A compact four-planet resonant chain at HD 158259

The SOPHIE search for northern extrasolar planets. XVII. A compact planetary system in a near 3:2 mean motion resonance chain
https://arxiv.org/abs/1911.13296

Quote :

Since 2011, the SOPHIE spectrograph has been used to search for Neptunes and Super-Earths in the northern hemisphere. As part of this observation program, 290 radial velocity measurements of HD 158259 were obtained. We present the analysis of this dataset. The radial velocity data, corrected from instrument systematics, are analysed with classical and ℓ1 periodograms. The stellar activity is modelled by a correlated Gaussian noise, and its impact on the planets detection is measured by a new technique based on cross-validation. Ancillary spectroscopic indices as well as photometric measurements are analysed to discuss the planetary origin of the signals. The stability of the system is assessed with numerical simulations. We report the detection of four planets in a chain of near 3:2 mean motion resonances around HD 158259 at 3.4, 5.2, 7.9 and 12 days, with a possible fifth planet at 17.4 days, also near the 3:2 resonance. Additionally, two low frequency signals are found in the data, and are attributed to a magnetic cycle and instrument systematics. The four planets are found to be outside of the two and three body resonances.

page 5 :

Since the system is closely packed, the planetary perturbations are strong. Therefore, inclinations far from the value of 90 degrees are significantly disfavored, since they correspond to large planet masses. This increases the transit probability. HD 158259 has been observed by TESS (Ricker et al. 2014; Sullivan et al. 2015), whose upcoming results will confirm whether it transits or not. If it does, since the target is very bright (V magnitude of 6.4) it will be an excellent target for further characterization.

Speak of which,

TESS just discovered a candidate transiting planet further inward. 1.27 Earth-radii in a 2.17-day orbit, putting it inward of the four planets.
https://exofop.ipac.caltech.edu/tess/target.php?id=188768068

Twitter :

Period ratio between the transiting planet and b is about 1.58, not sure if that's sufficiently close to 1.5 to be considered an extension of the near-3:2 chain.

Version 2 of the paper now includes the TESS planet, which has been confirmed with SOPHIE RV as a ~2.2 Earth mass planet with a density similar to the Earth.

The planet designations have also been revised since version 1, now b refers to the innermost planet.

https://www.aanda.org/articles/aa/abs/2020/04/aa37254-19/aa37254-19.html  
We need follow up this system

tommi59 wrote:

https://www.aanda.org/articles/aa/abs/2020/04/aa37254-19/aa37254-19.html  
We need follow up this system

Indeed. I wonder what TESS will reveal about the system?
Threads merged.

https://www.unige.ch/communication/communiques/en/2020/un-systeme-de-six-planetes-presque-en-rythme/

Astronomy: six planets (almost) in rythm

Tess excluded any other confirmed planets transiting in this system (I mean c,d,e,f,g ) Longer period planet may transit