Investigating the Circumstellar Environments of the Cool Hypergiants

Details Investigating the Circumstellar Environments of the Cool Hypergiants Investigating the Circumstellar Environments of the Cool Hypergiants

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.6502s&link_type=abstract

American Astronomical Society, AAS Meeting #211, #65.02; Bulletin of the American Astronomical Society, Vol. 39, p.855

Astronomy and Astrophysics

Astronomy

Scientific paper

The cool hypergiants are among a few highly unstable, very massive stars that lie on or near the empirical upper luminosity boundary in the HR diagram (Humphreys & Davidson 1979, 1994). As a consequence of the very high mass-loss rates observed for these stars (>10-5 Mo/yr), they are expected to have extensive circumstellar (CS) nebulosity (e.g. IRC+10420, VY CMa and NML Cyg). I investigate the cool hypergiants' CS environments and discuss how the presence and extent of CS nebulosity provide a record of their evolutionary histories. Each star's local interstellar environment can also play an important role in shaping the CS nebulosity and determining what we observe. I will focus on the interaction between NML Cyg's strong post-Main Sequence wind and the disruptive UV radiation from over one hundred massive O stars within the relatively nearby (>80; pc) and powerful Cyg OB2 association. The extremely luminous OH/IR M-type hypergiant NML Cyg is surrounded by an inverted HII region, where gas is ionized externally by Lyman continuum radiation from Cyg OB2. High-angular resolution, high-contrast HST and mid-IR AO images of NML Cyg reveal an enigmatic asymmetric CS cocoon likely shaped through photo-dissociation and grain destruction by the near-UV radiation from the massive, hot stars within Cyg OB2.

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