Planet in the 40 Eridani system

https://sites.psu.edu/eprv2017/files/2017/03/EPRV_III_Program-2hk96fs.pdf

Matias Diaz
Disentanging doppler signal and stellar activity: the case of HD 26965.

minimum mass 8.10 mass Earth
orbital period 42.37 days
data from HIRES, PFS, CHIRON and HARPS over a timespan of 15 years.

Quote :

We report the discovery of a radial velocity (RV) signal that could be interpreted as a planet candidate orbiting the bright, metal-poor K dwarf HD26965, with an orbital period of 42.37 days, or alternatively, as the presence of residual, uncorrected rotational activity in the data. We will show why the latter is favored and makes this dataset an excellent test case for building new correlated noise models to remove the effects due to magnetic activity on Doppler measurements.

(emphasis mine)

Not going to get too excited about this one until more data becomes available.

The first super-Earth Detection from the High Cadence and High Radial Velocity Precision Dharma Planet Survey
https://arxiv.org/abs/1807.07098

Quote :

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≈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±0.47MEarth, period of 42.38±0.01 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.

Nice update. I wonder how much this world would have been affected by the evolution of 40 Eridani B.

Never been particularly convincing...

The death of Vulcan: NEID reveals the planet candidate orbiting HD 26965 is stellar activity
https://arxiv.org/abs/2404.17494

Quote :

We revisit the long-studied radial velocity (RV) target HD26965 using recent observations from the NASA-NSF 'NEID' precision Doppler facility. Leveraging a suite of classical activity indicators, combined with line-by-line RV analyses, we demonstrate that the claimed 45-day signal previously identified as a planet candidate is most likely an activity-induced signal. Correlating the bulk (spectrally-averaged) RV with canonical line activity indicators confirms a multi-day 'lag' between the observed activity indicator time series and the measured RV. When accounting for this lag, we show that much of the observed RV signal can be removed by a linear detrending of the data. Investigating activity at the line-by-line level, we find a depth-dependent correlation between individual line RVs and the bulk RVs, further indicative of periodic suppression of convective blueshift causing the observed RV variability, rather than an orbiting planet. We conclude that the combined evidence of the activity correlations and depth dependence is consistent with a radial velocity signature dominated by a rotationally-modulated activity signal at a period of ∼42 days. We hypothesize that this activity signature is due to a combination of spots and convective blueshift suppression. The tools applied in our analysis are broadly applicable to other stars, and could help paint a more comprehensive picture of the manifestations of stellar activity in future Doppler RV surveys.

By the way something has to be orbiting out there.