2012/07/25 by Yong Zhang, Chih-Hao Hsia, Sun Kwok · 1 citation
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Galactic halo #Galaxy #Halo #Interstellar medium #Nebula #Physics #Planetary nebula #Sky #Stars #Stellar, planetary, and galactic studies #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/755/1/53
15 pages, 2 figures, accepted by ApJ
openalex publication_date 2012/07/25 · arxiv created 2012/07/26 · arxiv updated 2015/06/05 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We report the discovery of an extended halo (∼40' in diameter) around the planetary nebula NGC 7293 (the Helix Nebula) observed in the 12 μm band from the Wide-field Infrared Survey Explorer all-sky survey. The mid-infrared halo has an axisymmetric structure with a sharp boundary to the northeast and a more diffuse boundary to the southwest, suggesting an interaction between the stellar wind and the interstellar medium (ISM). The symmetry axis of the halo is well aligned with that of a northeast arc, suggesting that the two structures are physically associated. We have attempted to fit the observed geometry with a model of a moving steady-state stellar wind interacting with the ISM. Possible combinations of the ISM density and the stellar velocity are derived from these fittings. The discrepancies between the model and the observations suggest that the stellar mass loss has a more complicated history, including possible time and angle dependences.