Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.9706s&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #97.06; Bulletin of the American Astronomical Society, Vol. 24, p.1273
Other
Scientific paper
Following the identification of the Cyg OB1 supershell, a nearly complete infrared supershell surrounding the Cyg OB1 association (Saken et al. 1992, ApJ, 397, 537), we have begun a search of the IRAS image data for other supershell candidates. This paper will discuss some of our candidates and their dynamical evolution. If we assume that the Cyg OB1 supershell was produced by winds and supernovae from spatially-distributed massive stars, we can model the dynamics as a set of ~ 3 overlapping bubbles. In spherical geometry, the radius and velocity of a bubble driven by a constant wind luminosity into a medium of constant ambient density rho_o = 1.4\: m_H\: n_o, yields a shell age of t = (2.2 times 10(5) yrs) (n_o / L38)(1/3) D_{1.5 \: kpc}(5/3) , far less than the association age of 5 Myr inferred from the main-sequence turnoff. Pushing all the scaling parameters to reasonable limits one could arrive at a bubble age of 10(6) yrs -- still a factor of 5 less than the inferred association age. We favor a scenario involving non-coeval star formation. The evolved supergiants in the H-R diagram probably formed several Myr earlier than the 25 -- 45 Msun stars now on the main sequence. If we adopt an age for Cyg OB1 in the range 1 -- 2 Myr, the initially most massive stars may now be Wolf-Rayet stars, and the superbubble could be driven entirely by winds. Other examples we have seen range from individual windblown shells around association sub-clusters (Cas OB6) to large cavities that have apparently blown out of the Galactic disk (R103). Thus, the picture that emerges is quite different from the canonical spherical supershell with a constant, central energy source. Instead, we propose that such shells start as overlapping bubbles from sub-clusters of the association, resulting in the observed non-spherical structure. Non-coeval star formation may be important in characterizing the dynamics of the shell, since the shell would grow to a fairly large size before the first SN, and the rise in mechanical luminosity over the first 4 -- 6 Myr.
Fesen Robert A.
Saken Jon Mitchell
Shull Michael J.
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