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The planetary nebula (PN) A30 is believed to have undergone a very latethermal pulse resulting in the ejection of knots of hydrogen-poor material.Using HST images we have detected the angular expansion of these knots andderived an age of 850+280-150 yr. To investigate the spectral and spatialproperties of the soft X-ray emission detected by ROSAT, we have obtainedChandra and XMM-Newton observations of A30. The X-ray emission from A30 can beseparated into two components: a point-source at the central star and diffuseemission associated with the hydrogen-poor knots and the cloverleaf structureinside the nebular shell. To help us assess the role of the current stellarwind in powering this X-ray emission, we have determined the stellar parametersof the central star of A 30 using a non-LTE model fit to its optical and UVspectrum. The spatial distribution and spectral properties of the diffuse X-rayemission is suggestive that it is generated by the post-born-again and presentfast stellar winds interacting with the hydrogen-poor ejecta of the born-againevent. This emission can be attributed to shock-heated plasma, as thehydrogen-poor knots are ablated by the stellar winds, under which circumstancesthe efficient mass-loading of the present fast stellar wind raises its densityand damps its velocity to produce the observed diffuse soft X-rays. Chargetransfer reactions between the ions of the stellar winds and material of theborn-again ejecta has also been considered as a possible mechanism for theproduction of diffuse X-ray emission, and upper limits on the expected X-rayproduction by this mechanism have been derived. The origin of the X-rayemission from the central star of A 30 is puzzling: shocks in the present faststellar wind and photospheric emission can be ruled out, while the developmentof a new, compact hot bubble confining the fast stellar wind seems implausible.

Rebirth of X-ray Emission from the Born-Again Planetary Nebula A 30