The first super-Earth Detection from the High Cadence and High Radial Velocity Precision Dharma Planet Survey (1807.07098v1)

Abstract: The Dharma Planet Survey (DPS) aims to monitor about 150 nearby very bright FGKM dwarfs (within 50 pc) during 2016$-$2020 for low-mass planet detection and characterization using the TOU very high resolution optical spectrograph (R$\approx$100,000, 380-900nm). TOU was initially mounted to the 2-m Automatic Spectroscopic Telescope at Fairborn Observatory in 2013-2015 to conduct a pilot survey, then moved to the dedicated 50-inch automatic telescope on Mt. Lemmon in 2016 to launch the survey. Here we report the first planet detection from DPS, a super-Earth candidate orbiting a bright K dwarf star, HD 26965. It is the second brightest star ($V=4.4$ mag) on the sky with a super-Earth candidate. The planet candidate has a mass of 8.47$\pm0.47M_{\rm Earth}$, period of $42.38\pm0.01$ d, and eccentricity of $0.04^{+0.05}_{-0.03}$. This RV signal was independently detected by Diaz et al. (2018), but they could not confirm if the signal is from a planet or from stellar activity. The orbital period of the planet is close to the rotation period of the star (39$-$44.5 d) measured from stellar activity indicators. Our high precision photometric campaign and line bisector analysis of this star do not find any significant variations at the orbital period. Stellar RV jitters modeled from star spots and convection inhibition are also not strong enough to explain the RV signal detected. After further comparing RV data from the star's active magnetic phase and quiet magnetic phase, we conclude that the RV signal is due to planetary-reflex motion and not stellar activity.

• The paper presents the detection of an 8.47 Earth-mass super-Earth candidate orbiting the K dwarf HD 26965.
• It employs high cadence RV observations with the TOU spectrograph at a resolution of 100,000 to enhance sensitivity and reduce aliasing.
• The study rigorously distinguishes planetary signals from stellar activity, setting a new standard in exoplanet detection methodologies.

Overview of the First Super-Earth Detection from the Dharma Planet Survey

The paper "The First Super-Earth Detection from the High Cadence and High Radial Velocity Precision Dharma Planet Survey," authored by Bo Ma et al., presents significant findings from the Dharma Planet Survey (DPS). The DPS was conceived to monitor approximately 150 nearby FGKM dwarf stars with the TOU spectrograph to detect low-mass planets. The key outcome of the paper is the detection of a super-Earth candidate orbiting the K dwarf star HD 26965, showcasing the capability of the DPS methodology.

Key Findings

The DPS utilizes the TOU spectrograph, characterized by a high spectral resolution of about 100,000 and a wavelength range of 380-900 nm, adapted to the automatic 50-inch telescope at Mt. Lemmon. The super-Earth candidate orbiting HD 26965, a star with visual magnitude V=4.4, exhibits a mass of 8.47 Earth masses, with an orbital period of 42.38 days and an eccentricity of 0.04. The detection was corroborated with radial velocity (RV) signals that rule out substantial stellar activity as the cause of this signal.

Methodological Approaches

The detection of the super-Earth capitalized on a strategy of high cadence RV measurements, crucial for enhancing sensitivity to low-mass exoplanets. The research detailed meticulous observations, leveraging a unique methodology that involved initially observing stars for 30 consecutive nights followed by additional observations over 420 days. This minimized aliasing effects and enhanced data reliability. In addition, to counter stellar activity, which often complicates planet detection, advanced RV modeling and data correlation with photometric data were conducted.

Discussion on Stellar Activity

A pivotal aspect of the research was distinguishing planetary signals from stellar noise, especially since the orbital period was close to HD 26965’s stellar rotation period. The researchers conducted a thorough analysis, including RV data over active and quiet magnetic phases of the star, alongside a line bisector analysis, to ensure the signal originated from planetary influences rather than intrinsic stellar variations. Their analysis did not find significant line profile variations correlating with the RV signal, supporting the planet hypothesis.

Implications and Future Work

The detection of HD 26965b, being one of the brightest stars with a confirmed super-Earth, highlights the potential of the DPS approach in discovering significant exoplanets around nearby bright stars. The paper reinforces the necessity for high cadence observations in RV surveys, especially for detecting planets within the habitable zones of their stars. Future expansions of such methodologies could lead to more discoveries that will significantly impact astronomical studies on planet formation and habitability.

In conclusion, this paper not only adds a valuable discovery to exoplanet catalogs but also exemplifies effective methodologies in distinguishing planetary signals from stellar activities. It suggests that with continued advancements and adaptations in observational strategies, the DPS could substantially expand our understanding of low-mass exoplanets’ prevalence and properties.