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Register a new userThe First Neptune Analog or Super-Earth with Neptune-like Orbit: MOA-2013-BLG-605Lb
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We present the discovery of the first Neptune analog exoplanet or super-Earth with Neptune-like orbit, MOA-2013-BLG-605Lb. This planet has a mass similar to that of Neptune or a super-Earth and it orbits at $9sim 14$ times the expected position of the snow-line, $a_{rm snow}$, which is similar to Neptunes separation of $ 11,a_{rm snow}$ from the Sun. The planet/host-star mass ratio is $q=(3.6pm0.7)times 10^{-4}$ and the projected separation normalized by the Einstein radius is $s=2.39pm0.05$. There are three degenerate physical solutions and two of these are due to a new type of degeneracy in the microlensing parallax parameters, which we designate the wide degeneracy. The three models have (i) a Neptune-mass planet with a mass of $M_{rm p}=21_{-7}^{+6} M_{Earth}$ orbiting a low-mass M-dwarf with a mass of $M_{rm h}=0.19_{-0.06}^{+0.05} M_odot$, (ii) a mini-Neptune with $M_{rm p}= 7.9_{-1.2}^{+1.8} M_{Earth}$ orbiting a brown dwarf host with $M_{rm h}=0.068_{-0.011}^{+0.019} M_odot$ and (iii) a super-Earth with $M_{rm p}= 3.2_{-0.3}^{+0.5} M_{Earth}$ orbiting a low-mass brown dwarf host with $M_{rm h}=0.025_{-0.004}^{+0.005} M_odot$ which is slightly favored. The 3-D planet-host separations are 4.6$_{-1.2}^{+4.7}$ AU, 2.1$_{-0.2}^{+1.0}$ AU and 0.94$_{-0.02}^{+0.67}$ AU, which are $8.9_{-1.4}^{+10.5}$, $12_{-1}^{+7}$ or $14_{-1}^{+11}$ times larger than $a_{rm snow}$ for these models, respectively. The Keck AO observation confirm that the lens is faint. This discovery suggests that low-mass planets with Neptune-like orbit are common. So processes similar to the one that formed Neptune in our own Solar System or cold super-Earth may be common in other solar systems.
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We analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and planetary masses of Mh = 0.11+/-0.01 M_{sun} and Mp = 9.2+/-2.2M_Earth, corresponding to a very late M dwarf and sub-Neptune-mass planet, respectively. The system lies at DL = 0.81 +/- 0.10 kpc with projected separation r = 0.92 +/- 0.16 AU. Because of the hosts a-priori-unlikely close distance, as well as the unusual nature of the system, we consider the possibility that the microlens parallax signal, which determines the host mass and distance, is actually due to xallarap (source orbital motion) that is being misinterpreted as parallax. We show a result that favors the parallax solution, even given its close host distance. We show that future high-resolution astrometric measurements could decisively resolve the remaining ambiguity of these solutions.
We present the discovery of a Neptune-mass planet orbiting a 0.8 +- 0.3 M_Sun star in the Galactic bulge. The planet manifested itself during the microlensing event MOA 2011-BLG-028/OGLE-2011-BLG-0203 as a low-mass companion to the lens star. The analysis of the light curve provides the measurement of the mass ratio: (1.2 +- 0.2) x 10^-4, which indicates the mass of the planet to be 12-60 Earth masses. The lensing system is located at 7.3 +- 0.7 kpc away from the Earth near the direction to Baades Window. The projected separation of the planet, at the time of the microlensing event, was 3.1-5.2 AU. Although the microlens parallax effect is not detected in the light curve of this event, preventing the actual mass measurement, the uncertainties of mass and distance estimation are narrowed by the measurement of the source star proper motion on the OGLE-III images spanning eight years, and by the low amount of blended light seen, proving that the host star cannot be too bright and massive. We also discuss the inclusion of undetected parallax and orbital motion effects into the models, and their influence onto the final physical parameters estimates.
We report the discovery of a low mass-ratio planet $(q = 1.3times10^{-4})$, i.e., 2.5 times higher than the Neptune/Sun ratio. The planetary system was discovered from the analysis of the KMT-2017-BLG-0165 microlensing event, which has an obvious short-term deviation from the underlying light curve produced by the host of the planet. Although the fit improvement with the microlens parallax effect is relatively low, one component of the parallax vector is strongly constrained from the light curve, making it possible to narrow down the uncertainties of the lens physical properties. A Bayesian analysis yields that the planet has a super-Neptune mass $(M_{2}=34_{-12}^{+15}~M_{oplus})$ orbiting a Sun-like star $(M_{1}=0.76_{-0.27}^{+0.34}~M_{odot})$ located at $4.5~{rm kpc}$. The blended light is consistent with these host properties. The projected planet-host separation is $a_{bot}={3.45_{-0.95}^{+0.98}}~{rm AU}$, implying that the planet is located outside the snowline of the host, i.e., $a_{sl}sim2.1~{rm AU}$. KMT-2017-BLG-0165Lb is the sixteenth microlensing planet with mass ratio $q<3times10^{-4}$. Using the fifteen of these planets with unambiguous mass-ratio measurements, we apply a likelihood analysis to investigate the form of the mass-ratio function in this regime. If we adopt a broken power law for the form of this function, then the break is at $q_{rm br}simeq0.55times10^{-4}$, which is much lower than previously estimated. Moreover, the change of the power law slope, $zeta>3.3$ is quite severe. Alternatively, the distribution is also suggestive of a pile-up of planets at Neptune-like mass ratios, below which there is a dramatic drop in frequency.
GJ1214b is thought to be either a mini-Neptune with a thick, hydrogen-rich atmosphere, or a planet with a composition dominated by water. In the case of a hydrogen-rich atmosphere, molecular absorption and scattering processes may result in detectable radius variations as a function of wavelength. The aim of this paper is to measure these variations. We have obtained observations of the transit of GJ1214b in the r- and I-band with the INT, in the g, r, i and z bands with the 2.2 meter MPI/ESO telescope, in the Ks-band with the NOT, and in the Kc-band with the WHT. By comparing the transit depth between the the different bands, which is a measure for the planet-to-star size ratio, the atmosphere is investigated. We do not detect clearly significant variations in the planet-to-star size ratio as function of wavelength. Although the ratio at the shortest measured wavelength, in g-band, is 2sigma larger than in the other bands. The uncertainties in the Ks and Kc bands are large, due to systematic features in the light curves. The tentative increase in the planet-to-star size ratio at the shortest wavelength could be a sign of an increase in the effective planet-size due to Rayleigh scattering, which would require GJ1214b to have a hydrogen-rich atmosphere. If true, then the atmosphere has to have both clouds, to suppress planet-size variations at red optical wavelengths, as well as a sub-solar metallicity, to suppress strong molecular features in the near- and mid-infrared. However, star spots, which are known to be present on the hoststars surface, can (partly) cancel out the expected variations in planet-to-star size ratio, due to the lower surface temperature of the spots . A hypothetical spot-fraction of 10% would be able to raise the infrared points sufficiently with respect to the optical measurements to be inconsistent with a water-dominated atmosphere. [abridged]
We present the analysis of high-resolution images of MOA-2013-BLG-220, taken with the Keck adaptive optics system 6 years after the initial observation, identifying the lens as a solar-type star hosting a super-Jupiter mass planet. The masses of planets and host-stars discovered by microlensing are often not determined from light curve data, while the star-planet mass-ratio and projected separation in units of Einstein ring radius are well measured. High-resolution follow-up observations after the lensing event is complete can resolve the source and lens. This allows direct measurements of flux, and the amplitude and direction of proper motion, giving strong constraints on the system parameters. Due to the high relative proper motion, $mu_{rm rel,Geo} = 12.62pm0.11$ mas/yr, the source and lens were resolved in 2019, with a separation of $77.1pm0.5$ mas. Thus, we constrain the lens flux to $K_{rm Keck,lens}= 17.92pm0.02$. By combining constraints from the model and Keck flux, we find the lens mass to be $M_L = 0.88pm0.05 M_odot$ at $D_L = 6.72pm0.59$ kpc. With a mass-ratio of $q=(3.00pm0.03)times10^{-3}$ the planets mass is determined to be $M_P = 2.74pm0.17 M_{J}$ at a separation of $r_perp = 3.03pm0.27$ AU. The lens mass is much higher than the prediction made by the Bayesian analysis that assumes all stars have an equal probability to host a planet of the measured mass ratio, and suggests that planets with mass ratios of a few 10$^{-3}$ are more common orbiting massive stars. This demonstrates the importance of high-resolution follow-up observations for testing theories like these.
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