2009ApJ...694.1481M

We report the serendipitous detection by the XMM-Newton X-ray Observatory of an X-ray source at the position of the Type I (He- and N-rich) bipolar planetary nebula (PN) Hb 5. The Hb 5 X-ray source appears marginally resolved. While the small number of total counts (∼170) and significant off-axis angle of the X-ray source (∼7'.8) precludes a definitive spatial analysis, the morphology of the X-ray emission appears to trace the brightest features seen in optical images of Hb 5. The X-ray spectrum is indicative of a thermal plasma at a temperature between 2.4 and 3.7 MK and appears to display strong Neon emission. The inferred X-ray luminosity is L_X= 1.5x10³²erg/s. These results suggest that the detected X-ray emission is dominated by shock-heated gas in the bipolar nebula, although we cannot rule out the presence of a pointlike component at the position of the central star. The implications for and correspondence with current models of shock-heated gas in PNe is discussed.