Magnetic activity among cool stars in the HR-diagram

报告题目    Magnetic activity among cool stars in the HR-diagram

报告人     Prof. Juergen Schmitt

报告人单位  Hamburg Observatory, Germany

报告语言   英文

报告时间   2023128(星期五)上午10:00-11:30

报告地点   1号楼412会议室



Magnetic fields are the ultimate origin of a plethora of so-called "activity" phenomena observed on the Sun over almost the entire electromagnetic range.  Similar features of magnetic "activity" can be observed in many thousands of stars. Soft X-ray emission diagnoses hot, thermal plasma heated up to coronal temperatures of more than a million degrees and is the best proxy indicator for such magnetic activity since it can be detected against a completely X-ray dark stellar photospheric background. UV- and optical emission diagnoses cooler plasma and in particular the photospheric magnetic fields themselves, however, the applicability and usefulness of these indicators depend strongly on the effective temperature of the underlying star.  Nonthermal emission is diagnosed at radio and gamma-ray wavelengths and can usually be detected only on stars with activity levels some orders of magnitude above solar level.  I review the magnetic activity signatures observed in the cool half of the HR-diagram primarily from a X-ray point of view to delineate which stars show magnetic activity, but argue at the same time that all cool stars are magnetically active to some extent.   I will also present results from the recently conducted eROSITA all-sky survey.