期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 476, 期 1, 页码 908-926出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/sty212
关键词
stars: activity; stars: chromospheres; stars: late-type; stars: rotation
资金
- National Natural Science Foundation of China [11390371, 11233004, 11573035, 11625313, 11550110492]
- National Key Basic Research Program of China (973 program) [2014CB845701]
- Astronomical Big Data Joint Research Center
- Alibaba Cloud
- Chinese Academy of Sciences
- National Development and Reform Commission
We use the LAMOST spectra of member stars in Pleiades, M34, Praesepe, and Hyades to study how chromospheric activity varies as a function of mass and rotation at different age. We measured excess equivalent widths of H alpha, H beta, and Ca II K based on estimated chromospheric contributions from old and inactive field dwarfs, and excess luminosities are obtained by normalizing bolometric luminosity, for more than 700 late-type stars in these open clusters. Results indicate two activity sequences in cool spot coverage and Ha excess emission among GK dwarfs in Pleiades andMdwarfs in Praesepe and Hyades, paralleling with well-known rotation sequences. A weak dependence of chromospheric emission on rotation exists among ultrafast rotators in saturated regime with Rossby number Ro less than or similar to 0.1. In the unsaturated regime, chromospheric and coronal emission show similar dependence on Ro, but with a shift towards larger Ro, indicating chromospheric emission gets easily saturated than coronal emission, and/or convective turnover time-scales based on X-ray data do not work well with chromospheric emission. More interestingly, our analysis shows fully convective slow rotators obey the rotation-chromospheric activity relation similar to hotter stars, confirming the previous finding. We found correlations among H alpha, H beta, and Ca II K emissions, in which H alpha losses are more important than Ca II K for cooler and more active stars. In addition, a weak correlation is seen between chromospheric emission and photospheric activity that shows dependence on stellar spectral type and activity level, which provides some clues on how spot configuration varies as a function of mass and activity level.
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