387 research outputs found
Evidence for the importance of resonance scattering in X-ray emission line profiles of the O star Puppis
We fit the Doppler profiles of the He-like triplet complexes of \ion{O}{7}
and \ion{N}{6} in the X-ray spectrum of the O star Puppis, using
XMM-Newton RGS data collected over ks of exposure. We find that they
cannot be well fit if the resonance and intercombination lines are constrained
to have the same profile shape. However, a significantly better fit is achieved
with a model incorporating the effects of resonance scattering, which causes
the resonance line to become more symmetric than the intercombination line for
a given characteristic continuum optical depth . We discuss the
plausibility of this hypothesis, as well as its significance for our
understanding of Doppler profiles of X-ray emission lines in O stars.Comment: 29 pages, 8 figures, revised version accepted by Ap
Comparing view-based and map-based semantic labelling in real-time SLAM
Generally capable Spatial AI systems must build persistent scene representations where geometric models are combined with meaningful semantic labels. The many approaches to labelling scenes can be divided into two clear groups: view-based which estimate labels from the input view-wise data and then incrementally fuse them into the scene model as it is built; and map-based which label the generated scene model. However, there has so far been no attempt to quantitatively compare view-based and map-based labelling. Here, we present an experimental framework and comparison which uses real-time height map fusion as an accessible platform for a fair comparison, opening up the route to further systematic research in this area
Radiography in high mass X-ray binaries -- Micro-structure of the stellar wind through variability of the column density
In high mass X-ray binaries (HMXBs), an accreting compact object orbits a
high mass star which loses mass through a dense and inhomogeneous wind. Using
the compact object as an X-ray backlight, the time variability of the absorbing
column density in the wind can be exploited in order to shed light on the
micro-structure of the wind and obtain unbiased stellar mass loss rates for
high mass stars. We explore the impact of clumpiness on the variability of the
column density with a simplified wind model. In particular, we focus on the
standard deviation of the column density and the characteristic duration of
enhanced absorption episodes, and compare them with analytical predictions
based on the porosity length. We identified the favorable systems and orbital
phases to determine the wind micro-structure. The coherence time scale of the
column density is shown to be the self-crossing time of a clump in front of the
compact object. We provide a recipe to get accurate measurements of the size
and of the mass of the clumps, purely based on the observable time variability
of the column density. The coherence time scale grants direct access to the
size of the clumps while their mass can be deduced separately from the
amplitude of the variability. If it is due to unaccreted passing-by clumps, the
high column density variations in some HMXBs requires high mass clumps to
reproduce the observed peak-to-peak amplitude and coherence time scales. These
clump properties are hardly compatible with the ones derived from first
principles. Alternatively, other components could contribute to the variability
of the column density: larger orbital scale structures produced by a mechanism
still to be identified, or a dense environment in the immediate vicinity of the
accretor such as an accretion disk, an outflow or a spherical shell around the
magnetosphere of the accreting neutron star
Resonance Scattering In The X-Ray Emission Lines Profiles Of ζ Puppis
We present XMM-Newton Reflection Grating Spectrometer observations of pairs of X-ray emission line profiles from the O star ζ Pup that originate from the same He-like ion. The two profiles in each pair have different shapes and cannot both be consistently fit by models assuming the same wind parameters. We show that the differences in profile shape can be accounted for in a model including the effects of resonance scattering, which affects the resonance line in the pair but not the intercombination line. This implies that resonance scattering is also important in single resonance lines, where its effect is difficult to distinguish from a low effective continuum optical depth in the wind. Thus, resonance scattering may help reconcile X-ray line profile shapes with literature mass-loss rates
Discovery Of A Magnetic Field In The Rapidly Rotating O-Type Secondary Of The Colliding-Wind Binary HD 47129 (Plaskett\u27s Star)
We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett\u27s star) in the context of the Magnetism in Massive Stars survey. Eight independent Stokes V observations were acquired using the Echelle SpectroPolarimetric Device for the Observations of Stars (ESPaDOnS) spectropolarimeter at the Canada-France-Hawaii Telescope and the Narval spectropolarimeter at the Telescope Bernard Lyot. Using least-squares deconvolution we obtain definite detections of signal in Stokes V in three observations. No significant signal is detected in the diagnostic null (N) spectra. The Zeeman signatures are broad and track the radial velocity of the secondary component; we therefore conclude that the rapidly rotating secondary component is the magnetized star. Correcting the polarized spectra for the line and continuum of the (sharp-lined) primary, we measured the longitudinal magnetic field from each observation. The longitudinal field of the secondary is variable and exhibits extreme values of -810 +/- 150 and +680 +/- 190 G, implying a minimum surface dipole polar strength of 2850 +/- 500 G. In contrast, we derive an upper limit (3 sigma) to the primary\u27s surface magnetic field of 230 G. The combination of a strong magnetic field and rapid rotation leads us to conclude that the secondary hosts a centrifugal magnetosphere fed through a magnetically confined wind. We revisit the properties of the optical line profiles and X-ray emission - previously interpreted as a consequence of colliding stellar winds - in this context. We conclude that HD 47129 represents a heretofore unique stellar system - a close, massive binary with a rapidly rotating, magnetized component - that will be a rich target for further study
Optimization of Planck/LFI on--board data handling
To asses stability against 1/f noise, the Low Frequency Instrument (LFI)
onboard the Planck mission will acquire data at a rate much higher than the
data rate allowed by its telemetry bandwith of 35.5 kbps. The data are
processed by an onboard pipeline, followed onground by a reversing step. This
paper illustrates the LFI scientific onboard processing to fit the allowed
datarate. This is a lossy process tuned by using a set of 5 parameters Naver,
r1, r2, q, O for each of the 44 LFI detectors. The paper quantifies the level
of distortion introduced by the onboard processing, EpsilonQ, as a function of
these parameters. It describes the method of optimizing the onboard processing
chain. The tuning procedure is based on a optimization algorithm applied to
unprocessed and uncompressed raw data provided either by simulations, prelaunch
tests or data taken from LFI operating in diagnostic mode. All the needed
optimization steps are performed by an automated tool, OCA2, which ends with
optimized parameters and produces a set of statistical indicators, among them
the compression rate Cr and EpsilonQ. For Planck/LFI the requirements are Cr =
2.4 and EpsilonQ <= 10% of the rms of the instrumental white noise. To speedup
the process an analytical model is developed that is able to extract most of
the relevant information on EpsilonQ and Cr as a function of the signal
statistics and the processing parameters. This model will be of interest for
the instrument data analysis. The method was applied during ground tests when
the instrument was operating in conditions representative of flight. Optimized
parameters were obtained and the performance has been verified, the required
data rate of 35.5 Kbps has been achieved while keeping EpsilonQ at a level of
3.8% of white noise rms well within the requirements.Comment: 51 pages, 13 fig.s, 3 tables, pdflatex, needs JINST.csl, graphicx,
txfonts, rotating; Issue 1.0 10 nov 2009; Sub. to JINST 23Jun09, Accepted
10Nov09, Pub.: 29Dec09; This is a preprint, not the final versio
Rest-wavelength Fiducials for the ITER Core Imaging X-ray Spectrometer
Absolute wavelength references are needed to derive the plasma velocities from the Doppler shift of a given line emitted by a moving plasma. We show that such reference standards exist for the strongest x-ray line in neonlike W64+, which has become the line of choice for the ITER (Latin the way) core imaging x-ray spectrometer. Close-by standards are the Hf L3 line and the Ir L2 line, which bracket the W64+ line by 30 eV; other standards are given by the Ir L1 and L2 lines and the Hf L1 and L2 lines, which bracket the W64+ line by 40 and 160 eV, respectively. The reference standards can be produced by an x-ray tube built into the ITER spectrometer. We present spectra of the reference lines obtained with an x-ray microcalorimeter and compare them to spectra of the W64+ line obtained both with an x-ray microcalorimeter and a crystal spectromete
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