Stellar Parameters for HD 69830, a Nearby Star with Three Neptune Mass Planets and an Asteroid Belt

TL;DR

This study precisely measures the stellar parameters of HD 69830, a nearby star hosting three Neptune-mass planets and an asteroid belt, refining its age, composition, and habitable zone location using interferometry and spectral analysis.

Contribution

The paper provides the first direct interferometric measurement of HD 69830's angular diameter and refines its stellar parameters, age, and habitable zone location with spectral fitting and stellar models.

Findings

Stellar radius measured as 0.9058 R_sun

Age estimated at approximately 7.5 Gyr

Habitable zone ranges from 0.61 to 1.44 AU

Abstract

We used the CHARA Array to directly measure the angular diameter of HD 69830, home to three Neptune mass planets and an asteroid belt. Our measurement of 0.674+/-0.014 milli-arcseconds for the limb-darkened angular diameter of this star leads to a physical radius of R$_*$ = 0.9058$\pm$0.0190 R\sun and luminosity of L* = 0.622+/-0.014 Lsun when combined with a fit to the spectral energy distribution of the star. Placing these observed values on an Hertzsprung-Russel (HR) diagram along with stellar evolution isochrones produces an age of 10.6+/-4 Gyr and mass of 0.863$\pm$0.043 M\sun. We use archival optical echelle spectra of HD 69830 along with an iterative spectral fitting technique to measure the iron abundance ([Fe/H]=-0.04+/-0.03), effective temperature (5385+/-44 K) and surface gravity (log g = 4.49+/-0.06). We use these new values for the temperature and luminosity to calculate a more precise age of 7.5+/-Gyr. Applying the values of stellar luminosity and radius to recent models on the optimistic location of the habitable zone produces a range of 0.61-1.44 AU; partially outside the orbit of the furthest known planet (d) around HD 69830. Finally, we estimate the snow line at a distance of 1.95+/-0.19 AU, which is outside the orbit of all three planets and its asteroid belt.