Central stars of planetary nebulae
In addition to studies of massive stars, some low and intermediate mass stars pass through a phase at the end of their (long) life when a 'planetary nebula' is being formed, in which late pulses remove surface hydrogen layers, revealing a spectrum reminiscent of massive stars.
A subset of these central stars of planetary nebulae (CSPN) exhibit a Wolf-Rayet spectrum. I have studied a variety of these with Orsola De Marco, for example SwSt1.
Although many examples of carbon-sequence Wolf-Rayet CSPNe are known, we have identified the first unambiguous example of a nitrogen-sequence CSPNe, IC4663. The image of IC4663 on this page shows a greyscale Gemini image ([OIII]) plus a colour HST composite (RGB = Halpha, [OIII], V-band).
An ultraviolet to mid-infrared study of the physical and wind properties of HD164270 (WC9) and comparison to BD+30 3639 [WC9], Crowther, Morris and Smith 2006.
Physical and wind properties of [WC] stars, Crowther, 2007.
IC 4663: The first unambiguous [WN] Wolf-Rayet central star of a planetary nebula, Miszalski et al. 2012.