Mass ejection causes RW Cephei to dim

The cool hypergiant RW Cep has been keeping observers busy this year due to its unusual fade, which some have compared to the ‘great dimming’ of Betelgeuse in 2019–’20. A recent paper accepted for publication in the Astronomical Journal ( presents the first resolved images of RW Cep obtained with the CHARA array interferometer.

The researchers’ reconstructed near-infrared images of the star show a striking asymmetry in the disc illumination, with a bright patch offset from the centre and a darker zone to the west. They say this is evidence for a recent mass ejection event that created a dust cloud which now partially blocks the stellar photosphere, thereby explaining the dimming. The paper cites spectroscopy obtained by BAA member Robin Leadbeater.

For more information about observing RW Cep, look at John Toone’s article in the 2023 June Journal.

Jeremy Shears, Director of the BAA Variable Star Section

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