Journal
ASTRONOMICAL JOURNAL
Volume 158, Issue 4, Pages -Publisher
IOP Publishing Ltd
DOI: 10.3847/1538-3881/ab3e2f
Keywords
planets and satellites: composition; planets and satellites: detection; planets and satellites: fundamental parameters; planets and satellites: gaseous planets; methods: data analysis; techniques: photometric; techniques: radial velocities
Categories
Funding
- NSF [DGE 1752814]
- Royal Astronomical Society
- Emmanuel College, Cambridge
- NASA K2 Guest Observer program [80NSSC19K0099]
- NASA through the Sagan Fellowship Program
- INAF/Frontiera through the Progetti Premiali funding scheme of the Italian Ministry of Education, University, and Research
- John Templeton Foundation
- Carlsberg Foundation
- NASA Science Mission directorate
- NASA [NAS5-26555]
- NASA Office of Space Science [NNX13AC07G]
- Prodex Program of the Swiss Space Office (SSO)
- Harvard University Origins of Life Initiative (HUOLI)
- Scottish Universities Physics Alliance (SUPA)
- University of Geneva
- Smithsonian Astrophysical Observatory (SAO)
- Italian National Astrophysical Institute (INAF)
- University of St Andrews
- Queens University Belfast
- University of Edinburgh
- STFC [ST/S000488/1] Funding Source: UKRI
Ask authors/readers for more resources
Although several thousands of exoplanets have now been detected and characterized, observational biases have led to a paucity of long-period, low-mass exoplanets with measured masses and a corresponding lag in our understanding of such planets. In this paper we report the mass estimation and characterization of the long-period exoplanet Kepler-538b. This planet orbits a Sun-like star (V = 11.27) with M-* = 0.892(-0.035)(+0.051) M-circle dot and R-* = 0.8717(-0.0061)(+0.0064) R-circle dot. Kepler-538b is a 2.215(-0.034)(+0.040) R-circle plus sub-Neptune with a period of P = 81.73778 +/- 0.00013 days. It is the only known planet in the system. We collected radial velocity (RV) observations with the High Resolution Echelle Spectrometer (HIRES) on Keck I and High Accuracy Radial velocity Planet Searcher in North hemisphere (HARPS-N) on the Telescopio Nazionale Galileo (TNG). We characterized stellar activity by a Gaussian process with a quasi-periodic kernel applied to our RV and cross-correlation function FWHM observations. By simultaneously modeling Kepler photometry, RV, and FWHM observations, we found a semi-amplitude of K = 1.68(-0.38)(+0.39) m s(-1) and a planet mass of M-p = 10.6(-2.4)(+2.5) M-circle plus. Kepler-538b is the smallest planet beyond P = 50 days with an RV mass measurement. The planet likely consists of a significant fraction of ices (dominated by water ice), in addition to rocks/metals, and a small amount of gas. Sophisticated modeling techniques such as those used in this paper, combined with future spectrographs with ultra high-precision and stability will be vital for yielding more mass measurements in this poorly understood exoplanet regime. This in turn will improve our understanding of the relationship between planet composition and insolation flux and how the rocky to gaseous transition depends on planetary equilibrium temperature.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available