157 research outputs found
A Detailed Study of 2S 0114+650 with the RXTE
We present the results of a detailed study of the high mass X-ray binary 2S
0114+650 made with the pointed instruments onboard the Rossi X-ray Timing
Explorer. The spectral and temporal behaviour of this source was examined over
the pulse, orbital, and super-orbital timescales, covering 2 cycles of
the 30.7 d super-orbital modulation. Marginal evidence for variability of the
power law photon index over the pulse period was identified, similar to that
observed from other X-ray pulsars. If this variability is real it can be
attributed to a varying viewing geometry of the accretion region with the spin
of the neutron star. Variability of the neutral hydrogen column density over
the orbital period was observed, which we attribute to the line of sight motion
of the neutron star through the dense circumstellar environment. A reduction in
the power law photon index was observed during the orbital maximum, which we
speculate is due to absorption effects as the neutron star passes behind a
heavily absorbing region near the base of the supergiant companion's wind. No
significant variability of the column density was observed over the
super-orbital period, indicating that variable obscuration by a precessing warp
in an accretion disc is not the mechanism behind the super-orbital modulation.
In contrast, a significant increase in the power law photon index was observed
during the super-orbital minimum. We conclude that the observed super-orbital
modulation is tied to variability in the mass accretion rate due to some as yet
unidentified mechanism.Comment: 22 pages, 27 figures, accepted for publication in MNRAS after
moderate revisio
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
Dust Formation and He II 4686 emission in the Dense Shell of the Peculiar Type Ib Supernova 2006jc
We present evidence for the formation of dust grains in an unusual Type Ib SN
based on late-time spectra of SN 2006jc. The progenitor suffered an LBV-like
outburst just 2 yr earlier, and we propose that the dust formation is a
consequence of the SN blast wave overtaking that LBV-like shell. The key
evidence for dust formation is (a) the appearance of a red/near-IR continuum
source fit by 1600 K graphite grains, and (b) fading of the redshifted sides of
He I emission lines, yielding progressively more asymmetric blueshifted lines
as dust obscures receding material. This provides the strongest case yet for
dust formation in any SN Ib/c. Both developments occurred between 51 and 75 d
after peak, while other SNe observed to form dust did so after a few hundred
days. Geometric considerations indicate that dust formed in the dense swept-up
shell between the forward and reverse shocks, and not in the freely expanding
SN ejecta. Rapid cooling leading to dust formation may have been aided by
extremely high shell densities, as indicated by He I line ratios. The brief
epoch of dust formation is accompanied by He II 4686 emission and enhanced
X-ray emission. These clues suggest that the unusual dust formation in this
object was not due to properties of the SN itself, but instead -- like most
peculiarities of SN 2006jc -- was a consequence of the dense environment
created by an LBV-like eruption 2 yr before the SN.Comment: ApJ, accepted. added some discussion and 2 figures, better title,
conclusions same as previous version. 12 pages, 4 color fig
Optical variabilities in Be/X-ray binary system:GRO J2058+42
We present an analysis of long-term optical monitoring observations and
optical spectroscopic observations of the counterpart to CXOU J205847.5+414637
(high mass X-ray binary system). We search for a variability in the light curve
of Be star. We used differential magnitudes in the time series analysis. The
variability search in the optical light curve was made by using different
algorithms. The reduction and analysis of spectra were done by using MIDAS and
its suitable packages. We have performed a frequency search which gave us the
value 2.404 1/day. This value is attributed to the non-radial pulsation of Be
star. H alpha emission line profiles always show double-peaked emissions with a
mean equivalent width of 2.31 \pm 0.19 \AA ~and a peak separation of 516 \pm 45
km/s. This suggests that Be star disk is still present. CXOU J205847.5+414637
is in X-ray quiescent state.Comment: 8 pages, 9 figures. To appear at Astronomy and Astrophysic
Eta Carinae across the 2003.5 minimum: Spectroscopic Evidence for Massive Binary Interactions
We have analyzed high spatial, moderate spectral resolution observations of
Eta Carinae obtained with the STIS from 1998.0 to 2004.3. The spectra show
prominent P-Cygni lines in H I, Fe II and He I which are complicated by blends
and contamination by nebular emission and absorption along the line-of-sight
toward the observer. All lines show phase and species dependent variations in
emission and absorption. For most of the cycle the He I emission is blueshifted
relative to the H I and Fe II P-Cygni emission lines, which are approximately
centered at system velocity. The blueshifted He I absorption varies in
intensity and velocity throughout the 2024 day period. We construct radial
velocity curves for the absorption component of the He I and H I lines. The He
I absorption shows significant radial velocity variations throughout the cycle,
with a rapid change of over 200 km/s near the 2003.5 event. The H I velocity
curve is similar to that of the He I absorption, though offset in phase and
reduced in amplitude. We interpret the complex line profile variations in He I,
H I and Fe II to be a consequence of the dynamic interaction of the dense wind
of Eta Car A with the less dense, faster wind plus the radiation field of a hot
companion star, Eta Car B. During most of the orbit, Eta Car B and the He+
recombination zone are on the near side of Eta Car A, producing blueshifted He
I emission. He I absorption is formed in the part of the He+ zone that
intersects the line-of-sight toward Eta Car. We use the variations seen in He I
and the other P-Cygni lines to constrain the geometry of the orbit and the
character of Eta Car B.Comment: 16 pages, 18 figure
Two New LBV Candidates in the M33 Galaxy
We present two new luminous blue variable (LBV) candidate stars discovered in
the M33 galaxy. We identified these stars (Valeev et al. 2010) as massive star
candidates at the final stages of evolution, presumably with a notable
interstellar extinction. The candidates were selected from the Massey et al.
(2006) catalog based on the following criteria: emission in Halpha, V<18.5 and
0.35<(B-V)<1.2. The spectra of both stars reveal a broad and strong Halpha
emission with extended wings (770 and 1000 km/s). Based on the spectra we
estimated the main parameters of the stars. Object N45901 has a bolometric
luminosity log(L/Lsun)=6.0-6.2 with the value of interstellar extinction
Av=2.3+-0.1. The temperature of the star's photosphere is estimated as
Tstar~13000-15000K its probable mass on the Zero Age Main Sequence is
M~60-80Msun. The infrared excess in N45901 corresponds to the emission of warm
dust with the temperature Twarm~1000K, and amounts to 0.1% of the bolometric
luminosity. A comparison of stellar magnitude estimates from different catalogs
points to the probable variability of the object N45901. Bolometric luminosity
of the second object, N125093, is log(L/Lsun)=6.3-6.6, the value of
interstellar extinction is Av=2.75+-0.15. We estimate its photosphere's
temperature as Tstar~13000-16000K, the initial mass as M~90-120Msun. The
infrared excess in N125093 amounts to 5-6% of the bolometric luminosity. Its
spectral energy distribution reveals two thermal components with the
temperatures Twarm~1000K and Tcold~480K. The [CaII] lines (7291A and 7323A),
observed in LBV-like stars VarA and N93351 in M33, are also present in the
spectrum of N125093. These lines indicate relatively recent gas eruptions and
dust activity linked with them. High bolometric luminosity of these stars and
broad Halpha emissions allow classifying the studied objects as LBV candidates.Comment: 14 pages, 4 figure
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
On the nature of candidate luminous blue variables in M33
Luminous blue variables (LBVs) are expected to play an important role in
massive stellar evolution as well as being the progenitors of some of the most
luminous supernovae known. In this paper we provide a multiwavelength study of
the population of (candidate) LBVs identified within M33. New spectra provide
an observational baseline of >4yr with respect to published data, which is well
suited to identifying LBV outbursts. Multi-epoch optical and mid-IR surveys of
M33 further constrain the variability of the sample and permit a search for
dusty circumstellar ejecta. Spectroscopic and photometric variability appears
common amongst the sample, although in many cases further observations will be
required to determine its physical origin. Nevertheless, we report a new
outburst of M33 Var C, while the transition of the WNLh star B517 to a cooler B
supergiant phase between 1993-2010 confirms an LBV classification.
Proof-of-concept quantitative analysis is provided for Romano's star; the
results being consistent with the finding that its bolometric luminosity varies
during its LBV excursions. The combination of the temperature and luminosity of
two stars, the B hypergiant [HS80] 110A and the cool hypergiant B324, appears
to be in violation of the empirical Humphreys-Davidson limit. Mid-IR
observations demonstrate that a number of candidates appear associated with hot
circumstellar dust, although no objects as extreme as Eta Carinae are
identified. The combined multiwavelength dataset suggests that the population
of LBVs studied is contaminated by stars demonstrating the B[e] phenomenon. Of
these, a subset of optically faint, low luminosity stars associated with hot
dust are of particular interest since they appear similar to the likely
progenitors of SN 2008S and the 2008 NGC300 transient, albeit suffering less
intrinsic extinction. [ABRIDGED]Comment: 23 pages, 14 figures, accepted for publication in Astronomy and
Astrophysic
AUX1-mediated root hair auxin influx governs SCFTIR1/AFB-type Ca2+ signaling
Auxin is a key regulator of plant growth and development, but the causal relationship between hormone transport and root responses remains unresolved. Here we describe auxin uptake, together with early steps in signaling, in Arabidopsis root hairs. Using intracellular microelectrodes we show membrane depolarization, in response to IAA in a concentration- and pH-dependent manner. This depolarization is strongly impaired in aux1 mutants, indicating that AUX1 is the major transporter for auxin uptake in root hairs. Local intracellular auxin application triggers Ca2+ signals that propagate as long-distance waves between root cells and modulate their auxin responses. AUX1-mediated IAA transport, as well as IAA- triggered calcium signals, are blocked by treatment with the SCFTIR1/AFB - inhibitor auxinole. Further, they are strongly reduced in the tir1afb2afb3 and the cngc14 mutant. Our study reveals that the AUX1 transporter, the SCFTIR1/AFB receptor and the CNGC14 Ca2+ channel, mediate fast auxin signaling in roots
New method to characterize a machining system: application in turning
Many studies simulates the machining process by using a single degree of
freedom spring-mass sytem to model the tool stiffness, or the workpiece
stiffness, or the unit tool-workpiece stiffness in modelings 2D. Others impose
the tool action, or use more or less complex modelings of the efforts applied
by the tool taking account the tool geometry. Thus, all these models remain
two-dimensional or sometimes partially three-dimensional. This paper aims at
developing an experimental method allowing to determine accurately the real
three-dimensional behaviour of a machining system (machine tool, cutting tool,
tool-holder and associated system of force metrology six-component
dynamometer). In the work-space model of machining, a new experimental
procedure is implemented to determine the machining system elastic behaviour.
An experimental study of machining system is presented. We propose a machining
system static characterization. A decomposition in two distinct blocks of the
system "Workpiece-Tool-Machine" is realized. The block Tool and the block
Workpiece are studied and characterized separately by matrix stiffness and
displacement (three translations and three rotations). The Castigliano's theory
allows us to calculate the total stiffness matrix and the total displacement
matrix. A stiffness center point and a plan of tool tip static displacement are
presented in agreement with the turning machining dynamic model and especially
during the self induced vibration. These results are necessary to have a good
three-dimensional machining system dynamic characterization
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