resonant periods.

Motivation & Objective

• To characterize exoplanet candidates from the first Kepler data release.
• To determine the size and orbital period distribution of planetary candidates in the initial dataset.
• To identify and analyze multi-planet systems among the candidates.
• To assess the prevalence of false positives and the reliability of candidate detections in early data.
• To provide a public release of candidate data for community analysis, with 306 stars released and 400 held for follow-up.

Proposed method

• Utilized high-precision photometry from the Kepler space telescope on 156,097 stars over 33.5 days of science operations.
• Applied an improved data-processing pipeline to detect transit-like signals indicative of exoplanet candidates.
• Classified candidates by size (in Earth and Jupiter radii) and orbital period, focusing on those with radii < 0.5 Rj.
• Identified multi-planet systems through periodic transit signals in light curves.
• Conducted vetting to exclude likely false positives, including background binaries and stellar blends.
• Released data for 306 stars not prioritized for follow-up, primarily due to faintness or lack of initial 9.7-day data.

Experimental results

Research questions

• RQ1 What is the size distribution of exoplanet candidates in the first Kepler data set?
• RQ2 What is the orbital period distribution of these candidates, and is there a peak in occurrence?
• RQ3 How many multi-planet systems are present among the candidates, and what are their characteristics?
• RQ4 What fraction of candidates are likely false positives, and what are the main sources of contamination?
• RQ5 How do the properties of candidates larger than Jupiter compare to smaller ones in terms of period and magnitude distribution?

Key findings

• Over half of the 706 planetary candidates identified have radii less than half that of Jupiter, indicating a majority are Neptune-sized or smaller.
• The highest frequency of candidates occurs in the 2–5 day orbital period range, with a more prominent peak for larger planets.
• The occurrence frequency for super-Earth-sized candidates (2.3–2.5 R⊕) is approximately 5×10⁻⁴, for Neptune-sized 3×10⁻³, for Jupiter-sized 9×10⁻⁴, and for super-Jupiter-sized 2×10⁻⁴.
• One multi-planet system (KIC 7287995) hosts two super-Earth candidates (2.7 and 2.3 R⊕) with near-resonant periods of 5.96 and 12.04 days.
• Candidates larger than Jupiter show different period and magnitude distributions than smaller candidates, possibly indicating stellar companions or size estimation errors in dim stars.
• Five multi-planet systems were identified, including systems with Neptune-sized and super-Earth-sized planets, demonstrating Kepler’s capability to detect small planets around faint stars (down to 15th magnitude) even with limited data.