Stock, DJ; Barlow, MJ; (2014) Herschel-PACS measurements of nitrogen enrichment in nebulae around Wolf–Rayet stars. Monthly Notices of the Royal Astronomical Society , 441 (4) pp. 3065-3074. 10.1093/mnras/stu724.

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Abstract

For three nebulae that have early-WN Wolf–Rayet exciting stars, NGC 6888, WR 8 and Abell 48, we have obtained Herschel-PACS line scans of the [N III] 57-μm and [O III] 88-μm lines, along with the 122- and 205-μm lines of [N II]. From the former two lines we have derived N2+/O2+ abundance ratios, equal to the overall N/O ratio under a wide range of nebular conditions. We find that all of the nebulae observed possess significant nitrogen enrichment, with derived N/O ratios greater than solar. The two nebulae with massive Wolf–Rayet exciting stars, NGC 6888 and WR 8 are found to have N/O ratios that are enhanced by factors of 7 – 10 relative to the solar N/O ratio, consistent with an origin as material ejected just before the onset of the Wolf–Rayet phase. The other nebula, Abell 48, has recently been reclassified as a member of the rare class of three planetary nebulae that have early-WN central stars and are not of Peimbert type I. We derive a nebular N/O ratio for it that is a factor of 4 enhanced relative to solar and slightly above the range of N/O values that have been measured for the other three members of its [WN] planetary nebula class.

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