774 research outputs found
Echoes of a decaying planetary system: the gaseous and dusty disks surrounding three white dwarfs
We have performed a comprehensive ground-based observational program aimed at
characterizing the circumstellar material orbiting three single white dwarf
stars previously known to possess gaseous disks. Near-infrared imaging
unambiguously detects excess infrared emission towards Ton 345 and allows us to
refine models for the circumstellar dust around all three white dwarf stars. We
find that each white dwarf hosts gaseous and dusty disks that are roughly
spatially coincident, a result that is consistent with a scenario in which
dusty and gaseous material has its origin in remnant parent bodies of the white
dwarfs' planetary systems. We briefly describe a new model for the gas disk
heating mechanism in which the gaseous material behaves like a "Z II" region.
In this Z II region, gas primarily composed of metals is photoionized by
ultraviolet light and cools through optically thick allowed Ca II-line
emission.Comment: 43 pages, 9 tables, 9 figures. Accepted to Ap
A power challenging theory of society, or a conservative mindset? Upward and downward conspiracy theories as ideologically distinct beliefs
Even though conspiracy theories are diverse, they are typically construed as a homogeneous phenomenon. Based on classic theorizations of conspiracy theories by Popper (1945; 2002) and Moscovici (1987), we propose to distinguish between belief in upward conspiracy theories (i.e., targeting relatively powerful groups) and downward conspiracy theories (i.e., targeting relatively powerless groups). The former are theorized as power-challenging beliefs and the latter are theorized as being underpinned by conservative ideology. Across three studies conducted in Belgium (Total N = 2363), we show that these two types of conspiracy beliefs indeed relate differently to power-challenging attitudes (i.e., political extremism, feelings of leadership breakdown) and conservative ideology. Specifically, upward conspiracy beliefs were characterized by a U-shaped relationship with political orientation (i.e., an âextremismâ bias), and a strong relationship with feelings of leadership breakdown. By contrast, downward conspiracy beliefs were strongly associated with conservative ideology. Both types of conspiracy beliefs were, however, positively correlated
Interstellar absorptions and shocked clouds towards supernova remnant RX J0852.0-4622
We present results of survey of interstellar absorptions towards supernova
remnant (SNR) RX J0852.0-4622. The distribution of KI absorbers along the
distance of the background stars is indicative of a local region (d<600pc)
strongly depopulated by KI line-absorbing clouds. This fact is supported by the
behavior of the interstellar extinction. We find four high-velocity CaII
components with velocities of >100km/s towards three stars and identify them
with shocked clouds of Vela SNR. We reveal and measure acceleration of two
shocked clouds at the approaching and receding sides of Vela SNR along the same
sight line. The clouds acceleration, velocity, and CaII column density are used
to probe cloud parameters. The total hydrogen column density of both
accelerating clouds is found to be similar (~6*10^{17} cm) which
indicates that possibly there is a significant amount of small-size clouds in
the vicinity of Vela SNR.Comment: accepted in MNRA
Weighing the Giants - I. Weak-lensing masses for 51 massive galaxy clusters: project overview, data analysis methods and cluster images
This is the first in a series of papers in which we measure accurate
weak-lensing masses for 51 of the most X-ray luminous galaxy clusters known at
redshifts 0.15<z<0.7, in order to calibrate X-ray and other mass proxies for
cosmological cluster experiments. The primary aim is to improve the absolute
mass calibration of cluster observables, currently the dominant systematic
uncertainty for cluster count experiments. Key elements of this work are the
rigorous quantification of systematic uncertainties, high-quality data
reduction and photometric calibration, and the "blind" nature of the analysis
to avoid confirmation bias. Our target clusters are drawn from RASS X-ray
catalogs, and provide a versatile calibration sample for many aspects of
cluster cosmology. We have acquired wide-field, high-quality imaging using the
Subaru and CFHT telescopes for all 51 clusters, in at least three bands per
cluster. For a subset of 27 clusters, we have data in at least five bands,
allowing accurate photo-z estimates of lensed galaxies. In this paper, we
describe the cluster sample and observations, and detail the processing of the
SuprimeCam data to yield high-quality images suitable for robust weak-lensing
shape measurements and precision photometry. For each cluster, we present
wide-field color optical images and maps of the weak-lensing mass distribution,
the optical light distribution, and the X-ray emission, providing insights into
the large-scale structure in which the clusters are embedded. We measure the
offsets between X-ray centroids and Brightest Cluster Galaxies in the clusters,
finding these to be small in general, with a median of 20kpc. For offsets
<100kpc, weak-lensing mass measurements centered on the BCGs agree well with
values determined relative to the X-ray centroids; miscentering is therefore
not a significant source of systematic uncertainty for our mass measurements.
[abridged]Comment: 26 pages, 19 figures (Appendix C not included). Accepted after minor
revisio
An extreme value model for maximum wave heights based on weather types
Extreme wave heights are climate-related events. Therefore, special attention should be given to the large-scale weather patterns responsible for wave generation in order to properly understand wave climate variability. We propose a classification of weather patterns to statistically downscale daily significant wave height maxima to a local area of interest. The time-dependent statistical model obtained here is based on the convolution of the stationary extreme value model associated to each weather type. The interdaily dependence is treated by a climate-related extremal index. The model's ability to reproduce different time scales (daily, seasonal, and interannual) is presented by means of its application to three locations in the North Atlantic: Mayo (Ireland), La Palma Island, and Coruña (Spain)
An absorption-selected survey of neutral gas in the Milky Way halo
We aim at analysing systematically the distribution and physical properties
of neutral and mildly ionised gas in the Milky Way halo, based on a large
absorption-selected data set. Multi-wavelength studies were performed combining
optical absorption line data of CaII and NaI with follow-up HI 21-cm emission
line observations along 408 sight lines towards low- and high-redshift QSOs. We
made use of archival optical spectra obtained with UVES/VLT. HI data were
extracted from the Effelsberg-Bonn HI survey and the Galactic All-Sky survey.
For selected sight lines we obtained deeper follow-up observations using the
Effelsberg 100-m telescope. CaII (NaI) halo absorbers at intermediate and high
radial velocities are present in 40-55% (20-35%) of the sightlines, depending
on the column density threshold chosen. Many halo absorbers show
multi-component absorption lines, indicating the presence of sub-structure. In
65% of the cases, absorption is associated with HI 21-cm emission. The CaII
(NaI) column density distribution function follows a power-law with a slope of
-2.2 (-1.4). Our absorption-selected survey confirms our previous results that
the Milky Way halo is filled with a large number of neutral gas structures
whose high column density tail represents the population of common HI high- and
intermediate-velocity clouds seen in 21-cm observations. We find that CaII/NaI
column density ratios in the halo absorbers are typically smaller than those in
the Milky Way disc, in the gas in the Magellanic Clouds, and in damped
Lyman-alpha systems. The small ratios (prominent in particular in high-velocity
components) indicate a lower level of Ca depletion onto dust grains in Milky
Way halo absorbers compared to gas in discs and inner regions of galaxies.Comment: 17 pages, 20 figures, accepted by A&
Managing a document-based information space
We present a novel user interface in the form of a complementary virtual environment for managing personal document archives, i.e., for document filing and retrieval. Our implementation of a spatial medium for document interaction, exploratory search and active navigation plays to the strengths of human visual information processing and further stimulates it. Our system provides a high degree of immersion so that the user readily forgets the artificiality of our environment. Three well-integrated features support this immersion: first, we enable users to interact more naturally through gestures and postures (the system can be taught custom ones); second, we exploit 3D display technology; and third, we allow users to manage arrangements (manually edited structures, as well as computer-generated semantic structures). Our ongoing evaluation indicates that even non-expert users can efficiently work with the information in a document collection and that the process can actually be enjoyable. ACM Classification: H5.2 [Information interfaces and presentation]
Constraining GRB Emission Physics with Extensive Early-Time, Multiband Follow-up
Understanding the origin and diversity of emission processes responsible for
Gamma-ray Bursts (GRBs) remains a pressing challenge. While prompt and
contemporaneous panchromatic observations have the potential to test
predictions of the internal-external shock model, extensive multiband imaging
has been conducted for only a few GRBs. We present rich, early-time, multiband
datasets for two \swift\ events, GRB 110205A and GRB 110213A. The former shows
optical emission since the early stages of the prompt phase, followed by the
steep rising in flux up to ~1000s after the burst ( with
). We discuss this feature in the context of the
reverse-shock scenario and interpret the following single power-law decay as
being forward-shock dominated. Polarization measurements, obtained with the
RINGO2 instrument mounted on the Liverpool Telescope, also provide hints on the
nature of the emitting ejecta. The latter event, instead, displays a very
peculiar optical to near-infrared lightcurve, with two achromatic peaks. In
this case, while the first peak is probably due to the onset of the afterglow,
we interpret the second peak to be produced by newly injected material,
signifying a late-time activity of the central engine.Comment: 48 pages,11 figures, 24 tables. Accepted to The Astrophysical Journa
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