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Abstract Planets are a natural byproduct of the stellar formation process, resulting from local aggregations of material within the disks surrounding young stars. Whereas signatures of gas-giant planets at large orbital separations have been observed and successfully modeled within protoplanetary disks, the formation pathways of planets within their host star’s future habitable zones remain poorly understood. Analyzing multiple nights of observations conducted over a short, 2 month span with the MIRC-X and PIONIER instruments at the CHARA Array and VLTI, respectively, we uncover a highly active environment at the inner-edge of the planet formation region in the disk of HD 163296. In particular, we localize and track the motion of a disk feature near the dust-sublimation radius with a pattern speed of less than half the local Keplerian velocity, providing a potential glimpse at the planet formation process in action within the inner astronomical unit. We emphasize that this result is at the edge of what is currently possible with available optical interferometric techniques and behooves confirmation with a temporally dense followup observing campaign. 

Abstract Classical Wolf–Rayet (WR) stars are descendants of massive OB-type stars that have lost their hydrogen-rich envelopes and are in the final stages of stellar evolution, possibly exploding as Type Ib/c supernovae. It is understood that the mechanisms driving this mass loss are either strong stellar winds and or binary interactions, so intense studies of these binaries including their evolution can tell us about the importance of the two pathways in WR formation. WR 138 (HD 193077) has a period of just over 4 yr and was previously reported to be resolved through interferometry. We report on new interferometric data combined with spectroscopic radial velocities in order to provide a three-dimensional orbit of the system. The precision on our parameters tend to be about an order of magnitude better than previous spectroscopic techniques. These measurements provide masses of the stars, namely,M_WR= 13.93 ± 1.49M_⊙andM_O= 26.28 ± 1.71M_⊙. The derived orbital parallax agrees with the parallax from Gaia, namely, with a distance of 2.13 kpc. We compare the system’s orbit to models from BPASS, showing that the system likely may have been formed with little interaction but could have formed through some binary interactions either following or at the start of a red supergiant phase but with the most likely scenario occurring as the red supergiant phase starts for a ∼40M_⊙star. 

Abstract Classical Wolf–Rayet (W-R) stars are the descendants of massive OB stars that have lost their hydrogen envelopes and are burning helium in their cores prior to exploding as Type Ib/c supernovae. The mechanisms for losing their hydrogen envelopes are either through binary interactions or through strong stellar winds potentially coupled with episodic mass loss. Among the bright classical W-R stars, the binary system WR 137 (HD 192641; WC7d + O9e) is the subject of this paper. This binary is known to have a 13 yr period and produces dust near periastron. Here we report on interferometry with the Center for High Angular Resolution Astronomy Array collected over a decade of time and providing the first visual orbit for the system. We combine these astrometric measurements with archival radial velocities to measure masses of the stars ofM_WR= 9.5 ± 3.4M_⊙andM_O= 17.3 ± 1.9M_⊙when we use the most recent Gaia distance. These results are then compared to predicted dust distribution using these orbital elements, which match the observed imaging from JWST as discussed recently by Lau et al. Furthermore, we compare the system to the Binary Population And Spectral Synthesis models, finding that the W-R star likely formed through stellar winds and not through binary interactions. However, the companion O star did likely accrete some material from the W-R star’s mass loss to provide the rotation seen today that drives its status as an Oe star. 

Context.V838 Mon is a stellar merger remnant that erupted in a luminous red nova event in 2002. Although it has been well studied in the optical, near-infrared, and submillimeter regimes, its structure in the mid-infrared wavelengths remains elusive. Over the past two decades, only a handful of infrared interferometric studies have been performed, suggesting the presence of an elongated structure at multiple wavelengths. However, given the limited nature of these observations, the true morphology of the source has not yet been conclusively determined. Aims.By performing image reconstruction using observations taken at the VLTI and CHARA, we aim to map out the circumstellar environment in V838 Mon. Methods.We observed V838 Mon with the MATISSE (LMNbands) and GRAVITY (Kband) instruments at the VLTI as well as the MIRCX/MYSTIC (HKbands) instruments at the CHARA array. We geometrically modelled the squared visibilities and the closure phases in each of the bands to obtain the constraints on the physical parameters. Furthermore, we constructed high-resolution images of V838 Mon in theHKbands using the MIRA and SQUEEZE algorithms to study the immediate surroundings of the star. Lastly, we also modelled the spectral features seen in theKandMbands at various temperatures. Results.The image reconstructions show a bipolar structure that surrounds the central star in the post-merger remnant. In theKband, the super-resolved images show an extended structure (uniform disk diameter ~1.94 mas) with a clumpy morphology that is aligned along a north-west position angle (PA) of −40°. On the other hand, in theHband, the extended structure (uniform disk diameter ~1.18 mas) lies roughly along the same PA. Yet the northern lobe is slightly misaligned with respect to the southern lobe, which results in the closure phase deviations. Conclusions.The VLTI and CHARA imaging results show that V838 Mon is surrounded by features resembling jets that are intrinsically asymmetric. This is further confirmed by the closure phase modelling. Further observations with VLTI can help to determine whether this structure shows any variations over time and also if such bi-polar structures are commonly formed in other stellar merger remnants. 

Context.T Tauri stars are low-mass young stars whose disks provide the setting for planet formation, which is one of the most fundamental processes in astronomy. Yet the mechanisms of this are still poorly understood. SU Aurigae is a widely studied T Tauri star and here we present original state-of-the-art interferometric observations with better uv and baseline coverage than previous studies. Aims.We aim to investigate the characteristics of the circumstellar material around SU Aur, and constrain the disk geometry, composition and inner dust rim structure. Methods.The MIRC-X instrument at CHARA is a six-telescope optical beam combiner offering baselines up to 331 m. We undertook image reconstruction for model-independent analysis, and fitted geometric models such as Gaussian and ring distributions. Additionally, the fitting of radiative transfer models constrained the physical parameters of the disk. Results.Image reconstruction reveals a highly inclined disk with a slight asymmetry consistent with inclination effects obscuring the inner disk rim through absorption of incident star light on the near side and thermal re-emission/scattering of the far side. Geometric models find that the underlying brightness distribution is best modelled as a Gaussian with a Full-Width Half-Maximum of 1.53 ± 0.01 mas at an inclination of 56.9 ± 0.4° and a minor axis position angle of 55.9 ± 0.5°. Radiative transfer modelling shows a flared disk with an inner radius at 0.16 au which implies a grain size of 0.14 μm assuming astronomical silicates and a scale height of 9.0 au at 100 au. In agreement with the literature, only the dusty disk wind successfully accounts for the near infrared excess by introducing dust above the mid-plane. Conclusions.Our results confirm and provide better constraints than previous inner disk studies of SU Aurigae. We confirm the presence of a dusty disk wind in the cicumstellar environment, the strength of which is enhanced by a late infall event which also causes very strong misalignments between the inner and outer disks. 

Abstract We present preliminary results from our long-baseline interferometry (LBI) survey to constrain the multiplicity properties of intermediate-mass A-type stars within 80 pc. Previous multiplicity studies of nearby stars exhibit orbital separation distributions well fitted with a lognormal with peaks >15 au, increasing with primary mass. The A-star multiplicity survey of De Rosa et al., sensitive beyond 30 au but incomplete below 100 au, found a lognormal peak around 390 au. Radial velocity surveys of slowly rotating, chemically peculiar Am stars identified a significant number of very close companions with periods ≤5 days, ∼0.1 au, a result similar to surveys of O- and B-type primaries. With the improved performance of LBI techniques, we can probe these close separations for normal A-type stars where other surveys are incomplete. Our initial sample consists of 27 A-type primaries with estimated masses between 1.44 and 2.49 M ⊙ and ages 10–790 Myr, which we observed with the MIRC-X instrument at the CHARA Array. We use the open-source software CANDID to detect five companions, three of which are new, and derive a companion frequency of 0.19 − 0.06 + 0.11 over mass ratios of 0.25–1.0 and projected separations of 0.288–5.481 au. We find a probability of 10 −6 that our results are consistent with extrapolations based on previous models of the A-star companion population over the mass ratios and separations sampled. Our results show the need to explore these very close separations to inform our understanding of stellar formation and evolution processes. 

ABSTRACT We report near-infrared long-baseline interferometric observations of the Hyades multiple system HD 284163, made with the Center for High Angular Resolution Astronomy array, as well as almost 43 yr of high-resolution spectroscopic monitoring at the Center for Astrophysics. Both types of observations resolve the 2.39 d inner binary, and also an outer companion in a 43.1 yr orbit. Our observations, combined with others from the literature, allow us to solve for the 3D inner and outer orbits, which are found to be at nearly right angles to each other. We determine the dynamical masses of the three stars (good to better than 1.4 per cent for the inner pair), as well as the orbital parallax. The secondary component (0.5245 ± 0.0047 M⊙) is now the lowest mass star with a dynamical mass measurement in the cluster. A comparison of these measurements with current stellar evolution models for the age and metallicity of the Hyades shows good agreement. All three stars display significant levels of chromospheric activity, consistent with the classification of HD 284163 as an RS CVn object. We present evidence that a more distant fourth star is physically associated, making this a hierarchical quadruple system. 

The Michigan Young STar Imager at CHARA (MYSTIC) is a K-band interferometric beam combining instrument funded by the United States National Science Foundation, designed primarily for imaging sub-au scale disk structures around nearby young stars and to probe the planet formation process. Installed at the CHARA array in July 2021, with baselines up to 331 meters, MYSTIC provides a maximum angular resolution of λ/2B ∼ 0.7 mas. The instrument injects phase corrected light from the array into inexpensive, single-mode, polarization maintaining silica fibers, which are then passed via a vacuum feedthrough into a cryogenic dewar operating at 220 K for imaging. MYSTIC utilizes a high frame rate, ultra-low read noise SAPHIRA detector, and implements two beam combiners: a 6-telescope image plane beam combiner, based on the MIRC-X design, for targets as faint as 7.7 Kmag, as well as a 4-telescope integrated optic beam-combiner mode using a spare chip leftover from the GRAVITY instrument. MYSTIC is co-phased with the MIRC-X (J+H band) instrument for simultaneous fringe-tracking and imaging, and shares its software suite with the latter to allow a single observer to operate both instruments. Herein, we present the instrument design, review its operational performance, present early commissioning science observations, and propose upgrades to the instrument that could improve its K-band sensitivity to 10th magnitude in the near future. 

Abstract We present measurements of the interferometrically resolved binary star system 12 Com and the single giant star 31 Com in the cluster Coma Berenices. 12 Com is a double-lined spectroscopic binary system consisting of a G7 giant and an A3 dwarf at the cluster turnoff. Using an extensive radial velocity data set and interferometric measurements from the Palomar Testbed Interferometer and the Center for High Angular Resolution Astronomy array, we measured massesM₁= 2.64 ± 0.07M_⊙andM₂= 2.10 ± 0.03M_⊙. Interferometry also allows us to resolve the giant and measure its size asR₁= 9.12 ± 0.12 ± 0.01R_⊙. With the measured masses and radii, we find an age of 533 ± 41 ± 42 Myr. For comparison, we measure the radius of 31 Com to be 8.36 ± 0.15R_⊙. Based on the photometry and radius measurements, 12 Com A is likely the most evolved bright star in the cluster, large enough to be in the red giant phase, but too small to have core helium burning. Simultaneous knowledge of 12 Com A’s mass and photometry puts strong constraints on convective core overshooting during the main-sequence phase, which in turn reduces systematic uncertainties in the age. Increased precision in measuring this system also improves our knowledge of the progenitor of the cluster white dwarf WD1216+260.