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The Chandra Deep Field-North Survey: XVII. Evolution of magnetic activity in old late-type stars

E. D. Feigelson·A. E. Hornschemeier·G. Micela·F. E. Bauer·D. M. Alexander·W. N. Brandt·F. Favata·S. Sciortino·G. P. Garmire·Penn State·Johns Hopkins·Palermo·Cambridge·ESTEC
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Abstract

The extremely sensitive Chandra Deep Field-North (CDF-N) pencil-beam X-ray survey is used to identify and characterize the X-ray emission from old high-latitude main sequence Galactic stars. Our principal goal is to investigate the expected long-term decay of magnetic activity of late-type stars due to the gradual spindown of stellar rotation from a magnetized stellar wind. Eleven X-ray sources constitute a well-defined sample of 2 G, 2 K0-K4, and 7 M2-M5 stars with median distance around 300 pc. X-ray luminosities are typically log Lx ~ 27 erg/s and is dominated by flares rather than quiescent coronal emission. Models of the population indicates that the CDF-N stars are the most magnetically active old disk stars. A substantial decline in X-ray luminosities over the 1<t<11 Gyr age interval is required. This is the first demonstration that the coronal and flaring components of stellar magnetic activity -- and presumably the interior magnetic dynamos responsible for the reconnecting fields at the stellar surface -- exhibit long-term decay over the age of the Galactic disk. The model that best fits the magnitudes, spectral types and X-ray luminosities of the sample has Lx ~ 1/t^2 erg/s which is faster than the 1/t decay rate predicted from widely accepted rotational spindown rates and X-ray-activity relations.

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E. D. Feigelson, A. E. Hornschemeier, G. Micela, F. E. Bauer, D. M. Alexander, W. N. Brandt, F. Favata, S. Sciortino, G. P. Garmire, Penn State, Johns Hopkins, Palermo, Cambridge, ESTEC. 2004-05-03. The Chandra Deep Field-North Survey: XVII. Evolution of magnetic activity in old late-type stars. https://doi.org/10.1086/422248

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