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Title: The ups and downs of α Centauri

The following is a progress report on the long-term coronal (T ∼ 1 MK) activity of α Centauri A (HD 128620: G2 V) and B (HD 128621: K1 V). Since 2005, Chandra X-Ray Observatory has carried out semiannual pointings on AB, mainly with the High Resolution Camera, but also on two occasions with the Low-Energy Transmission Grating Spectrometer, fully resolving the close pair in all cases. During 2008-2013, Chandra captured the rise, peak, and initial decline of B's coronal luminosity. Together with previous high states documented by ROSAT and XMM-Newton, the long-term X-ray record suggests a period of 8.1 ± 0.2 yr, compared to 11 yr for the Sun, with a minimum-to-peak contrast of 4.5, about half the typical solar cycle amplitude. Meanwhile, the A component has been mired in a Maunder-Minimum-like low state since 2005, initially recognized by XMM-Newton. But now, A finally appears to be climbing out of the extended lull. If interpreted simply as an overlong cycle, the period would be 19.2 ± 0.7 yr, with a minimum-to-peak contrast of 3.4. The short X-ray cycle of B, and possibly long cycle of A, are not unusual compared with the diverse (albeit much lower amplitude) chromospheric variations recorded,more » for example, by the HK Project. Further, the deep low state of A also is not unusual, but instead is similar to the L {sub X}/L {sub bol} of the Sun during recent minima of the sunspot cycle.« less
Authors:
 [1]
  1. Center for Astrophysics and Space Astronomy, 389 UCB, University of Colorado, Boulder, CO 80309 (United States)
Publication Date:
OSTI Identifier:
22339994
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (New York, N.Y. Online); Journal Volume: 147; Journal Issue: 3; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; CAMERAS; CAPTURE; COMPARATIVE EVALUATIONS; LUMINOSITY; PEAKS; POWER TRANSMISSION; RESOLUTION; SOLAR CYCLE; SPECTROMETERS; SUN; SUNSPOTS; VARIATIONS; X RADIATION