We evaluate the performance of three beam-combination schemes, single-Bracewell, asymmetric dual-Bracewell, and symmetric dual-Bracewell, for the forthcoming Asgard/NOTT nulling interferometer at the Very Large Telescope Interferometer. Utilizing the SCIFYsim end-to-end simulator, we assess the instrument's performance by deriving the precision of calibrated null measurements as a function of stellar magnitude and simulating observations of varying hot exozodiacal dust (HEZD) distributions and a hot Jupiter. The study reveals distinct trade-offs for each observing mode. The single-Bracewell mode provides high throughput and preserves spatial information but suffers from poor error suppression. The asymmetric dual-Bracewell mode offers the strongest error suppression for detecting point-like sources, but it inherently suppresses symmetric astrophysical signals such as expected from HEZD. The symmetric dual-Bracewell mode provides a middle ground with modest error suppression while being sensitive to symmetric emission. We conclude that utilizing a combination of all three observing modes provides a robust strategy for detecting HEZD, constraining the structure of its distribution, and identifying false positives from stellar companions.
Chemical tracers provide some of the strongest observational signatures of ongoing planet formation and localized dynamical perturbations in protoplanetary disks. In particular, sulfur-bearing molecules are predicted to be enhanced in regions of shock heating, ice sublimation, and gravitational instability. Here, we present high-angular-resolution (≈0.^''2) Atacama Large Millimeter/submillimeter Array observations of ^12CO J=3-2, ^13CO J=3-2, CS J=7-6, and SO J_ N=8_8-7_7 toward the large, edge-on Gomez's Hamburger ('GoHam'; IRAS 18059-3211) disk. We detect a narrow, one-sided arc of SO emission that peaks near a previously-identified gas over-density, suggesting localized heating around an early-stage giant protoplanet or disk fragment. The edge-on geometry of GoHam enables us to place this chemical signature in the broader context of the disk gas and dust structure. To do so, we map the vertical distribution of molecular gas relative to millimeter- and (sub)-micron-sized dust, identify a pronounced north-south continuum asymmetry, and detect non-Keplerian ^12CO and ^13CO emission indicative of a disk wind. We also derive a dynamical stellar mass of 2.2 ± 0.5 M_⊙ and a revised dust-extinction-map-based distance of 139 ± 24 pc, which places GoHam in the outskirts of the Scorpius-Centaurus association. Together, these observations reveal a highly dynamic disk in which localized sulfur chemistry may trace one of the earliest observable stages of wide-separation giant planet formation.
WR 25 is a massive colliding-wind binary in the Carina nebula comprising a WN6ha primary star with an O5 companion in an eccentric 208-day orbit. Recent spectroscopic analysis estimates the total binary mass to approach 100 M⊙, and a primary-to-secondary mass ratio of q = M1/M2 ≈ 2, hinting at a very massive primary star. The presence of additional spectroscopic signatures from a third, “intruder” star was also noted, making it a candidate hierarchical triple system. In this study, we present a VLTI/PIONIER interferometric observation of WR 25, spatially resolving all three components for the first time. For the inner WN6ha + O5 binary, we find a projected angular separation of 1.68 ± 0.02 milliarcseconds (mas), corresponding to a projected physical separation of 3.90 ± 0.21 au at a distance of 2.32 ± 0.12 kpc. Leveraging the fortunate timing of the VLTI observation, which was obtained when the two components were passing the line of nodes, we determined the orbital semi-major axis a = 3.11 ± 0.20 au. Subsequently, the newly constrained total dynamical binary mass is 93 ± 18 M⊙, with a primary mass M1 = 62 ± 13 M⊙ and secondary mass M2 = 31 ± 7 M⊙. We detect the third star or tertiary with a projected angular separation of 27.69 ± 0.02 mas from the primary, with a chance alignment probability lower than 10−4. Using newly obtained brightness ratios between all components, we revisit archival spectroscopic data of WR 25 to disentangle spectra for individual components and derive their stellar parameters. The tertiary, which has a spectral type O7, is broadly coeval with the inner binary and has an evolutionary mass M3 = 25.6−2.3+2.8 M⊙ M 3 = 25 . 6 − 2.3 + 2.8 M ⊙ $ M_3=25.6^{+2.8}_{-2.3}\,M_\odot $ . Based on simulations, we estimate the tertiary period to be in the range 19–82 years. The newly confirmed triple nature of WR 25 thus makes it an important benchmark system to measure accurate dynamical masses of the inner binary and potentially the tertiary, to calibrate stellar evolution and atmosphere models, and to study its formation and stability as a hierarchical triple system.
T Coronae Borealis (T CrB, HD 143454) is a symbiotic recurrent nova consisting of a red giant and white dwarf with recent eruptions in 1866 and 1946 and an anticipated eruption in the mid-2020s. We report Center for High Angular Resolution Astronomy (or CHARA) Array observations collected with MIRC-X (H band) and MYSTIC (K band) in 2022-2025. We fit limb-darkened disk models constrained with literature limb-darkening coefficients to the squared visibilities as only the first visibility lobe is sampled. The average limb-darkened diameter of the star across these epochs is 0.70 +/- 0.04 mas in the H band and 0.72 +/- 0.07 mas in the K band. Adopting a distance of 914-22+24 pc, the corresponding stellar radius is 69 +/- 5 R circle dot in the H band and 71 +/- 8 R circle dot in the K band. These values are consistent with the Roche-lobe volume radius of 71 R circle dot inferred from published orbital solutions. These measurements provide a preeruption angular diameter and support a Roche-lobe-filling donor.
Almost two decades after their discovery, pulsars discoverable only through their single, dispersed radio pulses, known as rotating radio transients (RRATS), remain a poorly-understood class of objects. Compared to the overall pulsar population, few have timing solutions, limiting our ability to understand the mechanisms underlying their sporadic emission. Here, we present a single-pulse analysis of twelve sources from the PALFA survey, consisting of eleven objects initially identified as RRATs and one candidate fast radio burst. We present timing solutions for five of the sources with detections at a sufficient number of epochs and spin periods for two more. For all sources, we use a Bayesian framework to fit distributions of single-pulse energies, finding support for log-normal energy distributions and pulse-to-pulse wait times that are consistent with Poisson processes. Finally, we provide updates on the previously-published candidate fast radio burst J0613+18, with new indications that it is in fact extragalactic.
