924 research outputs found
Seeing Double at Neptune's South Pole
Keck near-infrared images of Neptune from UT 26 July 2007 show that the cloud
feature typically observed within a few degrees of Neptune's south pole had
split into a pair of bright spots. A careful determination of disk center
places the cloud centers at -89.07 +/- 0 .06 and -87.84 +/- 0.06 degrees
planetocentric latitude. If modeled as optically thick, perfectly reflecting
layers, we find the pair of features to be constrained to the troposphere, at
pressures greater than 0.4 bar. By UT 28 July 2007, images with comparable
resolution reveal only a single feature near the south pole. The changing
morphology of these circumpolar clouds suggests they may form in a region of
strong convection surrounding a Neptunian south polar vortex.Comment: 10 pages, 7 figures; accepted to Icaru
Retrieving Neptune's aerosol properties from Keck OSIRIS observations. I. Dark regions
We present and analyze three-dimensional data cubes of Neptune from the
OSIRIS integral-field spectrograph on the 10-m Keck telescope, from July 2009.
These data have a spatial resolution of 0.035"/pixel and spectral resolution of
R~3800 in the H and K broad bands. We focus our analysis on regions of
Neptune's atmosphere that are near-infrared dark- that is, free of discrete
bright cloud features. We use a forward model coupled to a Markov chain Monte
Carlo algorithm to retrieve properties of Neptune's aerosol structure and
methane profile above ~4 bar in these near-infrared dark regions.
Using a set of high signal-to-noise spectra in a cloud-free band from 2-12N,
we find that Neptune's cloud opacity is dominated by a compact, optically thick
cloud layer with a base near 3 bar and composed of low albedo, forward
scattering particles, with an assumed characteristic size of ~1m. Above
this cloud, we require a vertically extended haze of smaller (~0.1 m)
particles, which reaches from the upper troposphere (~0.6 bar) into the
stratosphere. The particles in this haze are brighter and more isotropically
scattering than those in the deep cloud. When we extend our analysis to 18
cloud-free locations from 20N to 87S, we observe that the optical depth in
aerosols above 0.5 bar decreases by a factor of 2-3 or more at mid- and
high-southern latitudes relative to low latitudes.
We also consider Neptune's methane (CH) profile, and find that our
retrievals indicate a strong preference for a low methane relative humidity at
pressures where methane is expected to condense. Our preferred solution at most
locations is for a methane relative humidity below 10% near the tropopause in
addition to methane depletion down to 2.0-2.5 bar. We tentatively identify a
trend of lower CH columns above 2.5 bar at mid- and high-southern latitudes
over low latitudes.Comment: Published in Icarus: 15 September 201
Comparing key compositional indicators in Jupiter with those in extra-solar giant planets
Spectroscopic transiting observations of the atmospheres of hot Jupiters
around other stars, first with Hubble Space Telescope and then Spitzer, opened
the door to compositional studies of exoplanets. The James Webb Space Telescope
will provide such a profound improvement in signal-to-noise ratio that it will
enable detailed analysis of molecular abundances, including but not limited to
determining abundances of all the major carbon- and oxygen-bearing species in
hot Jupiter atmospheres. This will allow determination of the carbon-to-oxygen
ratio, an essential number for planet formation models and a motivating goal of
the Juno mission currently around JupiterComment: Submitted to the Astro2020 Decadal Survey as a white paper; thematic
areas "Planetary Systems" and "Star and Planet Formation
Interplay between Freezing and Superconductivity in the Optimally Doped LaEu0.20Sr0.15CuO4 under Hydrostatic Pressure
We study the electronic properties of a LaEu0.20Sr0.15CuO4 single crystal
under hydrostatic pressure up to 2.9 GPa. Both the freezing of the Cu 3d
moments and the structural transition from the orthorhombic (LTO) to the
tetragonal (LTT) phase are observed via the relaxation of the nuclear
magnetization of La nuclei. Resistivity and magnetic susceptibility
measurements have been carried out under pressure on the same sample. The
combination of all data reveals the connection between glassy dynamics, charge
localization and the disappearance of superconductivity in the LTT phase.Comment: 5 pages, 4 figures, submitte
Mid-Infrared Ethane Emission on Neptune and Uranus
We report 8- to 13-micron spectral observations of Neptune and Uranus from
the NASA Infrared Telescope Facility spanning more than a decade. The
spectroscopic data indicate a steady increase in Neptune's mean atmospheric
12-micron ethane emission from 1985 to 2003, followed by a slight decrease in
2004. The simplest explanation for the intensity variation is an increase in
stratospheric effective temperature from 155 +/- 3 K in 1985 to 176 +/- 3 K in
2003 (an average rate of 1.2 K/year), and subsequent decrease to 165 +/- 3 K in
2004. We also detected variation of the overall spectral structure of the
ethane band, specifically an apparent absorption structure in the central
portion of the band; this structure arises from coarse spectral sampling
coupled with a non-uniform response function within the detector elements. We
also report a probable direct detection of ethane emission on Uranus. The
deduced peak mole fraction is approximately an order of magnitude higher than
previous upper limits for Uranus. The model fit suggests an effective
temperature of 114 +/- 3 K for the globally-averaged stratosphere of Uranus,
which is consistent with recent measurements indicative of seasonal variation.Comment: Accepted for publication in ApJ. 16 pages, 10 figures, 2 table
Planetary Science Goals for the Spitzer Warm Era
The overarching goal of planetary astronomy is to deduce how the present collection of objects found in our Solar System were formed from the original material present in the proto-solar nebula. As over two hundred exo-planetary systems are now known, and multitudes more are expected, the Solar System represents the closest and best system which we can study, and the only one in which we can clearly resolve individual bodies other than planets. In this White Paper we demonstrate how to use Spitzer Space Telescope InfraRed Array Camera Channels 1 and 2 (3.6 and 4.5 µm) imaging photometry with large dedicated surveys to advance our knowledge of Solar System formation and evolution. There are a number of vital, key projects to be pursued using dedicated large programs that have not been pursued during the five years of Spitzer cold operations. We present a number of the largest and most important projects here; more will certainly be proposed once the warm era has begun, including important observations of newly discovered objects
The direct Cu NQR Study of the Stripe Phase in the Lanthanum Cuprates
Using Cu NQR in Eu-doped La_(2-x)Sr_xCuO_4 we find the evidence of the pinned
stripe phase at 1.3K for 0.08<x<0.18. The pinned fraction increases by one
order of magnitude near hole doping x=1/8. The NQR lineshape reveals three
inequivalent Cu positions. A dramatic change of the NQR signal for x > 0.18
correlating with the onset of bulk superconductivity corresponds to the
depinning of the stripe phase.Comment: 4 pages, 3 figures, to appear in Physica C, Proceedings of the 6th
International Conference on Materials and Mechanisms of Superconductivity,
Houston, February 200
- …