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Exoplanets – worlds of other suns


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#481
Sciencerocks

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Minimizing the bias in exoplanet detection - application to radial velocities of LHS 1140
https://arxiv.org/abs/1807.02483
 

    A rocky planet orbiting LHS 1140 with a period of 24.7d has been found based on the discovery of transits in its light and high precision radial velocity data (Dittmann et al. 2017). This discovery by two independent methods is an observational tour-de-force, however, we find that a conservative analysis of the data gives a different solution. A three planet system is apparent in the radial velocity data based on our diagnosis of stellar activity. We encourage further targeted photometric and radial velocity observations in order to constrain the mini-Neptune and super-Earth mass objects apparently causing the 3.8 and 90 day radial velocity signals. We use our package Agatha (this https URL) to provide a comprehensive strategy to disentangle planetary signals from stellar activity in radial velocity data.

This appears to be independent from the Charbonneau study. This study finds evidence of 3 planets -- the already detected planet, a second planet at 92 days, and a third at 3.8 days, but they're less confident about the third planet. So since we have independent detection (and transits, most notably) of the 3.8 day planet from Charbonneau et al, this would seem to secure LHS 1140 as a 3-planet system.


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#482
Sciencerocks

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The 55 Cnc system reassessed
https://arxiv.org/abs/1807.04301

There's a full five-planet (+magnetic cycle) fit to the RV data.



#483
Sciencerocks

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The first super-Earth Detection from the High Cadence and High Radial Velocity Precision Dharma Planet Survey
https://arxiv.org/abs/1807.07098

    The Dharma Planet Survey (DPS) aims to monitor about 150 nearby very bright FGKM dwarfs (within 50 pc) during 2016−2020 for low-mass planet detection and characterization using the TOU very high resolution optical spectrograph (R≈100,000, 380-900nm). TOU was initially mounted to the 2-m Automatic Spectroscopic Telescope at Fairborn Observatory in 2013-2015 to conduct a pilot survey, then moved to the dedicated 50-inch automatic telescope on Mt. Lemmon in 2016 to launch the survey. Here we report the first planet detection from DPS, a super-Earth candidate orbiting a bright K dwarf star, HD 26965. It is the second brightest star (V=4.4 mag) on the sky with a super-Earth candidate. The planet candidate has a mass of 8.47±0.47MEarth, period of 42.38±0.01 d, and eccentricity of 0.04+0.05−0.03. This RV signal was independently detected by Diaz et al. (2018), but they could not confirm if the signal is from a planet or from stellar activity. The orbital period of the planet is close to the rotation period of the star (39−44.5 d) measured from stellar activity indicators. Our high precision photometric campaign and line bisector analysis of this star do not find any significant variations at the orbital period. Stellar RV jitters modeled from star spots and convection inhibition are also not strong enough to explain the RV signal detected. After further comparing RV data from the star's active magnetic phase and quiet magnetic phase, we conclude that the RV signal is due to planetary-reflex motion and not stellar activity.

 



#484
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Scientists identify exoplanets where life could develop as it did on Earth
August 1, 2018, University of Cambridge

 

Scientists have identified a group of planets outside our solar system where the same chemical conditions that may have led to life on Earth exist.

The researchers, from the University of Cambridge and the Medical Research Council Laboratory of Molecular Biology (MRC LMB), found that the chances for life to develop on the surface of a rocky planet like Earth are connected to the type and strength of light given off by its host star.

Their study, published in the journal Science Advances, proposes that stars which give off sufficient ultraviolet (UV) light could kick-start life on their orbiting planets in the same way it likely developed on Earth, where the UV light powers a series of chemical reactions that produce the building blocks of life.

The researchers have identified a range of planets where the UV light from their host star is sufficient to allow these chemical reactions to take place, and that lie within the habitable range where liquid water can exist on the planet's surface.

 

Read more at: https://phys.org/new...-earth.html#jCp


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#485
Sciencerocks

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A second planet with an Earth-like composition orbiting the nearby M dwarf LHS 1140
https://arxiv.org/abs/1808.00485

   

LHS 1140 is a nearby mid-M dwarf known to host a temperate rocky super-Earth (LHS 1140 b) on a 24.737-day orbit. Based on photometric observations by MEarth and Spitzer as well as Doppler spectroscopy from HARPS, we report the discovery of an additional transiting rocky companion (LHS 1140 c) with a mass of 1.81±0.39 MEarth and a radius of 1.282±0.024 REarth on a tighter, 3.77795-day orbit. We also obtain more precise estimates of the mass and radius of LHS 1140 b to be 6.98±0.98 MEarth and 1.727±0.032 REarth. The mean densities of planets b and c are 7.5±1.0 g/cm3 and 4.7±1.1 g/cm3, respectively, both consistent with the Earth's ratio of iron to magnesium silicate. The orbital eccentricities of LHS 1140 b and c are consistent with circular orbits and constrained to be below 0.06 and 0.31, respectively, with 90% confidence. Because the orbits of the two planets are co-planar and because we know from previous analyses of Kepler data that compact systems of small planets orbiting M dwarfs are commonplace, a search for more transiting planets in the LHS 1140 system could be fruitful. LHS 1140 c is one of the few known nearby terrestrial planets whose atmosphere could be studied with the upcoming James Webb Space Telescope.

1140b appears to be 4.7 g/cm^3 which is high enough to be earth like. Nice to see mass and radius being found for a habitual candidate. Wish they were swapped as 1.2 radius at 1.8 mass would be more earth like in gravity.



#486
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New methods confirmed 44 exoplanets including 16 earth sized exoplanets
brian wang | August 8, 2018
 

An international team of astronomers using data from NASA’s Kepler and the European Space Agency (ESA)’s Gaia space telescopes, as well as ground-based telescopes have confirmed 44 exoplanets. New techniques developed to validate the find could hugely accelerate the confirmation of more extrasolar planet candidates.

John Livingston, lead author of the study and a graduate student at the University of Tokyo combined resources led to the confirmed existence of these 44 exoplanets and described various details about them.

A portion of the findings yield some surprising characteristics: “For example, four of the planets orbit their host stars in less than 24 hours,” says Livingston. “In other words, a year on each of those planets is shorter than a day here on Earth.” These contribute to a small but growing list of “ultrashort-period” planets, so it could turn out they’re not as unusual as they might seem.

“It was also gratifying to verify so many small planets,” continues Livingston. “Sixteen were in the same size class as Earth, one in particular turning out to be extremely small — about the size of Venus — which was a nice affirmation as it’s close to the limit of what is possible to detect.”

 

https://www.nextbigf...exoplanets.html


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#487
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Revised Exoplanet Radii and Habitability Using Gaia Data Release 2
https://arxiv.org/abs/1808.04533

    Accurate stellar properties are crucial for determining exoplanet characteristics. Gaia DR2 presents revised distances, luminosities, and radii for 1.6 billion stars. Here, we report the calculation of revised radii and densities for 320 exoplanets using this data and present updated calculations of the incident flux received by 690 known exoplanets. This allows the likelihood that those planets orbit in the habitable zone of their host stars to be reassessed. As a result of this analysis, three planets can be added to the catalogue of potentially habitable worlds: HIP~67537~b, HD~148156~b, and HD~106720~b. In addition, the changed parameterisation of BD~+49~898 means that its planet, BD~+49~898~b, now receives an incident flux that places it outside the optimistic habitable zone region, as defined by \citep{Kopparapu2013,Kopparapu2014}. We find that use of the new \textit{Gaia} data results in a mean increase in calculated exoplanet radius of 3.76\%. Previously, CoRoT-3 b had been reported as having the highest density of all known exoplanets. Here, we use updated information to revise the calculated density of CoRoT-3~b from 26.4gcm−3 to 17.3±2.9gcm−3. We also report the densest exoplanet in our dataset, KELT-1~b, with a density of 23.7±4.0gcm−3. Overall, our results highlight the importance of ensuring the the parameterisation of known exoplanets be revisited whenever significant improvements are made to the precision of the stellar parameters upon which they are based.

 


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