Nearby super-Earths around M dwarfs

Search for Nearby Earth Analogs. II. detection of five new planets, eight planet candidates, and confirmation of three planets around nine nearby M dwarfs
https://arxiv.org/abs/2001.02577

Quote :

Zechmeister et al. (2009) surveyed 38 nearby M dwarfs from March 2000 to March 2007 with VLT2 and the UVES spectrometer. This data has recently been reanalyzed (Butler et al. 2019), yielding a significant improvement in the Doppler velocity precision. Spurred by this, we have combined the UVES data with velocity sets from HARPS, Magellan/PFS, and Keck/HIRES. Sixteen planet candidates have been uncovered orbiting nine M dwarfs. Five of them are new planets corresponding to radial velocity signals, which are not sensitive to the choice of noise models and are identified in multiple data sets over various timespans. Eight candidate planets require additional observation to be confirmed. We also confirm three previously reported planets. Among the new planets, GJ 180 d and GJ 229A c are super-Earths located in the conservative habitable zones of their host stars. We investigate their dynamical stability using the Monte Carlo approach and find both planetary orbits are robust to the gravitational perturbations of the companion planets. Due to their proximity to the Sun, the angular separation between the host stars and the potentially habitable planets in these two systems is 25 and 59 mas, respectively. They are thus good candidates for future direct imaging by JWST and E-ELT. In addition we find GJ 433 c, a cold super-Neptune belonging to an unexplored population of Neptune-like planets. With a separation of 0.5 as from its host star, GJ 433 c is probably the first realistic candidate for direct imaging of cold Neptunes. A comprehensive survey of these planets is important for the studies of planet formation.

They report GJ 229 as a 2-planet system, apparently recovering the planet that was disproven by Tumoi (2019) (see this post). I e-mailed the lead author and asked about the barycentric correction problem in the UVES data.

They do mention re-reducing the UVES data, maybe that addresses the issue?

Quote :

The UVES data has been re-reduced using a custom raw reduction package, and an upgraded version of code from Butler et al. (1996). The median velocity RMS of the stable stars is reduced to 3.6 m s⁻¹ (B19). The velocities reported here are the “unbinned” velocities published in B19.

Though would definitely be good to figure out why Tuomi et al. (2019) got different results.

I did get a response to the e-mail, which was

Quote :

I don't think GJ 229 Ac is caused by barycentric correction because it is identified in HARPS data as well. In addition, the UVES data is a new reduction by Paul Butler. Please read the discussion about GJ 229A (HD 42581) in section 4.2 carefully to see why GJ 229Ac is a bona fide super-Earth while GJ 229Ab (corresponding to the 470-day signal in Mikko's paper) is a candidate with some doubts due to its overlap with some activity signals.

Their orbit for GJ 229 B is a lot more circular than the astrometry-based orbit from Brandt et al. (2019). The astrometric orbit brings the brown dwarf to nearly 5 AU at periastron. I used Hanno Rein's rebound to integrate the system with the eccentric brown dwarf orbit, assuming coplanarity (giving planets b and c masses of 44 and 35 Earth masses).

System appears to hold up for at least 1 Myr without anything too catastrophic happening:

And now here's the press release. That artist's impression of GJ 229 Ac looks suspiciously terrestrial for a >7 Earth masses planet!