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1. Influence of the input-stage architecture on the in-laboratory test of a mid-infrared interferometer: application to the ALOHA up-conversion interferometer in the L band

   https://doi.org/10.1093/mnras/staa3283  

   Magri, Julie; Lehmann, Lucien; Grossard, Ludovic; Delage, Laurent; Reynaud, François; Chauvet, Mathieu; Bassignot, Florent; Krawczyk, Rodolphe; Le Duigou, Jean-Michel (December 2020, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT In the framework of the Astronomical Light Optical Hybrid Analysis (ALOHA) laboratory mid-infrared (MIR) up-conversion fibred interferometer in the L band, we report on the influence of the input-stage architecture. Using an amplitude division set-up in the visible or near-infrared is a straightforward choice in most cases. In the MIR context, the results are slightly different and we show that a wavefront division set-up is needed. These in-laboratory principle experiments allow us to measure a reliable 88 per cent instrumental contrast with high flux and to obtain fringes from faint sources at 3.5 μm with a spectral bandwith of 37 nm converted to 817 nm. An equivalent limiting L-band magnitude around 3.9, equivalent to 3.0 fW nm−1, could be demonstrated on 1 m class telescopes. This opens the possibility of planning future on-sky tests at the Center for High Angular Resolution Astronomy (CHARA) array and of predicting the performance attained. 

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2. SPRITEly: Time-domain Millimeter Interferometry at the Owens Valley Radio Observatory

   https://doi.org/10.3847/1538-3881/ad6cdb  

   Yurk, Nitika Yadlapalli; Ravi, Vikram; Hodges, Mark W; Lamb, James W; Hobbs, Richard; Woody, David P; Readhead, Anthony_C S (September 2024, The Astronomical Journal)

   Abstract Though the time-domain millimeter sky is yet to be well characterized, the scarcity of millimeter observing resources in the world at present hampers progress toward it. In efforts to bolster the exploration of millimeter transients, we present the Stokes Polarization Radio Interferometer for Time-Domain Experiments (SPRITEly). Located at the Owens Valley Radio Observatory, SPRITEly is currently deployed as a two-element short-baseline 90 GHz interferometer uniquely focused on monitoring bright variable millimeter-continuum sources. We leverage two existing 10.4 m antennas and their existing receiver systems to begin, but we make significant upgrades to the back-end system during the commissioning process. With the ability to achieve rms noise of a few mJy, we plan to monitor known variable sources along with new nearby transients detected from optical surveys at high cadence, with the goal of producing well-sampled light curves. Interpreting these data in conjunction with multiwavelength observations stands to provide insight into the physical properties of the sources that produce transient millimeter emission. We present commissioning and early-science observations that demonstrate the performance of the instrument, including observations of the flaring BL Lac object S2 0109+22 and a periastron passage of the binary T Tauri system DQ Tau. 

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3. Precise Age for the Binary HD 21278 in the Young α Persei Cluster

   https://doi.org/10.3847/1538-4357/ade0bb  

   Danner, Christopher A; Sandquist, Eric L; Schaefer, Gail H; Bedin, Luigi R; Farrington, Christopher D; Lanthermann, Cyprien; Kraus, Stefan; Klement, Robert; Anugu, Narsireddy; Monnier, John D; et al (July 2025, The Astrophysical Journal)

   Abstract We present a study of the double-lined spectroscopic binary HD 21278 that contains one of the brightest main-sequence stars in the youngαPersei open cluster. We analyzed new spectra and reanalyzed archived spectra to measure precise new radial velocity curves for the binary. We also obtained interferometric data using the CHARA Array at Mount Wilson to measure the sky positions of the two stars and the inclination of the ∼2 mas orbit. We determine that the two stars have masses of 5.381 ± 0.084M_⊙and 3.353 ± 0.064M_⊙. From isochrone fits, we find the cluster’s age to be 49  ±  7 Myr (using PARSEC models) or 49.5 ± 6 Myr (MIST models). Finally, we revisit the massive white dwarfs that are candidate escapees from theαPersei cluster to try to better characterize the massive end of the white dwarf initial–final mass relation. The implied progenitor masses challenge the idea that Chandrasekhar-mass white dwarfs are made by single stars with masses near 8M_⊙. 

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4. Patterns of siderophore production and utilization at Station ALOHA from the surface to mesopelagic waters

   https://doi.org/10.1002/lno.12746  

   Bundy, Randelle M; Manck, Lauren E; Repeta, Daniel J; Church, Matthew J; Hawco, Nicholas J; Boiteau, Rene M; Park, Jiwoon; DeLong, Edward F; Saito, Mak A (January 2025, Limnology and Oceanography)

   Abstract The North Pacific subtropical gyre is a globally important contributor to carbon uptake despite being a persistently oligotrophic ecosystem. Supply of the micronutrient iron to the upper ocean varies seasonally to episodically, and when coupled with rapid biological consumption, results in low iron concentrations. In this study, we examined changes in iron uptake rates, along with siderophore concentrations and biosynthesis potential at Station ALOHA across time (2013–2016) and depth (surface to 500 m) to observe changes in iron acquisition and internal cycling by the microbial community. The genetic potential for siderophore biosynthesis was widespread throughout the upper water column, and biosynthetic gene clusters peaked in spring and summer along with siderophore concentrations, suggesting changes in nutrient delivery, primary production, and carbon export seasonally impact iron acquisition. Dissolved iron turnover times, calculated from iron‐amended experiments in surface (15 m) and mesopelagic (300 m) waters, ranged from 9 to 252 d. The shortest average turnover times at both depths were associated with inorganic iron additions (14  9 d) and the longest with iron bound to strong siderophores (148  225 d). Uptake rates of siderophore‐bound iron were faster in mesopelagic waters than in the surface, leading to high Fe : C uptake ratios of heterotrophic bacteria in the upper mesopelagic. The rapid cycling and high demand for iron at 300 m suggest differences in microbial metabolism and iron acquisition in the mesopelagic compared to surface waters. Together, changes in siderophore production and consumption over the seasonal cycle suggest organic carbon availability impacts iron cycling at Station ALOHA. 

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5. Recent technical and scientific highlights from the CHARA Array

   https://doi.org/10.1117/12.2629048  

   Gies, Douglas R.; Anderson, Matthew D.; Anugu, Narsireddy; ten Brummelaar, Theo A.; Castillo, Victor; Farrington, Christopher D.; Golden, Steven; Jones, Jeremy W.; Klement, Robert; Koehler, Rainer; et al (August 2022, Optical and Infrared Interferometry and Imaging VIII)

   Mérand, Antoine; Sallum, Stephanie; Sanchez-Bermudez, Joel (Ed.)

   The Center for High Angular Resolution Astronomy (CHARA) Array is a six-element interferometer with baselines ranging from 34 to 331 m. Three new beam combiners are entering operation: MYSTIC is a 6-telescope combiner for K-band; SPICA is a 6-telescope combiner for the visible R-band; and SILMARIL is a 3-telescope combiner for high sensitivity in H and K-bands. A seventh, portable telescope will use fiber optics for beam transport and will increase the baselines to 1 km. Observing time is available through a program funded by NSF. The programs are solicited and peer-reviewed by NSF’s National Optical Infrared Astronomy Research Laboratory. The open community access has significantly expanded the range of astronomical investigations of stars and their environments. Here we summarize the scientific work and the on-going technical advances of the CHARA Array. 

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