11 research outputs found
Adaptive Optics for Astronomy
Adaptive Optics is a prime example of how progress in observational astronomy
can be driven by technological developments. At many observatories it is now
considered to be part of a standard instrumentation suite, enabling
ground-based telescopes to reach the diffraction limit and thus providing
spatial resolution superior to that achievable from space with current or
planned satellites. In this review we consider adaptive optics from the
astrophysical perspective. We show that adaptive optics has led to important
advances in our understanding of a multitude of astrophysical processes, and
describe how the requirements from science applications are now driving the
development of the next generation of novel adaptive optics techniques.Comment: to appear in ARA&A vol 50, 201
The formation of Kuiper-belt Binaries through Exchange Reactions
Recent observations have revealed an unexpectedly high binary fraction among
the Trans-Neptunian Objects (TNOs) that populate the Kuiper-belt. The
discovered binaries have four characteristics they comprise a few percent of
the TNOs, the mass ratio of their components is close to unity, their internal
orbits are highly eccentric, and the orbits are more than 100 times wider than
the primary's radius. In contrast, theories of binary asteroid formation tend
to produce close, circular binaries. Therefore, a new approach is required to
explain the unique characteristics of the TNO binaries. Two models have been
proposed. Both, however, require extreme assumptions on the size distribution
of TNOs. Here we show a mechanism which is guaranteed to produces binaries of
the required type during the early TNO growth phase, based on only one
plausible assumption, namely that initially TNOs were formed through
gravitational instabilities of the protoplanetary dust layer.Comment: 12pages, 4 figure
Observing solar-like oscillations
We review techniques for measuring stellar oscillations in solar-type stars. Despite great efforts, no unambiguous detections have been made. A new method, based on monitoring the equivalent widths of strong lines, shows promise but is yet to be confirmed. We also discuss several subtleties, such as the need to correct for CCD non-linearities and the importance of data weighting
Evidence for Young Volcanism on Mercury from the Third MESSENGER Flyby
During its first two flybys of Mercury, the MESSENGER spacecraft acquired images confirming that
pervasive volcanism occurred early in the planet\u2019s history. MESSENGER\u2019s third Mercury flyby
revealed a 290-kilometer-diameter peak-ring impact basin, among the youngest basins yet seen,
having an inner floor filled with spectrally distinct smooth plains. These plains are sparsely
cratered, postdate the formation of the basin, apparently formed from material that once
flowed across the surface, and are therefore interpreted to be volcanic in origin. An irregular
depression surrounded by a halo of bright deposits northeast of the basin marks a candidate
explosive volcanic vent larger than any previously identified on Mercury. Volcanism on the
planet thus spanned a considerable duration, perhaps extending well into the second half of
solar system history
Chaotic capture of Jupiter's Trojan asteroids in the early Solar System
Nature, 435, pp. 462-465, http://dx.doi.org./10.1038/nature03540International audienc