The NEID Earth Twin Survey. I. Confirmation of a 31-day planet orbiting HD 86728

TL;DR

The NEID Earth Twin Survey confirmed the existence of a 31-day orbiting exoplanet around HD 86728, demonstrating the survey's capability to detect small, Earth-like planets around quiet stars using radial velocity measurements.

Contribution

This paper reports the first confirmed exoplanet detection by the NEID Earth Twin Survey, showcasing its effectiveness in identifying small planets around RV-quiet stars.

Findings

Confirmed a 9.16 Earth-mass planet with a 31-day orbit.

Detected a semi-amplitude of 1.91 m/s in radial velocity.

Host star shows minimal intrinsic variability.

Abstract

With close to three years of observations in hand, the NEID Earth Twin Survey (NETS) is starting to unearth new astrophysical signals for a curated sample of bright, radial velocity (RV)-quiet stars. We present the discovery of the first NETS exoplanet, HD 86728 b, a $m_p\sin i = 9.16^{+0.55}_{-0.56}\ \rm{M}_\oplus$ planet on a circular, $P=31.1503^{+0.0062}_{-0.0066}$ d orbit, thereby confirming a candidate signal identified by Hirsch et al. (2021). We confirm the planetary origin of the detected signal, which has a semi-amplitude of just $K=1.91^{+0.11}_{-0.12}$ m s$^{-1}$, via careful analysis of the NEID RVs and spectral activity indicators, and we constrain the mass and orbit via fits to NEID and archival RV measurements. The host star is intrinsically quiet at the $\sim1$ m s$^{-1}$ level, with the majority of this variability likely stemming from short-timescale granulation. HD 86728 b is among the small fraction of exoplanets with similar masses and periods that have no known planetary siblings.