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Register a new userAstrophysical Parameters and Habitable Zone of the Exoplanet Hosting Star GJ 581
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Kaspar von Braun
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GJ 581 is an M dwarf host of a multiplanet system. We use long-baseline interferometric measurements from the CHARA Array, coupled with trigonometric parallax information, to directly determine its physical radius to be $0.299 pm 0.010 R_{odot}$. Literature photometry data are used to perform spectral energy distribution fitting in order to determine GJ 581s effective surface temperature $T_{rm EFF}=3498 pm 56$ K and its luminosity $L=0.01205 pm 0.00024 L_{odot}$. From these measurements, we recompute the location and extent of the systems habitable zone and conclude that two of the planets orbiting GJ 581, planets d and g, spend all or part of their orbit within or just on the edge of the habitable zone.
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We present an analysis of the significantly expanded HARPS 2011 radial velocity data set for GJ 581 that was presented by Forveille et al. (2011). Our analysis reaches substantially different conclusions regarding the evidence for a Super-Earth-mass planet in the stars Habitable Zone. We were able to reproduce their reported chi_{ u}^2 and RMS values only after removing some outliers from their models and refitting the trimmed down RV set. A suite of 4000 N-body simulations of their Keplerian model all resulted in unstable systems and revealed that their reported 3.6sigma detection of e=0.32 for the eccentricity of GJ 581e is manifestly incompatible with the systems dynamical stability. Furthermore, their Keplerian model, when integrated only over the time baseline of the observations, significantly increases the chi_{ u}^2 and demonstrates the need for including non-Keplerian orbital precession when modeling this system. We find that a four-planet model with all of the planets on circular or nearly circular orbits provides both an excellent self-consistent fit to their RV data and also results in a very stable configuration. The periodogram of the residuals to a 4-planet all-circular-orbit model reveals significant peaks that suggest one or more additional planets in this system. We conclude that the present 240-point HARPS data set, when analyzed in its entirety, and modeled with fully self-consistent stable orbits, by and of itself does offer significant support for a fifth signal in the data with a period near 32 days. This signal has a False Alarm Probability of <4% and is consistent with a planet of minimum mass of 2.2 Earth-masses, orbiting squarely in the stars Habitable Zone at 0.13 AU, where liquid water on planetary surfaces is a distinct possibility
The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. The study presented here yields directly determined values for 55 Cncs stellar astrophysical parameters based on improved interferometry: $R=0.943 pm 0.010 R_{odot}$, $T_{rm EFF} = 5196 pm 24$ K. We use isochrone fitting to determine 55 Cncs age to be 10.2 $pm$ 2.5 Gyr, implying a stellar mass of $0.905 pm 0.015 M_{odot}$. Our analysis of the location and extent of the systems habitable zone (0.67--1.32 AU) shows that planet f, with period $sim$ 260 days and $M sin i = 0.155 M_{Jupiter}$, spends the majority of the duration of its elliptical orbit in the circumstellar habitable zone. Though planet f is too massive to harbor liquid water on any planetary surface, we elaborate on the potential of alternative low-mass objects in planet fs vicinity: a large moon, and a low-mass planet on a dynamically stable orbit within the habitable zone. Finally, our direct value for 55 Cancris stellar radius allows for a model-independent calculation of the physical diameter of the transiting super-Earth 55 Cnc e ($sim 2.05 pm 0.15 R_{earth}$), which, depending on the planetary mass assumed, implies a bulk density of 0.76 $rho_{earth}$ or 1.07 $rho_{earth}$.
We report the detection of GJ 832c, a super-Earth orbiting near the inner edge of the habitable zone of GJ 832, an M dwarf previously known to host a Jupiter analog in a nearly-circular 9.4-year orbit. The combination of precise radial-velocity measurements from three telescopes reveals the presence of a planet with a period of 35.68+/-0.03 days and minimum mass (m sin i) of 5.4+/-1.0 Earth masses. GJ 832c moves on a low-eccentricity orbit (e=0.18+/-0.13) towards the inner edge of the habitable zone. However, given the large mass of the planet, it seems likely that it would possess a massive atmosphere, which may well render the planet inhospitable. Indeed, it is perhaps more likely that GJ 832c is a super-Venus, featuring significant greenhouse forcing. With an outer giant planet and an interior, potentially rocky planet, the GJ 832 planetary system can be thought of as a miniature version of our own Solar system.
The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. We use the CHARA Array to directly determine the following of 55 Cncs stellar astrophysical parameters: $R=0.943 pm 0.010 R_{odot}$, $T_{rm EFF} = 5196 pm 24$ K. Planet 55 Cnc f ($M sin i = 0.155 M_{Jupiter}$) spends the majority of the duration of its elliptical orbit in the circumstellar habitable zone (0.67--1.32 AU) where, with moderate greenhouse heating, it could harbor liquid water. Our determination of 55 Cancris stellar radius allows for a model-independent calculation of the physical diameter of the transiting super-Earth 55 Cnc e ($simeq 2.1 R_{earth}$), which, depending on the assumed literature value of planetary mass, implies a bulk density of 0.76 $rho_{earth}$ or 1.07 $rho_{earth}$.
The NASA Kepler mission has discovered thousands of new planetary candidates, many of which have been confirmed through follow-up observations. A primary goal of the mission is to determine the occurrance rate of terrestrial-size planets within the Habitable Zone (HZ) of their host stars. Here we provide a list of HZ exoplanet candidates from the Kepler Data Release 24 Q1-Q17 data vetting process. This work was undertaken as part of the Kepler Habitable Zone Working Group. We use a variety of criteria regarding HZ boundaries and planetary sizes to produce complete lists of HZ candidates, including a catalog of 104 candidates within the optimistic HZ and 20 candidates with radii less than two Earth radii within the conservative HZ. We cross-match our HZ candidates with the Data Release 25 stellar properties and confirmed planet properties to provide robust stellar parameters and candidate dispositions. We also include false positive probabilities recently calculated by Morton et al. (2016) for each of the candidates within our catalogs to aid in their validation. Finally, we performed dynamical analysis simulations for multi-planet systems that contain candidates with radii less than two Earth radii as a step toward validation of those systems.
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