A Super-Earth at Gliese 15

The NASA-UC-UH Eta-Earth Program: IV. A Low-mass Planet Orbiting an M Dwarf 3.6 PC from Earth
http://arxiv.org/abs/1408.5645

Quote :

We report the discovery of a low-mass planet orbiting Gl 15 A based on radial velocities from the Eta-Earth Survey using HIRES at Keck Observatory. Gl 15 Ab is a planet with minimum mass Msini = 5.35 ± 0.75 M ⊕ , orbital period P = 11.4433 ± 0.0016 days, and an orbit that is consistent with circular. We characterize the host star using a variety of techniques. Photometric observations at Fairborn Observatory show no evidence for rotational modulation of spots at the orbital period to a limit of ~0.1 mmag, thus supporting the existence of the planet. We detect a second RV signal with a period of 44 days that we attribute to rotational modulation of stellar surface features, as confirmed by optical photometry and the Ca II H & K activity indicator. Using infrared spectroscopy from Palomar-TripleSpec, we measure an M2 V spectral type and a sub-solar metallicity ([M/H] = -0.22, [Fe/H] = -0.32). We measure a stellar radius of 0.3863 ± 0.0021 R ⊙ based on interferometry from CHARA.

Also known as Groombridge 34 A (or GX Andromedae). We're knowing always better our own "neighbours".

Boy, that paper has a painfully mundane title.

But it's good to see the Eta-Earth survey is still doing things, considering they haven't published anything for a few years. I hope they've worked on their candidates from back then!

This planetary system is one more in a relatively close (~100 AU) binary. It is encouraging to see that the planet does not have a high eccentricity, which argues for either alignment between the stellar orbit and the protoplanetary disk, or that the planet formed close-in enough so that it could not be reached by Kozai oscillations to a high degree. Both circumstances are interesting, particularly the latter considering that the star is so late type that the ice line should be rather close-in, too.

Minimum mass is very close to or exceeding the value for an Earth-composition planet at the rocky/gaseous transition (which appears to occur at 1.5--1.6 Earth radii). I'd guess this one is likely a gas dwarf/sub-Neptune.

https://arxiv.org/abs/1710.01595

The CARMENES search for exoplanets around M dwarfs. First visual-channel radial-velocity measurements and orbital parameter updates of seven M-dwarf planetary systems

Context: The main goal of the CARMENES survey is to find Earth-mass planets around nearby M-dwarf stars. Seven M-dwarfs included in the CARMENES sample had been observed before with HIRES and HARPS and either were reported to have one short period planetary companion (GJ15A, GJ176, GJ436, GJ536 and GJ1148) or are multiple planetary systems (GJ581 and GJ876).
Aims: We aim to report new precise optical radial velocity measurements for these planet hosts and test the overall capabilities of CARMENES.
Methods: We combined our CARMENES precise Doppler measurements with those available from HIRES and HARPS and derived new orbital parameters for the systems. Bona-fide single planet systems are fitted with a Keplerian model. The multiple planet systems were analyzed using a self-consistent dynamical model and their best fit orbits were tested for long-term stability.
Results: We confirm or provide supportive arguments for planets around all the investigated stars except for GJ15A, for which we find that the post-discovery HIRES data and our CARMENES data do not show a signal at 11.4 days. Although we cannot confirm the super-Earth planet GJ15Ab, we show evidence for a possible long-period (P c = 7025 +972 −629 d) Saturn-mass (m c sini = 51.8 +5.5 −5.8 M ⊕ ) planet around GJ15A. In addition, based on our CARMENES and HIRES data we discover a second planet around GJ1148, for which we estimate a period P c = 532.6 +4.1 −2.5 d, eccentricity e c = 0.34 +0.05 −0.06 and minimum mass m c sini = 68.1 +4.9 −2.2 M ⊕ .
Conclusions: The CARMENES optical radial velocities have similar precision and overall scatter when compared to the Doppler measurements conducted with HARPS and HIRES. We conclude that CARMENES is an instrument that is up to the challenge of discovering rocky planets around low-mass stars

Also worth noting that the eccentricity of Gliese 876 d comes out as a far lower value than previous solutions, which puts it in line with the prediction that tidal circularisation should be fast.

Suárez-Mascareño et al. "HADES RV Programme with HARPS-N at TNG. VII. Rotation and activity of M-Dwarfs from time-series high-resolution spectroscopy of chromospheric indicators"
https://arxiv.org/abs/1712.07375

Quote :

For the case of GJ 15A b we obtain a range of masses of 5.4 - 5.7 M_⊕ if we use the mass provided in Howard et al. (2014). Recent observations with CARMENES and HARPS-N have added new insight on this system, challenging (Trifonov et al. (2017)) and supporting (Pinamonti et al. submitted) the existence of the planet. If we use the mass determined by Pinamonti et al. submitted, using the original Howard et al. (2014) data combined with our HARPS-N observations, the mass of GJ 15 A b would be 3.1 - 3.3 M_⊕.

Looks like there's going to be a bit of back-and-forth over the existence of this one.

Two planets at GJ 15A.

The HADES RV Programme with HARPS-N@TNG VIII. Gl15A: A multiple wide planetary system sculpted by binary interaction
https://arxiv.org/abs/1804.03476

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We present 20 years of radial velocity (RV) measurements of the M1 dwarf Gl15A, combining 5 years of intensive RV monitoring with the HARPS-N spectrograph with 15 years of archival HIRES/Keck RV data. We carry out an MCMC-based analysis of the RV time series, inclusive of Gaussian Process (GP) approach to the description of stellar activity induced RV variations.
Our analysis confirms the Keplerian nature and refines the orbital solution for the 11.44-day period super Earth, Gl15A\,b, reducing its amplitude to 1.68+0.17−0.18 m s−1 (Msini=3.03+0.46−0.44 M⊕), and successfully models a long-term trend in the combined RV dataset in terms of a Keplerian orbit with a period around 7600 days and an amplitude of 2.5+1.3−1.0 m s−1, corresponding to a super-Neptune mass (Msini=36+25−18 M⊕) planetary companion.
We also discuss the present orbital configuration of Gl15A planetary system in terms of the possible outcomes of Lidov-Kozai interactions with the wide-separation companion Gl15B in a suite of detailed numerical simulations. In order to improve the results of the dynamical analysis, we derive a new orbital solution for the binary system, combining our RV measurements with astrometric data from the WDS catalogue.
The eccentric Lidov-Kozai analysis shows the strong influence of Gl15B on the Gl15A planetary system, which can produce orbits compatible with the observed configuration for initial inclinations of the planetary system between 75∘ and 90∘, and can also enhance the eccentricity of the outer planet well above the observed value, even resulting in orbital instability, for inclinations around 0∘ and 15∘−30∘.
The Gl15A system is the multi-planet system closest to Earth, at 3.57 pc, and hosts the longest period RV sub-jovian mass planet discovered so far.