- The paper reveals that spatially resolved UV spectroscopy captured enhanced Mg II emissions and chromospheric changes preceding the optical dimming.
- The analysis identifies an outward-moving pulse, likely triggered by pulsation and large convective cell activity that drives mass ejection.
- The study employs 3D mapping and radial velocity measurements to advance models of mass loss in M supergiants.
Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse
This paper presents a comprehensive analysis of the Great Dimming event of Betelgeuse, a prominent M2Iab supergiant star, focusing on its spatially resolved ultraviolet (UV) spectroscopy. During late 2019 and early 2020, Betelgeuse underwent significant visual dimming, which drew considerable attention due to potential implications related to the stellar lifecycle, specifically concerning its candidacy for a Type II supernova event.
The authors leverage observations conducted with the Hubble Space Telescope's Space Telescope Imaging Spectrograph (STIS) to investigate the changes in Betelgeuse’s chromosphere—key indicators of plasma activity and mass ejection events. Noteworthy, the study identifies an increase in the ultraviolet spectrum and Mg II line emissions, particularly over the star's southern hemisphere, which preceded the optical dimming event. Such spatially resolved spectroscopic data facilitate the understanding of the star's photospheric expansion and the convective activities driving mass loss processes.
Crucially, the paper delineates the temporal dynamics of the event, outlining the outward movement of material as indicated by variations in the Mg II k-line profiles and corroborated by radial velocity measurements. These data suggest the presence of a pulse or acoustic shock between September and November 2019. They hypothesize that this led to the formation of a dust cloud in the star's southern hemisphere, possibly linking the dimming event with Betelgeuse's intrinsic pulsation cycle, characterized by approximately a 400-day period.
The authors detail substantial enhancements in brightness and electron density in the chromosphere, with the UV line profiles showing increased emission on the short wavelength side during the critical period. These measurements were integral to inferring outward material motion, supported by the elevated electron densities observed in C II diagnostics.
In terms of implications, this research significantly advances the understanding of mass loss mechanisms in M supergiants, particularly the interplay between convective photospheric elements and the chromospheric response. The study proposes potential scenarios involving a combination of large convective cell activity and pulsation-driven motion as primary factors in the mass ejection and subsequent dimming.
The investigations on whether Betelgeuse moved behind an interstellar cloud were decidedly null, thanks to 3D mapping efforts indicating a mostly dust-free region surrounding the star. This absence isolates the cause of dimming to Betelgeuse's intrinsic activities rather than external obscuration.
The findings underscore the importance of spatially resolved spectroscopic studies for stellar astrophysics, especially in deciphering complex phenomena like the Great Dimming. Moving forward, such insights could inform theoretical models of stellar evolution and mass loss while potentially serving as a predictive basis for similar events in other stellar bodies. As Betelgeuse approaches another pulsation minimum, further observations could refine these models, offering a deeper insight into stellar dynamics and life cycle processes.