GeminiFocus June 2012 | Page 20

For more information: Miszalski, B., Crowther, P. A., De Marco, O., Köppen, J., Moffat, A.F.J., Acker, A., and Hillwig, T. C., “IC 4663: the first unambiguous [WN] Wolf-Rayet central star of a planetary nebula,” Monthly Notices of the Royal Astronomical Society, 423: 934, 2012 Crowther, P. A., Morris, P. W., and Smith, J. D., “An Ultraviolet to Mid-Infrared Study of the Physical and Wind Properties of HD 164270 (WC9) and Comparison to BD +30 3639 ([WC9]),” Astrophysical Journal, 636: 1033, 2006 Crowther, P. A., “Physical Properties of Wolf-Rayet stars,” Annual Review of Astronomy & Astrophysics, 45: 177, 2007 Miszalski, B., “Ongoing surveys for close binary central stars and wider implications,” IAU Symposium 283, in press (arXiv:1110.1831), 2012 Figure 4. Atmospheric compositions (by mass) of a [WN3] star (IC 4663), an O(He) star (K 1-27), a [WC11] star (PM 1-188), and a PG 1159 star (PG 1159-035, the prototype of the class), from our study and Werner and Herwig (2006). Note the similarity between the [WN3] and O(He), and the [WC11] and PG 1159, compositions. The carbon-rich [WC]→PG 1159 evolutionary sequence is well established, but only with IC 4663 are we able to newly propose the heliumrich equivalent [WN]→O(He). Only the main subset of elements are used to illustrate the similarity between the two separate groups. 20 nature found in most [WC] atmospheres, it has never reproduced the extreme helium-rich nature of O(He) stars or IC 4663. This suggests another explanation is required to produce [WN] central stars and their O(He) progeny. At present it is unclear what this mechanism may be. Binary interactions may be the most promising avenue for investigation, especially considering the rapidly growing evidence for binarity in the central stars of planetary nebulae (Miszalski, IAU Symposium 283, in press, 2012; and references therein). Lack of radial velocity variability in IC 4663 suggests it is not a binary system, but it may have been in the past. One possible explanation for the formation of R Coronae Borealis stars, which share a similar hydrogen-deficient and helium-rich composition to IC 4663, involves a merger of two white dwarfs. There may also be some follow-on evolutionary ties to helium-rich novae and cataclysmic variables. Whatever the reason behind the unusual composition of IC 4663, solving this puzzle will certainly require new ideas enriched by the prospect of future [WN] discoveries. We look forward to further developments in this exciting field of study. GeminiFocus Rauch, T., Dreizler, S., and Wolff, B., “Spectral analysis of O(He)-type post-AGB stars,” Astronomy and Astrophysics, 338: 651, 1998 Smith, L. F., and Aller, L. H., “A Detailed Comparison of the Spectra of a Planetary Nucleus and a WolfRayet Star,” Astrophysical Journal, 164: 275, 1971 Werner, K., and Herwig, F., “The Elemental Abundances in Bare Planetary Nebula Central Stars and the Shell Burning in AGB Stars,” Publications of the Astronomical Society of the Pacific, 118: 183, 2006 Brent Miszalski is a SALT research fellow at the South African Astronomical Observatory and Southern African Large Telescope (SALT). He can be reached at: [email protected] Paul Crowther is a professor within the Department of Physics and Astronomy at the University of Sheffield. He can be reached at: [email protected] Anthony Moffat is an emeritus professor in the Départment de physique of the Université de Montréal and a member of the Centre de recherche d’astrophysique du Québec. He can be reached at: [email protected] We acknowledge the contribution of our co-authors in this work, Orsola De Marco, Joachim Köppen, Agnès Acker, and Todd Hillwig. June2012