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1. Vortex Fiber Nulling for Exoplanet Observations: First Direct Detection of M Dwarf Companions around HIP 21543, HIP 94666, and HIP 50319

   https://doi.org/10.3847/2041-8213/ad3619  

   Echeverri, Daniel; Xuan, Jerry W; Monnier, John D; Delorme, Jacques-Robert; Wang, Jason J; Jovanovic, Nemanja; Horstman, Katelyn; Ruane, Garreth; Mennesson, Bertrand; Serabyn, Eugene; et al (April 2024, The Astrophysical Journal Letters)

   Abstract Vortex fiber nulling (VFN) is a technique for detecting and characterizing faint companions at small separations from their host star. A near-infrared (∼2.3μm) VFN demonstrator mode was deployed on the Keck Planet Imager and Characterizer (KPIC) instrument at the Keck Observatory and presented earlier. In this Letter, we present the first VFN companion detections. Three targets, HIP 21543 Ab, HIP 94666 Ab, and HIP 50319 B, were detected with host–companion flux ratios between 70 and 430 at and within one diffraction beamwidth (λ/D). We complement the spectra from KPIC VFN with flux ratio and position measurements from the CHARA Array to validate the VFN results and provide a more complete characterization of the targets. This Letter reports the first direct detection of these three M dwarf companions, yielding their first spectra and flux ratios. Our observations provide measurements of bulk properties such as effective temperatures, radial velocities, and $v\sin i$, and verify the accuracy of the published orbits. These detections corroborate earlier predictions of the KPIC VFN performance, demonstrating that the instrument mode is ready for science observations. 

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2. TESS Observations of Kepler Systems with Transit Timing Variations

   https://doi.org/10.3847/1538-3881/ac7396  

   Jontof-Hutter, Daniel; Dalba, Paul A.; Livingston, John H. (July 2022, The Astronomical Journal)

   Abstract We identify targets in the Kepler field that may be characterized by transit timing variations and are detectable by the Transiting Exoplanet Survey Satellite (TESS). Despite the reduced signal-to-noise ratio of TESS transits compared to Kepler, we recover 48 transits from 13 systems in Sectors 14, 15, 26, 40 and 41. We find strong evidence of a nontransiting perturber orbiting Kepler-396 (KOI-2672) and explore two possible cases of a third planet in that system that could explain the measured transit times. We update the ephemerides and mass constraints where possible at KOI-70 (Kepler-20), KOI-82 (Kepler-102), KOI-94 (Kepler-89), KOI-137 (Kepler-18), KOI-244 (Kepler-25), KOI-245 (Kepler-37), KOI-282 (Kepler-130), KOI-377 (Kepler-9), KOI-620 (Kepler-51), KOI-806 (Kepler-30), KOI-1353 (Kepler-289), and KOI-1783 (Kepler-1662). 

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3. First VLTI/GRAVITY Observations of HIP 65426 b: Evidence for a Low or Moderate Orbital Eccentricity

   https://doi.org/10.3847/1538-3881/ad06b7  

   Blunt, Sarah; Balmer, W O; Wang, J J; Lacour, S; Petrus, S; Bourdarot, G; Kammerer, J; Pourré, N; Rickman, E; Shangguan, J; et al (November 2023, The Astronomical Journal)

   Abstract Giant exoplanets have been directly imaged over orders of magnitude of orbital separations, prompting theoretical and observational investigations of their formation pathways. In this paper, we present new VLTI/GRAVITY astrometric data of HIP 65426 b, a cold, giant exoplanet which is a particular challenge for most formation theories at a projected separation of 92 au from its primary. Leveraging GRAVITY’s astrometric precision, we present an updated eccentricity posterior that disfavors large eccentricities. The eccentricity posterior is still prior dependent, and we extensively interpret and discuss the limits of the posterior constraints presented here. We also perform updated spectral comparisons with self-consistent forward-modeled spectra, finding a best-fitExoREMmodel with solar metallicity and C/O = 0.6. An important caveat is that it is difficult to estimate robust errors on these values, which are subject to interpolation errors as well as potentially missing model physics. Taken together, the orbital and atmospheric constraints paint a preliminary picture of formation inconsistent with scattering after disk dispersal. Further work is needed to validate this interpretation. Analysis code used to perform this work is available on GitHub:https://github.com/sblunt/hip65426. 

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4. Seasonal Tropospheric Distribution and Air‐Sea Fluxes of Atmospheric Potential Oxygen From Global Airborne Observations

   https://doi.org/10.1029/2023GB007827  

   Jin, Yuming; Stephens, Britton B.; Keeling, Ralph F.; Morgan, Eric J.; Rödenbeck, Christian; Patra, Prabir K.; Long, Matthew C. (October 2023, Global Biogeochemical Cycles)

   Abstract Seasonal change of atmospheric potential oxygen (APO ∼ O₂ + CO₂) is a tracer for air‐sea O₂flux with little sensitivity to the terrestrial exchange of O₂and CO₂. In this study, we present the tropospheric distribution and inventory of APO in each hemisphere with seasonal resolution, using O₂and CO₂measurements from discrete airborne campaigns between 2009 and 2018. The airborne data are represented on a mass‐weighted isentropic coordinate (M_θe) as an alternative to latitude, which reduces the noise from synoptic variability in the APO cycles. We find a larger seasonal amplitude of APO inventory in the Southern Hemisphere relative to the Northern Hemisphere, and a larger amplitude in high latitudes (lowM_θe) relative to low latitudes (highM_θe) within each hemisphere. With a box model, we invert the seasonal changes in APO inventory to yield estimates of air‐sea flux cycles at the hemispheric scale. We found a larger seasonal net outgassing of APO in the Southern Hemisphere (518 ± 52.6 Tmol) than in the Northern Hemisphere (342 ± 52.1 Tmol). Differences in APO phasing and amplitude between the hemispheres suggest distinct physical and biogeochemical mechanisms driving the air‐sea O₂fluxes, such as fall outgassing of photosynthetic O₂in the Northern Hemisphere, possibly associated with the formation of the seasonal subsurface shallow oxygen maximum. We compare our estimates with four model‐ and observation‐based products, identifying key limitations in these products or in the tools used to create them. 

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5. Observations of Microlensed Images with Dual-field Interferometry: On-sky Demonstration and Prospects

   https://doi.org/10.3847/1538-4357/ad9b14  

   Mróz, Przemek; Dong, Subo; Mérand, Antoine; Shangguan, Jinyi; Woillez, Julien; Gould, Andrew; Udalski, Andrzej; Eisenhauer, Frank; Ryu, Yoon-Hyun; Wu, Zexuan; et al (February 2025, The Astrophysical Journal)

   Abstract Interferometric observations of gravitational microlensing events offer an opportunity for precise, efficient, and direct mass and distance measurements of lensing objects, especially those of isolated neutron stars and black holes. However, such observations have previously been possible for only a handful of extremely bright events. The recent development of a dual-field interferometer, GRAVITY Wide, has made it possible to reach out to significantly fainter objects and increase the pool of microlensing events amenable to interferometric observations by 2 orders of magnitude. Here, we present the first successful observation of a microlensing event with GRAVITY Wide and the resolution of microlensed images in the event OGLE-2023-BLG-0061/KMT-2023-BLG-0496. We measure the angular Einstein radius of the lens with subpercent precision,θ_E = 1.280 ± 0.009 mas. Combined with the microlensing parallax detected from the event light curve, the mass and distance to the lens are found to be 0.472 ± 0.012M_⊙and 1.81  ±  0.05 kpc, respectively. We present the procedure for the selection of targets for interferometric observations and discuss possible systematic effects affecting GRAVITY Wide data. This detection demonstrates the capabilities of the new instrument, and it opens up completely new possibilities for the follow-up of microlensing events and future routine discoveries of isolated neutron stars and black holes. 

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