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19 April 2024 |
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Article overview
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Stellar activity with LAMOST - II. Chromospheric activity in open clusters | | Xiang-Song Fang
; Gang Zhao
; Jing-Kun Zhao
; Yerra Bharat Kumar
; | | Date: |
23 Jan 2018 | | Abstract: | We use the LAMOST spectra of member stars in Pleiades, M34, Praesepe, and
Hyades to study how chromospheric activity vary as a function of mass and
rotation at different age. We measured excess equivalent widths of H$alpha$,
H$eta$, and Ca~{sc 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 H$alpha$ excess emission among GK dwarfs in Pleiades and M dwarfs in
Praesepe and Hyades, paralleling with well known rotation sequences. A weak
dependence of chromospheric emission on rotation exists among ultra fast
rotators in saturated regime with Rossby number Ro$lesssim0.1$. In the
unsaturated regime, chromospheric and coronal emission show similar dependence
on Ro, but with a shift toward 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 show 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$eta$, and
Ca~{sc ii} K emissions, in which H$alpha$ losses are more important than
Ca~{sc ii} K for cooler and more active stars. In addition, a weak correlation
is seen between chromospheric emission and photospheric activity that shows
dependency on stellar spectral type and activity level, which provides some
clues on how spot configuration vary as a function of mass and activity level. | | Source: | arXiv, 1801.7410 | | Services: | Forum | Review | PDF | Favorites | |
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