242 research outputs found
Interferometric view of the circumstellar envelopes of northern FU Orionis-type stars
FU Orionis-type objects are young, low-mass stars with large outbursts in
visible light that last for several years or decades. They are thought to
represent an evolutionary phase during the life of every young star when
accretion from the circumstellar disk is enhanced during recurring time
periods. These outbursts are able to rapidly build up the star while affecting
the circumstellar disk and thus the ongoing or future planet formation. In many
models infall from a circumstellar envelope seems to be necessary to trigger
the outbursts. We observed the J=10 rotational transition of CO and
CO towards eight northern FU Orionis-type stars (V1057 Cyg, V1515 Cyg,
V2492 Cyg, V2493 Cyg, V1735 Cyg, V733 Cep, RNO 1B and RNO 1C) and derive
temperatures and envelope masses and discuss the morphology and kinematics of
the circumstellar material. We detected extended CO emission associated with
all our targets. Smaller scale CO clumps were found to be associated with five
objects with radii of 20005000 AU and masses of 0.020.5 ;
these are clearly heated by the central stars. Three of these envelopes are
also strongly detected in the 2.7 mm continuum. No central CO clumps were
detected around V733 Cep and V710 Cas but there are many other clumps in their
environments. Traces of outflow activity were observed towards V1735 Cyg, V733
Cep and V710 Cas. The diversity of the observed envelopes enables us to set up
an evolutionary sequence between the objects. We find their evolutionary state
to range from early, embedded Class I stage to late, Class II-type objects with
very low-mass circumstellar material. The results reinforce the idea of FU
Orionis-type stars as representatives of a transitory stage between embedded
Class I young stellar objects and classical T-Tauri stars.Comment: 17 pages, 11 figures; accepted for publication in A&
Internet as an innovative tool for the development of food products
As a result of the fast innovation activity, the so called “many to many” communication channel has become one of the most important tools for the Hungarian food industry. The number of Internet users in Hungary was 6.5 million in 2011 that represents 65.4 percent of the total population. The Internet based social media provides a strong and active platform between food producers and consumers. The online platform gives up-to-date and precise information about food companies and food products to the consumers. The information flow is two-directional as food companies receive a precise overview on consumers, their habits and latent needs by using innovative market research methods. The aim of this paper is to present an example and to evaluate the customers’ socio-demographic profile and their preferences of a dominant food company and its product. We used data mining techniques to get more precise and the latest information about Hungarian food consumers. This survey supports more efficient marketing communication and strategies for the innovation of the food products
Mass transport from the envelope to the disk of V346 Nor: a case study for the luminosity problem in an FUor-type young eruptive star
A long-standing open issue of the paradigm of low-mass star formation is the
luminosity problem: most protostars are less luminous than theoretically
predicted. One possible solution is that the accretion process is episodic. FU
Ori-type stars (FUors) are thought to be the visible examples for objects in
the high accretion state. FUors are often surrounded by massive envelopes,
which replenish the disk material and enable the disk to produce accretion
outbursts. However, we have insufficient information on the envelope dynamics
in FUors, about where and how mass transfer from the envelope to the disk
happens. Here we present ALMA observations of the FUor-type star V346 Nor at
1.3 mm continuum and in different CO rotational lines. We mapped the density
and velocity structure of its envelope and analyze the results using channel
maps, position-velocity diagrams, and spectro-astrometric methods. We found
that V346 Nor is surrounded by gaseous material on 10000 au scale in which a
prominent outflow cavity is carved. Within the central 700 au, the
circumstellar matter forms a flattened pseudo-disk where material is infalling
with conserved angular momentum. Within 350 au, the velocity profile is
more consistent with a disk in Keplerian rotation around a central star of 0.1
. We determined an infall rate from the envelope onto the disk of
610yr, a factor of few higher than the
quiescent accretion rate from the disk onto the star, hinting for a mismatch
between the infall and accretion rates as the cause of the eruption.Comment: 16 pages, 8 figures, published in Ap
Magnetic resonance in the antiferromagnetic and normal state of NH_3K_3C_60
We report on the magnetic resonance of NH_3K_3C_60 powders in the frequency
range of 9 to 225 GHz. The observation of an antiferromagnetic resonance below
the phase transition at 40 K is evidence for an antiferromagnetically ordered
ground state. In the normal state, above 40 K, the temperature dependence of
the spin-susceptibilty measured by ESR agrees with previous static measurements
and is too weak to be explained by interacting localized spins in an insulator.
The magnetic resonance line width has an unusual magnetic-field dependence
which is large and temperature independent in the magnetically ordered state
and decreases rapidly above the transition. These observations agree with the
suggestion that NH_3K_3C_60 is a metal in the normal state and undergoes a
Mott-Hubbard metal to insulator transition at 40 K.Comment: 4 pages, 5 figures. Submitted to Phys. Rev.
NEATH II: NH as a tracer of imminent star formation in quiescent high-density gas
Star formation activity in molecular clouds is often found to be correlated
with the amount of material above a column density threshold of . Attempts to connect this column density threshold to a density above which star formation can occur are limited by the fact
that the volume density of gas is difficult to reliably measure from
observations. We post-process hydrodynamical simulations of molecular clouds
with a time-dependent chemical network, and investigate the connection between
commonly-observed molecular species and star formation activity. We find that
many molecules widely assumed to specifically trace the dense, star-forming
component of molecular clouds (e.g. HCN, HCO, CS) actually also exist in
substantial quantities in material only transiently enhanced in density, which
will eventually return to a more diffuse state without forming any stars. By
contrast, NH only exists in detectable quantities above a volume
density of , the point at which CO, which reacts
destructively with NH, begins to deplete out of the gas phase onto
grain surfaces. This density threshold for detectable quantities of NH
corresponds very closely to the volume density at which gas becomes
irreversibly gravitationally bound in the simulations: the material traced by
NH never reverts to lower densities, and quiescent regions of molecular
clouds with visible NH emission are destined to eventually form stars.
The NH line intensity is likely to directly correlate with the star
formation rate averaged over timescales of around a Myr.Comment: 10 pages, 10 figures. MNRAS accepte
Non-Equilibrium Abundances Treated Holistically (NEATH): the molecular composition of star-forming clouds
Much of what we know about molecular clouds, and by extension star formation,
comes from molecular line observations. Interpreting these correctly requires
knowledge of the underlying molecular abundances. Simulations of molecular
clouds typically only model species that are important for the gas
thermodynamics, which tend to be poor tracers of the denser material where
stars form. We construct a framework for post-processing these simulations with
a full time-dependent chemical network, allowing us to model the behaviour of
observationally-important species not present in the reduced network used for
the thermodynamics. We use this to investigate the chemical evolution of
molecular gas under realistic physical conditions. We find that molecules can
be divided into those which reach peak abundances at moderate densities () and decline sharply thereafter (such as CO and HCN), and
those which peak at higher densities and then remain roughly constant (e.g.
NH, NH). Evolving the chemistry with physical properties held
constant at their final values results in a significant overestimation of
gas-phase abundances for all molecules, and does not capture the drastic
variations in abundance caused by different evolutionary histories. The
dynamical evolution of molecular gas cannot be neglected when modelling its
chemistry.Comment: 14 pages, 13 figures. MNRAS accepte
Classical Wakimoto Realizations of Chiral WZNW Bloch Waves
It is well-known that the chiral WZNW Bloch waves satisfy a quadratic
classical exchange algebra which implies the affine Kac-Moody algebra for the
corresponding currents. We here obtain a direct derivation of the exchange
algebra by inverting the symplectic form on the space of Bloch waves, and give
a completely algorithmic construction of its generalized free field
realizations that extend the classical Wakimoto realizations of the current
algebra.Comment: 13 pages, LaTe
Generalized Drinfeld-Sokolov Reductions and KdV Type Hierarchies
Generalized Drinfeld-Sokolov (DS) hierarchies are constructed through local
reductions of Hamiltonian flows generated by monodromy invariants on the dual
of a loop algebra. Following earlier work of De Groot et al, reductions based
upon graded regular elements of arbitrary Heisenberg subalgebras are
considered. We show that, in the case of the nontwisted loop algebra
, graded regular elements exist only in those Heisenberg
subalgebras which correspond either to the partitions of into the sum of
equal numbers or to equal numbers plus one . We prove that the
reduction belonging to the grade regular elements in the case yields
the matrix version of the Gelfand-Dickey -KdV hierarchy,
generalizing the scalar case considered by DS. The methods of DS are
utilized throughout the analysis, but formulating the reduction entirely within
the Hamiltonian framework provided by the classical r-matrix approach leads to
some simplifications even for .Comment: 43 page
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