Three New “51 Pegasi–Type” Planets

TLDR

The three detected planets, together with 51 Peg b, may define a new class of close‑orbit, Jupiter‑mass planets with circular orbits and radii < 0.2 AU. We detected three short‑period, Jupiter‑mass planets around HR 3522, HR 5185, and HR 458 with circular or.

Abstract

We report Keplerian Doppler velocity variations, consistent with orbiting "51 Pegasi-type" planets, for the three stars HR 3522 (G8V), HR 5185 (F7V), and HR 458 (F8V). HR 3522 exhibits a velocity semiamplitude of 77 m s-1 and a period of 14.65 days, implying a semimajor axis of 0.11 AU and a minimum mass for the companion of M2 sin i = 0.84MJUP. For HR 5185, the semiamplitude is 469 m s-1, and the period is 3.3128 days, implying an orbital radius of 0.0462 AU and a minimum mass of 3.87MJUP. For HR 458, the semiamplitude is 74 m s-1, and the period is 4.61 days, implying an orbital radius of 0.057 AU and a minimum mass of 0.68MJUP. These three companions, along with 51 Peg b, may constitute a heretofore unrecognized class of planets, defined by circular orbits, Jupiter-like masses, and orbital radii less than ~0.2 AU. The relatively large orbital radius for HR 3522 (0.11 AU) precludes tidal circularization, suggesting that the circular orbits are primordial. During the past 9 years, the velocity residuals to the Keplerian fit of HR 3522 exhibit a long-term systematic trend, suggestive of an additional companion. HR 5185 exhibits velocity residuals that fluctuate erratically by ~70 m s-1, which are as yet unaccounted for. HR 5185 has a rotation period very close to the orbital period of the planet, suggesting that the companion may have tidally locked the primary.