A&A 508, 1417-1421 (2009)
DOI: 10.1051/0004-6361/200912945

51 Pegasi – a planet-bearing Maunder minimum candidate

K. Poppenhäger¹, J. Robrade¹, J. H. M. M. Schmitt¹, and J. C. Hall<sup>2

1</sup>  Hamburger Sternwarte, University Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
    e-mail: katja.poppenhaeger@hs.uni-hamburg.de
²  Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA

Received 21 July 2009 / Accepted 7 October 2009

Abstract
We observed 51 Peg, the first detected planet-bearing star, in a 55 ks XMM-Newton pointing and in 5 ks pointings each with Chandra HRC-I and ACIS-S. The star has a very low count rate in the XMM observation, but is clearly visible in the Chandra images due to the detectors' different sensitivity at low X-ray energies. This allows a temperature estimate for 51 Peg's corona of  MK; the detected ACIS-S photons can be plausibly explained by emission lines of a very cool plasma near 200 eV. The constantly low X-ray surface flux and the flat-activity profile seen in optical  data suggest that 51 Peg is a Maunder minimum star; an activity enhancement due to a Hot Jupiter, as proposed by recent studies, seems to be absent. The star's X-ray fluxes in different instruments are consistent with the exception of the HRC Imager, which might have a larger effective area below 200 eV than given in the calibration.

Key words: stars: coronae -- stars: activity -- stars: individual: 51 Peg -- X-rays: stars -- X-rays: individuals: 51 Peg

© ESO 2009

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