Optical, UV, and X-ray evidence for a 7-yr stellar cycle in Proxima Centauri Article Swipe
YOU?
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· 2016
· Open Access
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· DOI: https://doi.org/10.1093/mnras/stw2570
· OA: W2528041613
Stars of stellar type later than about M3.5 are believed to be fully\nconvective and therefore unable to support magnetic dynamos like the one that\nproduces the 11-year solar cycle. Because of their intrinsic faintness, very\nfew late M stars have undergone long-term monitoring to test this prediction,\nwhich is critical to our understanding of magnetic field generation in such\nstars. Magnetic activity is also of interest as the driver of UV and X-ray\nradiation, as well as energetic particles and stellar winds, that affect the\natmospheres of close-in planets that lie within habitable zones, such as the\nrecently discovered Proxima b. We report here on several years of optical, UV,\nand X-ray observations of Proxima Centauri (GJ 551; dM5.5e): 15 years of ASAS\nphotometry in the V band (1085 nights) and 3 years in the I band (196 nights),\n4 years of Swift XRT and UVOT observations (more than 120 exposures), and 9\nsets of X-ray observations from other X-ray missions (ASCA, XMM-Newton, and\nthree Chandra instruments) spanning 22 years. We confirm previous reports of an\n83-day rotational period and find strong evidence for a 7-year stellar cycle,\nalong with indications of differential rotation at about the solar level.\nX-ray/UV intensity is anti-correlated with optical V-band brightness for both\nrotational and cyclical variations. From comparison with other stars observed\nto have X-ray cycles we deduce a simple empirical relationship between X-ray\ncyclic modulation and Rossby number, and we also present Swift UV grism spectra\ncovering 2300-6000 {\\AA}.\n
