Looking Deep into the Cat's Eye: Structure and Rotation in the Fast Wind of the PN Central Star of NGC 6543

We present HST/STIS time-series spectroscopy of the central star of the "Cat's Eye" planetary nebula NGC 6543. Intensive monitoring of the UV lines over a 5.8 hr period reveals well-defined details of large-scale structure in the fast wind, which are exploited to provide new constraints on the rotation rate of the central star. We derive characteristics of the line profile variability that support a physical origin due to corotating interaction regions (CIRs) that are rooted at the stellar surface. The recurrence time of the observed spectral signatures of the CIRs is used to estimate the rotation period of the central star and, adopting a radius between 0.3 and 0.6 R _⊙ constrains the rotational velocity to the range 54 km s^-1 <= v _rot <= 108 km s^-1. The implications of these results for single star evolution are discussed based on models calculated here for low-mass stars. Our models predict a subsurface convective layer in NGC 6543 which we argue to be causally connected to the occurrence of structure in the fast wind.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program 12489.