The Spatially Resolved Bipolar Nebula of Sakurai's Object

Sakurai's object (V4334 Sgr), the final flash object discovered in the mid-1990s, underwent rapid cooling during the first decade of the 21st century becoming as faint as K ∼ 25. This stage of evolution has ceased. Between observations in 2010 September and 2013 April V4334 Sgr brightened >2 mag to K = 14.2 and the effective temperature increased to ∼590 K. AO images show a central source and two extended globules defining a 13° position angle. The globules span a spatial extent of ∼0 3 in 2013. This spatial extent is consistent with sizes derived from spectral energy distributions taken over the previous decade and a debris cloud expanding at 0.055 mas d −1 since late 1998. Near-simultaneous 0.85–2.5 μm spectra reveal helium lines attributed to a wind-interaction shock. The He i 1.0830 μm emission has a spectral width of ∼1000 km s −1 and a spatial extent of ∼1 4. The helium shell is fragmented, spatially asymmetric, and five times larger than the dust debris cloud. [C i ] and [N i ] forbidden lines are present in the 1 μm region spectrum. The forbidden line spectrum is similar to that of proto-planetary nebulae. The [C i ] 9850 Å line is spatially extended. The expansion velocity and change of angular size limit the distance to 2.1–3.7 kpc.