1,656 research outputs found
A dazzling number of beetles (Coleoptera) in a hibernating nest of red wood ants, Formica Rufa Linnaeus (Hymenoptera : Formicidae)
status: publishe
The Influence of Non-Uniform Cloud Cover on Transit Transmission Spectra
We model the impact of non-uniform cloud cover on transit transmission
spectra. Patchy clouds exist in nearly every solar system atmosphere, brown
dwarfs, and transiting exoplanets. Our major findings suggest that fractional
cloud coverage can exactly mimic high mean molecular weight atmospheres and
vice-versa over certain wavelength regions, in particular, over the Hubble
Space Telescope (HST) Wide Field Camera 3 (WFC3) bandpass (1.1-1.7 m). We
also find that patchy cloud coverage exhibits a signature that is different
from uniform global clouds. Furthermore, we explain analytically why the
"patchy cloud-high mean molecular weight" degeneracy exists. We also explore
the degeneracy of non-uniform cloud coverage in atmospheric retrievals on both
synthetic and real planets. We find from retrievals on a synthetic solar
composition hot Jupiter with patchy clouds and a cloud free high mean molecular
weight warm Neptune, that both cloud free high mean molecular weight
atmospheres and partially cloudy atmospheres can explain the data equally well.
Another key find is that the HST WFC3 transit transmission spectra of two well
observed objects, the hot Jupiter HD189733b and the warm Neptune HAT-P-11b, can
be explained well by solar composition atmospheres with patchy clouds without
the need to invoke high mean molecular weight or global clouds. The degeneracy
between high molecular weight and solar composition partially cloudy
atmospheres can be broken by observing the molecular Rayleigh scattering
differences between the two. Furthermore, the signature of partially cloudy
limbs also appears as a 100 ppm residual in the ingress and egress of the
transit light curves, provided the transit timing is known to seconds.Comment: Accepted to ApJ Feb. 8, 201
Chemical evolution of the M82 B fossil starburst
M82 B is an old starburst site located in the eastern part of the M82 disc.
We derive the distributions of age and metallicity of the star clusters located
in this region of M82 by using theoretical evolutionary population synthesis
models. Our analysis is based on the comparison of the photometry
obtained by de Grijs et al. (2001) with the colours of single-generation
stellar populations. We show that M82 B went through a chemical enrichment
phase up to super-solar metallicities around the time of the last close
encounter between M82 and its large neighbour galaxy M81. We date and confirm
the event triggering the enhanced cluster formation at about 1 Gyr ago. At
almost the same time an additional, distinct subpopulation of metal-poor
clusters formed in the part of M82 B nearest to the galactic centre. The
formation of these peculiar clusters may be related to infall of circumgalactic
gas onto M82 B.Comment: 14 pages, accepted for publication in MNRA
An Observational Diagnostic for Distinguishing Between Clouds and Haze in Hot Exoplanet Atmospheres
The nature of aerosols in hot exoplanet atmospheres is one of the primary
vexing questions facing the exoplanet field. The complex chemistry, multiple
formation pathways, and lack of easily identifiable spectral features
associated with aerosols make it especially challenging to constrain their key
properties. We propose a transmission spectroscopy technique to identify the
primary aerosol formation mechanism for the most highly irradiated hot Jupiters
(HIHJs). The technique is based on the expectation that the two key types of
aerosols -- photochemically generated hazes and equilibrium condensate clouds
-- are expected to form and persist in different regions of a highly irradiated
planet's atmosphere. Haze can only be produced on the permanent daysides of
tidally-locked hot Jupiters, and will be carried downwind by atmospheric
dynamics to the evening terminator (seen as the trailing limb during transit).
Clouds can only form in cooler regions on the night side and morning terminator
of HIHJs (seen as the leading limb during transit). Because opposite limbs are
expected to be impacted by different types of aerosols, ingress and egress
spectra, which primarily probe opposing sides of the planet, will reveal the
dominant aerosol formation mechanism. We show that the benchmark HIHJ,
WASP-121b, has a transmission spectrum consistent with partial aerosol coverage
and that ingress-egress spectroscopy would constrain the location and formation
mechanism of those aerosols. In general, using this diagnostic we find that
observations with JWST and potentially with HST should be able to distinguish
between clouds and haze for currently known HIHJs.Comment: 10 pages, 4 figures, accepted to ApJ Letter
Impact phenomena as factors in the evolution of the Earth
It is estimated that 30 to 200 large impact basins could have been formed on the early Earth. These large impacts may have resulted in extensive volcanism and enhanced endogenic geologic activity over large areas. Initial modelling of the thermal and subsidence history of large terrestrial basins indicates that they created geologic and thermal anomalies which lasted for geologically significant times. The role of large-scale impact in the biological evolution of the Earth has been highlighted by the discovery of siderophile anomalies at the Cretaceous-Tertiary boundary and associated with North American microtektites. Although in neither case has an associated crater been identified, the observations are consistent with the deposition of projectile-contaminated high-speed ejecta from major impact events. Consideration of impact processes reveals a number of mechanisms by which large-scale impact may induce extinctions
Coupling of Josephson flux-flow oscillators to an external RC load
We investigate by numerical simulations the behavior of the power dissipated
in a resistive load capacitively coupled to a Josephson flux flow oscillator
and compare the results to those obtained for a d.c. coupled purely resistive
load. Assuming realistic values for the parameters R and C, both in the high-
and in the low-Tc case the power is large enough to allow the operation of such
a device in applications.Comment: uuencoded, gzipped tar archive containing 11 pages of REVTeX text + 4
PostScript figures. To appear in Supercond. Sci. Techno
Triggering the Formation of Halo Globular Clusters with Galaxy Outflows
We investigate the interactions of high-redshift galaxy outflows with
low-mass virialized (Tvir < 10,000K) clouds of primordial composition. While
atomic cooling allows star formation in larger primordial objects, such
"minihalos" are generally unable to form stars by themselves. However, the
large population of high-redshift starburst galaxies may have induced
widespread star formation in these objects, via shocks that caused intense
cooling both through nonequilibrium H2 formation and metal-line emission. Using
a simple analytic model, we show that the resulting star clusters naturally
reproduce three key features of the observed population of halo globular
clusters (GCs). First, the 10,000 K maximum virial temperature corresponds to
the ~ 10^6 solar mass upper limit on the stellar mass of GCs. Secondly, the
momentum imparted in such interactions is sufficient to strip the gas from its
associated dark matter halo, explaining why GCs do not reside in dark matter
potential wells. Finally, the mixing of ejected metals into the primordial gas
is able to explain the ~ 0.1 dex homogeneity of stellar metallicities within a
given GC, while at the same time allowing for a large spread in metallicity
between different clusters. To study this possibility in detail, we use a
simple 1D numerical model of turbulence transport to simulate mixing in
cloud-outflow interactions. We find that as the shock shears across the side of
the cloud, Kelvin-Helmholtz instabilities arise, which cause mixing of enriched
material into > 20% of the cloud. Such estimates ignore the likely presence of
large-scale vortices, however, which would further enhance turbulence
generation. Thus quantitative mixing predictions must await more detailed
numerical studies.Comment: 21 pages, 11 figures, Apj in pres
Recommended from our members
Contrasting effects of changing rhythm and content on auditory distraction in immediate memory
Across five experiments, the temporal regularity and content of an irrelevant speech stream were varied and their effects on a serial recall task examined. Variations of the content, but not the rhythm, of the irrelevant speech stimuli reliably disrupted serial recall performance in all experiments. Bayesian analyses supported the null hypothesis over the hypothesis that irregular rhythms would disrupt memory to a greater extent than regular rhythms. Pooling the data in a combined analysis revealed that regular presentation of the irrelevant speech was significantly more disruptive to serial recall than irregular presentation. These results are consistent with the idea that auditory distraction is sensitive to both intra-item and inter-item relations and challenge an orienting-based account of auditory distraction
- …