Astronomy and Astrophysics – Astronomy
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008apj...678l.121a&link_type=abstract
The Astrophysical Journal, Volume 678, Issue 2, pp. L121-L124.
Astronomy and Astrophysics
Astronomy
5
Stars: Binaries: Visual, Stars: Coronae, Stars: Individual (Hd 128620), Stars: Individual (Hd 128621), X-Rays: Stars
Scientific paper
Beginning in 2003, XMM-Newton snapshot monitoring of α Centauri (HD 128620, 128621: G2 V, K1 V) documented a steady fading of the primary's X-ray corona, which had all but disappeared by early 2005. The steep decline in LX was at odds with the previous two decades of high-energy measurements, which showed only modest variability of the Sun-like star. A Chandra LETGS spectrum in 2007 June, however, fully resolved the source of the curious X-ray darkening: a depletion of plasma above ~2 MK had substantially depressed the line spectrum where the XMM-Newton response peaks (λ<~30 Å), even though the overall coronal luminosity, dominated by longer wavelength emissions, had declined only slightly. This is reminiscent of the Sun's magnetic activity cycle, where the 2-3 MK active regions of sunspot maximum give way to the spatially pervasive, but cycle-independent, 1 MK ``quiet corona'' at minimum. This emphasizes that any discussion of cyclic coronal variability in low-activity stars will depend crucially on the energy coverage of the measurements.
Ayres Thomas R.
Judge Philip G.
Saar Steven H.
Schmitt Jurgen H. M. M.
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