Search for: All records

We report the analysis of a planetary microlensing event AT2021uey. The event was observed outside the Galactic bulge and alerted both space-(Gaia) and ground-based (ZTF and ASAS-SN) surveys. From the observed data, we find that the lens system is located at a distance of ∼1 kpc and comprises an M-dwarf host star of about half a solar mass, orbited by a Jupiter-like planet beyond the snowline. The source star could be a metal-poor giant located in the halo according to the spectral analyses and modelling. Hence, AT2021uey is a unique example of the binary-lens event outside the bulge that is offered by a disc-halo lens-source combination. 

During the last 25 yr, hundreds of binary stars and planets have been discovered toward the Galactic bulge by microlensing surveys. Thanks to a new generation of large-sky surveys, it is now possible to regularly detect microlensing events across the entire sky. The OMEGA Key Projet at the Las Cumbres Observatory carries out automated follow-up observations of microlensing events alerted by these surveys with the aim of identifying and characterizing exoplanets as well as stellar remnants. In this study, we present the analysis of the binary lens event Gaia20bof. By automatically requesting additional observations, the OMEGA Key Project obtained dense time coverage of an anomaly near the peak of the event, allowing characterization of the lensing system. The observed anomaly in the lightcurve is due to a binary lens. However, several models can explain the observations. Spectroscopic observations indicate that the source is located at ≤2.0 kpc, in agreement with the parallax measurements from Gaia. While the models are currently degenerate, future observations, especially the Gaia astrometric time series as well as high-resolution imaging, will provide extra constraints to distinguish between them. 

Context. Gravitational microlensing is a method that is used to discover planet-hosting systems at distances of several kiloparsec in the Galactic disk and bulge. We present the analysis of a microlensing event reported by the Gaia photometric alert team that might have a bright lens. Aims: In order to infer the mass and distance to the lensing system, the parallax measurement at the position of Gaia21blx was used. In this particular case, the source and the lens have comparable magnitudes and we cannot attribute the parallax measured by Gaia to the lens or source alone. Methods: Since the blending flux is important, we assumed that the Gaia parallax is the flux-weighted average of the parallaxes of the lens and source. Combining this assumption with the information from the microlensing models and the finite source effects we were able to resolve all degeneracies and thus obtained the mass, distance, luminosities and projected kinematics of the binary lens and the source. Results: According to the best model, the lens is a binary system at 2.18 ± 0.07 kpc from Earth. It is composed of a G star with 0.95 ± 0.17 M⊙ and a K star with 0.53 ± 0.07 M⊙. The source is likely to be an F subgiant star at 2.38 ± 1.71 kpc with a mass of 1.10 ± 0.18 M⊙. Both lenses and the source follow the kinematics of the thin-disk population. We also discuss alternative models, that are disfavored by the data or by prior expectations, however. 

We report discovering an exoplanet from following up a microlensing event alerted by Gaia. The event Gaia22dkv is toward a disk source rather than the traditional bulge microlensing fields. Our primary analysis yields a Jovian planet with at a projected orbital separation au, and the host is a ∼1.1 M ⊙ turnoff star at ∼1.3 kpc. At , the host is far brighter than any previously discovered microlensing planet host, opening up the opportunity to test the microlensing model with radial velocity (RV) observations. RV data can be used to measure the planet's orbital period and eccentricity, and they also enable searching for inner planets of the microlensing cold Jupiter, as expected from the "inner–outer correlation" inferred from Kepler and RV discoveries. Furthermore, we show that Gaia astrometric microlensing will not only allow precise measurements of its angular Einstein radius θ E but also directly measure the microlens parallax vector and unambiguously break a geometric light-curve degeneracy, leading to the definitive characterization of the lens system. 

Abstract We report discovering an exoplanet from following up a microlensing event alerted by Gaia. The event Gaia22dkv is toward a disk source rather than the traditional bulge microlensing fields. Our primary analysis yields a Jovian planet with $M_{\mathrm{p}}={0.59}_{-0.05}^{+0.15}{M}_{\mathrm{J}}$at a projected orbital separation $r_{\perp }={1.4}_{-0.3}^{+0.8}$au, and the host is a ∼1.1M_⊙turnoff star at ∼1.3 kpc. At $r\prime \approx 14$, the host is far brighter than any previously discovered microlensing planet host, opening up the opportunity to test the microlensing model with radial velocity (RV) observations. RV data can be used to measure the planet’s orbital period and eccentricity, and they also enable searching for inner planets of the microlensing cold Jupiter, as expected from the “inner–outer correlation” inferred from Kepler and RV discoveries. Furthermore, we show that Gaia astrometric microlensing will not only allow precise measurements of its angular Einstein radiusθ_Ebut also directly measure the microlens parallax vector and unambiguously break a geometric light-curve degeneracy, leading to the definitive characterization of the lens system. 

As the Kepler mission has done for hot exoplanets, the ESA Euclid and NASA Roman missions have the potential to create a breakthrough in our understanding of the demographics of cool exoplanets, including unbound, or free-floating, planets (FFPs). Roman will dedicate part of its core survey program to the detection of cool exoplanets via microlensing, while Euclid may undertake a microlensing program as an ancillary science goal. In this study, we demonstrate the complementarity of the two missions and propose two joint surveys to better constrain the mass and distance of microlensing events. We first demonstrate that an early brief Euclid survey (~7 h) of the Roman microlensing fields will allow the measurement of at least 30% of the events’ relative proper motions µ rel and 42% of the lens magnitudes. This survey would place strong constraints on the mass and distance on thousands of microlensing events observed by Roman just after the first year of observation. Then, we study the potential of simultaneous observations by Roman and Euclid to enable the measurement of the microlensing parallax for the shortest microlensing events and, ultimately, obtain a direct measurement of the masses, distances, and transverse motions of FFPs. Using detailed simulations of the joint detection yield we show that within one year Roman-Euclid observations will be at least an order of magnitude more sensitive than current ground-based measurements. The recent tentative detection of an excess of short-duration events by the OGLE survey is consistent with a scenario of up to ten Earth-mass FFPs per Galactic star. For such a scenario a joint Roman-Euclid campaign should detect around 130 FFP events within a year, including 110 with measured parallax that strongly constrain the FFP mass, and around 30 FFP events with direct mass and distance measurements. The ability of the joint survey to completely break the microlens mass-distance-velocity degeneracy for a significant subset of events provides a unique opportunity to verify unambiguously the FFP hypothesis or else place abundance limits for FFPs between Earth and Jupiter masses that are up to two orders of magnitude stronger than provided by ground-based surveys. Finally, we study the capabilities of the joint survey to enhance the detection and characterization of exomoons, and find that it could lead to the detection of the first exomoon. 

We present the discovery and validation of two TESS exoplanets orbiting nearby M dwarfs: TOI-2084 b, and TOI-4184b. We characterized the host stars by combining spectra fromShane/Kast andMagellan/FIRE, spectral energy distribution analysis, and stellar evolutionary models. In addition, we used Gemini-South/Zorro & -North/Alopeke high-resolution imaging, archival science images, and statistical validation packages to support the planetary interpretation. We performed a global analysis of multi-colour photometric data from TESS and ground-based facilities in order to derive the stellar and planetary physical parameters for each system. We find that TOI-2084 band TOI-4184 bare sub-Neptune-sized planets with radii ofR_p= 2.47 ± 0.13R_⊕andR_p= 2.43 ± 0.21R_⊕, respectively. TOI-2084 b completes an orbit around its host star every 6.08 days, has an equilibrium temperature ofT_eq= 527 ± 8 K and an irradiation ofS_p= 12.8 ± 0.8S_⊕. Its host star is a dwarf of spectral M2.0 ± 0.5 at a distance of 114 pc with an effective temperature ofT_eff= 3550 ± 50 K, and has a wide, co-moving M8 companion at a projected separation of 1400 au. TOI-4184 b orbits around an M5.0 ± 0.5 type dwarf star (K_mag= 11.87) each 4.9 days, and has an equilibrium temperature ofT_eq= 412 ± 8 K and an irradiation ofS_p= 4.8 ± 0.4S_⊕. TOI-4184 is a metal poor star ([Fe/H] = −0.27 ± 0.09 dex) at a distance of 69 pc with an effective temperature ofT_eff= 3225 ± 75 K. Both planets are located at the edge of the sub-Jovian desert in the radius-period plane. The combination of the small size and the large infrared brightness of their host stars make these new planets promising targets for future atmospheric exploration with JWST.