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تسجيل مستخدم جديدThe 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
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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.
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Context. Planetary companions of a fixed mass induce larger amplitude reflex motions around lower-mass stars, which helps make M dwarfs excellent targets for extra-solar planet searches. State of the art velocimeters with $sim$1m/s stability can dete
ct very low-mass planets out to the habitable zone of these stars. Low-mass, small, planets are abundant around M dwarfs, and most known potentially habitable planets orbit one of these cool stars. Aims. Our M-dwarf radial velocity monitoring with HARPS on the ESO 3.6m telescope at La Silla observatory makes a major contribution to this sample. Methods. We present here dense radial velocity (RV) time series for three M dwarfs observed over $sim5$ years: GJ 3293 (0.42M$_odot$), GJ 3341 (0.47M$_odot$), and GJ 3543 (0.45M$_odot$). We extract those RVs through minimum $chi^2$ matching of each spectrum against a high S/N ratio stack of all observed spectra for the same star. We then vet potential orbital signals against several stellar activity indicators, to disentangle the Keplerian variations induced by planets from the spurious signals which result from rotational modulation of stellar surface inhomogeneities and from activity cycles. Results. Two Neptune-mass planets - $msin(i)=1.4pm0.1$ and $1.3pm0.1M_{nept}$ - orbit GJ 3293 with periods $P=30.60pm0.02$ d and $P=123.98pm0.38$ d, possibly together with a super-Earth - $msin(i)sim7.9pm1.4M_oplus$ - with period $P=48.14pm0.12;d$. A super-Earth - $msin(i)sim6.1M_oplus$ - orbits GJ 3341 with $P=14.207pm0.007;d$. The RV variations of GJ 3543, on the other hand, reflect its stellar activity rather than planetary signals.
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We have performed simulations to investigate the dynamics of the M dwarf star GJ 876 in an attempt to reveal any stabilizing mechanism for sustaining the system.We simulated different coplanar and noncoplanar configurations of two-planet systems and
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