Details

Autor(en) / Beteiligte

• Jeffries, R. D.
• Jackson, R. J.
• Briggs, K. R.
• Evans, P. A.
• Pye, J. P.

Titel

Investigating coronal saturation and supersaturation in fast-rotating M-dwarf stars

Ist Teil von

• Monthly notices of the Royal Astronomical Society, 2011-03, Vol.411 (3), p.2099-2112

Ort / Verlag

Oxford, UK: Blackwell Publishing Ltd

Erscheinungsjahr

2011

Link zum Volltext

Quelle

Wiley Online Library (Online service)

Beschreibungen/Notizen

• 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 'supersaturation'. 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, supersaturation is not convincingly displayed by M-dwarfs, despite the presence of many objects in our sample with log N R < −1.8, where supersaturation is observed to occur in higher mass stars. Instead, it appears that a short rotation period is the primary predictor of supersaturation; P ≤ 0.3 d for K-dwarfs and perhaps P ≤ 0.2 d for M-dwarfs. These observations favour the 'centrifugal stripping' model for supersaturation, where coronal structures are forced open or become radiatively unstable as the Keplerian corotation radius moves inside the X-ray-emitting coronal volume.