Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. II. Planetary Systems Observed During Campaigns 1–7

摘要

We recently used near-infrared spectroscopy to improve the characterization of 76?low-mass stars around which K2 had detected 79?candidate transiting planets. 29 of these worlds were new discoveries that had not previously been published. We calculate the false positive probabilities that the transit-like signals are actually caused by non-planetary astrophysical phenomena and reject five new?transit-like events and three previously reported events as false positives. We also statistically validate 17?planets (7 of which were previously unpublished), confirm the earlier validation of 22?planets, and announce 17?newly discovered planet candidates. Revising the properties of the associated planet candidates based on the updated host star characteristics and refitting the transit photometry, we find that our sample contains 21?planets or planet candidates with radii smaller than 1.25 R ⊕, 18?super-Earths (1.25–2 R ⊕), 21?small Neptunes (2–4 R ⊕), three?large Neptunes (4–6 R ⊕), and eight?giant planets (>6 R ⊕). Most of these planets are highly irradiated, but EPIC?206209135.04 (K2-72e, ), EPIC?211988320.01 (), and EPIC?212690867.01 () orbit within optimistic habitable zone boundaries set by the "recent Venus" inner limit and the "early Mars" outer limit. In total, our planet sample includes eight moderately irradiated 1.5–3 R ⊕ planet candidates (F p ??20 F ⊕) orbiting brighter stars (Ks?