Eve J. Lee

Variations in the Galactic star formation rate and density thresholds for star formation

The conversion of gas into stars is a fundamental process in astrophysics and cosmology. Stars are known to form from the gravitational collapse of dense clumps in interstellar molecular clouds, and it has been proposed that the resulting star formation rate is proportional to either the amount of mass above a threshold gas surface density, or the gas volume density. These star formation prescriptions appear to hold in nearby molecular clouds in our Milky Way Galaxys disc as well as in distant galaxies where the star formation rates are often much larger. The inner 500 pc of our Galaxy, the Central Molecular Zone (CMZ), contains the largest concentration of dense, high-surface density molecular gas in the Milky Way, providing an environment where the validity of star formation prescriptions can be tested. Here, we show that by several measures, the current star formation rate in the CMZ is an order-of-magnitude lower than the rates predicted by the currently accepted prescriptions. In particular, the region 1 degrees several 10(3) cm(-3)) molecular gas - enough to form 1000 Orion-like clusters - but the present-day star formation rate within this gas is only equivalent to that in Orion. In addition to density, another property of molecular clouds must be included in the star formation prescription to predict the star formation rate in a given mass of molecular gas. We discuss which physical mechanisms might be responsible for suppressing star formation in the CMZ.

Make Super-Earths, Not Jupiters: Accreting Nebular Gas onto Solid Cores at 0.1?AU and Beyond

Close-in super-Earths having radii 1--4

BREEDING SUPER-EARTHS AND BIRTHING SUPER-PUFFS IN TRANSITIONAL DISKS

R_\oplus

To Cool is to Accrete: Analytic Scalings for Nebular Accretion of Planetary Atmospheres

may possess hydrogen atmospheres comprising a few percent by mass of their rocky cores. We determine the conditions under which such atmospheres can be accreted by cores from their parent circumstellar disks. Accretion from the nebula is problematic because it is too efficient: we find that 10-

RADIATION-HYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR OUTFLOWS: SYNTHETIC OBSERVATIONS AND DATA COMPARISONS

M_\oplus

SUBSTELLAR OBJECTS IN NEARBY YOUNG CLUSTERS (SONYC). II. THE BROWN DWARF POPULATION OF ρ OPHIUCHI

cores embedded in solar metallicity disks tend to undergo runaway gas accretion and explode into Jupiters, irrespective of orbital location. The threat of runaway is especially dire at

PHYSICAL PROPERTIES OF MOLECULAR CLOUDS FOR THE ENTIRE MILKY WAY DISK

\sim

OBSERVATIONAL EVIDENCE OF DYNAMIC STAR FORMATION RATE IN MILKY WAY GIANT MOLECULAR CLOUDS

0.1 AU, where solids may coagulate on timescales orders of magnitude shorter than gas clearing times; thus nascent atmospheres on close-in orbits are unlikely to be supported against collapse by planetesimal accretion. The time to runaway accretion is well approximated by the cooling time of the atmospheres innermost convective zone, whose extent is controlled by where H

TIME-VARYING DYNAMICAL STAR FORMATION RATE

_2

A metallicity recipe for rocky planets

dissociates. Insofar as the temperatures characterizing H