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Register a new userDiscovery of a bright microlensing event with planetary features towards the Taurus region: a super Earth planet
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The transient event labeled as TCP J05074264+2447555 recently discovered towards the Taurus region was quickly recognized to be an ongoing microlensing event on a source located at distance of only $700-800$ pc from Earth. Here, we show that observations with high sampling rate close to the time of maximum magnification revealed features that imply the presence of a binary lens system with very low mass ratio components. We present a complete description of the binary lens system which hosts an Earth-like planet with most likely mass of $9.2pm 6.6$ M$_{oplus}$. Furthermore, the source estimated location and detailed Monte Carlo simulations allowed us to classify the event as due to the closest lens system, being at a distance of $simeq 380$ pc and mass $simeq 0.25$ M$_{odot}$.
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We present the analysis of the planetary microlensing event OGLE-2014-BLG-1760, which shows a strong light curve signal due to the presence of a Jupiter mass-ratio planet. One unusual feature of this event is that the source star is quite blue, with $V-I = 1.48pm 0.08$. This is marginally consistent with source star in the Galactic bulge, but it could possibly indicate a young source star in the far side of the disk. Assuming a bulge source, we perform a Bayesian analysis assuming a standard Galactic model, and this indicates that the planetary system resides in or near the Galactic bulge at $D_L = 6.9 pm 1.1 $ kpc. It also indicates a host star mass of $M_* = 0.51 pm 0.44 M_odot$, a planet mass of $m_p = 180 pm 110 M_oplus$, and a projected star-planet separation of $a_perp = 1.7pm 0.3,$AU. The lens-source relative proper motion is $mu_{rm rel} = 6.5pm 1.1$ mas/yr. The lens (and stellar host star) is predicted to be very faint, so it is most likely that it can detected only when the lens and source stars are partially resolved. Due to the relatively high relative proper motion, the lens and source will be resolved to about $sim46,$mas in 6-8 years after the peak magnification. So, by 2020 - 2022, we can hope to detect the lens star with deep, high resolution images.
We aim to find missing microlensing planets hidden in the unanalyzed lensing events of previous survey data. For this purpose, we conduct a systematic inspection of high-magnification microlensing events, with peak magnifications $A_{rm peak}gtrsim 30$, in the data collected from high-cadence surveys in and before the 2018 season. From this investigation, we identify an anomaly in the lensing light curve of the event KMT-2018-BLG-1025. The analysis of the light curve indicates that the anomaly is caused by a very low mass-ratio companion to the lens. We identify three degenerate solutions, in which the ambiguity between a pair of solutions (solutions B) is caused by the previously known close--wide degeneracy, and the degeneracy between these and the other solution (solution A) is a new type that has not been reported before. The estimated mass ratio between the planet and host is $qsim 0.8times 10^{-4}$ for the solution A and $qsim 1.6times 10^{-4}$ for the solutions B. From the Bayesian analysis conducted with measured observables, we estimate that the masses of the planet and host and the distance to the lens are $(M_{rm p}, M_{rm h}, D_{rm L})sim (6.1~M_oplus, 0.22~M_odot, 6.7~{rm kpc})$ for the solution A and $sim (4.4~M_oplus, 0.08~M_odot, 7.5~{rm kpc})$ for the solutions B. The planet mass is in the category of a super-Earth regardless of the solutions, making the planet the eleventh super-Earth planet, with masses lying between those of Earth and the Solar systems ice giants, discovered by microlensing.
We report the first planet discovery from the two-wheeled Kepler (K2) mission: HIP 116454 b. The host star HIP 116454 is a bright (V = 10.1, K = 8.0) K1-dwarf with high proper motion, and a parallax-based distance of 55.2 +/- 5.4 pc. Based on high-resolution optical spectroscopy, we find that the host star is metal-poor with [Fe/H] = -.16 +/- .18, and has a radius R = 0.716 +/- .0024 R_sun and mass M = .775 +/- .027 Msun. The star was observed by the Kepler spacecraft during its Two-Wheeled Concept Engineering Test in February 2014. During the 9 days of observations, K2 observed a single transit event. Using a new K2 photometric analysis technique we are able to correct small telescope drifts and recover the observed transit at high confidence, corresponding to a planetary radius of Rp = 2.53 +/- 0.18 Rearth. Radial velocity observations with the HARPS-N spectrograph reveal a 11.82 +/- 1.33 Mearth planet in a 9.1 day orbit, consistent with the transit depth, duration, and ephemeris. Follow-up photometric measurements from the MOST satellite confirm the transit observed in the K2 photometry and provide a refined ephemeris, making HIP 116454 b amenable for future follow-up observations of this latest addition to the growing population of transiting super-Earths around nearby, bright stars.
KMT-2016-BLG-2605, with planet-host mass ratio $q=0.012pm 0.001$, has the shortest Einstein timescale, $t_e = 3.41pm 0.13,$days, of any planetary microlensing event to date. This prompts us to examine the full sample of 7 short ($t_e<7,$day) planetary events with good $q$ measurements. We find that six have clustered Einstein radii $theta_e = 115pm 20,muas$ and lens-source relative proper motions $mu_relsimeq 9.5pm 2.5,masyr$. For the seventh, these two quantities could not be measured. These distributions are consistent with a Galactic-bulge population of very low-mass (VLM) hosts near the hydrogen-burning limit. This conjecture could be verified by imaging at first adaptive-optics light on next-generation (30m) telescopes. Based on a preliminary assessment of the sample, planetary companions (i.e., below the deuterium-burning limit) are divided into genuine planets, formed in their disks by core accretion, and very low-mass brown dwarfs, which form like stars. We discuss techniques for expanding the sample, which include taking account of the peculiar anomaly dominated morphology of the KMT-2016-BLG-2605 light curve.
We present the bright (V$_{mag} = 9.12$), multi-planet system TOI-431, characterised with photometry and radial velocities. We estimate the stellar rotation period to be $30.5 pm 0.7$ days using archival photometry and radial velocities. TOI-431b is a super-Earth with a period of 0.49 days, a radius of 1.28 $pm$ 0.04 R$_{oplus}$, a mass of $3.07 pm 0.35$ M$_{oplus}$, and a density of $8.0 pm 1.0$ g cm$^{-3}$; TOI-431d is a sub-Neptune with a period of 12.46 days, a radius of $3.29 pm 0.09$ R$_{oplus}$, a mass of $9.90^{+1.53}_{-1.49}$ M$_{oplus}$, and a density of $1.36 pm 0.25$ g cm$^{-3}$. We find a third planet, TOI-431c, in the HARPS radial velocity data, but it is not seen to transit in the TESS light curves. It has an $M sin i$ of $2.83^{+0.41}_{-0.34}$ M$_{oplus}$, and a period of 4.85 days. TOI-431d likely has an extended atmosphere and is one of the most well-suited TESS discoveries for atmospheric characterisation, while the super-Earth TOI-431b may be a stripped core. These planets straddle the radius gap, presenting an interesting case-study for atmospheric evolution, and TOI-431b is a prime TESS discovery for the study of rocky planet phase curves.
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