33,717 research outputs found
Thermalization and Cooling of Plasmon-Exciton Polaritons: Towards Quantum Condensation
We present indications of thermalization and cooling of quasi-particles, a
precursor for quantum condensation, in a plasmonic nanoparticle array. We
investigate a periodic array of metallic nanorods covered by a polymer layer
doped with an organic dye at room temperature. Surface lattice resonances of
the array---hybridized plasmonic/photonic modes---couple strongly to excitons
in the dye, and bosonic quasi-particles which we call
plasmon-exciton-polaritons (PEPs) are formed. By increasing the PEP density
through optical pumping, we observe thermalization and cooling of the strongly
coupled PEP band in the light emission dispersion diagram. For increased
pumping, we observe saturation of the strong coupling and emission in a new
weakly coupled band, which again shows signatures of thermalization and
cooling.Comment: 8 pages, 5 figures including supplemental material. The newest
version includes new measurements and corrections to the interpretation of
the result
Temporal evolution of multiple evaporating ribbon sources in a solar flare
We present new results from the Interface Region Imaging Spectrograph showing
the dynamic evolution of chromospheric evaporation and condensation in a flare
ribbon, with the highest temporal and spatial resolution to date. IRIS observed
the entire impulsive phase of the X-class flare SOL2014-09-10T17:45 using a 9.4
second cadence `sit-and-stare' mode. As the ribbon brightened successively at
new positions along the slit, a unique impulsive phase evolution was observed
for many tens of individual pixels in both coronal and chromospheric lines.
Each activation of a new footpoint displays the same initial coronal up-flows
of up to ~300 km/s, and chromospheric downflows up to 40 km/s. Although the
coronal flows can be delayed by over 1 minute with respect to those in the
chromosphere, the temporal evolution of flows is strikingly similar between all
pixels, and consistent with predictions from hydrodynamic flare models. Given
the large sample of independent footpoints, we conclude that each flaring pixel
can be considered a prototypical, `elementary' flare kernel.Comment: Accepted for publication - ApJ letter
Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars III. Iron, Magnesium, and Silicon
We use thermochemical equilibrium calculations to model iron, magnesium, and
silicon chemistry in the atmospheres of giant planets, brown dwarfs, extrasolar
giant planets (EGPs), and low-mass stars. The behavior of individual Fe-, Mg-,
and Si-bearing gases and condensates is determined as a function of
temperature, pressure, and metallicity. Our results are thus independent of any
particular model atmosphere. The condensation of Fe metal strongly affects iron
chemistry by efficiently removing Fe-bearing species from the gas phase.
Monatomic Fe is the most abundant Fe-bearing gas throughout the atmospheres of
EGPs and L dwarfs and in the deep atmospheres of giant planets and T dwarfs.
Mg- and Si-bearing gases are effectively removed from the atmosphere by
forsterite (Mg2SiO4) and enstatite (MgSiO3) cloud formation. Monatomic Mg is
the dominant magnesium gas throughout the atmospheres of EGPs and L dwarfs and
in the deep atmospheres of giant planets and T dwarfs. Silicon monoxide (SiO)
is the most abundant Si-bearing gas in the deep atmospheres of brown dwarfs and
EGPs, whereas SiH4 is dominant in the deep atmosphere of Jupiter and other gas
giant planets. Several other Fe-, Mg-, and Si-bearing gases become increasingly
important with decreasing effective temperature. In principle, a number of Fe,
Mg, and Si gases are potential tracers of weather or diagnostic of temperature
in substellar atmospheres.Comment: 42 pages, 15 figures, submitted to the Astrophysical Journa
Detailed compositional analysis of the heavily polluted DBZ white dwarf SDSS J073842.56+183509.06: A window on planet formation?
We present a new model atmosphere analysis of the most metal contaminated
white dwarf known, the DBZ SDSS J073842.56+183509.06. Using new high resolution
spectroscopic observations taken with Keck and Magellan, we determine precise
atmospheric parameters and measure abundances of 14 elements heavier than
helium. We also report new Spitzer mid-infrared photometric data that are used
to better constrain the properties of the debris disk orbiting this star. Our
detailed analysis, which combines data taken from 7 different observational
facilities (GALEX, Gemini, Keck, Magellan, MMT, SDSS and Spitzer) clearly
demonstrate that J0738+1835 is accreting large amounts of rocky
terrestrial-like material that has been tidally disrupted into a debris disk.
We estimate that the body responsible for the photospheric metal contamination
was at least as large Ceres, but was much drier, with less than 1% of the mass
contained in the form of water ice, indicating that it formed interior to the
snow line around its parent star. We also find a correlation between the
abundances (relative to Mg and bulk Earth) and the condensation temperature;
refractory species are clearly depleted while the more volatile elements are
possibly enhanced. This could be the signature of a body that formed in a lower
temperature environment than where Earth formed. Alternatively, we could be
witnessing the remains of a differentiated body that lost a large part of its
outer layers.Comment: 16 pages, 17 figures, accepted for publication in The Astrophysical
Journa
Parent Stars of Extrasolar Planets. XII. Additional evidence for trends with vsini, condensation temperature, and chromospheric activity
Several recent studies have reported differences in vsini,
abundance-condensation temperature trends, and chromospheric activity between
samples of stars with and without Doppler-detected planets. These findings have
been disputed, and the status of these results remains uncertain. We evaluate
these claims using additional published data and find support for all three.Comment: 4 pages, 4 figures; accepted for publication in MNRAS as a Lette
- …