488 research outputs found
Spectral and Spin Measurement of Two Small and Fast-Rotating Near-Earth Asteroids
In May 2012 two asteroids made near-miss "grazing" passes at distances of a
few Earth-radii: 2012 KP24 passed at nine Earth-radii and 2012 KT42 at only
three Earth-radii. The latter passed inside the orbital distance of
geosynchronous satellites. From spectral and imaging measurements using NASA's
3-m Infrared Telescope Facility (IRTF), we deduce taxonomic, rotational, and
physical properties. Their spectral characteristics are somewhat atypical among
near-Earth asteroids: C-complex for 2012 KP24 and B-type for 2012 KT42, from
which we interpret the albedos of both asteroids to be between 0.10 and 0.15
and effective diameters of 20+-2 and 6+-1 meters, respectively. Among B-type
asteroids, the spectrum of 2012 KT42 is most similar to 3200 Phaethon and 4015
Wilson-Harrington. Not only are these among the smallest asteroids spectrally
measured, we also find they are among the fastest-spinning: 2012 KP24 completes
a rotation in 2.5008+-0.0006 minutes and 2012 KT42 rotates in 3.634+-0.001
minutes.Comment: 4 pages, 3 figures, accepted for publication in Icaru
Colors and taxonomy of Centaurs and Trans-Neptunian Objects
The study of the surface properties of Centaurs and Trans-Neptunian Objects
(TNOs) provides essential information about the early conditions and evolution
of the outer Solar System. Due to the faintness of most of these distant and
icy bodies, photometry currently constitutes the best technique to survey a
statistically significant number of them. Our aim is to investigate color
properties of a large sample of minor bodies of the outer Solar System, and set
their taxonomic classification. We carried out visible and near-infrared
photometry of Centaurs and TNOs, making use, respectively, of the FORS2 and
ISAAC instruments at the Very Large Telescope (European Southern Observatory).
Using G-mode analysis, we derived taxonomic classifications according to the
Barucci et al. (2005a) system. We report photometric observations of 31
objects, 10 of them have their colors reported for the first time ever. 28
Centaurs and TNOs have been assigned to a taxon. We combined the entire sample
of 38 objects taxonomically classified in the framework of our programme (28
objects from this work; 10 objects from DeMeo et al. 2009a) with previously
classified TNOs and Centaurs, looking for correlations between taxonomy and
dynamics. We compared our photometric results to literature data, finding hints
of heterogeneity for the surfaces of 4 objects.Comment: 7 pages, 4 figures. To be published in Astronomy and Astrophysic
STS-74/Mir Photogrammetric Appendage Structural Dynamics Experiment Preliminary Data Analysis
The Photogrammetric Appendage Structural Dynamics Experiment was designed, developed, and flown to demonstrate and prove measurement of the structural vibration response of a Russian Space Station Mir solar array using photogrammetric methods. The experiment flew on the STS-74 Space Shuttle mission to Mir in November 1995 and obtained video imagery of solar array structural response to various excitation events. The video imagery has been digitized and triangulated to obtain response time history data at discrete points on the solar array. This data has been further processed using the Eigensystem Realization Algorithm modal identification technique to determine the natural vibration frequencies, damping, and mode shapes of the solar array. The results demonstrate that photogrammetric measurement of articulating, non-optically targeted, flexible solar arrays and appendages is a viable, low-cost measurement option for the International Space Station
Discovery of carbon monoxide in the upper atmosphere of Pluto
Pluto's icy surface has changed colour and its atmosphere has swelled since
its last closest approach to the Sun in 1989. The thin atmosphere is produced
by evaporating ices, and so can also change rapidly, and in particular carbon
monoxide should be present as an active thermostat. Here we report the
discovery of gaseous CO via the 1.3mm wavelength J=2-1 rotational transition,
and find that the line-centre signal is more than twice as bright as a
tentative result obtained by Bockelee-Morvan et al. in 2000. Greater
surface-ice evaporation over the last decade could explain this, or increased
pressure could have caused the atmosphere to expand. The gas must be cold, with
a narrow line-width consistent with temperatures around 50 K, as predicted for
the very high atmosphere, and the line brightness implies that CO molecules
extend up to approximately 3 Pluto radii above the surface. The upper
atmosphere must have changed markedly over only a decade since the prior
search, and more alterations could occur by the arrival of the New Horizons
mission in 2015.Comment: 5 pages; accepted for publication in MNRAS Letter
Evolution from protoplanetary to debris discs: The transition disc around HD 166191
HD 166191 has been identified by several studies as hosting a rare and
extremely bright warm debris disc with an additional outer cool disc component.
However, an alternative interpretation is that the star hosts a disc that is
currently in transition between a full gas disc and a largely gas-free debris
disc. With the help of new optical to mid-IR spectra and Herschel imaging, we
argue that the latter interpretation is supported in several ways: i) we show
that HD 166191 is co-moving with the ~4 Myr-old Herbig Ae star HD 163296,
suggesting that the two have the same age, ii) the disc spectrum of HD 166191
is well matched by a standard radiative transfer model of a gaseous
protoplanetary disc with an inner hole, and iii) the HD 166191 mid-IR silicate
feature is more consistent with similarly primordial objects. We note some
potential issues with the debris disc interpretation that should be considered
for such extreme objects, whose lifetime at the current brightness is mush
shorter than the stellar age, or in the case of the outer component requires a
mass comparable to the solid component of the Solar nebula. These aspects
individually and collectively argue that HD 166191 is a 4-5 Myr old star that
hosts a gaseous transition disc. Though it does not argue in favour of either
scenario, we find strong evidence for 3-5 um disc variability. We place HD
166191 in context with discs at different evolutionary stages, showing that it
is a potentially important object for understanding the protoplanetary to
debris disc transition.Comment: accepted to MNRAS, fixed typos in abstract and axis labe
Epidemiology, genetics, and subtyping of preserved ratio impaired spirometry (PRISm) in COPDGene.
BackgroundPreserved Ratio Impaired Spirometry (PRISm), defined as a reduced FEV1 in the setting of a preserved FEV1/FVC ratio, is highly prevalent and is associated with increased respiratory symptoms, systemic inflammation, and mortality. Studies investigating quantitative chest tomographic features, genetic associations, and subtypes in PRISm subjects have not been reported.MethodsData from current and former smokers enrolled in COPDGene (n = 10,192), an observational, cross-sectional study which recruited subjects aged 45-80 with ≥10 pack years of smoking, were analyzed. To identify epidemiological and radiographic predictors of PRISm, we performed univariate and multivariate analyses comparing PRISm subjects both to control subjects with normal spirometry and to subjects with COPD. To investigate common genetic predictors of PRISm, we performed a genome-wide association study (GWAS). To explore potential subgroups within PRISm, we performed unsupervised k-means clustering.ResultsThe prevalence of PRISm in COPDGene is 12.3%. Increased dyspnea, reduced 6-minute walk distance, increased percent emphysema and decreased total lung capacity, as well as increased segmental bronchial wall area percentage were significant predictors (p-value <0.05) of PRISm status when compared to control subjects in multivariate models. Although no common genetic variants were identified on GWAS testing, a significant association with Klinefelter's syndrome (47XXY) was observed (p-value < 0.001). Subgroups identified through k-means clustering include a putative "COPD-subtype", "Restrictive-subtype", and a highly symptomatic "Metabolic-subtype".ConclusionsPRISm subjects are clinically and genetically heterogeneous. Future investigations into the pathophysiological mechanisms behind and potential treatment options for subgroups within PRISm are warranted.Trial registrationClinicaltrials.gov Identifier: NCT000608764
Tohoku-Hiroshima-Nagoya planetary spectra library: A method for characterizing planets in the visible to near infrared
There has not been a comprehensive framework for comparing spectral data from
different planets.Such a framework is needed for the study of extrasolar
planets and objects within the solar system. We have undertaken observations to
compile a library of planet spectra for all planets, some moons, and some dwarf
planets in the solar system to study their general spectroscopic and
photometric natures. During May and November of 2008, we acquired spectra for
the planets using TRISPEC, which is capable of simultaneous three-band
spectroscopy in a wide wavelength range of 0.45 - 2.5 microns with low
resolving power (lambda-over-Delta-lambda is 140 - 360). Patterns emerge from
comparing the spectra. Analyzing their general spectroscopic and photometric
natures, we show that it is possible to distinguish between gas planets, soil
planets and ice planets. These methods can be applied to extrasolar
observations using low resolution spectrography or broad-band filters. The
present planet spectral library is the first library to contain observational
spectra for all of the solar system planets, based on simultaneous observations
in visible and near infrared wavelengths. This library will be a useful
reference for analyzing extrasolar planet spectra, and for calibrating
planetary data sets.Comment: 11 pages, 6 figures, Accepted on 28/08/2009 to appear in Section 10.
Planets and planetary systems of Astronomy and Astrophysic
NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results
The NEOWISE dataset offers the opportunity to study the variations in albedo
for asteroid classification schemes based on visible and near-infrared
observations for a large sample of minor planets. We have determined the
albedos for nearly 1900 asteroids classified by the Tholen, Bus and Bus-DeMeo
taxonomic classification schemes. We find that the S-complex spans a broad
range of bright albedos, partially overlapping the low albedo C-complex at
small sizes. As expected, the X-complex covers a wide range of albedos. The
multi-wavelength infrared coverage provided by NEOWISE allows determination of
the reflectivity at 3.4 and 4.6 m relative to the visible albedo. The
direct computation of the reflectivity at 3.4 and 4.6 m enables a new
means of comparing the various taxonomic classes. Although C, B, D and T
asteroids all have similarly low visible albedos, the D and T types can be
distinguished from the C and B types by examining their relative reflectance at
3.4 and 4.6 m. All of the albedo distributions are strongly affected by
selection biases against small, low albedo objects, as all objects selected for
taxonomic classification were chosen according to their visible light
brightness. Due to these strong selection biases, we are unable to determine
whether or not there are correlations between size, albedo and space
weathering. We argue that the current set of classified asteroids makes any
such correlations difficult to verify. A sample of taxonomically classified
asteroids drawn without significant albedo bias is needed in order to perform
such an analysis.Comment: Accepted to Ap
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