44 Validated Planets from K2 Campaign 10

Abstract: We present 44 validated planets from the 10$^\mathrm{th}$ observing campaign of the NASA $K2$ mission, as well as high resolution spectroscopy and speckle imaging follow-up observations. These 44 planets come from an initial set of 72 vetted candidates, which we subjected to a validation process incorporating pixel-level analyses, light curve analyses, observational constraints, and statistical false positive probabilities. Our validated planet sample has median values of $R_p$ = 2.2 $R_\oplus$, $P_\mathrm{orb}$ = 6.9 days, $T_{\mathrm{eq}}$ = 890 K, and $J$ = 11.2 mag. Of particular interest are four ultra-short period planets ($P_\mathrm{orb} \lesssim 1$ day), 16 planets smaller than 2 $R_\oplus$, and two planets with large predicted amplitude atmospheric transmission features orbiting infrared-bright stars. We also present 27 planet candidates, most of which are likely to be real and worthy of further observations. Our validated planet sample includes 24 new discoveries, and has enhanced the number of currently known super-Earths ($R_p \approx 1-2 R_\oplus$), sub-Neptunes ($R_p \approx 2-4 R_\oplus$), and sub-Saturns ($R_p \approx 4-8 R_\oplus$) orbiting bright stars ($J = 8-10$ mag) by $\sim$4%, $\sim$17%, and $\sim$11%, respectively.

• The paper introduces a robust validation framework that combines statistical FPP calculations with high-resolution imaging to confirm 44 planets from an initial 72 candidates.
• The study reports median planetary characteristics of 2.2 Earth radii, a 6.9-day orbital period, and 890 K equilibrium temperatures, including detections of ultra-short period and rocky planets.
• The diverse sample, featuring planets around various stellar types, opens new avenues for atmospheric studies and deeper insights into planet formation and evolution.

Overview of "44 Validated Planets from K2 Campaign 10"

The study presented by Livingston et al. outlines the discovery and validation of 44 planets from NASA's K2 mission's 10th observing campaign (C10). The methodology comprises a robust analysis pipeline combining high-resolution spectroscopy, speckle imaging, and statistical validation techniques to authenticate the planetary nature of the transiting objects discovered in the campaign.

Key Findings and Methodology

1. Validation Framework: The validation process began with an initial set of 72 candidates, of which 44 were confirmed as bona fide planets. The paper describes a detailed statistical approach to eliminate false positives, incorporating False Positive Probability (FPP) calculations with a threshold of 1% for validation. The paper also highlights the use of speckle imaging to rule out close false positive scenarios which could corrupt light curves.
2. Planetary Characteristics: The validated planets exhibit median characteristics: a planetary radius ($R_p$) of 2.2 Earth radii, an orbital period ($P_{\text{orb}}$) of 6.9 days, and an equilibrium temperature of 890 K. Notably, the study reports four ultra-short period planets ($P_{\text{orb}} < 1$ day) and 16 planets with radii less than 2 Earth radii, which are likely rocky exoplanets.
3. Diverse Host Stars: The campaign's focus on the ecliptic plane allowed for the discovery of planets orbiting a variety of stellar types, enhancing the breadth of known planetary systems. The study notes the detection efficiency for brighter stars and a significant number of M-dwarfs, providing a diverse sample for atmospheric characterization.
4. Sample Enhancement: The addition of these 44 planets increased the population of known super-Earths, sub-Neptunes, and sub-Saturns orbiting bright stars by approximately 4%, 17%, and 11%, respectively. This suggests the efficacy of campaign-specialized field targeting.
5. Follow-Up Possibilities: The characterization potential for a subset of these planets is substantial. Given their host stars' brightness and the solar-like environments, several of these planets are promising targets for atmospheric studies using transmission spectroscopy and radial velocities to constrain their masses and atmospheric compositions.

Implications and Future Directions

• Methodological Impacts: This study reinforces the importance of employing multi-faceted validation processes, including adaptive statistical models and high-resolution imaging, for confirming planetary candidates, significantly reducing incidences of false positives.
• Planet Formation and Dynamics: Insights into the diversity and characteristics of C10 planets contribute to our understanding of planetary formation and evolution, especially as it pertains to smaller stretches between stellar radii and orbital proximity, a distinguishing feature for ultra-short period planets.
• Target for Future Research: The planets identified represent a rich source for subsequent observational campaigns. Especially, the possibility of characterizing atmospheric compositions of some of these exoplanets via future missions (e.g., JWST, PLATO) or ground-based telescopes could provide breakthroughs in understanding atmospheric processes and the potential habitability of exoplanets.

In sum, the paper by Livingston et al. delineates a significant step forward in cataloging and understanding the nature of exoplanets in varied stellar environments, setting a firm foundation for future research focused on detailed planetary characterization. Its methodological thoroughness also serves as a template for future campaigns seeking to maximize planet discovery and validation.