  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
T<1MK; the detected ACIS-S photons can be plausibly explained by emission lines
of a very cool plasma near 200eV. The constantly low X-ray surface flux and the
flat-activity profile seen in optical CaII 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 200eV than given in the calibration.
