J/AJ/129/393           UBV photometry in W3                         (Oey+, 2005)
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Beginning of ReadMe : J/AJ/129/393 UBV photometry in W3 (Oey+, 2005) ================================================================================ Hierarchical triggering of star formation by superbubbles in W3/W4. Oey M.S., Watson A.M., Kern K., Walth G.L. <Astron. J., 129, 393-401 (2005)> =2005AJ....129..393O ================================================================================ ADC_Keywords: Interstellar medium ; Photometry, UBV Keywords: ISM: bubbles - ISM: clouds - ISM: individual (W3, W4) - ISM: structure - open clusters and associations: individual (IC 1795, IC 1805) - stars: formation Abstract: It is generally believed that expanding superbubbles and mechanical feedback from massive stars trigger star formation, because there are numerous examples of superbubbles showing secondary star formation at their edges. However, although these systems show an age sequence, they do not provide strong evidence of a causal relationship. The W3/W4 Galactic star-forming complex suggests a three-generation hierarchy: the supergiant shell structures correspond to the oldest generation; these triggered the formation of IC 1795 in W3, the progenitor of a molecular superbubble that in turn triggered the current star-forming episodes in the embedded regions W3-North, W3-Main, and W3-OH. We present UBV photometry and spectroscopic classifications for IC 1795, which show an age of 3-5 Myr. This age is intermediate between the reported 6-20 Myr age of the supergiant shell system and the extremely young ages (10^4^-10^5^yr) for the embedded knots of the ultracompact HII regions, W3-North, W3-Main, and W3-OH. Thus, an age sequence is indeed confirmed for the entire W3/W4 hierarchical system. This therefore provides some of the first convincing evidence that superbubble action and mechanical feedback are indeed a triggering mechanism for star formation. Description: Our UBV imaging was obtained on 1999 October 6-9 at the 84cm telescope of the Observatorio Astronomico Nacional at San Pedro Martir (SPM), Baja California Norte, Mexico. Spectroscopic observations of candidates for the earliest-type stars were obtained with the 2.1m telescope at SPM during the nights of 1999 October 15-17.

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