Author ORCID Identifier


Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Physics and Astronomy

First Advisor

Dr. Russel J. White

Second Advisor

Dr. Todd Henry

Third Advisor

Dr. Wei-Chun Jao

Fourth Advisor

Dr. Sebastien Lepine

Fifth Advisor

Dr. Thomas Megeath


We explore star-star and cluster-cluster interactions in the Gum Nebula. The hot stars zeta Pup and gamma2 Vel powering the Gum Nebula photoevaporate dense cloud cores into cometlike shapes, called cometary globules. According to our analysis of HIRES spectra from the Keck I telescope, the stellar association near cometary globule CG 30 (FUV flux ratio G_0 = 6.6+3.2-2.7) has an accretion disk fraction of only 29% +/- 14%, low for the association’s young age of 0.5 -- 2 Myr. This low accretor fraction serves as evidence for hot-star erosion of young stars' protoplanetary disks.

We find another seven associations in the Gum Nebula, three of which are new (Yep 1, 2, and 3), for a total sample of 8. We identify a total of 1873 stellar members of these associations and obtain high dispersion CHIRON spectra of 284 stars. We also obtain high-quality spectra of 81 spectral standard stars with high SNR >~ 100. This catalogue is made available to all CHIRON users. The 8 associations are aged 2 -- 650 Myr and have G_0 = 2.1 -- 17.0. The five youngest associations (

We serendipitously discover that the associations UPK 535 and Yep 3 collided with each other 0.84 +/- 0.03 Myr ago. According to our Monte Carlo simulation, a mean of 54 +/- 7 pairs of stars come within 1 pc of each other. The tightest star-star interaction is on average 0.13 +/- 0.06 pc, or 27,000 +/- 12,000 AU, less than the radial extent of the Sun's Oort cloud (~50,000 AU). The strongest impulse on a star's Oort cloud comets (if present) is on average 2.7+3.1-1.1 Msun/pc2/km s, large enough to throw 410+560-190 of every million comets' inward and potentially cause heavy bombardment events. Other associations in the vicinity have also recently interacted, suggesting cluster interactions may play a larger role in star, cluster, and exoplanet evolution than previously considered, at least in the Gum Nebula straddling the Galactic plane.

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