The Stellar Wind Bubble NGC2359 - Part One - CO VLA and Optical Observations

Details The Stellar Wind Bubble NGC2359 - Part One - CO VLA and Optical Observations The Stellar Wind Bubble NGC2359 - Part One - CO VLA and Optical Observations

Jan 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981apj...243..184s&link_type=abstract

Astrophysical Journal, Vol.243, P. 184, 1981

Astronomy and Astrophysics

Astrophysics

36

Scientific paper

The symmetric ring nebula NGC 2359 ≡ S298 is believed to be an interstellar bubble blown by stellar winds from the Wolf-Rayet star HD 56925. Microwave observations of the nebula in CO and 13CO, and 20 cm VLA observations, are compared to narrow-band [O III] photographs of the region. Tile observations demonstrate for the first time that the stellar wind bubble is interacting with neutral material. Three CO clouds are observed, spread in velocity over 30 km s-1 and centered on the mean Hα velocity for the H II region. The CO velocities fall within the velocity range observed in the optical shell, suggesting that the neutral clouds may be driven to supersonic velocities by the stellar winds. At least one of the clouds appears to be in direct contact with the stellar wind bubble. To test for signs of recent star formation, a search was made for H2O maser emission, with negative results.
Optical counterparts for two of the CO clouds have been identified on narrow-band filter photographs of the nebula. The high resolution 20 cm VLA observations resolve the filamentary structure of the shell, completing the bubble in regions obscured by the CO clouds. The VLA map agrees well with the optical photographs in regions which are free of CO. A search at 6 and 20 cm failed to reveal radio continuum emission from the W-R star at levels above 0.6 and 2.0 mJy, respectively, providing an upper limit for the mass-loss rate of Mdot = 7 × 10-5 Msun.
Kinematic parameters inferred from the observations are compared to theoretical models for the evolution of stellar wind shells. It is shown that modest mass-loss rates can account for the supersonic motions observed in NGC 2359, even for models in which the stellar winds impact directly on the shell without the aid of a hot intermediate layer.
Simple isotropic homogeneous models for the evolution of stellar wind shells produce serious inconsistencies when applied to NGC 2359. These assumptions are clearly violated in this object, which is bounded by dense neutral clouds in the east, and by low density ionized gas in the west. Pressure effects from the nonuniformly ionized ambient medium may contribute to the stellar wind pressures and modify the evolution of the nebula.

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