A Super-Earth Orbiting Near the Inner Edge of the Habitable Zone around the M4.5-dwarf Ross 508

TL;DR

This paper reports the discovery of a super-Earth orbiting near the habitable zone of the M4.5 dwarf Ross 508 using near-infrared radial velocity measurements, highlighting the effectiveness of this method for cool stars.

Contribution

It presents the first near-infrared RV detection of a low-mass planet around Ross 508, demonstrating the method's potential for finding habitable-zone planets around M dwarfs.

Findings

Discovery of Ross 508 b with a 10.77-day orbit and 4 Earth masses.

Planet's insolation is about 1.4 times Earth's, near the habitable zone.

No significant stellar activity signals detected at the planet's period.

Abstract

We report the near-infrared radial-velocity (RV) discovery of a super-Earth planet on a 10.77-day orbit around the M4.5 dwarf Ross 508 ($J_\mathrm{mag}=9.1$). Using precision RVs from the Subaru Telescope IRD (InfraRed Doppler) instrument, we derive a semi-amplitude of $3.92^{+0.60}_{-0.58}$ ${\rm m\,s}^{-1}$, corresponding to a planet with a minimum mass $m \sin i = 4.00^{+0.53}_{-0.55}\ M_{\oplus}$. We find no evidence of significant signals at the detected period in spectroscopic stellar activity indicators or MEarth photometry. The planet, Ross 508 b, has a semimajor-axis of $0.05366^{+0.00056}_{-0.00049}$ au. This gives an orbit-averaged insolation of $\approx$1.4 times the Earth's value, placing Ross 508 b near the inner edge of its star's habitable zone. We have explored the possibility that the planet has a high eccentricity and its host is accompanied by an additional unconfirmed companion on a wide orbit. Our discovery demonstrates that the near-infrared RV search can play a crucial role to find a low-mass planet around cool M dwarfs like Ross 508.