# The Great Dimming of the hypergiant star RW Cephei: CHARA Array images and spectral analysis

**Authors:** N. Anugu, F. Baron, D. R. Gies, C. Lanthermann, G. H. Schaefer, K. A. Shepard, T. ten Brummelaar, J. D. Monnier, S. Kraus, J. -B. Le Bouquin, C. L. Davies, J. Ennis, T. Gardner, A. Labdon, R. M. Roettenbacher, B. R. Setterholm, W. Vollmann, C. Sigismondi  
**arXiv:** [2307.04926](https://arxiv.org/abs/2307.04926)  
**Date:** 2023-07-10  
**Summary page:** https://www.summarizepaper.com/en/paper/2307.04926v1/

## Key points

- The hypergiant star RW Cephei is experiencing a deep photometric minimum
- Similar to the Great Dimming of Betelgeuse in 2019-2020
- Anugu et al. present first resolved images of RW Cephei using CHARA Array interferometer
- Stellar radius estimated to be between 900 and 1760 times that of our Sun
- One of the largest stars known in the Milky Way
- Reconstructed near-infrared images show asymmetry in disk illumination
- Bright patch offset from center, darker zone to the west
- Imaging results depend on assumptions about extended flux, two cases presented
- Recent near-infrared spectrum shows fading more pronounced at visual wavelengths compared to near-infrared wavelengths, expected for dust extinction
- Dimming likely caused by recent surface mass ejection event generating a dust cloud partially blocking photosphere
- Findings contribute to understanding extreme stellar variability and similar phenomena in massive stars
- Contributes significantly to knowledge of RW Cephei's behavior during current photometric minimum
- Highlights similarities with other well-known dimming events in massive stars like Betelgeuse
- Further investigations will deepen understanding of stellar evolution and variability in extreme astrophysical environments

## Summary

The hypergiant star RW Cephei is currently experiencing a deep photometric minimum that began several years ago. This phenomenon bears a striking resemblance to the Great Dimming of the red supergiant Betelgeuse, which occurred in 2019-2020. In a recent study, Anugu et al. present the first resolved images of RW Cephei obtained with the CHARA Array interferometer. The authors estimate the stellar radius of RW Cephei to be between 900 and 1760 times that of our Sun based on angular diameter and Gaia distance measurements. This makes RW Cephei one of the largest stars known in the Milky Way. The reconstructed near-infrared images reveal an intriguing asymmetry in the disk illumination, with a bright patch offset from the center and a darker zone to the west. It is important to note that the imaging results depend on assumptions made about extended flux, and two cases are presented: one allowing for extended emission and another without it. Additionally, Anugu et al. present a recent near-infrared spectrum of RW Cephei, which demonstrates that the fading is much more pronounced at visual wavelengths compared to near-infrared wavelengths as expected for extinction by dust. Based on their observations, the authors propose that RW Cephei's dimming is likely caused by a recent surface mass ejection event that generated a dust cloud partially blocking its photosphere. These findings provide valuable insights into understanding extreme stellar variability and offer further evidence for similar phenomena occurring in different types of massive stars. Overall, this study contributes significantly to our knowledge of RW Cephei's behavior during its current photometric minimum and highlights its similarities with other well-known dimming events in massive stars like Betelgeuse. Further investigations into these phenomena will deepen our understanding of stellar evolution and variability in extreme astrophysical environments.