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Abstract KMT-2018-BLG-0029Lb and OGLE-2019-BLG-0960Lb were the lowest mass-ratio microlensing planets at the time of discovery. For both events, microlensing parallax measurements from the Spitzer Space Telescope implied lens systems that were more distant and massive than those inferred from the ground-based parallax. Here, we report on the detection of excess flux aligned to the event locations using Keck Adaptive Optics imaging, which is consistent with the expected brightness of main-sequence hosts under the ground-based parallax, but inconsistent with that predicted by Spitzer. Based on the excess flux, ground-based parallax, and angular Einstein radius, we determine KMT-2018-BLG-0029Lb to be a 4.2 ± 0.5M_⊕planet orbiting a 0.70 ± 0.07M_⊙host at a projected separation of 3.1 ± 0.3 au, and OGLE-2019-BLG-0960Lb to be a 2.0 ± 0.2M_⊕planet orbiting a 0.40 ± 0.03M_⊙host at a projected separation of 1.7 ± 0.1 au. We report on additional light-curve models for KMT-2018-BLG-0029 under the generalized inner-outer (offset) degeneracy, which were not reported in the original analysis. We point out inconsistencies in the inner/outer labeling of the degenerate models in the lens and source planes, and advocate for the lens-plane convention, which refers to the planet being closer or further to the host star compared to the image it perturbs. Lastly, we discuss the possibility of breaking this degeneracy via ground concurrent observations with the Roman Space Telescope. 

ABSTRACT We identify the progenitor star of SN 2023ixf in Messier 101 using Keck/NIRC2 adaptive optics imaging and pre-explosion Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) images. The supernova, localized with diffraction spikes and high-precision astrometry, unambiguously coincides with a progenitor candidate of $$m_\text{F814W}=24.87\pm 0.05$$ (AB). Given its reported infrared excess and semiregular variability, we fit a time-dependent spectral energy distribution (SED) model of a dusty red supergiant (RSG) to a combined data set of HST optical, ground-based near-infrared, and Spitzer Infrared Array Camera (IRAC) [3.6], [4.5] photometry. The progenitor resembles an RSG of $$T_\text{eff}=3488\pm 39$$ K and $$\log (L/\mathrm{L}_\odot)=5.15\pm 0.02$$, with a $$0.13\pm 0.01$$ dex ($$31.1\pm 1.7$$ per cent) luminosity variation at a period of $$P=1144.7\pm 4.8$$ d, obscured by a dusty envelope of $$\tau =2.92\pm 0.02$$ at $$1\, \mu \text{m}$$ in optical depth (or $$A_\text{V}=8.43\pm 0.11$$ mag). The signatures match a post-main-sequence star of $$18.2_{-0.6}^{+1.3}\, \mathrm{M}_\odot$$ in zero-age main-sequence mass, among the most massive SN II progenitor, with a pulsation-enhanced mass-loss rate of $$\dot{M}=(4.32\pm 0.26)\times 10^{-4} \, \mathrm{M}_\odot \, \text{yr}^{-1}$$. The dense and confined circumstellar material is ejected during the last episode of radial pulsation before the explosion. Notably, we find strong evidence for variations of $$\tau$$ or $$T_\text{eff}$$ along with luminosity, a necessary assumption to reproduce the wavelength-dependent variability, which implies periodic dust sublimation and condensation. Given the observed SED, partial dust obscuration remains possible, but any unobstructed binary companion over $$5.6\, \mathrm{ M}_\odot$$ can be ruled out. 

Abstract The offset microlensing degeneracy, recently proposed by Zhang et al., has been shown to generalize the close–wide and inner–outercausticdegeneracies into a unified regime ofmagnificationdegeneracy in the interpretation of two-body planetary microlensing observations. While the inner–outer degeneracy expects the source trajectory to pass equidistant to the planetary caustics of the degenerate lens configurations, the offset degeneracy states that the same mathematical expression applies to any combination of the close, wide, and resonant caustic topologies, where the projected star–planet separations differ by an offset (s_A≠s_B) that depends on where the source trajectory crosses the lens axis. An important implication is that thes_A= 1/s_Bsolution of the close–wide degeneracy never strictly manifests in observations except when the source crosses a singular point near the primary. Nevertheless, the offset degeneracy was proposed upon numerical calculations, and no theoretical justification was given. Here, we provide a theoretical treatment of the offset degeneracy, which demonstrates its nature as a mathematical degeneracy. From first principles, we show that the offset degeneracy formalism is exact to zeroth order in the mass ratio (q) for two cases: when the source crosses the lens axis inside of caustics, and for ${(s_{\mathrm{A}}-s_{\mathrm{B}})}^6\ll 1$when crossing outside of caustics. The extent to which the offset degeneracy persists in oblique source trajectories is explored numerically. Finally, it is shown that the superposition principle allows for a straightforward generalization toN-body microlenses withN− 1 planetary lens components (q≪ 1), which results in a 2^N−1-fold degeneracy. 

Precise and accurate mass and radius measurements of evolved stars are crucial to calibrating stellar models. Stars in detached eclipsing binaries (EBs) are excellent potential calibrators because their stellar parameters can be measured with fractional uncertainties of a few percent, independent of stellar models. The All-Sky Automated Survey for Supernovae (ASAS-SN) has identified tens of thousands of EBs, >35,000 of which were included in the ASAS-SN eclipsing binaries catalog. Here, we select eight EBs from this sample that contain giants based on their Gaia colors and absolute magnitudes. We use LBT/PEPSI, APF, and CHIRON to obtain multi-epoch spectra of these binaries and measure their radial velocities using two-dimensional cross-correlation methods. We simultaneously fit the ASAS-SN light curves and the radial velocities with PHOEBE to derive accurate and precise masses and radii with fractional uncertainties of $\lesssim 3\%$. For four systems, we also include Transiting Exoplanet Survey Satellite (TESS) light curves in our PHOEBE models, which significantly improves the radius determinations. In seven of our systems, both components have evolved off of the main sequence, and one system has a giant star component with a main sequence, Sun-like companion. Finally, we compare our mass and radius measurements to single-star evolutionary tracks and distinguish between systems that are first ascent red giant branch stars and those that are likely core helium-burning stars.