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Register a new userOGLE-2017-BLG-1434Lb: Confirmation of a Cold Super-Earth using Keck Adaptive Optics
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The microlensing event OGLE-2017-BLG-1434 features a cold super-Earth planet which is one of eleven microlensing planets with a planet-host star mass ratio $q < 1 times 10^{-4}$. We provide an additional mass-distance constraint on the lens host using near-infrared adaptive optics photometry from Keck/NIRC2. We are able to determine a flux excess of $K_L = 16.96 pm 0.11$ which most likely comes entirely from the lens star. Combining this with constraints from the large Einstein ring radius, $theta_E=1.40 pm 0.09;mas$ and OGLE parallax we confirm this event as a super-Earth with mass $m_p = 4.43 pm 0.25M_odot$. This system lies at a distance of $D_L = 0.86 pm 0.05,kpc$ from Earth and the lens star has a mass of $M_L=0.234pm0.012M_odot$. We confirm that with a star-planet mass ratio of $q=0.57 times 10^{-4}$, OGLE-2017-BLG-1434 lies near the inflexion point of the planet-host mass-ratio power law.
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We report the discovery of a planetary system in which a super-earth orbits a late M-dwarf host. The planetary system was found from the analysis of the microlensing event OGLE-2017-BLG-0482, wherein the planet signal appears as a short-term anomaly to the smooth lensing light curve produced by the host. Despite its weak signal and short duration, the planetary signal was firmly detected from the dense and continuous coverage by three microlensing surveys. We find a planet/host mass ratio of $qsim 1.4times 10^{-4}$. We measure the microlens parallax $pi_{rm E}$ from the long-term deviation in the observed lensing light curve, but the angular Einstein radius $theta_{rm E}$ cannot be measured because the source trajectory did not cross the planet-induced caustic. Using the measured event timescale and the microlens parallax, we find that the masses of the planet and the host are $M_{rm p}=9.0_{-4.5}^{+9.0} M_oplus$ and $M_{rm host}=0.20_{-0.10}^{+0.20} M_odot$, respectively, and the projected separation between them is $a_perp=1.8_{-0.7}^{+0.6}$ au. The estimated distance to the lens is $D_{rm L}=5.8_{-2.1}^{+1.8}$ kpc. The discovery of the planetary system demonstrates that microlensing provides an important method to detect low-mass planets orbiting low-mass stars.
We report the analysis of the microlensing event OGLE-2018-BLG-0677. A small feature in the light curve of the event leads to the discovery that the lens is a star-planet system. Although there are two degenerate solutions that could not be distinguished for this event, both lead to a similar planet-host mass ratio. We perform a Bayesian analysis based on a Galactic model to obtain the properties of the system and find that the planet corresponds to a super-Earth/sub-Neptune with a mass $M_{mathrm{planet}} = {3.96}^{+5.88}_{-2.66}mathrm{M_oplus}$. The host star has a mass $ M_{mathrm{host}} = {0.12}^{+0.14}_{-0.08}mathrm{M_odot}$. The projected separation for the inner and outer solutions are ${0.63}^{+0.20}_{-0.17}$~AU and ${0.72}^{+0.23}_{-0.19}$~AU respectively. At $Deltachi^2=chi^2({rm 1L1S})-chi^2({rm 2L1S})=46$, this is by far the lowest $Deltachi^2$ for any securely-detected microlensing planet to date, a feature that is closely connected to the fact that it is detected primarily via a dip rather than a bump.
We present adaptive optics imaging from the NIRC2 instrument on the Keck-2 telescope that resolves the exoplanet host (and lens) star as it separates from the brighter source star. These observations yield the $K$-band brightness of the lens and planetary host star, as well as the lens-source relative proper motion, $mu_{rm rel,H}$. in the heliocentric reference frame. The $mu_{rm rel,H}$ measurement allows determination of the microlensing parallax vector, $pi_E$, which had only a single component determined by the microlensing light curve. The combined measurements of $mu_{rm rel,H}$ and $K_L$ provide the masses of the host stat, $M_{rm host} = 0.426pm 0.037 M_odot$, and planet, $m_p = 3.27 pm 0.32 M_{rm Jup}$ with a projected separation of $3.4pm 0.5,$AU. This confirms the tentative conclusion of a previous paper (Dong et al. 2009) that this super-Jupiter mass planet, OGLE-2005-BLG-071Lb, orbits an M-dwarf. Such planets are predicted to be rare by the core accretion theory and have been difficult to find with other methods, but there are two such planets with firm mass measurements from microlensing, and an additional 11 planetary microlens events with host mass estimates $< 0.5M_odot$ and planet mass estimates $> 2$ Jupiter masses that could be confirmed by high angular follow-up observations. We also point out that OGLE-2005-BLG-071L has separated far enough from its host star that it should be possible to measure the host star metallicity withspectra from a high angular resolution telescope such as Keck, the VLT, the Hubble Space Telescope or the James Webb Space Telescope.
We present Keck/NIRC2 adaptive optics imaging of planetary microlensing event MOA-2007-BLG-400 that resolves the lens star system from the source. We find that the MOA-2007-BLG-400L planetary system consists of a $1.71pm 0.27 M_{rm Jup}$ planet orbiting a $0.69pm 0.04M_{odot}$ K-dwarf host star at a distance of $6.89pm 0.77,$kpc from the Sun. So, this planetary system probably resides in the Galactic bulge. The planet-host star projected separation is only weakly constrained due to the close-wide light curve degeneracy; the 2$sigma$ projected separation range is 0.6--$7.2,$AU. This host mass is at the top end of the range of masses predicted by a standard Bayesian analysis that assumes that all stars have an equal chance of hosting a star of the observed mass ratio. This and the similar result for event MOA-2013-BLG-220 suggests that more massive stars may be more likely to host planets with a mass ratio in the $0.002 < q < 0.004$ range that orbit beyond the snow line. These results also indicate the importance of host star mass measurements for exoplanets found by microlensing. The microlensing survey imaging data from NASAs Nancy Grace Roman Space Telescope (formerly WFIRST) mission will be doing mass measurements like this for a huge number of planetary events. This host lens is the highest contrast lens-source detected in microlensing mass measurement analysis (the lens being 10$times$ fainter than the source). We present an improved method of calculating photometry and astrometry uncertainties based on the Jackknife method, which produces more accurate errors that are $sim$$2.5 times$ larger than previous estimates.
We report the discovery of a cold Super-Earth planet (m_p=4.4 +/- 0.5 M_Earth) orbiting a low-mass (M=0.23 +/- 0.03 M_Sun) M dwarf at projected separation a_perp = 1.18 +/- 0.10 AU, i.e., about 1.9 times the snow line. The system is quite nearby for a microlensing planet, D_Lens = 0.86 +/- 0.09 kpc. Indeed, it was the large lens-source relative parallax pi_rel=1.0 mas (combined with the low mass M) that gave rise to the large, and thus well-measured, microlens parallax that enabled these precise measurements. OGLE-2017-BLG-1434Lb is the eighth microlensing planet with planet-host mass ratio q < 1 * 10^-4. We apply a new planet-detection sensitivity method, which is a variant of V/V_max, to seven of these eight planets to derive the mass-ratio function in this regime. We find dN/d(ln q) ~ q^p, with p = 1.05 (+0.78,-0.68), which confirms the turnover in the mass function found by Suzuki et al. relative to the power law of opposite sign n = -0.93 +/- 0.13 at higher mass ratios q >~ 2 * 10^-4. We combine our result with that of Suzuki et al. to obtain p = 0.73 (+0.42,-0.34).
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