The morphology of the ǫ Eridani dust ring is reproduced by a numerical simulation of dust particles captured into the 5:3 and 3:2 exterior mean-motion resonances with a 0.3 eccentricity 10 −4 solar mass planet at periastron at a semi-major axis of 40 AU. The morphology will differ when the planet is at apastron, in about 140 years. Moderate eccentricity planets in outer extra-solar systems will cause observable variations in the morphology of associated dusty rings.

Outflows from young stellar objects (YSOs) have been identified as a possible source of turbulence in molecular clouds. To investigate the relationship between outflows, cloud dynamics, and turbulence, we compare the kinematics of the molecular gas associated with NGC 1333, traced in 13 CO (1-0), with the distribution of YSOs within. We find a velocity dispersion of $1-1.6 km s À1 in 13 CO that does not significantly vary across the cloud and is uncorrelated with the number of nearby young stellar outflows identified from optical and submillimeter observations. However, from velocity channel maps we identify about 20 depressions in the 13 CO intensity of scales k0.1-0.2 pc and velocity widths 1-3 km s À1 . The depressions exhibit limb-brightened rims in both individual velocity channel maps and position-velocity diagrams, suggesting that they are slowly expanding cavities. We interpret these depressions to be remnants of past YSO outflow activity: if these cavities are presently empty, they would fill in on timescales of $10 6 yr. This can exceed the lifetime of a YSO outflow phase or the transit time of the central star through the cavity, explaining the absence of any clear correlation between the cavities and YSO outflows. We find that the momentum and energy deposition associated with the expansion of the cavities is sufficient to power the turbulence in the cloud. In this way we conclude that the cavities are an important intermediate step between the conversion of YSO outflow energy and momentum into cloud turbulent motions.

To ascertain the nature of the brightest compact mid-infrared sources in the Large Magellanic Cloud (LMC), we have applied an updated version of the Buchanan et al. (2006) 2MASS-MSX color classification system, which is based on the results of Spitzer Space Telescope spectroscopy, to a mid-infrared (8 µm) flux-limited sample of 250 LMC objects for which 2MASS and MSX photometry is available. The resulting 2MASS-MSX ("JHK8") color-based classifications of these sources, which constitute the most mid-IR-luminous objects in the LMC, were augmented, cross-checked, and corrected where necessary via a variety of independent means, such that only 47 sources retain tentative classifications and only 10 sources cannot be classified at all. The sample is found to consist primarily of carbon-rich asymptotic giant branch (AGB) stars (∼ 35%), red supergiants (∼18%), and compact H ii regions (∼ 30%), with additional, small populations of oxygen-rich AGB stars (∼ 4%), dusty, early-type emission-line stars (∼ 3%), and foreground, O-rich AGB stars in the Milky Way (∼ 3%). The very large ratio of C-rich to O-rich objects among the luminous and heavily dust-enshrouded AGB stars in our LMC IR source sample is consistent with the hypothesis that