37 research outputs found
Disc-Disc Encounters between Low-Mass Protoplanetary Accretion Discs
Simulations of the collapse and fragmentation of turbulent molecular clouds
and dense young clusters show that encounters between disc-surrounded stars are
relatively common events which should significantly influence the resulting
disc structure. In turn this should alter the accretion rate of disc matter
onto the star and the conditions under which planet formation occurs. Although
the effects of star-disc encounters have been previously investigated, very
little is known about encounters where both stars are surrounded by discs. In
this paper encounters of such disc-disc systems are studied quantitatively. It
is found that for low-mass discs (= 0.01 M_\sun) the results from
star-disc encounters can be straightforwardly generalized to disc-disc
encounters as long as there is no mass transport between the discs. Differences
to star-disc encounters occur naturally where significant amounts of matter are
transported between the discs. In this case it is found that although the mass
distribution does not change significantly, matter caught onto highly eccentric
orbits is transported surprisingly far inside the disc. The captured mass
partly replenishes the disc, but has a much lower angular momentum. This can
lead to a reduction of the angular momentum in the entire disc and thus
considerably increased accretion shortly after the encounter as well as in the
long term.Comment: 24 pages, 10 figures, accepted by Ap
A Spitzer search for cold dust within globular clusters
Globular cluster stars evolving off the main sequence are known to lose mass,
and it is expected that some of the lost material should remain within the
cluster as an intracluster medium (ICM). Most attempts to detect such an ICM
have been unsuccessful. The Multiband Imaging Photometer for Spitzer on the
Spitzer Space Telescope was used to observe eight Galactic globular clusters in
an attempt to detect the thermal emission from ICM dust. Most clusters do not
have significant detections at 70 microns; one cluster, NGC 6341, has tentative
evidence for the presence of dust, but 90 micron observations do not confirm
the detection. Individual 70 micron point sources which appear in several of
the cluster images are likely to be background galaxies. The inferred dust mass
and upper limits are < 4e-4 solar masses, well below expectations for cluster
dust production from mass loss in red and asymptotic giant branch stars. This
implies that either globular cluster dust production is less efficient, or that
ICM removal or dust destruction is more efficient, than previously believed. We
explore several possibilities for ICM removal and conclude that present data do
not yet permit us to distinguish between them.Comment: AJ in press; 30 pages with 8 figure
Investigation of Core Degradation (COBE).
Abstract not availableJRC.(ISIS)-Institute For Systems, Informatics And Safet