NaSt1 ( aka Wolf-Rayet 122 ) is a peculiar emission-line star embedded in an extended nebula of [ N ii ] emission with a compact dusty core .
This object was characterized by Crowther & Smith ( 1999 ) as a Wolf-Rayet ( WR ) star cloaked in an opaque nebula of CNO-processed material , perhaps analogous to \eta Car and its Homunculus nebula , albeit with a hotter central source .
To discern the morphology of the [ N ii ] nebula we performed narrowband imaging using the Hubble Space Telescope and Wide-field Camera 3 .
The images reveal that the nebula has a disk-like geometry tilted \approx 12 ^ { \circ } from edge-on , composed of a bright central ellipsoid surrounded by a larger clumpy ring .
Ground-based spectroscopy reveals radial velocity structure ( \pm 10 km s ^ { -1 } ) near the outer portions of the nebula ’ s major axis , which is likely to be the imprint of outflowing gas .
Near-infrared adaptive-optics imaging with Magellan AO has resolved a compact ellipsoid of K _ { s } -band emission aligned with the larger [ N ii ] nebula , which we suspect is the result of scattered He i line emission ( \lambda 2.06 \mu m ) .
Observations with the Chandra X-ray Observatory have revealed an X-ray point source at the core of the nebula that is heavily absorbed at energies < 1 keV and has properties consistent with WR stars and colliding-wind binaries .
We suggest that NaSt1 is a WR binary embedded in an equatorial outflow that formed as the result of non-conservative mass transfer .
NaSt1 thus appears to be a rare and important example of a stripped-envelope WR forming through binary interaction , caught in the brief Roche-lobe overflow phase .