98 research outputs found
A 2.3-Day Periodic Variability in the Apparently Single Wolf-Rayet Star WR 134: Collapsed Companion or Rotational Modulation?
We present the results of an intensive campaign of spectroscopic and
photometric monitoring of the peculiar Wolf-Rayet star WR 134 from 1989 to
1997.
This unprecedentedly large data set allows us to confirm unambiguously the
existence of a coherent 2.25 +/- 0.05 day periodicity in the line-profile
changes of He II 4686, although the global pattern of variability is different
from one epoch to another. This period is only marginally detected in the
photometric data set. Assuming the 2.25 day periodic variability to be induced
by orbital motion of a collapsed companion, we develop a simple model aiming at
investigating (i) the effect of this strongly ionizing, accreting companion on
the Wolf-Rayet wind structure, and (ii) the expected emergent X-ray luminosity.
We argue that the predicted and observed X-ray fluxes can only be matched if
the accretion on the collapsed star is significantly inhibited. Additionally,
we performed simulations of line-profile variations caused by the orbital
revolution of a localized, strongly ionized wind cavity surrounding the X-ray
source. A reasonable fit is achieved between the observed and modeled
phase-dependent line profiles of He II 4686. However, the derived size of the
photoionized zone substantially exceeds our expectations, given the observed
low-level X-ray flux. Alternatively, we explore rotational modulation of a
persistent, largely anisotropic outflow as the origin of the observed cyclical
variability. Although qualitative, this hypothesis leads to greater consistency
with the observations.Comment: 34 pages, 16 figures. Accepted by the Astrophysical Journa
Modeling the RXTE light curve of Carinae from a 3-D SPH simulation of its binary wind collision
The very massive star system Carinae exhibits regular 5.54-year
(2024-day) period disruptive events in wavebands ranging from the radio to
X-ray. There is a growing consensus that these events likely stem from
periastron passage of an (as yet) unseen companion in a highly eccentric
() orbit. This paper presents three-dimensional (3-D)
Smoothed Particle Hydrodynamics (SPH) simulations of the orbital variation of
the binary wind-wind collision, and applies these to modeling the X-ray light
curve observed by the Rossi X-ray Timing Explorer (RXTE). By providing a global
3-D model of the phase variation of the density of the interacting winds, the
simulations allow computation of the associated variation in X-ray absorption,
presumed here to originate from near the apex of the wind-wind interaction
cone. We find that the observed RXTE light curve can be readily fit if the
observer's line of sight is within this cone along the general direction of
apastron. Specifically, the data are well fit by an assumed inclination for the orbit's polar axis, which is thus consistent with orbital
angular momentum being along the inferred polar axis of the Homunculus nebula.
The fits also constrain the position angle that an orbital-plane
projection makes with the apastron side of the semi-major axis, strongly
excluding positions along or to the retrograde side of the
axis, with the best fit position given by . Overall the
results demonstrate the utility of a fully 3-D dynamical model for constraining
the geometric and physical properties of this complex colliding-wind binary
system.Comment: 5 pages, 4 figures, accepted to MNRAS Letter
The XMM-Newton serendipitous ultraviolet source survey catalogue
The XMM-Newton Serendipitous Ultraviolet Source Survey (XMM-SUSS) is a
catalogue of ultraviolet (UV) sources detected serendipitously by the Optical
Monitor (XMM-OM) on-board the XMM-Newton observatory. The catalogue contains
ultraviolet-detected sources collected from 2,417 XMM-OM observations in 1-6
broad band UV and optical filters, made between 24 February 2000 and 29 March
2007. The primary contents of the catalogue are source positions, magnitudes
and fluxes in 1 to 6 passbands, and these are accompanied by profile
diagnostics and variability statistics. The XMM-SUSS is populated by 753,578 UV
source detections above a 3 sigma signal-to-noise threshold limit which relate
to 624,049 unique objects. Taking account of substantial overlaps between
observations, the net sky area covered is 29-54 square degrees, depending on UV
filter. The magnitude distributions peak at 20.2, 20.9 and 21.2 in UVW2, UVM2
and UVW1 respectively. More than 10 per cent of sources have been visited more
than once using the same filter during XMM-Newton operation, and > 20 per cent
of sources are observed more than once per filter during an individual visit.
Consequently, the scope for science based on temporal source variability on
timescales of hours to years is broad. By comparison with other astrophysical
catalogues we test the accuracy of the source measurements and define the
nature of the serendipitous UV XMM-OM source sample. The distributions of
source colours in the UV and optical filters are shown together with the
expected loci of stars and galaxies, and indicate that sources which are
detected in multiple UV bands are predominantly star-forming galaxies and stars
of type G or earlier.Comment: Accepted for publication in MNRA
XMM-Newton X-ray study of early type stars in the Carina OB1 association
<p><b>Aims:</b> X-ray properties of the stellar population in the Carina OB1 association are examined with special emphasis on early-type stars. Their spectral characteristics provide some clues to understanding the nature of X-ray formation mechanisms in the winds of single and binary early-type stars.</p>
<p><b>Methods:</b> A timing and spectral analysis of five observations with XMM-Newton is performed using various statistical tests and thermal spectral models.</p>
<p><b>Results:</b> 235 point sources have been detected within the field of view. Several of these sources are probably pre-main sequence stars with characteristic short-term variability. Seven sources are possible background AGNs. Spectral analysis of twenty four sources of type OB and WR 25 was performed. We derived spectral parameters of the sources and their fluxes in three energy bands. Estimating the interstellar absorption for every source and the distance to the nebula, we derived X-ray luminosities of these stars and compared them to their bolometric luminosities. We discuss possible reasons for the fact that, on average, the observed X-ray properties of binary and single early type stars are not very different, and give several possible explanations.</p>
Accretion vs colliding wind models for the gamma-ray binary LS I +61 303: an assessment
LS I +61 303 is a puzzling Be/X-ray binary with variable gamma-ray emission
at up TeV energies. The nature of the compact object and the origin of the
high-energy emission are unclear. One family of models invokes particle
acceleration in shocks from the collision between the B-star wind and a
relativistic pulsar wind, while another centers on a relativistic jet powered
by accretion. Recent high-resolution radio observations showing a putative
"cometary tail" pointing away from the Be star near periastron have been cited
as support for the pulsar-wind model. We wish here to carry out a quantitative
assessment of these competing models for this extraordinary source. We apply a
3D SPH code for dynamical simulations of both the pulsar-wind-interaction and
accretion-jet models. The former yields a description of the shape of the
wind-wind interaction surface. The latter provides an estimation of the
accretion rate. The results allow critical evaluation of how the two distinct
models confront the data in various wavebands under a range of conditions. When
one accounts for the 3D dynamical wind interaction under realistic constraints
for the relative strength of the B-star and pulsar winds, the resulting form of
the interaction front does not match the putative "cometary tail" claimed from
radio observations. On the other hand, dynamical simulations of the
accretion-jet model indicate that the orbital phase variation of accretion
power includes a secondary broad peak well away from periastron, thus providing
a plausible way to explain the observed TeV gamma ray emission toward apastron.
We conclude that the colliding-wind model is not clearly established for LS I
+61 303, while the accretion-jet model can reproduce many key characteristics
of the observed TeV gamma-ray emission.Comment: Accepted for publication in A&A. The resolution of the figures is
lower than in the journal paper to minimize file sizes. Seven pages, 5
figure
Determination of icariin in urine by high performance liquid chromatography with tandem mass-spectrometric detection
C использованием метода высокоэффективной жидкостной хроматографии-тандемной масс-спектрометрии разработан способ селективного определения икариина в пробах мочи. Для анализа биологических проб использовали обращенно-фазовый вариант высокоэффективной хроматографии на сорбентах с привитыми C18 группами. Определение осуществляли методом тандемной масс-спектрометрии с ионизацией электрораспылением в режиме регистрации выбранных ионных переходов для положительных ионов (энергия соударений - 40 %, ионный переход - с m/z = 677.2433 → 313.0703 (100 %), 369.1330 (35 %)). Выбрана процедура пробоподготовки, включающая в себя твёрдофазную экстракцию на картриджах SUPELCO HLB, концентрирование органического экстракта в токе азота и перерастворение сухого остатка. Предел детектирования составил 1 нг∙мл⁻¹. При валидации методики оценивали степень извлечения икариина из биологической жидкости (97 %), селективность и специфичность определения целевого соединения, а также влияние матрицы на ионизацию (4 %).Using the liquid chromatography tandem mass spectrometry, the approach for the selective detection of icariin in urine samples was developed. Biological samples analysis was performed by the reversed-phase chromatography using the C18 sorbent. The method of tandem mass spectrometry with the multiple reaction monitoring (MRM) mode using the electrospray ionization technique in positive ion mode was used (the collision energy - 40 %, m/z = 677.2433 → 313.0703 (100 %), 369.1330 (35 %)). The sample preparation procedure comprising of the solid-phase extraction based on SUPELCO HLB cartridges, the evaporation of the organic extract in a stream of nitrogen and the reconstitution of residue was selected. The detection limit was 1 ng ml⁻¹. During the method validation, the extraction of icariin from a biological fluid (97%), the selectivity and the specificity of the target compound as well as the matrix effects of ionization (4 %) were studied
Intermediate resolution H-beta spectroscopy and photometric monitoring of 3C 390.3 I. Further evidence of a nuclear accretion disk
We have monitored the AGN 3C390.3 between 1995 and 2000.Two large amplitude
outbursts, of different duration, in continuum and H beta light were observed
ie.: in October 1994 a brighter flare that lasted about 1000 days and in July
1997 another one that lasted about 700 days were detected. The flux in the H
beta wings and line core vary simultaneously, a behavior indicative of
predominantly circular motions in the BLR.Important changes of the Hbeta
emission profiles were detected: at times, we found profiles with prominent
asymmetric wings, as those normaly seen in Sy1s, while at other times, we
observe profiles with weak almost symmetrical wings, similar to those seen in
Sy1.8s. We found that the radial velocity difference between the red and blue
bumps is anticorrelated with the light curves of H beta and continuum
radiation.e found that the radial velocity difference between the red and blue
bumps is anticorrelated with the light curves of H-beta and continuum
radiation. Theoretical H-beta profiles were computed for an accretion disk, the
observed profiles are best reproduced by an inclined disk (25 deg) whose region
of maximum emission is located roughly at 200 Rg. The mass of the black hole in
3C 390.3, estimated from the reverberation analysis is Mrev = 2.1 x 10^9 Msun,
ie. 5 times larger than previous estimatesComment: 18 pages, 13 figures, 4 tables. to appear in Astronomy and
Astrophysic
A model for the thermal radio-continuum emission from radiative shocks in colliding stellar winds
Aims. The interaction of two isotropic stellar winds is studied in order to
calculate the free-free emission from the wind collision region. The effects of
the binary separation and the wind momentum ratio on the emission from the
wind-wind interaction region are investigated. Methods. We developed a
semi-analytical model for calculating the thermal emission from colliding
stellar winds. Assuming radiative shocks for the compressed layer, which are
expected in close binaries, we obtained the emission measure of the thin shell.
Then, we computed the total optical depth along each line of sight to obtain
the emission from the whole configuration. Results. Here, we present
predictions of the free-free emission at radio frequencies from analytic,
radiative shock models in colliding wind binaries. It is shown that the
emission from the wind collision region mainly arises from the optically thick
region of the compressed layer and scales as ~ D^{4/5}, where D is the binary
separation. The predicted flux density from the wind collision region becomes
more important as the frequency increases, showing higher spectral indices than
the expected 0.6 value from the unshocked winds. We also investigate the
emission from short-period WR+O systems calculated with our analytic
formulation. In particular, we apply the model to the binary systems WR 98 and
WR 113 and compare our results with the observations. Our theoretical results
are in good agreement with the observed thermal spectra from these sources.Comment: Accepted for publication in Astronomy and Astrophysics, 12 pages, 10
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