503 research outputs found
The Wolf-Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud: spectroscopy, orbital analysis, formation, and evolution
Massive Wolf-Rayet (WR) stars dominate the radiative and mechanical energy
budget of galaxies and probe a critical phase in the evolution of massive stars
prior to core-collapse. It is not known whether core He-burning WR stars
(classical WR, cWR) form predominantly through wind-stripping (w-WR) or binary
stripping (b-WR). With spectroscopy of WR binaries so-far largely avoided due
to its complexity, our study focuses on the 44 WR binaries / binary candidates
of the Large Magellanic Cloud (LMC, metallicity Z~0.5 Zsun), identified on the
basis of radial velocity variations, composite spectra, or high X-ray
luminosities. Relying on a diverse spectroscopic database, we aim to derive the
physical and orbital parameters of our targets, confronting evolution models of
evolved massive stars at sub-solar metallicity, and constraining the impact of
binary interaction in forming them. Spectroscopy is performed using the Potsdam
Wolf-Rayet (PoWR) code and cross-correlation techniques. Disentanglement is
performed using the code Spectangular or the shift-and-add algorithm.
Evolutionary status is interpreted using the Binary Population and Spectral
Synthesis (BPASS) code, exploring binary interaction and chemically-homogeneous
evolution.
No obvious dichotomy in the locations of apparently-single and binary WN
stars on the Hertzsprung-Russell diagram is apparent. According to commonly
used stellar evolution models (BPASS, Geneva), most apparently-single WN stars
could not have formed as single stars, implying that they were stripped by an
undetected companion. Otherwise, it must follow that pre-WR mass-loss/mixing
(e.g., during the red supergiant phase) are strongly underestimated in standard
stellar evolution models.Comment: accepted to A&A on 10.05.2019; 69 pages (25 main paper + 44
appendix); Corrigendum: Shenar et al. 2020, A&A, 641, 2: An unfortunate typo
in the implementation of the "transformed radius" caused errors of up to
~0.5dex in the derived mass-loss rates. This has now been correcte
OrCaCel - OrganoCat plant and pulping combinations for the full valorisation of lignocellulose from marginal land grown perennial plants
Southern Massive Stars at High Angular Resolution: Observational Campaign and Companion Detection
Multiplicity is one of the most fundamental observable properties of massive
O-type stars and offers a promising way to discriminate between massive star
formation theories. Nevertheless, companions at separations between 1 and 100
mas remain mostly unknown due to intrinsic observational limitations. [...] The
Southern MAssive Stars at High angular resolution survey (SMASH+) was designed
to fill this gap by providing the first systematic interferometric survey of
Galactic massive stars. We observed 117 O-type stars with VLTI/PIONIER and 162
O-type stars with NACO/SAM, respectively probing the separation ranges 1-45 and
30-250mas and brightness contrasts of Delta H < 4 and Delta H < 5. Taking
advantage of NACO's field-of-view, we further uniformly searched for visual
companions in an 8''-radius down to Delta H = 8. This paper describes the
observations and data analysis, reports the discovery of almost 200 new
companions in the separation range from 1mas to 8'' and presents the catalog of
detections, including the first resolved measurements of over a dozen known
long-period spectroscopic binaries.
Excluding known runaway stars for which no companions are detected, 96
objects in our main sample (DEC < 0 deg; H<7.5) were observed both with PIONIER
and NACO/SAM. The fraction of these stars with at least one resolved companion
within 200mas is 0.53. Accounting for known but unresolved spectroscopic or
eclipsing companions, the multiplicity fraction at separation < 8'' increases
to f_m = 0.91 +/- 0.03. The fraction of luminosity class V stars that have a
bound companion reaches 100% at 30mas while their average number of physically
connected companions within 8'' is f_c = 2.2 +/- 0.3. This demonstrates that
massive stars form nearly exclusively in multiple systems. Additionally, the
nine non-thermal (NT) radio emitters observed by SMASH+ are all resolved [...]Comment: 57 pages, 20 figures, 7 tables; accepted for publication in ApJ
Massive open star clusters using the VVV survey II. Discovery of six clusters with Wolf-Rayet stars
Context: The ESO Public Survey "VISTA Variables in the V\'ia L\'actea" (VVV)
provides deep multi-epoch infrared observations for an unprecedented 562 sq.
degrees of the Galactic bulge, and adjacent regions of the disk. In this survey
nearly 150 new open clusters and cluster candidates have been discovered. Aims:
This is the second in a series of papers about young, massive open clusters
observed using the VVV survey. We present the first study of six recently
discovered clusters. These clusters contain at least one newly discovered
Wolf-Rayet (WR) star. Methods: Following the methodology presented in the first
paper of the series, wide-field, deep JHKs VVV observations, combined with new
infrared spectroscopy, are employed to constrain fundamental parameters for a
subset of clusters. Results: We affirm that the six studied stellar groups are
real young (2-7 Myr) and massive (between 0.8 and 2.2 10^3 Msol) clusters. They
are highly obscured (Av ~ 5-24 mag) and compact (1-2 pc). In addition to WR
stars, two of the six clusters also contain at least one red supergiant star.
We claim the discovery of 8 new WR stars, and 3 stars showing WR-like emission
lines which could be classified WR or OIf. Preliminary analysis provides
initial masses of ~30-50 Msol for the WR stars. Finally,we discuss the spiral
structure of the Galaxy using as tracers the six new clusters together with the
previously studied VVV clusters.Comment: 17 pages, 8 figurs, accepted in A&
Linear and nonlinear rheology of wormlike micelles
Several surfactant molecules self-assemble in solution to form long,
cylindrical, flexible wormlike micelles. These micelles can be entangled with
each other leading to viscoelastic phases. The rheological properties of such
phases are very interesting and have been the subject of a large number of
experimental and theoretical studies in recent years. We shall report on our
recent work on the macrorheology, microrheology and nonlinear flow behaviour of
dilute aqueous solutions of a surfactant CTAT (Cetyltrimethylammonium
Tosilate). This system forms elongated micelles and exhibits strong
viscoelasticity at low concentrations ( 0.9 wt%) without the addition of
electrolytes. Microrheology measurements of have been done using
diffusing wave spectroscopy which will be compared with the conventional
frequency sweep measurements done using a cone and plate rheometer. The second
part of the paper deals with the nonlinear rheology where the measured shear
stress is a nonmonotonic function of the shear rate . In
stress-controlled experiments, the shear stress shows a plateau for
larger than some critical strain rate, similar to the earlier
reports on CPyCl/NaSal system. Cates et al have proposed that the plateau is a
signature of mechanical instability in the form of shear bands. We have carried
out extensive experiments under controlled strain rate conditions, to study the
time-dependence of shear stress. The measured time series of shear stress has
been analysed in terms of correlation integrals and Lyapunov exponents to show
unambiguously that the behaviour is typical of low dimensional dynamical
systems.Comment: 15 pages, 10 eps figure
The Role of Disgust in Posttraumatic Stress: A Critical Review of the Empirical Literature
The current review provides a detailed analysis of the burgeoning literature examining the role of disgust in understanding posttraumatic stress symptomatology. Research in this area generally converges to suggest (1) posttraumatic stress is associated with the experience of elevated disgust, (2) individual differences in disgust vulnerabilities may relate to increased posttraumatic stress symptom levels, (3) retrospective report of peritraumatic disgust is related to posttraumatic stress symptom levels, and (4) posttraumatic stress symptom levels appear to be associated with increased disgust, including in response to traumatic event cues. Importantly, much of this research suggests observed relations between disgust and posttraumatic stress are at least somewhat unique from relations between fear/anxiety and posttraumatic stress. Future research is now needed to identify mechanisms involved in these relations in order to inform the prevention and treatment of disgust-related posttraumatic stress disorder
'If you had only listened carefully...':the discursive construction of emerging leadership in a UK all-women management team
Increasingly, feminist linguistic research has adopted a discursive perspective to learn how women and men 'do' leadership in gendered ways. 'Women' as a social category is made relevant to this study by virtue of the lack of female senior leaders in UK businesses (Sealy and Vinnicombe, 2013). Much previous research has analysed leadership discourse in mixed gender groups, relying on theories that imply comparisons between men and women. Using an Interactional Sociolinguistic approach, this study aims to learn more about how women perform leadership in the absence of men by analysing the spoken interactions of a women-only team who were engaged in a competitive leadership task. The analysis reveals that the women accomplish leadership in multiple and complex ways that defy binary gendered classifications. Nonetheless, there is a distinctive gendered dynamic to the team's interactions which, it is argued, might be disadvantageous to women aspiring to senior positions
The Juno Magnetic Field Investigation
The Juno Magnetic Field investigation (MAG) characterizes Jupiter's planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to approx. 20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of 's three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno's massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = 1.6 x 10(exp. 6) nT per axis) with a resolution of approx. 0.05 nT in the most sensitive dynamic range (+/-1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through the imager field of view and also provides a continuous record of radiation exposure. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors, and residual spacecraft fields andor sensor offsets are monitored in flight taking advantage of Juno's spin (nominally 2 rpm) to separate environmental fields from those that rotate with the spacecraft
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