5,010 research outputs found
Modeling the submillimeter emission from the Cepheus A young stellar cluster: Evidence for large scale collapse
Evidence for a large scale flow of low density gas onto the Cepheus A young
stellar cluster is presented. Observations of K-band near-infrared and
multi-transition CS and N2H+ millimeter line emission are shown in relation to
a sub-millimeter map of the cool dust around the most embedded stars. The
near-infrared emission is offset from the dust peak suggesting a shift in the
location of star formation over the history of the core. The CS emission is
concentrated toward the core center but N2H+ peaks in two main cores offset
from the center, opposite to the chemistry observed in low mass cores. A
starless core with strong CS but weak N2H+ emission is found toward the western
edge of the region. The average CS(2-1) spectrum over the cluster forming core
is asymmetrically self-absorbed suggesting infall. We analyze the large scale
dynamics by applying a one-dimensional radiative transfer code to a model
spherical core with constant temperature and linewidth, and a density profile
measured from an archival 850 micron map of the region. The best fit model that
matches the three CS profiles requires a low CS abundance in the core and an
outer, infalling envelope with a low density and undepleted CS abundance. The
integrated intensities of the two N2H+ lines is well matched with a constant
N2H+ abundance. The envelope infall velocity is tightly constrained by the
CS(2-1) asymmetry and is sub-sonic but the size of the infalling region is
poorly determined. The picture of a high density center with depleted CS slowly
accreting a low density outer envelope with normal CS abundance suggests that
core growth occurs at least partially by the dissipation of turbulent support
on large scales.Comment: 8 pages, 5 figures, accepted by Astronomy and Astrophysic
Groupoid equivalence and the associated iterated crossed product
Given groupoids and and a -equivalence we may form the
transformation groupoid . Given a separable groupoid
dynamical system we may restrict to
an action of on and form the crossed product . We show that there is an action of on
and that the iterated crossed product is
naturally isomorphic to the crossed product .Comment: 18 pages; changed typo in titl
870 micron Imaging of a Transitional Disk in Upper Scorpius: Holdover from the Era of Giant Planet Formation?
We present 880 micron images of the transition disk around the star [PZ99]
J160421.7-213028, a solar-mass star in the nearby Upper Scorpius association.
With a resolution down to 0.34 arcsec, we resolve the inner hole in this disk,
and via model fitting to the visibilities and spectral energy distribution we
determine both the structure of the outer region and the presence of sparse
dust within the cavity. The disk contains about 0.1 Jupiter masses of
mm-emitting grains, with an inner disk edge of about 70 AU. The inner cavity
contains a small amount of dust with a depleted surface density in a region
extending from about 20-70 AU. Taking into account prior observations
indicating little to no stellar accretion, the lack of a binary companion, and
the presence of dust near 0.1 AU, we determine that the most likely mechanism
for the formation of this inner hole is the presence of one or more giant
planets.Comment: 12 pages, 7 figures. To appear in the Astrophysical Journa
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