# 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/fr/paper/2307.04926v1/

## Abstract

The cool hypergiant star RW Cephei is currently in a deep photometric minimum that began several years ago. This event bears a strong similarity to the Great Dimming of the red supergiant Betelgeuse that occurred in 2019-2020. We present the first resolved images of RW Cephei that we obtained with the CHARA Array interferometer. The angular diameter and Gaia distance estimates indicate a stellar radius of 900 - 1760 R_sun which makes RW Cep one of the largest stars known in the Milky Way. The reconstructed, near-infrared images show a striking asymmetry in the disk illumination with a bright patch offset from center and a darker zone to the west. The imaging results depend on assumptions made about the extended flux, and we present two cases with and without allowing extended emission. We also present a recent near-infrared spectrum of RW Cep that demonstrates that the fading is much larger at visual wavelengths compared to that at near-infrared wavelengths as expected for extinction by dust. We suggest that the star's dimming is the result of a recent surface mass ejection event that created a dust cloud that now partially blocks the stellar photosphere.