Multiwavelength observations of NaSt1 (WR 122): Equatorial mass loss and X-rays from an interacting Wolf-Rayet binary

Jon Mauerhan, Nathan Smith, Schuyler D. Van Dyk, Katie M. Morzinski, Laird M. Close, Philip M. Hinz, Jared R. Males, Timothy J. Rodigas

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


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. The object was previously characterized as a Wolf-Rayet (WR) star cloaked in an opaque nebula of CNO-processed material, perhaps analogous to η Car and its Homunculus nebula, albeit with a hotter central source. To discern the morphology of the [NII] nebula we performed narrow-band imaging using the Hubble Space Telescope and Wide-field Camera 3. The images reveal that the nebula has a disc-like geometry tilted ≈12° from edge-on, composed of a bright central ellipsoid surrounded by a larger clumpy ring. Ground-based spectroscopy reveals radial velocity structure (±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 MagellanAOhas resolved a compact ellipsoid of Ks-band emission aligned with the larger [N II] nebula, which we suspect is the result of scattered He I line emission (λ2.06 μm). 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.

Original languageEnglish (US)
Pages (from-to)2551-2563
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Jul 1 2015


  • Stars: Wolf-Rayet
  • Stars: emission-line, Be
  • Stars: individual: NaSt1
  • Stars: mass loss
  • Stars: peculiar

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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