2026/01/31 by Brian E. Wood, Hans‐Reinhard Müller, Dean Hartshorn +2 · 1 voice
Physics and Astronomy · #Astronomy and Astrophysical Research #Scientific Research and Discoveries #Stellar, planetary, and galactic studies
paper · doi:10.3847/1538-4357/ae315b
openalex publication_date 2026/02/05 · openalex created_date 2026/02/07 · openalex updated_date 2026/06/11
Abstract We present new Hubble Space Telescope (HST) UV spectra of the K2 V star HD 166620, the first star clearly recognized to be in a “magnetic grand minimum” state analogous to the Sun’s “Maunder minimum” in the late 1600s. The stellar H I Ly α surface fluxes are extremely low, about a factor of 2 below fluxes observed during solar minimum, and also significantly lower than those of τ Ceti (G8 V) and HD 191408 (K2.5 V), two stars more similar to HD 166620 in spectral type and age (∼10 Gyr) than the Sun. The τ Ceti data that are compared with HD 166620 include both old archival data and a new HST observation as well. The Ly α data are used to confirm a nondetection of astrospheric Ly α absorption for this star, suggesting a very weak wind with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:mo><</mml:mo> <mml:mn>0.1</mml:mn> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> . The very compact astrosphere inferred for τ Ceti indicates that the star’s debris disk is at least partly exposed to the interstellar medium (ISM), and we discuss possible consequences.