Adaptive Optics Imaging Breaks the Central Caustic Cusp Approach Degeneracy in High Magnification Microlensing Events

We report new results for the gravitational microlensing target OGLE-2011-BLG-0950 from adaptive optics (AO) images using the Keck observatory. The original analysis by Choi et al. 2012 reports degenerate solutions between planetary and stellar binary lens systems. This is due to a degeneracy in high magnification events where the shape of the light curve peak can be explained by a source approach to two different cusp geometries with different source radius crossing times. This particular case is the most important type of degeneracy for exoplanet demographics, because the distinction between a planetary mass or stellar binary companion has direct consequences for microlensing exoplanet statistics. The 8 and 10-year baselines between the event and the Keck observations allow us to directly measure a relative proper motion of $4.20\pm 0.21\,$mas/yr, which confirms the detection of the lens star system and directly rules out the planetary companion models that predict a ${\sim}4 \times$ smaller relative proper motion. The combination of the lens brightness and close stellar binary light curve parameters yield primary and secondary star masses of $M_{A} = 1.12^{+0.06}_{-0.04}M_\odot$ and $M_{B} = 0.47^{+0.04}_{-0.03}M_\odot$ at a distance of $D_L = 6.70^{+0.55}_{-0.30}\,$kpc, and a primary-secondary projected separation of $0.39^{+0.05}_{-0.04}\,$AU. Since this degeneracy is likely to be common, the high resolution imaging method described here will be used to disentangle the central caustic cusp approach degeneracy for events observed by the \textit{Roman} exoplanet microlensing survey using the \textit{Roman} images taken near the beginning or end of the survey.Comment: Revised version, 19 pages, 8 figures. AJ, 164, 21

ARES: VI. Viability of one-dimensional retrieval models for transmission spectroscopy characterization of exo-atmospheres in the era of JWST and Ariel

Observed exoplanet transit spectra are usually retrieved using 1D models to determine atmospheric composition. However, planetary atmospheres are 3D. With the new state-of-the-art James Webb Space Telescope (JWST) and future space telescopes such as Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large-survey), we will be able to obtain increasingly accurate transit spectra. The 3D effects on the spectra will be visible, and we can expect biases in the 1D extractions. In order to elucidate these biases, we have built theoretical observations of transit spectra, from 3D atmospheric modeling through transit modeling to instrument modeling. For this purpose, we used a global climate model (GCM) to simulate the atmosphere, a 3D radiative transfer model to calculate theoretical transmission spectra, and adapted instrument software from JWST and Ariel to reproduce telescope noise. Next, we used a 1D radiative transfer inversion model to retrieve the known input atmosphere and disentangle any biases that might be observed. The study was done from warm planets to ultra-hot planets to assess biases as a function of average planet temperature. Three-dimensional effects are observed to be strongly nonlinear from the coldest to the hottest planets. These effects also depend on the planet’s metallicity and gravity. Considering equilibrium chemistry, 3D effects are observed through very strong variations in certain features of the molecule or very small variations over the whole spectrum. We conclude that we cannot rely on the uncertainty of retrievals at all pressures, and that we must be cautious about the results of retrievals at the top of the atmosphere. However the results are still fairly close to the truth at mid-altitudes (those probed). We also need to be careful with the chemical models used for planetary atmosphere. If the chemistry of one molecule is not correctly described, this will bias all the others, and the retrieved temperature as well. Finally, although fitting a wider wavelength range and higher resolution has been shown to increase retrieval accuracy, we show that this could depend on the wavelength range chosen, due to the accuracy on modeling the different features. In any case, 1D retrievals are still correct for the detection of molecules, even in the event of an erroneous abundance retrieval

ARES VI: Are 1D retrieval models accurate enough to characterize exo-atmospheres with transmission spectroscopy in the era of JWST and Ariel?

International audienceThe observed exoplanets transit spectra are usually retrieved using one-dimensional models to determine atmospheric composition. However, planetary atmospheres are three-dimensional. With the new state-of-the-art James Webb Space Telescope (JWST) and future space telescopes such as Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large-survey), we will be able to obtain increasingly accurate transit spectra. The 3D effects on the spectra will be visible, and we can expect biases in the 1D extractions. In order to elucidate these biases, we have built theoretical observations of transit spectra, from 3D atmospheric modeling through transit modeling to instrument modeling. For that purpose, we used a Global Climate Model (GCM) to simulate the atmosphere, a 3D-radiative transfer model to calculate theoretical transmission spectra, and adapted instrument software from JWST and Ariel to reproduce telescope noise. Next, we used a 1D-radiative transfer inversion model to retrieve the known input atmosphere and disentangle any biases that might be observed. The study has been done from warm planets to ultra-hot planets to assess biases as a function of average planet temperature. Three-dimensional effects are observed to be strongly non-linear from the coldest to the hottest planets. These effects also depend on the planet's metallicity and gravity. Considering equilibrium chemistry, 3D effects are observed through very strong variations for certain features of the molecule, or very small variations over the whole spectrum. We conclude that we cannot rely on the uncertainty of retrievals at all pressures, and that we must be cautious about the results of retrievals at the top of the atmosphere. However the results are still fairly close to the truth at mid altitudes (those probed). We also need to be careful about the chemical models used for planetary atmosphere. If the chemistry of one molecule is not correctly described, this will bias all the others, as well as the retrieved temperature. Finally, although fitting a wider wavelength range and higher resolution has been shown to increase retrievals accuracy, we show that this could depend on the wavelength range chosen, due to the accuracy on modeling the different features. In any case, 1D retrievals are still correct for the detection of molecules, even in the event of an erroneous abundance retrieval

Precise Mass Measurement of OGLE-2013-BLG-0132/MOA-2013-BLG-148: A Saturn-mass Planet Orbiting an M Dwarf

We revisit the planetary microlensing event OGLE-2013-BLG-0132/MOA-2013-BLG-148 using Keck adaptive optics imaging in 2013 with NIRC2 and in 2020, 7.4 yr after the event, with OSIRIS. The 2020 observations yield a source and lens separation of 56.91 ± 0.29 mas, which provides us with a precise measurement of the heliocentric proper motion of the event μ _rel,hel = 7.695 ± 0.039 mas yr ^−1 . We measured the magnitude of the lens in the K band as K _lens = 18.69 ± 0.04. Using these constraints, we refit the microlensing light curve and undertake a full reanalysis of the event parameters including the microlensing parallax π _E and the distance to the source D _S . We confirm the results obtained in the initial study by Mróz et al. and improve significantly upon the accuracy of the physical parameters. The system is an M dwarf of 0.495 ± 0.054 M _⊙ orbited by a cold, Saturn-mass planet of 0.26 ± 0.028 M _Jup at projected separation r _⊥ = 3.14 ± 0.28 au. This work confirms that the planetary system is at a distance of 3.48 ± 0.36 kpc, which places it in the Galactic disk and not the Galactic bulge