Building a homogeneous catalog of K2 planets

[christinahedges]

Homogeneous planet catalogs enable the accurate study of the occurrence rates of planets. Although the first four years of Kepler data have been searched thoroughly by the official Kepler pipeline (Jenkins et al. 2010), providing a complete and well characterized catalog (Thompson et al. 2018, and references therein), the search for planets in the K2 phase of the mission was left to the community (e.g. Foreman-Mackey et al. 2015; Montet et al. 2015; Barros et al. 2016; Crossfield et al. 2016; Pope et al. 2016; Dressing et al. 2017; Vanderburg et al. 2016; Luger et al. 2016, 2018; Petigura et al. 2018; Livingston et al. 2018; Mayo et al. 2018; Yu et al. 2018).

Planet searches in the K2 dataset by the community are driven primarily by planets that are high value for follow-up, either from the ground or from space. These high-value targets tend to be bright stars, with larger planets. This has caused the K2 exoplanet catalog to be less homogeneous and less complete than than the original Kepler mission catalog. A reliable, complete, and well-characterized catalog of K2 planets across all Campaigns is vital to enable new planet occurrence rate studies, and to fully identify and rank the best planets for follow-up observations (e.g. atmosphere observations with the Hubble or James Webb Space Telescopes). The K2 planet sample is expected to complement that of TESS, by adding smaller and cooler planets on longer orbits, owing to Kepler’s higher precision.

[kstassun]

Several authors have carried out systematic assessment or re-assessment of properties of planets and their host stars, especially with the advent of parallaxes from Gaia. A partial listing of these systematic studies includes Stassun et al. (2017), Johns et al. (2018), Berger et al. (2018), Narang et al. (2018), Bashi et al. (2018), and Stassun et al. (2018). These studies attempt to minimize systematics by applying consistent assumptions and approaches to the determination of the stellar and planet properties. For example, it is now possible to determine accurate, empirical stellar radii from the Gaia parallaxes together with a bolometric flux from the broadband spectral energy distribution (e.g., Stassun et al. 2018), but this requires an accurate effective temperature and ideally also metallicity; as high quality spectroscopic followup measurements of these properties become available for more of the Kepler and K2 planet-host stars, it will become possible to extend these systematic reassessments of planet properties to the full population of Kepler and K2 planets, including those that are yet to be discovered from the archival light curves.

[christinahedges]

Hi @kstassun, thanks for the input on this! Gaia has been an amazing source of information on Kepler host stars, and you're right there's been some fantastic work putting it to maximum use.

In this project we were really angling towards building a thorough planet search, as we know that there are biases in the current K2 planet catalog. If I've understood you correctly, you're highlighting work that has improved the stellar host parameters, capitalizing on Gaia and other surveys. I think this project has been really well tackled by the community, and I know lots of people are working towards learning more, so I'm not going to open a new project for this. (This repo is really trying to be science opportunities, and I think this question is being actively answered.) But thanks for bringing this up! It's an hugely important part of a good exoplanet catalog, and you've added lots of excellent citations and literature for everyone!