246 research outputs found
First detection of phase-dependent colliding wind X-ray emission outside the Milky Way
After having reported the detection of X-rays emitted by the peculiar system
HD5980, we assess here the origin of this high-energy emission from additional
X-ray observations obtained with XMM-Newton. This research provides the first
detection of apparently periodic X-ray emission from hot gas produced by the
collision of winds in an evolved massive binary outside the Milky Way. It also
provides the first X-ray monitoring of a Luminous Blue Variable only years
after its eruption and shows that the dominant source of the X-rays is not
associated with the ejecta.Comment: 13 pages, 3 figures and 1 table, accepted for publication in ApJ
(letters
FUSE observations of HD 5980: The wind structure of the eruptor
HD 5980 is a unique system containing one massive star (star A) that is
apparently entering the luminous blue variable phase, and an eclipsing
companion (star B) that may have already evolved beyond this phase to become a
Wolf-Rayet star. In this paper we present the results from FUSE observations
obtained in 1999, 2000, and 2002 and one far-UV observation obtained by
ORFEUS/BEFS in 1993 shortly before the first eruption of HD 5980. The eight
phase-resolved spectra obtained by FUSE in 2002 are analyzed in the context of
a wind-eclipse model. This analysis shows that the wind of the eruptor obeyed a
very fast velocity law in 2002, which is consistent with the line-driving
mechanism. Large amplitude line-profile variations on the orbital period are
shown to be due to the eclipse of star B by the wind of star A, although the
eclipse due to gas flowing in the direction of star B is absent. This can only
be explained if the wind of star A is not spherically symmetric, or if the
eclipsed line radiation is "filled-in" by emission originating from somewhere
else in the system, e.g., in the wind-wind collision region. Except for a
slightly lower wind speed, the ORFEUS/BEFS spectrum is very similar to the
spectrum obtained by FUSE at the same orbital phase: there is no indication of
the impending eruption. However, the trend for decreasing wind velocity
suggests the occurrence of the "bi-stability" mechanism, which in turn implies
that the restructuring of the circumbinary environment caused by the transition
from "fast, rarefied wind" to "slow, dense wind" was observed as the eruptive
event. The underlying mechanism responsible for the long-term decrease in wind
velocity that precipitated this change remains an open issue.Comment: 19 pages, 13 figure
Wind and nebula of the M33 variable GR290 (WR/LBV)
Context: GR290 (M33/V532=Romano's Star) is a suspected post-LBV star located
in M33 galaxy that shows a rare Wolf-Rayet spectrum during its minimum light
phase. In spite of many studies, its atmospheric structure, its circumstellar
environment and its place in the general context of massive stars evolution is
poorly known. Aims: Detailed study of its wind and mass loss, and study of the
circumstellar environment associated to the star. Methods: Long-slit spectra of
GR290 were obtained during its present minimum luminosity phase with the GTC
together with contemporaneous BVRI photometry. The data were compared with
non-LTE model atmosphere synthetic spectra computed with CMFGEN and with CLOUDY
models for ionized interstellar medium regions. Results: The current
mag, is the faintest at which this source has ever been observed. The non-LTE
models indicate effective temperature =27-30 kK at radius
=27-21 Rsun and mass loss rate Msun
yr. The terminal wind speed =620 is faster
than ever before recorded while the current luminosity Lsun is the lowest ever deduced. It is overabundant in He and N and
underabundant in C and O. It is surrounded by an unresolved compact HII region
with dimensions 4 pc, from where H-Balmer, HeI lines and [OIII] and [NII]
are detected. In addition, we find emission from a more extended interstellar
medium (ISM) region which appears to be asymmetric, with a larger extent to the
East (16-40 pc) than to the West. Conclusions: In the present long lasting
visual minimum, GR290 is in a lower bolometric luminosity state with higher
mass loss rate. The nearby nebular emission seems to suggest that the star has
undergone significant mass loss over the past years and is nearing
the end stages of its evolution.Comment: submitted to A&A, 12 pages, 9 figures, 7 table
First Detection of Phase-dependent Colliding Wind X-ray Emission outside the Milky Way
After having reported the detection of X-rays emitted by the peculiar system HD 5980, we assess here the origin of this high-energy emission from additional X-ray observations obtained with XMM-Newton. This research provides the first detection of apparently periodic X-ray emission from hot gas produced by the collision of winds in an evolved massive binary outside the Milky Way. It also provides the first X-ray monitoring of a Luminous Blue Variable only years after its eruption and shows that the source of the X-rays is not associated with the ejecta
An experimental investigation of chatter effects on tool life
Tool wear is one of the most important considerations in machining operations as it affects surface quality and integrity, productivity and cost. The most commonly used model for tool life analysis is the one proposed by F.W. Taylor about a century ago. Although the extended form of this equation includes the effects of important cutting conditions on tool wear, tool life studies are mostly performed under stable cutting conditions where the effect of chatter vibrations are not considered. This paper presents an empirical attempt to understand tool life under vibratory cutting conditions. Tool wear data are collected in turning and milling on different work materials under stable and chatter conditions. The effects of cutting conditions as well as severity of chatter on tool life are analyzed. The results indicate significant reduction in tool life due to chatter as expected. They also show that the severity of chatter, and thus the vibration amplitude, strongly reduces the life of cutting tools. These results can be useful in evaluating the real cost of chatter by including the reduced tool life. They can also be useful in justifying the cost of chatter suppression and more rigid machining systems
Multi-scale community organization of the human structural connectome and its relationship with resting-state functional connectivity
The human connectome has been widely studied over the past decade. A principal finding is that it can be decomposed into communities of densely interconnected brain regions. Past studies have often used single-scale modularity measures in order to infer the connectome's community structure, possibly overlooking interesting structure at other organizational scales. In this report, we used the partition stability framework, which defines communities in terms of a Markov process (random walk), to infer the connectome's multi-scale community structure. Comparing the community structure to observed resting-state functional connectivity revealed communities across a broad range of scales that were closely related to functional connectivity. This result suggests a mapping between communities in structural networks, models of influence-spreading and diffusion, and brain function. It further suggests that the spread of influence among brain regions may not be limited to a single characteristic scal
Multi-scale community organization of the human structural connectome and its relationship with resting-state functional connectivity
The human connectome has been widely studied over the past decade. A
principal finding is that it can be decomposed into communities of densely
interconnected brain regions. This result, however, may be limited
methodologically. Past studies have often used a flawed modularity measure in
order to infer the connectome's community structure. Also, these studies relied
on the intuition that community structure is best defined in terms of a
network's static topology as opposed to a more dynamical definition. In this
report we used the partition stability framework, which defines communities in
terms of a Markov process (random walk), to infer the connectome's multi-scale
community structure. Comparing the community structure to observed
resting-state functional connectivity revealed communities across a broad range
of dynamical scales that were closely related to functional connectivity. This
result suggests a mapping between communities in structural networks, models of
communication processes, and brain function. It further suggests that
communication in the brain is not limited to a single characteristic scale,
leading us to posit a heuristic for scale-selective communication in the
cerebral cortex.Comment: Corrected small typographical mistakes, changed order of authors and
funding information, and also chose a more efficient compression for figure
A Changing Wind Collision
We report on the first detection of a global change in the X-ray emitting properties of a wind–wind collision, thanks to XMM-Newton observations of the massive Small Magellenic Cloud (SMC) system HD 5980. While its light curve had remained unchanged between 2000 and 2005, the X-ray flux has now increased by a factor of ~2.5, and slightly hardened. The new observations also extend the observational coverage over the entire orbit, pinpointing the light-curve shape. It has not varied much despite the large overall brightening, and a tight correlation of fluxes with orbital separation is found without any hysteresis effect. Moreover, the absence of eclipses and of absorption effects related to orientation suggests a large size for the X-ray emitting region. Simple analytical models of the wind–wind collision, considering the varying wind properties of the eruptive component in HD 5980, are able to reproduce the recent hardening and the flux-separation relationship, at least qualitatively, but they predict a hardening at apastron and little change in mean flux, contrary to observations. The brightness change could then possibly be related to a recently theorized phenomenon linked to the varying strength of thin-shell instabilities in shocked wind regions
BRITE-Constellation reveals evidence for pulsations in the enigmatic binary Carinae
Car is a massive, eccentric binary with a rich observational history.
We obtained the first high-cadence, high-precision light curves with the
BRITE-Constellation nanosatellites over 6 months in 2016 and 6 months in 2017.
The light curve is contaminated by several sources including the Homunculus
nebula and neighboring stars, including the eclipsing binary
CPD592628. However, we found two coherent oscillations in the light
curve. These may represent pulsations that are not yet understood but we
postulate that they are related to tidally excited oscillations of Car's
primary star, and would be similar to those detected in lower-mass eccentric
binaries. In particular, one frequency was previously detected by van Genderen
et al. and Sterken et al. through the time period of 1974 to 1995 through
timing measurements of photometric maxima. Thus, this frequency seems to have
been detected for nearly four decades, indicating that it has been stable in
frequency over this time span. These pulsations could help provide the first
direct constraints on the fundamental parameters of the primary star if
confirmed and refined with future observations.Comment: 8 pages, 4 figures, accepted to MNRA
- …