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Register a new userOGLE-2017-BLG-1522: A giant planet around a brown dwarf located in the Galactic bulge
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We report the discovery of a giant planet in the OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite the relatively short event timescale of $t_{rm E} sim 7.5$ days. The Einstein radius is unusually small, $theta_{rm E} = 0.065,$mas, implying that the lens system either has very low mass or lies much closer to the microlensed source than the Sun, or both. A Bayesian analysis yields component masses $(M_{rm host}, M_{rm planet})=(46_{-25}^{+79}, 0.75_{-0.40}^{+1.26})~M_{rm J}$ and source-lens distance $D_{rm LS} = 0.99_{-0.54}^{+0.91}~{rm kpc}$, implying that this is a brown-dwarf/Jupiter system that probably lies in the Galactic bulge, a location that is also consistent with the relatively low lens-source relative proper motion $mu = 3.2 pm 0.5~{rm mas}~{rm yr^{-1}}$. The projected companion-host separation is $0.59_{-0.11}^{+0.12}~{rm AU}$, indicating that the planet is placed beyond the snow line of the host, i.e., $a_{sl} sim 0.12~{rm AU}$. Planet formation scenarios combined with the small companion-host mass ratio $q sim 0.016$ and separation suggest that the companion could be the first discovery of a giant planet that formed in a protoplanetary disk around a brown dwarf host.
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We present the analysis of the binary-lens microlensing event OGLE-2013-BLG-0911. The best-fit solutions indicate the binary mass ratio of q~0.03 which differs from that reported in Shvartzvald+2016. The event suffers from the well-known close/wide degeneracy, resulting in two groups of solutions for the projected separation normalized by the Einstein radius of s~0.15 or s~7. The finite source and the parallax observations allow us to measure the lens physical parameters. The lens system is an M-dwarf orbited by a massive Jupiter companion at very close (M_{host}=0.30^{+0.08}_{-0.06} M_{Sun}, M_{comp}=10.1^{+2.9}_{-2.2} M_{Jup}, a_{exp}=0.40^{+0.05}_{-0.04} au) or wide (M_{host}=0.28^{+0.10}_{-0.08} M_{Sun}, M_{comp}=9.9^{+3.8}_{-3.5}M_{Jup}, a_{exp}=18.0^{+3.2}_{-3.2} au) separation. Although the mass ratio is slightly above the planet-brown dwarf (BD) mass-ratio boundary of q=0.03 which is generally used, the median physical mass of the companion is slightly below the planet-BD mass boundary of 13M_{Jup}. It is likely that the formation mechanisms for BDs and planets are different and the objects near the boundaries could have been formed by either mechanism. It is important to probe the distribution of such companions with masses of ~13M_{Jup} in order to statistically constrain the formation theories for both BDs and massive planets. In particular, the microlensing method is able to probe the distribution around low-mass M-dwarfs and even BDs which is challenging for other exoplanet detection methods.
We report the discovery of an exoplanet in microlensing event OGLE-2015-BLG-1649. The planet/host-star mass ratio is $q =7.2 times 10^{-3}$ and the projected separation normalized by the Einstein radius is $s = 0.9$. The upper limit of the lens flux is obtained from adaptive optics observations by IRCS/Subaru, which excludes the probability of a G-dwarf or more massive host star and helps to put a tighter constraint on the lens mass as well as commenting on the formation scenarios of giant planets orbiting low-mass stars. We conduct a Bayesian analysis including constraints on the lens flux to derive the probability distribution of the physical parameters of the lens system. We thereby find that the masses of the host star and planet are $M_{L} = 0.34 pm 0.19 M_{odot}$ and $M_{p} = 2.5^{+1.5}_{-1.4} M_{Jup}$, respectively. The distance to the system is $D_{L} = 4.23^{+1.51}_{-1.64}$kpc. The projected star-planet separation is $a_{perp} = 2.07^{+0.65}_{-0.77}$AU. The lens-source relative proper motion of the event is quite high, at $sim 7.1 , {rm mas/yr}$. Therefore, we may be able to determine the lens physical parameters uniquely or place much stronger constraints on them by measuring the color-dependent centroid shift and/or the image elongation with additional high resolution imaging already a few years from now.
We report a giant exoplanet discovery in the microlensing event OGLE-2017-BLG-1049, which is a planet-host star mass ratio of $q=9.53pm0.39times10^{-3}$ and has a caustic crossing feature in the Korea Microlensing Telescope Network (KMTNet) observations. The caustic crossing feature yields an angular Einstein radius of $theta_{rm E}=0.52 pm 0.11 {rm mas}$. However, the microlens parallax is not measured because of the time scale of the event $t_{rm E}simeq 29 {rm days}$, which is not long enough in this case to determine the microlens parallax. Thus, we perform a Bayesian analysis to estimate physical quantities of the lens system. From this, we find that the lens system has a star with mass $M_{rm h}=0.55^{+0.36}_{-0.29} M_{odot}$ hosting a giant planet with $M_{rm p}=5.53^{+3.62}_{-2.87} M_{rm Jup}$, at a distance of $D_{rm L}=5.67^{+1.11}_{-1.52} {rm kpc}$. The projected star-planet separation in units of the Einstein radius $(theta_{rm E})$ corresponding to the total mass of the lens system is $a_{perp}=3.92^{+1.10}_{-1.32} rm{au}$. This means that the planet is located beyond the snow line of the host. The relative lens-source proper motion is $mu_{rm rel}sim 7 rm{mas yr^{-1}}$, thus the lens and source will be separated from each other within 10 years. Then the flux of the host star can be measured by a 30m class telescope with high-resolution imaging in the future, and thus its mass can be determined.
We report the discovery of OGLE-2016-BLG-1190Lb, which is likely to be the first Spitzer microlensing planet in the Galactic bulge/bar, an assignation that can be confirmed by two epochs of high-resolution imaging of the combined source-lens baseline object. The planets mass M_p= 13.4+-0.9 M_J places it right at the deuterium burning limit, i.e., the conventional boundary between planets and brown dwarfs. Its existence raises the question of whether such objects are really planets (formed within the disks of their hosts) or failed stars (low mass objects formed by gas fragmentation). This question may ultimately be addressed by comparing disk and bulge/bar planets, which is a goal of the Spitzer microlens program. The host is a G dwarf M_host = 0.89+-0.07 M_sun and the planet has a semi-major axis a~2.0 AU. We use Kepler K2 Campaign 9 microlensing data to break the lens-mass degeneracy that generically impacts parallax solutions from Earth-Spitzer observations alone, which is the first successful application of this approach. The microlensing data, derived primarily from near-continuous, ultra-dense survey observations from OGLE, MOA, and three KMTNet telescopes, contain more orbital information than for any previous microlensing planet, but not quite enough to accurately specify the full orbit. However, these data do permit the first rigorous test of microlensing orbital-motion measurements, which are typically derived from data taken over <1% of an orbital period.
We present the analysis of microlensing event OGLE-2006-BLG-284, which has a lens system that consists of two stars and a gas giant planet with a mass ratio of $q_p = (1.26pm 0.19) times 10^{-3}$ to the primary. The mass ratio of the two stars is $q_s = 0.289pm 0.011$, and their projected separation is $s_s = 2.1pm 0.7,$AU, while the projected separation of the planet from the primary is $s_p = 2.2pm 0.8,$AU. For this lens system to have stable orbits, the three-dimensional separation of either the primary and secondary stars or the planet and primary star must be much larger than that these projected separations. Since we do not know which is the case, the system could include either a circumbinary or a circumstellar planet. Because there is no measurement of the microlensing parallax effect or lens system brightness, we can only make a rough Bayesian estimate of the lens system masses and brightness. We find host star and planet masses of $M_{L1} = 0.35^{+0.30}_{-0.20},M_odot$, $M_{L2} = 0.10^{+0.09}_{-0.06},M_odot$, and $m_p = 144^{+126}_{-82},M_oplus$, and the $K$-band magnitude of the combined brightness of the host stars is $K_L = 19.7^{+0.7}_{-1.0}$. The separation between the lens and source system will be $sim 90,$mas in mid-2020, so it should be possible to detect the host system with follow-up adaptive optics or Hubble Space Telescope observations.
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