Herschel ★-PACS measurements of nitrogen enrichment in nebulae around Wolf–Rayet stars

• Published in: Monthly notices of the Royal Astronomical Society Vol. 441; no. 4; pp. 3065 - 3074
• Main Authors: Stock, D. J., Barlow, M. J.
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 11-07-2014
• Subjects: Astronomy; Matter & antimatter; Stars & galaxies; stars: mass-loss; stars: massive; stars: Wolf–Rayet–ISM: abundances; stars: winds, outflows; circumstellar matter
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stu724

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.