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Type of Document	Dissertation
Author	Sargent, Anneila Isabel
URN	etd-09082004-115311
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-09082004-115311
Title	Molecular clouds and star formation
Degree	PhD
Option	Astronomy
Advisory Committee	Advisor Name Title Peter Goldreich Committee Chair
Keywords	nebulae:general clusters:associations interstellar:molecules stars:formation
Date of Defense	1977-10-14
Availability	unrestricted
Abstract NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in the .pdf document. Observations of the J = 1 -> 0 transition of 12CO were made in and around the region occupied by the young OB association Cepheus OB3 to determine the connection between newly formed stars and molecular clouds. An extended (20 pc x 60 pc) molecular cloud was detected and mapped, and additional observations of 13CO and H2CO were made at selected positions. The total mass of the cloud is [...]. A range of velocities is seen over the cloud complex. This is comparable with the stellar velocities in the association. Within the molecular cloud are found three regions in which different stages of star formation are identified. In one an embedded star may be present. Another appears to be collapsing on a time scale of [...] years to form a new subgroup of the OB association. The mass of this region, [...], is sufficient to produce only the number of O and B stars typically found in association subgroups, suggesting that lower mass stars must form under different conditions. The third displays signs of enhanced density and is probably the precursor of a star forming region. All three regions are situated in that part of the molecular cloud which is closest to the association stars. The membership and ages of the subgroups of the Cepheus OB3 association have been re-examined, and their places of origin determined. Ages of [...] years and [...] years are found for younger and older subgroups respectively. Their birthplaces are not coincident but are situated at that end of the cloud where star formation still appears to be taking place. The younger subgroup appears to have formed closer to the active regions than did the older subgroup, so that there is a well-defined age sequence across the association which continues into the cloud. There is currently little direct interaction between the stars and the molecular cloud, although a few younger subgroup stars still lie close to or within the complex. The absence of primeval gas in the environs of the older subgroup is attributed to the unusually high velocity of separation between these stars and the cloud. It appears that the younger and still-forming subgroups of Cepheus OB3 are created in a different way from the older subgroup. However, the way in which star formation is initiated in this association remains uncertain.
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