期刊
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN
卷 63, 期 -, 页码 S547-S554出版社
OXFORD UNIV PRESS
DOI: 10.1093/pasj/63.sp2.S547
关键词
stars: activity; stars: chromospheres; stars: late-type; stars: Population II
资金
- Japan Society for the Promotion of Science [22540255]
- Grants-in-Aid for Scientific Research [22540255] Funding Source: KAKEN
Based on the near-IR spectra of 33 late-type stars in a wide metallicity range (mainly dwarfs and partly giants) obtained with IRCS+AO188 of the Subaru Telescope, we confirmed that the He I 10830 angstrom line is seen in absorption in almost all moderately to extremely metal-poor stars of thick disk and halo population (from [Fe/H] similar to -0.5 down to [Fe/H] similar to -3.7), the strength of which is almost constant irrespective of the metallicity. This is evidence that chromospheric activity at a basal level persists, even for such old stars, despite that their rotations are considered to be slowed down and incapable of sustaining a dynamo, suggesting that some kind of chromospheric heating mechanism independent of rotation/magnetism (e.g., acoustic heating) may take place.
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