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26 April 2024 |
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Investigating coronal saturation and super-saturation in fast-rotating M-dwarf stars | | R. D. Jeffries
; R. J. Jackson
; K. R. Briggs
; P. A. Evans
; J. P. Pye
; | | Date: |
11 Oct 2010 | | Abstract: | At fast rotation rates the coronal activity of G- and K-type stars has been
observed to "saturate" and then decline again at even faster rotation rates --
a phenomenon dubbed "super-saturation". In this paper we investigate coronal
activity in fast-rotating M-dwarfs using deep XMM-Newton observations of 97
low-mass stars of known rotation period in the young open cluster NGC 2547, and
combine these with published X-ray surveys of low-mass field and cluster stars
of known rotation period. Like G- and K-dwarfs, we find that M-dwarfs exhibit
increasing coronal activity with decreasing Rossby number N_R, the ratio of
period to convective turnover time, and that activity saturates at L_x/L_bol ~
10^-3 for log N_R < -0.8. However, super-saturation is not convincingly
displayed by M-dwarfs, despite the presence of many objects in our sample with
log N_R < -1.8, where super-saturation is observed to occur in higher mass
stars. Instead, it appears that a short rotation period is the primary
predictor of super-saturation; P <=0.3d for K-dwarfs and perhaps P <=0.2d for
M-dwarfs. These observations favour the "centrifugal stripping" model for
super-saturation, where coronal structures are forced open or become
radiatively unstable as the Keplerian co-rotation radius moves inside the X-ray
emitting coronal volume. | | Source: | arXiv, 1010.2152 | | Services: | Forum | Review | PDF | Favorites | |
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