121 research outputs found
Dynamics of the 6.7 and 12.2 GHz methanol masers around Cepheus A HW2
The 6.7 GHz methanol maser is exclusively associated with high-mass star
formation. However, it remains unclear what structures harbour the methanol
masers. Cepheus A is one of the closest regions of massive star formation,
making it an excellent candidate for detailed studies. We determine the
dynamics of maser spots in the high-mass star-forming region Cepheus A in order
to infer where and when the maser emission occurs. Very long baseline
interferometry (VLBI) observations of the 6.7 and 12.2 GHz methanol masers
allows for mapping their spatial and velocity distribution. Phase-referencing
is used to determine the astrometric positions of the maser emission, and
multi-epoch observations can reveal 3D motions. The 6.7 GHz methanol masers are
found in a filamentary structure over ~1350 AU, straddling the waist of the
radio jet HW2. The positions agree well with previous observations of both the
6.7 and 12.2 GHz methanol masers. The velocity field of the maser spots does
not show any sign of rotation, but is instead consistent with an infall
signature. The 12.2 GHz methanol masers are closely associated with the 6.7 GHz
methanol masers, and the parallax that we derive confirms previous
measurements. We show that the methanol maser emission very likely arises in a
shock interface in the equatorial region of Cepheus A HW2 and presents a model
in which the maser emission occurs between the infalling gas and the accretion
disk/process.Comment: 9 pages, 5 figures; accepted for publication in Astronomy and
Astrophysic
EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions III. The flux-limited sample
Theoretical simulations and observations at different angular resolutions
have shown that magnetic fields have a central role in massive star formation.
Like in low-mass star formation, the magnetic field in massive young stellar
objects can either be oriented along the outflow axis or randomly. Measuring
the magnetic field at milliarcsecond resolution (10-100 au) around a
substantial number of massive young stellar objects permits determining with a
high statistical significance whether the direction of the magnetic field is
correlated with the orientation of the outflow axis or not. In late 2012, we
started a large VLBI campaign with the European VLBI Network to measure the
linearly and circularly polarized emission of 6.7 GHz methanol masers around a
sample of massive star-forming regions. This paper focuses on the first seven
observed sources, G24.78+0.08, G25.65+1.05, G29.86-0.04, G35.03+0.35,
G37.43+1.51, G174.20-0.08, and G213.70-12.6. For all these sources, molecular
outflows have been detected in the past. We detected a total of 176 methanol
masing cloudlets toward the seven massive star-forming regions, 19% of which
show linearly polarized emission. The methanol masers around the massive young
stellar object MM1 in G174.20-0.08 show neither linearly nor circularly
polarized emission. The linear polarization vectors are well ordered in all the
other massive young stellar objects. We measured significant Zeeman splitting
toward both A1 and A2 in G24.78+0.08, and toward G29.86-0.04 and G213.70-12.6.
By considering all the 19 massive young stellar objects reported in the
literature for which both the orientation of the magnetic field at
milliarcsecond resolution and the orientation of outflow axes are known, we
find evidence that the magnetic field (on scales 10-100 au) is preferentially
oriented along the outflow axes.Comment: 17 pages, 10 figures, 9 tables, accepted by Astronomy & Astrophysics.
arXiv admin note: text overlap with arXiv:1306.633
Possible magnetic field variability during the 6.7 GHz methanol maser flares of G09.62+0.20
(Abridged) Recently, the magnetic field induced Zeeman splitting was measured
for the strongest known 6.7 GHz methanol maser, which arises in the massive
star forming region G09.62+0.20. This maser is one of a handful of periodically
flaring methanol masers. The 100-m Effelsberg telescope was used to monitor the
6.7 GHz methanol masers of G09.62+0.20. With the exception of a two week period
during the peak of the maser flare, we measure a constant magnetic field of
B_||~11+-2 mG in the two strongest maser components of G09.62+0.20 that are
separated by over 200 AU. In the two week period that coincides exactly with
the peak of the maser flare of the strongest maser feature, we measure a sharp
decrease and possible reversal of the Zeeman splitting. The exact cause of both
maser and polarization variability is still unclear, but it could be related to
either background amplification of polarized emission or the presence of a
massive protostar with a close-by companion. Alternatively, the polarization
variability could be caused by non-Zeeman effects related to the radiative
transfer of polarized maser emission.Comment: 4 pages, 3 figures, accepted for publication Astronomy and
Astrophysic
Magnetic field regulated infall on the disc around the massive protostar Cepheus A HW2
We present polarization observations of the 6.7-GHz methanol masers around
the massive protostar Cepheus A HW2 and its associated disc. The data were
taken with the Multi-Element Radio Linked Interferometer Network. The maser
polarization is used to determine the full three-dimensional magnetic field
structure around Cepheus A HW2. The observations suggest that the masers probe
the large scale magnetic field and not isolated pockets of a compressed field.
We find that the magnetic field is predominantly aligned along the protostellar
outflow and perpendicular to the molecular and dust disc. From the
three-dimensional magnetic field orientation and measurements of the magnetic
field strength along the line of sight, we are able to determine that the high
density material, in which the masers occurs, is threaded by a large scale
magnetic field of ~23 mG. This indicates that the protostellar environment at
~1000 AU from Cepheus A HW2 is slightly supercritical (lambda approximately
1.7) and the relation between density and magnetic field is consistent with
collapse along the magnetic field lines. Thus, the observations indicate that
the magnetic field likely regulates accretion onto the disc. The magnetic field
dominates the turbulent energies by approximately a factor of three and is
sufficiently strong to be the crucial component stabilizing the massive
accretion disc and sustaining the high accretion rates needed during massive
star-formation.Comment: 10 pages, 6 figures; accepted for publication in MNRAS. High
resolution version can be found at
http://www.astro.uni-bonn.de/~wouter/papers/papers.shtm
Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
Over 100 trigonometric parallaxes and proper motions for masers associated
with young, high-mass stars have been measured with the BeSSeL Survey, a VLBA
key science project, the EVN, and the Japanese VERA project. These measurements
provide strong evidence for the existence of spiral arms in the Milky Way,
accurately locating many arm segments and yielding spiral pitch angles ranging
from 7 to 20 degrees. The widths of spiral arms increase with distance from the
Galactic center. Fitting axially symmetric models of the Milky Way with the 3-D
position and velocity information and conservative priors for the solar and
average source peculiar motions, we estimate the distance to the Galactic
center, Ro, to be 8.34 +/- 0.16 kpc, a circular rotation speed at the Sun, To,
to be 240 +/- 8 km/s, and a rotation curve that is nearly flat (a slope of -0.2
+/- 0.4 km/s/kpc) between Galactocentric radii of 5 and 16 kpc. Assuming a
"universal" spiral galaxy form for the rotation curve, we estimate the thin
disk scale length to be 2.44 +/- 0.16 kpc. The parameters Ro and To are not
highly correlated and are relatively insensitive to different forms of the
rotation curve. Adopting a theoretically motivated prior that high-mass star
forming regions are in nearly circular Galactic orbits, we estimate a global
solar motion component in the direction of Galactic rotation, Vsun = 14.6 +/-
5.0 km/s. While To and Vsun are significantly correlated, the sum of these
parameters is well constrained, To + Vsun = 255.2 +/- 5.1 km/s, as is the
angular speed of the Sun in its orbit about the Galactic center, (To + Vsun)/Ro
= 30.57 +/- 0.43 km/s/kpc. These parameters improve the accuracy of estimates
of the accelerations of the Sun and the Hulse-Taylor binary pulsar in their
Galactic orbits, significantly reducing the uncertainty in tests of
gravitational radiation predicted by general relativity.Comment: 38 pages, 6 tables, 6 figures; v2 fixed typos and updated pulsar
section; v3 replaced fig 2 (wrong file
Integrated energy design: education and training in cross-disciplinary teams implementing energy performance of buildings directive (EPBD)
In Europe, energy and climate policies started to take shape from the 1990s onwards culminating with the ambitious 20-20-20 climate goals and the Low-Carbon Europe roadmap 2050. The European Commission empower the importance of achieving the objective of the recast Directive on energy performance of buildings (EPBD) that new buildings built from 2021 onwards will have to be nearly zero-energy buildings. The general belief is that the energy performance optimization of buildings requires an integrated design approach and cross-disciplinary teamwork to optimize the building's energy use and quality of indoor environment while satisfying the occupants' needs.In this context, there is a substantial need for professionals such as architects and engineers specifically trained and educated in integrated design approach and trained to work in cross-disciplinary teams. To be able to push forward the development, it is essential that educational institutions foster professionals with such knowledge, skills and competences. An initiative toward this direction is the EU-project of IDES-EDU: "Master and Post-Graduate education and training in multi-disciplinary teams".The paper describes the necessity of more integrated and cross-disciplinary approaches to building design through state-of-the-art of the building sector and educational initiatives in the participating countries in the project, and through theory of design processes. The paper also communicates the results of newly developed cross-disciplinary education established by fifteen different educational institutions in Europe. Finally, the paper explains and discusses the challenges encountered during development and implementation of the education across different professions and countries. (C) 2013 Elsevier Ltd. All rights reserved.info:eu-repo/semantics/publishedVersio
Self-Aligned Bilayers for Flexible Free-Standing Organic Field-Effect Transistors
[Image: see text] Free-standing and flexible field-effect transistors based on 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene)/polystyrene bilayers are obtained by well-controlled phase separation of both components. The phase separation is induced by solvent vapor annealing of initially amorphous blend films, leading to crystallization of TIPS-pentacene as the top layer. The crystallinity and blend morphology strongly depend on the molecular weight of polystyrene, and under optimized conditions, distinct phase separation with a well-defined and trap-free interface between both fractions is achieved. Due to the distinct bilayer morphology, the resulting flexible field-effect transistors reveal similar charge carrier mobilities as rigid devices and additionally pronounced environmental and bias stress stabilities. The performance of the flexible transistors remains stable up to a strain of 1.8%, while above this deformation, a close relation between current and strain is observed that is required for applications in strain sensors
The properties and polarization of the H2O and CH3OH maser environment of NGC7538-IRS1
NGC7538 is a complex massive star-forming region. The region is composed of
several radio continuum sources, one of which is IRS1, a high-mass protostar,
from which a 0.3 pc molecular bipolar outflow was detected. Several maser
species have been detected around IRS1. The CH3OH masers have been suggested to
trace a Keplerian-disk, while the H2O masers are almost aligned to the outflow.
More recent results suggested that the region hosts a torus and potentially a
disk, but with a different inclination than the Keplerian-disk that is supposed
to be traced by the CH3OH masers. Tracing the magnetic field close to
protostars is fundamental for determining the orientation of the disk/torus.
Recent studies showed that during the protostellar phase of high-mass star
formation the magnetic field is oriented along the outflows and around or on
the surfaces of the disk/torus. The observations of polarized maser emissions
at milliarcsecond resolution can make a crucial contribution to understanding
the orientation of the magnetic field and, consequently, the orientation of the
disk/torus in NGC7538-IRS1. The NRAO Very Long Baseline Array was used to
measure the linear polarization and the Zeeman-splitting of the 22GHz H2O
masers toward NGC7538-IRS1. The European VLBI Network and the MERLIN telescopes
were used to measure the linear polarization and the Zeeman-splitting of the
6.7GHz CH3OH masers toward the same region. We detected 17 H2O masers and 49
CH3OH masers at high angular resolution. We detected linear polarization
emission toward two H2O masers and toward twenty CH3OH masers. The CH3OH
masers, most of which only show a core structure, seem to trace rotating and
potentially infalling gas in the inner part of a torus. Significant
Zeeman-splitting was measured in three CH3OH masers. [...] We also propose a
new description of the structure of the NGC7538-IRS1 maser region.Comment: 13 pages, 9 figures, 4 Tables, accepted by Astronomy & Astrophysic
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