New HARPS M dwarf systems - GJ 3138, GJ 3323, GJ 273 (Luyten's Star), GJ 628 (Wolf 1061), and GJ 3293

The HARPS search for southern extra-solar planets XLI. A dozen planets around the M dwarfs GJ 3138, GJ 3323, GJ 273, GJ 628, and GJ 3293
https://arxiv.org/abs/1703.05386

Quote :

Context. Low mass stars are currently the best targets for searches for rocky planets in the habitable zone of their host star. Over the last 13 years, precise radial velocities measured with the HARPS spectrograph have identified over a dozen super-Earths and Earth-mass planets (msin i<10Mearth ) around M dwarfs, with a well understood selection function. This well defined sample informs on their frequency of occurrence and on the distribution of their orbital parameters, and therefore already constrains our understanding of planetary formation. The subset of these low-mass planets that were found within the habitable zone of their host star also provide prized targets for future atmospheric biomarkers searches. Aims. We are working to extend this planetary sample to lower masses and longer periods through dense and long-term monitoring of the radial velocity of a small M dwarf sample. Methods. We obtained large numbers of HARPS spectra for the M dwarfs GJ 3138, GJ 3323, GJ 273, GJ 628 and GJ 3293, from which we derived radial velocities (RVs) and spectroscopic activity indicators. We searched them for variabilities, periodicities, Keplerian modulations and correlations, and attribute the radial-velocity variations to combinations of planetary companions and stellar activity. Results. We detect 12 planets, of which 9 are new with masses ranging from 1.17 to 10.5 Mearth . Those planets have relatively short orbital periods (P<40 d), except two of them with periods of 217.6 and 257.8 days. Among these systems, GJ 273 harbor two planets with masses close to the one of the Earth. With a distance of 3.8 parsec only, GJ 273 is the second nearest known planetary system - after Proxima Centauri - with a planet orbiting the circumstellar habitable zone.

Planets at Wolf 1061 were also reported here. Worth noting the new fit for the period for Wolf 1061 d is much greater than the fit proposed earlier.

Why didn't they give the argument of periastron values for the orbits? It's significant for determining transit probabilities and likely timings.

Anyone here knows the distance of GJ 3138? It's been hard to find more details of this star.

Now I found it GJ 3138 (HIP 10037) it's at 29.904 parsecs on the constellation of Cetus.

http://server3.sky-map.org/starview?object_type=1&object_id=1454371&object_name=HIP+10037&locale=EN

For GJ 3293, see also :

https://solar-flux.forumotion.com/t1599-planets-at-gj-3293-and-gj-3341-from-harps

Two Neptune-mass planets - msin(i) = 1:4  0:1 and 1:3  0:1Mnept - orbit GJ 3293 with periods P = 30:60  0:02 d and P = 123:98  0:38 d, possibly together with a super-Earth - msin(i)  7:9  1.4 earth M with period P = 48:14  0:12

Finaly, 4 planets for the system :

Update on Luyten's Star

GJ 273: On the formation, dynamical evolution and habitability of a planetary system hosted by an M dwarf at 3.75 parsec
https://arxiv.org/abs/2006.09403

Quote :

Planets orbiting low-mass stars such as M dwarfs are now considered a cornerstone in the search for life-harbouring planets. GJ273 is a planetary system orbiting an M dwarf only 3.75 pc away, composed of two confirmed planets, GJ273b and GJ273c, and two promising candidates, GJ273d and GJ273e. Planet GJ273b resides in the habitable zone. Currently, due to a lack of observed planetary transits, only the minimum masses of the planets are known.Despite being an interesting system, the GJ273 planetary system is still poorly studied. We aim at precisely determine the physical parameters of the individual planets, in particular to break the mass--inclination degeneracy to accurately determine the mass of the planets. Moreover, we present thorough characterisation of planet GJ273b in terms of its potential habitability. We explored the planetary formation and hydration phases of GJ273 during the first 100 Myr. Then, we analysed the stability of the system. We also searched for regions which may harbour minor bodies such as an asteroid belt and Kuiper belt analogues. We found that the four-planet configuration of the system allows us to break the mass--inclination degeneracy with the following masses: 2.89≤Mb≤3.03M⊕, 1.18≤Mc≤1.24M⊕, 10.80≤Md≤11.35M⊕, and 9.30≤Me≤9.70M⊕. That is an Earth-mass planet, a super-Earth and two mini-Neptunes. Moreover, GJ273b is found to be an efficient water captor and GJ273c likely a dry planet. Several stable regions are predicted where minor bodies might reside. We comprehensively discuss the habitability of GJ273b.

A Volume-Limited Radio Search for Magnetic Activity in 140 Exoplanets with the Very Large Array
https://arxiv.org/abs/2404.16940

Quote :

We present results from a search for radio emission in 77 stellar systems hosting 140 exoplanets, predominantly within 17.5 pc using the Very Large Array (VLA) at 4−8 GHz. This is the largest and most sensitive search to date for radio emission in exoplanetary systems in the GHz frequency range. We obtained new observations of 58 systems, and analyzed archival observations of an additional 19 systems. Our choice of frequency and volume limit are motivated by radio detections of ultracool dwarfs (UCDs), including T dwarfs with masses at the exoplanet threshold of ∼13MJ. Our surveyed exoplanets span a mass range of ≈10−3−10MJ and semi-major axes of ≈10−2−10AU. We detect a single target - GJ 3323 (M4) hosting two exoplanets with minimum masses of 2 and 2.3M⊕ - with a circular polarization fraction of ≈40%; the radio luminosity agrees with its known X-ray luminosity and the Güdel-Benz relation for stellar activity suggesting a likely stellar origin, but the high circular polarization fraction may also be indicative of star-planet interaction. For the remaining sources our 3σ upper limits are generally Lν≲1012.5ergs−1Hz−1, comparable to the lowest radio luminosities in UCDs. Our results are consistent with previous targeted searches of individual systems at GHz frequencies while greatly expanding the sample size. Our sensitivity is comparable to predicted fluxes for some systems considered candidates for detectable star-planet interaction. Observations with future instruments such as the Square Kilometer Array and Next Generation Very Large Array will be necessary to further constrain emission mechanisms from exoplanet systems at GHz frequencies.