27,585 research outputs found
Projection effects in galaxy cluster samples: insights from X-ray redshifts
Up to now, the largest sample of galaxy clusters selected in X-rays comes
from the ROSAT All-Sky Survey (RASS). Although there have been many interesting
clusters discovered with the RASS data, the broad point spread function (PSF)
of the ROSAT satellite limits the amount of spatial information of the detected
objects. This leads to the discovery of new cluster features when a
re-observation is performed with higher resolution X-ray satellites. Here we
present the results from XMM-Newton observations of three clusters:
RXCJ2306.6-1319, ZwCl1665 and RXCJ0034.6-0208, for which the observations
reveal a double or triple system of extended components. These clusters belong
to the extremely expanded HIghest X-ray FLUx Galaxy Cluster Sample
(eeHIFLUGCS), which is a flux-limited cluster sample ( erg s cm in the keV energy band). For
each structure in each cluster, we determine the redshift with the X-ray
spectrum and find that the components are not part of the same cluster. This is
confirmed by an optical spectroscopic analysis of the galaxy members.
Therefore, the total number of clusters is actually 7 and not 3. We derive
global cluster properties of each extended component. We compare the measured
properties to lower-redshift group samples, and find a good agreement. Our flux
measurements reveal that only one component of the ZwCl1665 cluster has a flux
above the eeHIFLUGCS limit, while the other clusters will no longer be part of
the sample. These examples demonstrate that cluster-cluster projections can
bias X-ray cluster catalogues and that with high-resolution X-ray follow-up
this bias can be corrected
VISIR-VLT high resolution study of the extended emission of four obscured post-AGB candidates
The onset of the asymmetry of planetary nebulae (PNe) is expected to occur
during the late Asymptotic Giant Branch (AGB) and early post-AGB phases of low-
and intermediate-mass stars. Among all post-AGB objects, the most heavily
obscured ones might have escaped the selection criteria of previous studies
detecting extreme axysimmetric structures in young PNe. Since the most heavily
obscured post-AGB sources can be expected to descend from the most massive PN
progenitors, these should exhibit clear asymmetric morphologies. We have
obtained VISIR-VLT mid-IR images of four heavily obscured post-AGB objects
barely resolved in previous Spitzer IRAC observations to analyze their
morphology and physical conditions across the mid-IR. The VISIR-VLT images have
been deconvolved, flux calibrated, and used to construct RGB composite pictures
as well as color and optical depth maps that allow us to study the morphology
and physical properties of the extended emission of these sources. We have
detected extended emission from the four objects in our sample and resolved it
into several structural components that are greatly enhanced in the temperature
and optical depth maps. They reveal the presence of asymmetry in three young
PNe (IRAS 15534-5422, IRAS 17009-4154, and IRAS 18454+0001), where the
asymmetries can be associated with dusty torii and slightly bipolar outflows.
The fourth source (IRAS 18229-1127), a possible post-AGB star, is better
described as a rhomboidal detached shell. The heavily obscured sources in our
sample do not show extreme axisymmetric morphologies. This is at odds with the
expectation of highly asymmetrical morphologies in post-AGB sources descending
from massive PN progenitors. The sources presented in this paper may be
sampling critical early phases in the evolution of massive PN progenitors,
before extreme asymmetries develop.Comment: 9 pages, 4 figure
Effect of training and familiarity on responsiveness to human cues in domestic dogs (<i>Canis familiaris</i>)
Domestic dogs (Canis familiaris) seem to possess an evolved competency to follow human-given cues, often out-performing their wild progenitor the wolf (Canis lupus) on cue-following tasks. However, domestication may not be solely responsible for the socio-cognitive skills of dogs, with ontogenetic experience also playing a role. This research evaluated the effects of intensive training on cue-following behaviour using an unreinforced object-choice paradigm. The responses of dogs that were trained to competitive levels were compared to those of pet dogs with only basic training, and dogs living in an animal shelter that demonstrated no or only rudimentary following of basic commands. Using a cue-following task where three types of cues were presented by familiar and unfamiliar human partners, the number of cues followed by each training group were recorded. All dogs found cues where gesture was combined with a congruent head and eye movement easier to follow than either gesture or eye gaze alone. Whether the cue-giver was familiar or not had a significant effect on number of cues followed in homed dogs, and the performance of shelter dogs was comparable to the other groups when faced with an unfamiliar cue-giver. Contrary to predictions, level of training did not improve performance on the cue-following task. This work does provide support for the presence of an evolved adaptation to exploit social cues provided by humans that can be augmented by familiarity with the cue giver. However, additional joint activity as experienced in an intensive training regime does not seem to increase accuracy in following human-given cues
Shear-melting of a hexagonal columnar crystal by proliferation of dislocations
A hexagonal columnar crystal undergoes a shear-melting transition above a
critical shear rate or stress. We combine the analysis of the shear-thinning
regime below the melting with that of synchrotron X-ray scattering data under
shear and propose the melting to be due to a proliferation of dislocations,
whose density is determined by both techniques to vary as a power law of the
shear rate with a 2/3 exponent, as expected for a creep model of crystalline
solids. Moreover, our data suggest the existence under shear of a line hexatic
phase, between the columnar crystal and the liquid phase
A search for magnetic fields on central stars in planetary nebulae
One of the possible mechanisms responsible for the panoply of shapes in
planetary nebulae is the presence of magnetic fields that drive the ejection of
ionized material during the proto-planetary nebula phase. Therefore, detecting
magnetic fields in such objects is of key importance for understanding their
dynamics. Still, magnetic fields have not been detected using polarimetry in
the central stars of planetary nebulae. Circularly polarized light spectra have
been obtained with the Focal Reducer and Low Dispersion Spectrograph at the
Very Large Telescope of the European Southern Observatory and the Intermediate
dispersion Spectrograph and Imaging System at the William Herschel Telescope.
Nineteen planetary nebulae spanning very different morphology and evolutionary
stages have been selected. Most of central stars have been observed at
different rotation phases to point out evidence of magnetic variability. In
this paper, we present the result of two observational campaigns aimed to
detect and measure the magnetic field in the central stars of planetary nebulae
on the basis of low resolution spectropolarimetry. In the limit of the adopted
method, we can state that large scale fields of kG order are not hosted on the
central star of planetary nebulae.Comment: Paper accepted to be published in Astronomy and Astrophysics on
20/01/201
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