1999/11/08 by K. Hamaguchi, Kenji Hamaguchi, H. Terada +5 · 1 citation
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Dynamo #Flare #Flare star #Galaxy #K-type main-sequence star #Luminosity #Magnetic field #Physics #Solar and Space Plasma Dynamics #Star formation #Stars #Stellar, planetary, and galactic studies #T Tauri star #Young stellar object #astro-ph
paper · pdf · doi:10.1086/308607
17pages, 4figuares, to appear in ApJ
arxiv created 1999/11/08 · openalex publication_date 2000/04/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Hard X-ray emissions from the Herbig Be star MWC 297 were discovered in three separate observations spanning 5 days in 1994 April with the Advanced Satellite for Cosmology and Astrophysics ( ASCA ). An X-ray flare was found at the beginning of the second observation with a maximum luminosity of ≈4.9 × 10 32 ergs s -1 , which is 5 times larger than that of the quiescent phase (the first observation). It then declined with an e -folding time of ≈5.6 × 10 4 s to the preflare level in the third observation. The X-ray spectra are explained by absorbed thin thermal plasma models. The temperature of ≈2.7 keV in the quiescent phase is significantly higher than those of main-sequence OB stars and similar to those of low-mass young stellar objects (YSOs) and other Herbig Ae/Be stars observed with ASCA . The temperature increased in the flare phase to about 6.7 keV at the flux maximum, then decreased to 3.2 keV in the decay phase. These facts strongly suggest that X-rays from Herbig Ae/Be stars, at least for MWC 297, are attributable to magnetic activity similar to that in low-mass YSOs. Since no theory predicts surface convection zones in massive stars like MWC 297, our results may require a mechanism other than the conventional stellar dynamo theory. Possible magnetic activity could be either the stellar interior shear or the inherited magnetic field from the parent molecular cloud.