547 research outputs found
Optical and infrared polarimetry of the transient LMXB Cen X-4 in quiescence
We present the first optical and infrared polarimetric study of the low mass
transient X-ray binary Cen X-4 during its quiescent phase. This work is aimed
to search for an intrinsic linear polarisation component in the system emitted
radiation that might be due, e.g., to synchrotron emission from a compact jet,
or to Thomson scattering with free electrons in an accretion disc. Multiband
(BVRI) optical polarimetric observations were obtained during two nights in
2008 at the ESO La Silla 3.6 m telescope (EFOSC2) in polarimetric mode. These
observations cover about the 30% of the 15.1 hours orbital period. J-band
observations were obtained in 2007 with the NICS (TNG) instrument at La Palma,
for a totality of 1 hour observation. We obtained 3-sigma upper limits to the
polarisation degree in all the optical bands, with the most constraining one
being in the I-band (P<0.5%). No phase-correlated variability has been noticed
in all the filters. The J-band observations provided a 6% upper limit on the
polarisation level. The constraining upper limits to the polarisation in the
optical allowed us to evaluate the contribution of the possible emission of a
relativistic particles jet to the total system radiation to be less then the
10%. This is in agreement with the observation of a spectral energy
distribution typical of a single black body of a K-spectral type main sequence
star irradiated from the compact object. Due to the low S/N ratio it was not
possible to investigate the possible dependency of the polarisation degree from
the wavelength, that could be suggestive of polarisation induced by Thomson
scattering of radiation with free electrons in the outer part of the accretion
disc. Observations with higher S/N ratio are required to examine in depth this
hypothesis, searching for significant phase-correlated variability.Comment: 7 pages, 9 figures, accepted for publication in section 7. Stellar
structure and evolution of Astronomy and Astrophysic
Next-to-Leading Order NMSSM Decays with CP-odd Higgs Bosons and Stops
We compute the full next-to-leading order supersymmetric (SUSY) electroweak
(EW) and SUSY-QCD corrections to the decays of CP-odd NMSSM Higgs bosons into
stop pairs. In our numerical analysis we also present the decay of the heavier
stop into the lighter stop and an NMSSM CP-odd Higgs boson. Both the EW and the
SUSY-QCD corrections are found to be significant and have to be taken into
account for a proper prediction of the decay widths.Comment: 28 pages, 10 figure
Different twins in the millisecond pulsar recycling scenario: optical polarimetry of PSR J1023+0038 and XSS J12270-4859
We present the first optical polarimetric study of the two transitional
pulsars PSR J1023+0038 and XSS J12270-4859. This work is focused on the search
for intrinsical linear polarisation (LP) in the optical emission from the two
systems. We carried out multiband optical and NIR photo-polarimetry of the two
systems using the ESO NTT at La Silla (Chile), equipped with the EFOSC2 and the
SOFI instruments. XSS J12270-4859 was observed during its radio-pulsar state;
we did not detect LP in all bands, with 3 sigma upper limits of, e.g., 1.4% in
the R-band. We built the NIR-optical averaged spectral energy distribution
(SED) of the system, that could be well described by an irradiated black body
with radius and albedo ,
without the need of further components (thus excluding the visible presence of
an extended accretion disc and/or of relativistic jets). The case was different
for PSR J1023+0038, that was in its accretion phase during our campaign. We
measured a LP of and in the V and R bands,
respectively. The phase-resolved polarimetric curve of the source in the R-band
reveals a hint of a sinusoidal modulation at the source 4.75 hr orbital period,
peaked at the same orbital phase as the light curve. The measured LP of PSR
J1023+0038 could in principle be interpreted as scattering with free electrons
(that can be found in the accretion disc of the system or even in the hot
corona that surrounds the disc itself) or to synchrotron emission from a
relativistic particles jet or outflow. However, the NIR-optical SED of the
system built starting from our dataset did not suggest the presence of a jet.
We conclude that the optical LP observed for PSR J1023+0038 is possibly due to
Thomson scattering with electrons in the disc, as also suggested from the
possible modulation of the R-band LP at the system orbital period.Comment: 10 pages, 8 figures, 4 tables. Accepted for publication in Sec. 7.
Stellar structure and evolution of Astronomy and Astrophysic
The long-term evolution of the X-ray pulsar XTE J1814-338: a receding jet contribution to the quiescent optical emission?
We present a study of the quiescent optical counterpart of the Accreting
Millisecond X-ray Pulsar XTE J1814-338, carrying out multiband (BVR) orbital
phase-resolved photometry using the ESO VLT/FORS2. The optical light curves are
consistent with a sinusoidal variability modulated with the orbital period,
showing evidence for a strongly irradiated companion star, in agreement with
previous findings. The observed colours cannot be accounted for by the
companion star alone, suggesting the presence of an accretion disc during
quiescence. The system is fainter in all analysed bands compared to previous
observations. The R band light curve displays a possible phase offset with
respect to the B and V band. Through a combined fit of the multi-band light
curves we derive constraints on the companion star and disc fluxes, on the
system distance and on the companion star mass. The irradiation luminosity
required to account for the observed day-side temperature of the companion star
is consistent with the spin-down luminosity of a millisecond radio pulsar. The
flux decrease and spectral evolution of the quiescent optical emission observed
comparing our data with previous observations, collected over 5 years, cannot
be well explained with the contribution of an irradiated companion star and an
accretion disc alone. The progressive flux decrease as the system gets bluer
could be due to a continuum component evolving towards a lower, bluer spectrum.
While most of the continuum component is likely due to the disc, we do not
expect it to become bluer in quiescence. Hence we hypothesize that an
additional component, such as synchrotron emission from a jet was contributing
significantly in the earlier data obtained during quiescence and then
progressively fading or moving its break frequency toward longer wavelengths.Comment: 7 pages, 8 figures, accepted for publication in Section 7. Stellar
structure and evolution of Astronomy and Astrophysic
The importance of warehouses in logistics outsourcing: benchmarking the perspectives of 3PL providers and shippers
Purpose: An ever-increasing number of companies outsource logistics activities to third-party logistics (3PL) providers to beat the competition. From the buyer's (shippers') perspective, selecting the right 3PL provider is crucial, and from the 3PL provider's perspective, it is imperative to be attractive and to retain clients. To this aim, a potential lever can be physical assets, such as warehouses, which the literature has traditionally neglected. The objective is to benchmark the importance of warehouses for 3PL providers to attract/retain clients and for shippers to select the right 3PL provider. Design/methodology/approach: The authors performed an empirical investigation through interviews on dyads (3PL providers/shippers) and utilized the Best-Worst Method (BWM) to rank the criteria used in the 3PL buying process and allow the warehouse's role to emerge. Findings: Results show that the 3PL buying process consists of four phases and three evaluation steps. The selection criteria are classified into three groups: order qualifiers, order winners and retention factors. The warehouse has different levels of importance throughout the process. It appears that it can indirectly enhance the attractiveness and retention capability of 3PL providers through other selection criteria. Originality/value: By combining the resource-based view and the customer value theory, this research extends the theory on logistics outsourcing by studying the phases of the 3PL buying process and scrutinizing the criteria used in different evaluation steps. The research adds a double perspective of analysis (3PL providers and shippers), which is missing in the literature, and focuses on the importance of warehouses
1RXS J180408.9-342058: an ultra compact X-ray binary candidate with a transient jet
We present a detailed NIR/optical/UV study of the transient low mass X-ray
binary 1RXS J180408.9-342058 performed during its 2015 outburst, aimed at
determining the nature of its companion star. We obtained three optical spectra
at the 2.1 m San Pedro Martir Observatory telescope (Mexico). We performed
optical and NIR photometric observations with both the REM telescope and the
New Technology Telescope (NTT) in La Silla. We obtained optical and UV
observations from the Swift archive. Finally, we performed optical polarimetry
of the source by using the EFOSC2 instrument mounted on the NTT. The optical
spectrum of the source is almost featureless since the hydrogen and He I
emissions lines, typically observed in LMXBs, are not detected. Similarly,
carbon and oxygen lines are neither observed. We marginally detect the He II
4686 AA emission line, suggesting the presence of helium in the accretion disc.
No significant optical polarisation level was observed. The lack of hydrogen
and He I emission lines in the spectrum implies that the companion is likely
not a main sequence star. Driven by the tentative detection of the He II 4686
AA emission line, we suggest that the system could harbour a helium white
dwarf. If this is the case, 1RXS J180408.9-342058 would be an ultra-compact
X-ray binary. By combining an estimate of the mass accretion rate together with
evolutionary tracks for a He white dwarf, we obtain a tentative orbital period
of ~ 40 min. On the other hand, we also built the NIR-optical-UV spectral
energy distribution (SED) of the source at two different epochs. One SED was
gathered when the source was in the soft X-ray state, and it is consistent with
the presence of a single thermal component. The second SED, obtained when the
source was in the hard X-ray state, shows a thermal component together with a
tail in the NIR, likely indicating the presence of a (transient) jet.Comment: 8 pages, 5 figures, 4 tables. Accepted for publication in Astronomy &
Astrophysics (Section 7
Multi-objective evolutionary–fuzzy augmented flight control for an F16 aircraft
In this article, the multi-objective design of a fuzzy logic augmented flight controller for a high performance fighter jet (the Lockheed-Martin F16) is described. A fuzzy logic controller is designed and its membership functions tuned by genetic algorithms in order to design a roll, pitch, and yaw flight controller with enhanced manoeuverability which still retains safety critical operation when combined with a standard inner-loop stabilizing controller. The controller is assessed in terms of pilot effort and thus reduction of pilot fatigue. The controller is incorporated into a six degree of freedom motion base real-time flight simulator, and flight tested by a qualified pilot instructor
The puzzling case of the accreting millisecond X-ray pulsar IGR J00291+5934: flaring optical emission during quiescence
We present an optical (gri) study during quiescence of the accreting
millisecond X-ray pulsar IGR J00291+5934 performed with the 10.4m Gran
Telescopio Canarias (GTC) in August 2014. Despite the source being in
quiescence at the time of our observations, it showed a strong optical flaring
activity, more pronounced at higher frequencies (i.e. the g band). Once the
flares were subtracted, we tentatively recovered a sinusoidal modulation at the
system orbital period in all bands, even if a significant phase shift with
respect to an irradiated star, typical of accreting millisecond X-ray pulsars
is detected. We conclude that the observed flaring could be a manifestation of
the presence of an accretion disc in the system. The observed light curve
variability could be explained by the presence of a superhump, which might be
another proof of the formation of an accretion disc. In particular, the disc at
the time of our observations was probably preparing to the new outburst of the
source, that happened just a few months later, in 2015.Comment: 6 pages, 2 figures, 1 table. Accepted for publication in A&
Light neutralino in the MSSM: An update with the latest LHC results
We discuss the scenario of light neutralino dark matter in the minimal
supersymmetric standard model, which is motivated by the results of some of the
direct detection experiments --- DAMA, CoGENT, and CRESST. We update our
previous analysis with the latest results of the LHC. We show that new LHC
constraints disfavour the parameter region that can reproduce the results of
DAMA and CoGENT.Comment: 4 pages, 4 figures, to appear in the conference proceedings of TAUP
2011, Munich Germany, 5-9 September 201
Polarimetric and spectroscopic optical observations of the ultra-compact X-ray binary 4U 0614+091
Aims: We present a polarimetric and spectroscopic study of the persistent
ultra compact X-ray binary 4U 0614+091 aimed at searching for the emission of a
relativistic particle jet and at unveiling the orbital period of the system.
Methods: We obtained r-band polarimetric observations with the Telescopio
Nazionale Galileo (TNG) equipped with the PAOLO polarimeter and with the Nordic
Optical Telescope (NOT) equipped with the ALFOSC instrument, covering ~ 2 hours
and ~ 0.5 hours observations, respectively. We carried out low resolution
spectroscopy of the system using the ESO Very Large Telescope equipped with
FORS1 for ~ 1.5 hours (16 spectra covering the range 430-800 nm). Results: The
polarimetric analysis performed starting from the TNG dataset revealed a
polarisation degree in the r-band of 3 % +/- 1 %. From the NOT dataset, due to
the lower S/N ratio, we could obtain only a 3 sigma upper limit of 3.4 %. From
the joining of a spectroscopic and photometric analysis, through the study of
the equivalent width variations of the CII 724 nm line and the r-band light
curve, we could find a hint of a ~ 45 min periodicity. Conclusions: A
polarisation degree P of ~ 3 % in the r-band is consistent with the emission of
a relativistic particle jet, which is supposed to emit intrinsically linearly
polarised synchrotron radiation. Since no variations of P with time have been
detected, and the accretion disc of the system does not contain ionised
hydrogen, scattering by free electrons in the accretion disc has been rejected.
The period of ~ 45 min obtained through the analysis of the system light curve
and of the equivalent width variations of the selected spectral line is
probably linked to the presence of a hot spot or a superhump in the accretion
disc, and lead to an orbital period > 1 hour for the binary system.Comment: 8 pages, 6 figures, 4 tables. Accepted for publication in Astronomy &
Astrophysics (Section 7
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