3,096 research outputs found
An Investigation of the Large-scale Variability of the Apparently Single Wolf-Rayet Star WR 1
In recent years, much studies have focused on determining the origin of the
large-scale line-profile and/or photometric patterns of variability displayed
by some apparently single Wolf-Rayet stars, with the existence of an unseen
(collapsed?) companion or of spatially extended wind structures as potential
candidates. We present observations of WR 1 which highlight the unusual
character of the variations in this object. Our narrowband photometric
observations reveal a gradual increase of the stellar continuum flux amounting
to Delta v = 0.09 mag followed by a decline on about the same timescale (3-4
days). Only marginal evidence for variability is found during the 11 following
nights.
Strong, daily line-profile variations are also observed but they cannot be
easily linked to the photometric variations.
Similarly to the continuum flux variations, coherent time-dependent changes
are observed in 1996 in the centroid, equivalent width, and skewness of He II
4686. Despite the generally coherent nature of the variations, we do not find
evidence in our data for the periods claimed in previous studies. While the
issue of a cyclical pattern of variability in WR 1 is still controversial, it
is clear that this object might constitute in the future a cornerstone for our
understanding of the mechanisms leading to the formation of largely anisotropic
outflows in Wolf-Rayet stars.Comment: 11 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
Revealing evolved massive stars with Spitzer
Massive evolved stars loss a large fraction of their mass via copious stellar
wind or instant outbursts and during certain evolutionary phases they can be
identified via the presence of their circumstellar nebulae. In this paper, we
present the results of search for compact nebulae (reminiscent of circumstellar
nebulae around evolved massive stars) using archival 24 m data obtained
with the Multiband Imaging Photometer for Spitzer. We discovered 115 nebulae,
most of which bear a striking resemblance to the circumstellar nebulae
associated with Luminous Blue Variables (LBVs) and late WN-type (WNL)
Wolf-Rayet (WR) stars in the Milky Way and the Large Magellanic Cloud (LMC). We
interpret this similarity as an indication that the central stars of detected
nebulae are either LBVs or related evolved massive stars. Our interpretation is
supported by follow-up spectroscopy of two dozens of these central stars, most
of which turns out to be either candidate LBVs (cLBVs), blue supergiants or WNL
stars. We expect that the forthcoming spectroscopy of the remaining objects
from our list, accompanied by the spectrophotometric monitoring of the already
discovered cLBVs, will further increase the known population of Galactic LBVs,
which in turn would have profound consequences for better understanding the LBV
phenomenon and its role in the transition between hydrogen burning O stars and
helium burning WR stars. We also report the detection of an arc-like structure
attached to the cLBV HD326823 and an arc associated with the LBV R99 (HD269445)
in the LMC.Comment: 9 pages, 10 figures, accepted to MNRA
The bright optical afterglow of the long GRB 001007
We present optical follow up observations of the long GRB 001007 between 6.14
hours and ~468 days after the event. An unusually bright optical afterglow (OA)
was seen to decline following a steep power law decay with index alpha = -2.03
+/- 0.11, possibly indicating a break in the light curve at t - to < 3.5 days,
as found in other bursts. Upper limits imposed by the LOTIS alerting system
6.14 hours after the gamma ray event provide tentative (1.2 sigma) evidence for
a break in the optical light curve. The spectral index beta of the OA yields
-1.24 +/- 0.57. These values may be explained both by several fireball jet
models and by the cannonball model. Fireball spherical expansion models are not
favoured. Late epoch deep imaging revealed the presence of a complex host
galaxy system, composed of at least two objects located 1.2" (1.7 sigma) and
1.9" (2.7 sigma) from the afterglow position.Comment: 7 pages, 5 figures, published in A&
Measurement of the electron structure function F2e at LEP energies
The hadronic part of the electron structure function F2e has been measured for the first time, using e+e−e+e− data collected by the DELPHI experiment at LEP, at centre-of-mass energies of √s=91.2-209.5 GeV. The data analysis is simpler than that of the measurement of the photon structure function. The electron structure function View the MathML sourceF2e data are compared to predictions of phenomenological models based on the photon structure function. It is shown that the contribution of large target photon virtualities is significant. The data presented can serve as a cross-check of the photon structure function View the MathML sourceF2γ analyses and help in refining existing parameterisations
First Observation of CP Violation in B0->D(*)CP h0 Decays by a Combined Time-Dependent Analysis of BaBar and Belle Data
We report a measurement of the time-dependent CP asymmetry of B0->D(*)CP h0
decays, where the light neutral hadron h0 is a pi0, eta or omega meson, and the
neutral D meson is reconstructed in the CP eigenstates K+ K-, K0S pi0 or K0S
omega. The measurement is performed combining the final data samples collected
at the Y(4S) resonance by the BaBar and Belle experiments at the
asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The
data samples contain ( 471 +/- 3 ) x 10^6 BB pairs recorded by the BaBar
detector and ( 772 +/- 11 ) x 10^6, BB pairs recorded by the Belle detector. We
measure the CP asymmetry parameters -eta_f S = +0.66 +/- 0.10 (stat.) +/- 0.06
(syst.) and C = -0.02 +/- 0.07 (stat.) +/- 0.03 (syst.). These results
correspond to the first observation of CP violation in B0->D(*)CP h0 decays.
The hypothesis of no mixing-induced CP violation is excluded in these decays at
the level of 5.4 standard deviations.Comment: 9 pages, 2 figures, submitted to Physical Review Letter
Study of CP violation in Dalitz-plot analyses of B0 --> K+K-KS, B+ --> K+K-K+, and B+ --> KSKSK+
We perform amplitude analyses of the decays , , and , and measure CP-violating
parameters and partial branching fractions. The results are based on a data
sample of approximately decays, collected with the
BABAR detector at the PEP-II asymmetric-energy factory at the SLAC National
Accelerator Laboratory. For , we find a direct CP asymmetry
in of , which differs
from zero by . For , we measure the
CP-violating phase .
For , we measure an overall direct CP asymmetry of
. We also perform an angular-moment analysis of
the three channels, and determine that the state can be described
well by the sum of the resonances , , and
.Comment: 35 pages, 68 postscript figures. v3 - minor modifications to agree
with published versio
Integrating water exclusion theory into βcontacts to predict binding free energy changes and binding hot spots
10.1186/1471-2105-15-57BMC Bioinformatics151-BBMI
Measurement of CP Asymmetries and Branching Fractions in Charmless Two-Body B-Meson Decays to Pions and Kaons
We present improved measurements of CP-violation parameters in the decays
, , and , and of
the branching fractions for and . The
results are obtained with the full data set collected at the
resonance by the BABAR experiment at the PEP-II asymmetric-energy factory
at the SLAC National Accelerator Laboratory, corresponding to
million pairs. We find the CP-violation parameter values and
branching fractions where in each case, the first uncertainties are statistical
and the second are systematic. We observe CP violation with a significance of
6.7 standard deviations for and 6.1 standard deviations for
, including systematic uncertainties. Constraints on the
Unitarity Triangle angle are determined from the isospin relations
among the rates and asymmetries. Considering only the solution
preferred by the Standard Model, we find to be in the range
at the 68% confidence level.Comment: 18 pages, 11 postscript figures, submitted to Phys. Rev.
Measurement of ISR-FSR interference in the processes e+ e- --> mu+ mu- gamma and e+ e- --> pi+ pi- gamma
Charge asymmetry in processes e+ e- --> mu+ mu- gamma and e+ e- --> pi+ pi-
gamma is measured using 232 fb-1 of data collected with the BABAR detector at
center-of-mass energies near 10.58 GeV. An observable is introduced and shown
to be very robust against detector asymmetries while keeping a large
sensitivity to the physical charge asymmetry that results from the interference
between initial and final state radiation. The asymmetry is determined as
afunction of the invariant mass of the final-state tracks from production
threshold to a few GeV/c2. It is compared to the expectation from QED for e+ e-
--> mu+ mu- gamma and from theoretical models for e+ e- --> pi+ pi- gamma. A
clear interference pattern is observed in e+ e- --> pi+ pi- gamma, particularly
in the vicinity of the f_2(1270) resonance. The inferred rate of lowest order
FSR production is consistent with the QED expectation for e+ e- --> mu+ mu-
gamma, and is negligibly small for e+ e- --> pi+ pi- gamma.Comment: 32 pages,29 figures, to be submitted to Phys. Rev.
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