@article{discovery10093774,
           pages = {3065--3074},
            note = {This version is the version of record. For information on re-use, please refer to the publisher's terms and conditions.},
          number = {4},
         journal = {Monthly Notices of the Royal Astronomical Society},
            year = {2014},
           title = {Herschel-PACS measurements of nitrogen enrichment in nebulae around Wolf-Rayet stars},
           month = {July},
          volume = {441},
       publisher = {OXFORD UNIV PRESS},
        keywords = {circumstellar matter, stars: massive, stars: mass-loss, stars: winds, outflows, stars: Wolf-Rayet-ISM: abundances},
        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-{\ensuremath{\mu}}m and [O III] 88-{\ensuremath{\mu}}m lines, along with the 122- and 205-{\ensuremath{\mu}}m 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.},
             url = {https://doi.org/10.1093/mnras/stu724},
          author = {Stock, DJ and Barlow, MJ}
}