Near-ultraviolet Stellar Activity and Brightness Fluctuations of the Alpha Centauri AB Star System from Weeks to Decades—Inputs for Reflected-light Spectroscopy with HWO Journal Article uri icon

Overview

abstract

  • Abstract; ; We present the most comprehensive near-UV (NUV: 2550–3255 Å) activity record to date for the Alpha Centauri AB system, combining archival International Ultraviolet Explorer and Hubble Space Telescope observations spanning nearly 5 decades with new high-cadence Colorado Ultraviolet Transit Experiment (CUTE) measurements. We show that Alpha Centauri A exhibits predominantly quiescent NUV behavior, with the majority of observations remaining within ±1; σ; of the median flux and only rare chromospheric flaring events (∼1 flare every 12 yr), consistent with its weak chromospheric activity and 19 yr stellar cycle inferred from X-ray and far-UV observations. In contrast, Alpha Centauri B displays a broader variability envelope, characterized by more frequent and higher-amplitude chromospheric excursions that track its well-established ∼8 yr magnetic activity cycle. Using Lomb–Scargle analysis of the Mg; II; index derived from CUTE observations, we estimate the rotational period of Alpha Centauri A to be on a timescale of ∼15–20 days. We also confirm the coherence of the stellar activity cycle of Alpha Centauri B in the NUV with its X-ray activity cycle. These data establish a critical reference framework for interpreting reflected-light observations of terrestrial exoplanets and for assessing the detectability of ozone and other biosignature-related features at NUV wavelengths with future facilities such as the Habitable Worlds Observatory (HWO). These results indicate that HWO observations of terrestrial exoplanets in reflected-light photometry and spectroscopy around magnetically inactive early G-type stars and early K-type stars may be expected to show 10%–20% and 30%–40% temporal flux variability, respectively, over the course of months to years from the changing stellar inputs alone.;

publication date

  • July 1, 2026

Date in CU Experts

  • June 25, 2026 7:36 AM

Full Author List

  • Bhattacharyya D; France K; Rao S; Escobar S; Wilson DJ; Egan A; Chamberlin P; Sreejith AG; Brown A

author count

  • 9

Other Profiles

International Standard Serial Number (ISSN)

  • 0004-6256

Electronic International Standard Serial Number (EISSN)

  • 1538-3881

Additional Document Info

start page

  • 27

end page

  • 27

volume

  • 172

issue

  • 1