---
title: "New Spatially Resolved Observations of Betelgeuse from the VLA and ALMA: Evidence for Atmospheric Perturbations from a Close Companion"
description: "Abstract We present new spatially resolved observations of the red supergiant Betelgeuse ( α Orionis) at seven frequencies: 22 GHz ( λ 1.4cm), 44 GHz ( λ 6.8 mm), 107 GHz ( λ 2.8 mm), 136 GHz ( λ 2.2 mm), 224 GHz ( λ 1.3 mm), 338 GHz ( λ 0.89 mm), and 485 GHz ( λ 0.62 mm), using the Karl G. Jansky Very Large Array…"
datePublished: "2026-09-01"
lastmod: "2026-10-28T08:30:19+00:00"
authors:
  - "L. D. Matthews"
  - "A. K. Dupree"
  - "A. M. S. Richards"
  - "W. R. F. Dent"
journal: "The Astronomical Journal"
publisher: "American Astronomical Society"
doi: "10.3847/1538-3881/ae953d"
publicationType: "journal-article"
schemaType: "ScholarlyArticle"
volume: "172"
issue: "3"
pages: "184"
license: "https://creativecommons.org/licenses/by/4.0/"
sponsor: "Space Telescope Science Institute; National Science Foundation"
language: "en-GB"
slug: "10.3847-1538-3881-ae953d"
---

# New Spatially Resolved Observations of Betelgeuse from the VLA and ALMA: Evidence for Atmospheric Perturbations from a Close Companion

**Authors:** L. D. Matthews, A. K. Dupree, A. M. S. Richards, W. R. F. Dent  
**Journal:** The Astronomical Journal  
**Publisher:** American Astronomical Society  
**Published:** 2026-09-01  
**Volume:** 172  
**Issue:** 3  
**Pages:** 184  
**DOI:** [10.3847/1538-3881/ae953d](https://dx.doi.org/10.3847/1538-3881/ae953d)

## Abstract

Abstract We present new spatially resolved observations of the red supergiant Betelgeuse ( α Orionis) at seven frequencies: 22 GHz ( λ 1.4cm), 44 GHz ( λ 6.8 mm), 107 GHz ( λ 2.8 mm), 136 GHz ( λ 2.2 mm), 224 GHz ( λ 1.3 mm), 338 GHz ( λ 0.89 mm), and 485 GHz ( λ 0.62 mm), using the Karl G. Jansky Very Large Array and the Atacama Large Millimeter/submillimeter Array. These observations (spanning 2021–2026) enable a characterization of the mean brightness temperature ( T B ), shape, and symmetry of the star’s extended atmosphere. At 22 GHz and 44 GHz T B has increased following the historic lows observed in 2019, just prior to the Great Dimming of late 2019/early 2020. We find that T B peaks at a larger projected radius (≳2.7 R ⋆ ) than in measurements prior to 2016, consistent with a possible evolution in the atmospheric density profile. In addition we find a systematic decrease in T B from ≈3500 K at ∼2.7 R ⋆ to T B ≈ 2220 K at ∼1.2 R ⋆ , confirming a previously reported temperature minimum between the photosphere and chromosphere. At all observed frequencies T B is lower than temperatures inferred from ultraviolet measurements at comparable radii, indicating the continued presence of cooler plasma ( T ≤ T eff ) mixed with the warmer chromospheric material. The new measurements yield a global spectral index α = 1.35 ± 0.03, with no evidence for a change in α over more than two decades in frequency. Recently, evidence of a close-in companion to Betelgeuse has been reported, with an orbital separation r ∼ 2.3 R ⋆ . We have identified a correlation between the ellipticity of Betelgeuse, as obtained from radio measurements, and the companion’s orbital phase. The results are consistent with periodic perturbations of the atmosphere by the companion.

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