3,518 research outputs found
Circumbinary Molecular Rings Around Young Stars in Orion
We present high angular resolution 1.3 mm continuum, methyl cyanide molecular
line, and 7 mm continuum observations made with the Submillimeter Array and the
Very Large Array, toward the most highly obscured and southern part of the
massive star forming region OMC1S located behind the Orion Nebula. We find two
flattened and rotating molecular structures with sizes of a few hundred
astronomical units suggestive of circumbinary molecular rings produced by the
presence of two stars with very compact circumstellar disks with sizes and
separations of about 50 AU, associated with the young stellar objects 139-409
and 134-411. Furthermore, these two circumbinary rotating rings are related to
two compact and bright {\it hot molecular cores}. The dynamic mass of the
binary systems obtained from our data are 4 M for 139-409 and
0.5 M for 134-411. This result supports the idea that
intermediate-mass stars will form through {\it circumstellar disks} and
jets/outflows, as the low mass stars do. Furthermore, when intermediate-mass
stars are in multiple systems they seem to form a circumbinary ring similar to
those seen in young, multiple low-mass systems (e.g., GG Tau and UY Aur).Comment: Accepted by Astronomy and Astrophysic
A contracting circumbinary molecular ring with an inner cavity of about 140 AU around Ori 139-409
Sensitive and subarcsecond resolution ( 0.7\arcsec) CHOH(7
6) line and 890 m continuum observations made with the
Submillimeter Array (SMA) towards the hot molecular circumbinary ring
associated with the young multiple star Ori 139-409 are presented. The
CHOH(7 - 6) emission from the ring is well resolved at
this angular resolution revealing an inner cavity with a size of about 140 AU.
A LTE model of a Keplerian disk with an inner cavity of the same size confirms
the presence of this cavity. Additionally, this model suggests that the
circumbinary ring is contracting with a velocity of V 1.5 km
s toward the binary central compact circumstellar disks reported at a
wavelength of 7 mm. {\bf The inner central cavity seems to be formed by the
tidal effects of the young stars in the middle of the ring.} The ring appears
to be not a stationary object. Furthermore, the infall velocity we determine is
about a factor of 3 slower than the free-fall velocity corresponding to the
dynamical mass. This would correspond to a mass accretion rate of about
10 M/yr. We found that the dust emission associated with Ori
139-409 appears to be arising from the circumstellar disks with no strong
contribution from the molecular gas ring. A simple comparison with other
classical molecular dusty rings (e.g. GG Tau, UZ Tau, and UY Aur) suggests that
Ori 139-409 could be one of the youngest circumbinary rings reported up to
date. Finally, our results confirm that the circumbinary rings are actively
funneling fresh gas material to the central compact binary circumstellar disks,
i.e. to the protostars in the very early phases of their evolution.Comment: Accepted by MNRA
Nonclassical Kinetics in Constrained Geometries: Initial Distribution Effects
We present a detailed study of the effects of the initial distribution on the
kinetic evolution of the irreversible reaction A+B -> 0 in one dimension. Our
analytic as well as numerical work is based on a reaction-diffusion model of
this reaction. We focus on the role of initial density fluctuations in the
creation of the macroscopic patterns that lead to the well-known kinetic
anomalies in this system. In particular, we discuss the role of the long
wavelength components of the initial fluctuations in determining the long-time
behavior of the system. We note that the frequently studied random initial
distribution is but one of a variety of possible distributions leading to
interesting anomalous behavior. Our discussion includes an initial distribution
with correlated A-B pairs and one in which the initial distribution forms a
fractal pattern. The former is an example of a distribution whose long
wavelength components are suppressed, while the latter exemplifies one whose
long wavelength components are enhanced, relative to those of the random
distribution.Comment: To appear in International Journal of Bifurcation and Chaos Vol. 8
No.
Nonstationarity in the Specification of the Environmental Kuznets Curve
Numerous studies have addressed the question of the econometric specification of the Environmental Kuznets Curve (EKC). This paper adds preliminary results on nonstationarity and its effect on functional form using a panel data set for the U.S. by state from 1929 to 1994. It is found that unit-root tests strongly support a unit root in pollutants (sulfur dioxide and nitrogen oxide) and income when testing individual states. The results from panel data unit root tests provide mixed evidence about nonstationarity in EKC data.Environmental Kuznets curve, fixed and random effects, parametric models, water pollution, watershed, nonstationarity, unit-roots, Environmental Economics and Policy,
Radio Continuum Sources Associated with AB Aur
We present high angular resolution, high-sensitivity Very Large Array
observations at 3.6 cm of the Herbig Ae star AB Aur. This star is of interest
since its circumstellar disk exhibits characteristics that have been attributed
to the presence of an undetected low mass companion or giant gas planet. Our
image confirms the continuum emission known to exist in association with the
star, and detects a faint protuberance that extends about to its
SE. Previous theoretical considerations and observational results are
consistent with the presence of a companion to AB Aur with the separation and
position angle derived from our radio data. We also determine the proper motion
of AB Aur by comparing our new observations with data taken about 17 years ago
and find values consistent with those found by Hipparcos.Comment: 6 pages, 1 figur
Empirical model of the behavior of the income velocity of money in Colombia, 1982 – 2001
The study of the income velocity of money is important since monetary factors play a causal role in output fluctuations. The issue of the stability of money demand is critical in assessing the monetary aggregates, M1/M3, usefulness for the formulation of monetary policy. In Colombia, the M1 income velocity of money has been very volatile whereas the M3 velocity has been pretty stable over the last 20 years. Contrary to the assumption underlying the Quantity Theory of Money, the evidence here indicates that the income velocity of money is not constant in Colombia for the 1982 – 2001 period. The statistical results show that there is a positive relationship between the Colombian inflation rate and the M1 and M3 income velocities of money. A higher rate of inflation will translate into a higher nominal interest rate. The higher the interest rates the higher the opportunity cost of holding money and so the greater the income velocity
The migration-remittances-development-nexus: ‘Mi casa con Remesas’ and transnational flows between Colombia and London
Zapata GP. The migration-remittances-development-nexus: ‘Mi casa con Remesas’ and transnational flows between Colombia and London. COMCAD Arbeitspapiere - Working Papers, 106. Bielefeld: COMCAD - Center on Migration, Citizenship and Development; 2011
Explosive Disintegration of a Massive Young Stellar System in Orion
Young massive stars in the center of crowded star clusters are expected to
undergo close dynamical encounters that could lead to energetic, explosive
events. However, there has so far never been clear observational evidence of
such a remarkable phenomenon. We here report new interferometric observations
made with the Submillimeter Array (SMA) that indicate the well known enigmatic
wide-angle outflow located in the Orion BN/KL star-forming region to have been
produced by such a violent explosion during the disruption of a massive young
stellar system, and that this was caused by a close dynamical interaction about
500 years ago. This outflow thus belongs to a totally different family of
molecular flows which is not related to the classical bipolar flows that are
generated by stars during their formation process. Our molecular data allow us
to create a 3D view of the debris flow and to link this directly to the well
known Orion H "fingers" farther outComment: Accepted by ApJ Letters The 3D movie can be found in:
ftp://ftp.mpifr-bonn.mpg.de/outgoing/lzapata/movie.gi
Carbon Dioxide (CO2) Emissions in Latin America: Looking for the Existence of Environmental Kuznets Curves
We estimated environmental Kuznets curve (EKC) for carbon dioxide for 16 Latin American countries using nonparametric, semi-parametric, and parametric specifications. Results indicated that most of the Latin American countries are still in the rising portion of the EKC with respect to CO2 pollution.Environmental Economics and Policy,
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