2011/08/18 by T. R. Ayres · 2 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Flare star #Galaxy #K-type main-sequence star #Physics #ROSAT #Red supergiant #Star cluster #Stars #Stellar, planetary, and galactic studies #Supergiant #T Tauri star
paper · pdf · doi:10.1088/0004-637x/738/2/120
openalex publication_date 2011/08/18 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/04
Alpha Persei (HD 20902: F5 Iab) is a luminous, nonvariable supergiant located at the blue edge of the Cepheid instability strip. It is one of the brightest coronal X-ray sources in the young open cluster bearing its name, yet warm supergiants as a class generally avoid conspicuous high-energy activity. The Cosmic Origins Spectrograph on the Hubble Space Telescope has recently uncovered additional oddities. The 1290–1430 Å far-ultraviolet (FUV) spectrum of α Per is dominated by photospheric continuum emission, with numerous superposed absorption features, mainly stellar. However, the normal proxies of coronal activity, such as the Si iv 1400 Å doublet ( T ∼ 8 × 10 4 K), are very weak, as are the chromospheric C ii 1335 Å multiplet ( T ∼ 3 × 10 4 K) and O i 1305 Å triplet. In fact, the Si iv features of α Per are not only narrower than those of later, G-type supergiants of similar L X / L bol , but are also fainter (in L Si iv / L bol ) by two orders of magnitude. Further, a reanalysis of the ROSAT pointing on α Per finds the X-ray centroid offset from the stellar position by 9'', at a moderate level of significance. The FUV and X-ray discrepancies raise the possibility that the coronal source might be unrelated to the supergiant, perhaps an accidentally close dwarf cluster member; heretofore unrecognized in the optical, lost in the glare of the bright star.