# Wolf 503 b: Characterization of a Sub-Neptune Orbiting a Metal-Poor K Dwarf

**Authors:** Alex S. Polanski, Ian J. M. Crossfield, Jennifer A. Burt, Grzegorz Nowak, Mercedes López-Morales, Annelies Mortier, Ennio Poretti, Aida Behmard, Björn Benneke, Sarah Blunt, Aldo S. Bonomo, R. Paul Butler, Ashley Chontos, Rosario Cosentino, Jeffrey D. Crane, Xavier Dumusque, Benjamin J. Fulton, Adriano Ghedina, Varoujan Gorjian, Samuel K. Grunblatt  
**arXiv:** [2107.08092](https://arxiv.org/abs/2107.08092)  
**Date:** 2021-07-16  
**Summary page:** https://www.summarizepaper.com/en/paper/2107.08092v1/

## Key points

- Researchers used radial velocity measurements from multiple instruments to study the sub-Neptune exoplanet Wolf 503 b
- Wolf 503 b has a radius of $2.043\pm0.069 ~\rm{R}_{\oplus}$ and orbits the K-dwarf Wolf 503
- Analysis of short-cadence $K2$ campaign 17 photometry and joint radial velocity-transit fit refined orbital and transit parameters
- Orbit eccentricity was constrained to be $0.41\pm0.05$, providing valuable information for further observations
- Mass of Wolf 503 b was determined to be $6.26^{+0.69}_{-0.70}~\rm{M}_{\odot}$ with a bulk density of $\rho = 2.92\pm ^{+0.50}_{-0.44}$ $\rm{g}~\rm{cm}^{-3}$
- Interior composition models suggest Earth-like core with significant $\rm{H}_2\rm{O}$ mass fraction or modest H/He envelope
- Low H/He mass fraction combined with advanced age of host star positions Wolf 503 b as an ideal candidate for investigating XUV-driven mass loss in exoplanets
- Brightness of host star makes Wolf 503 b an attractive target for future transmission spectroscopy studies

## Summary

In a recent study, researchers utilized radial velocity measurements from multiple instruments to provide detailed insights into the sub-Neptune exoplanet known as Wolf 503 b. This exoplanet has a radius of $2.043\pm0.069 ~\rm{R}_{\oplus}$ and orbits the quiet K-dwarf Wolf 503 (HIP 67285). By analyzing previously unused short-cadence $K2$ campaign 17 photometry and conducting a joint radial velocity-transit fit, the team was able to refine the orbital and transit parameters of Wolf 503 b. The eccentricity of the orbit was constrained to be $0.41\pm0.05$, providing valuable information for further observations. Additionally, additional transit observations by $Spitzer$ allowed for an improved orbital ephemeris, setting the stage for future follow-up studies. The mass of Wolf 503 b was determined to be $6.26^{+0.69}_{-0.70}~\rm{M}_{\odot}$ with a calculated bulk density of $\rho = 2.92\pm ^{+0.50}_{-0.44}$ $\rm{g}~\rm{cm}^{-3}$. Interior composition models revealed that this density is consistent with either an Earth-like core with a significant $\rm{H}_2\rm{O}$ mass fraction ($45^{+19.12}_{-16.15}\%$) or a modest H/He envelope ($0.5\pm0.28$%). The low H/He mass fraction combined with the advanced age of Wolf 503 (11$\pm$2 Gyrs) positions this sub-Neptune as an ideal candidate for investigating theories related to XUV-driven mass loss in exoplanets. Moreover, the brightness of its host star ($J=8.3$ mag) makes it an attractive target for transmission spectroscopy studies in the future. Overall, these findings shed light on the intriguing characteristics of Wolf 503 b and highlight its potential significance in advancing our understanding of planetary formation and evolution processes in distant solar systems.