3,543 research outputs found
Feedback from massive stars at low metallicities : MUSE observations of N44 and N180 in the Large Magellanic Cloud
Accepted for publication in MNRAS, 27 pages, 21 figuresWe present MUSE integral field data of two HII region complexes in the Large Magellanic Cloud (LMC), N44 and N180. Both regions consist of a main superbubble and a number of smaller, more compact HII regions that formed on the edge of the superbubble. For a total of 11 HII regions, we systematically analyse the radiative and mechanical feedback from the massive O-type stars on the surrounding gas. We exploit the integral field property of the data and the coverage of the HeII5412 line to identify and classify the feedback-driving massive stars, and from the estimated spectral types and luminosity classes we determine the stellar radiative output in terms of the ionising photon flux . We characterise the HII regions in terms of their sizes, morphologies, ionisation structure, luminosity and kinematics, and derive oxygen abundances via emission line ratios. We analyse the role of different stellar feedback mechanisms for each region by measuring the direct radiation pressure, the pressure of the ionised gas, and the pressure of the shock-heated winds. We find that stellar winds and ionised gas are the main drivers of HII region expansion in our sample, while the direct radiation pressure is up to three orders of magnitude lower than the other terms. We relate the total pressure to the star formation rate per unit area, , for each region and find that stellar feedback has a negative effect on star formation, and sets an upper limit to as a function of increasing pressure.Peer reviewe
2013 National Lawyers Convention: Intellectual Property: Intellectual Property, Free Markets, and Competition Policy
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Interpretations of Presburger Arithmetic in Itself
Presburger arithmetic PrA is the true theory of natural numbers with
addition. We study interpretations of PrA in itself. We prove that all
one-dimensional self-interpretations are definably isomorphic to the identity
self-interpretation. In order to prove the results we show that all linear
orders that are interpretable in (N,+) are scattered orders with the finite
Hausdorff rank and that the ranks are bounded in terms of the dimension of the
respective interpretations. From our result about self-interpretations of PrA
it follows that PrA isn't one-dimensionally interpretable in any of its finite
subtheories. We note that the latter was conjectured by A. Visser.Comment: Published in proceedings of LFCS 201
A probable Keplerian disk feeding an optically revealed massive young star
The canonical picture of star formation involves disk-mediated accretion,
with Keplerian accretion disks and associated bipolar jets primarily observed
in nearby, low-mass young stellar objects (YSOs). Recently, rotating gaseous
structures and Keplerian disks have been detected around a number of massive (M
> 8 solar masses) YSOs (MYSOs) including several disk-jet systems. All of the
known MYSO systems are located in the Milky Way, and all are embedded in their
natal material. Here we report the detection of a rotating gaseous structure
around an extragalactic MYSO in the Large Magellanic Cloud. The gas motions
show radial flow of material falling from larger scales onto a central
disk-like structure, the latter exhibiting signs of Keplerian rotation, i.e., a
rotating toroid feeding an accretion disk and thus the growth of the central
star. The system is in almost all aspects comparable to Milky Way high-mass
young stellar objects accreting gas via a Keplerian disk. The key difference
between this source and its Galactic counterparts is that it is optically
revealed, rather than being deeply embedded in its natal material as is
expected of such a young massive star. We suggest that this is the consequence
of the star having formed in a low-metallicity and low-dust content
environment, thus providing important constraints for models of the formation
and evolution of massive stars and their circumstellar disks.Comment: 20 pages, 9 page
A probable Keplerian disk feeding an optically revealed massive young star.
The canonical picture of star formation involves disk-mediated accretion, with Keplerian accretion disks and associated bipolar jets primarily observed in nearby, low-mass young stellar objects (YSOs). Recently, rotating gaseous structures and Keplerian disks have been detected around several massive (M > 8 M ) YSOs (MYSOs) , including several disk-jet systems . All the known MYSO systems are in the Milky Way, and all are embedded in their natal material. Here we report the detection of a rotating gaseous structure around an extragalactic MYSO in the Large Magellanic Cloud. The gas motion indicates that there is a radial flow of material falling from larger scales onto a central disk-like structure. The latter exhibits signs of Keplerian rotation, so that there is a rotating toroid feeding an accretion disk and thus the growth of the central star. The system is in almost all aspects comparable to Milky Way high-mass YSOs accreting gas from a Keplerian disk. The key difference between this source and its Galactic counterparts is that it is optically revealed rather than being deeply embedded in its natal material as is expected of such a massive young star. We suggest that this is the consequence of the star having formed in a low-metallicity and low-dust content environment. Thus, these results provide important constraints for models of the formation and evolution of massive stars and their circumstellar disks. [Abstract copyright: © 2023. The Author(s).
Slow group velocity and Cherenkov radiation
We theoretically study the effect of ultraslow group velocities on the
emission of Vavilov-Cherenkov radiation in a coherently driven medium. We show
that in this case the aperture of the group cone on which the intensity of the
radiation peaks is much smaller than that of the usual wave cone associated
with the Cherenkov coherence condition. We show that such a singular behaviour
may be observed in a coherently driven ultracold atomic gas.Comment: 4 pages, 4 figure
Découverte d'une faune de mammifères dans le Lutétien supérieur de la Défense, à Puteaux près Paris (Hauts de Seine)
Identifying novel genetic determinants of hemostatic balance
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73734/1/j.1538-7836.2005.01461.x.pd
MetExplore: a web server to link metabolomic experiments and genome-scale metabolic networks
High-throughput metabolomic experiments aim at identifying and ultimately quantifying all metabolites present in biological systems. The metabolites are interconnected through metabolic reactions, generally grouped into metabolic pathways. Classical metabolic maps provide a relational context to help interpret metabolomics experiments and a wide range of tools have been developed to help place metabolites within metabolic pathways. However, the representation of metabolites within separate disconnected pathways overlooks most of the connectivity of the metabolome. By definition, reference pathways cannot integrate novel pathways nor show relationships between metabolites that may be linked by common neighbours without being considered as joint members of a classical biochemical pathway. MetExplore is a web server that offers the possibility to link metabolites identified in untargeted metabolomics experiments within the context of genome-scale reconstructed metabolic networks. The analysis pipeline comprises mapping metabolomics data onto the specific metabolic network of an organism, then applying graph-based methods and advanced visualization tools to enhance data analysis. The MetExplore web server is freely accessible at http://metexplore.toulouse.inra.fr
The Green Bank Ammonia Survey: Unveiling the Dynamics of the Barnard 59 star-forming Clump
Understanding the early stages of star formation is a research field of
ongoing development, both theoretically and observationally. In this context,
molecular data have been continuously providing observational constraints on
the gas dynamics at different excitation conditions and depths in the sources.
We have investigated the Barnard 59 core, the only active site of star
formation in the Pipe Nebula, to achieve a comprehensive view of the kinematic
properties of the source. These information were derived by simultaneously
fitting ammonia inversion transition lines (1,1) and (2,2). Our analysis
unveils the imprint of protostellar feedback, such as increasing line widths,
temperature and turbulent motions in our molecular data. Combined with
complementary observations of dust thermal emission, we estimate that the core
is gravitationally bound following a virial analysis. If the core is not
contracting, another source of internal pressure, most likely the magnetic
field, is supporting it against gravitational collapse and limits its star
formation efficiency.Comment: 18 pages, 18 figure
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