47 research outputs found
Circumstellar molecular composition of the oxygen-rich AGB star IK Tau: I. Observations and LTE chemical abundance analysis
The aim of this paper is to study the molecular composition in the
circumstellar envelope around the oxygen-rich star IK Tau. We observed IK Tau
in several (sub)millimeter bands using the APEX telescope during three
observing periods. To determine the spatial distribution of the
emission, mapping observations were performed. To
constrain the physical conditions in the circumstellar envelope, multiple
rotational CO emission lines were modeled using a non local thermodynamic
equilibrium radiative transfer code. The rotational temperatures and the
abundances of the other molecules were obtained assuming local thermodynamic
equilibrium. An oxygen-rich Asymptotic Giant Branch star has been surveyed in
the submillimeter wavelength range. Thirty four transitions of twelve molecular
species, including maser lines, were detected. The kinetic temperature of the
envelope was determined and the molecular abundance fractions of the molecules
were estimated. The deduced molecular abundances were compared with
observations and modeling from the literature and agree within a factor of 10,
except for SO, which is found to be almost a factor 100 stronger than
predicted by chemical models. From this study, we found that IK Tau is a good
laboratory to study the conditions in circumstellar envelopes around
oxygen-rich stars with (sub)millimeter-wavelength molecular lines. We could
also expect from this study that the molecules in the circumstellar envelope
can be explained more faithful by non-LTE analysis with lower and higher
transition lines than by simple LTE analysis with only lower transition lines.
In particular, the observed CO line profiles could be well reproduced by a
simple expanding envelope model with a power law structure.Comment: 13 pages, 14 figures, 8 tables *Accepted for publication in Astronomy
and Astrophysic
Energy-dependent solar neutrino flux depletion in the Exact Parity Model and implications for SNO, SuperKamiokande and BOREXINO
Energy-dependent solar neutrino flux reduction caused by the
Mikheyev-Smirnov-Wolfenstein (MSW) effect is applied to the Exact Parity Model.
Several scenarios are possible, depending on the region of parameter space
chosen. The interplay between intergenerational MSW transitions and vacuum
``intragenerational'' ordinary-mirror neutrino oscillations is discussed.
Expectations for the ratio of charged to neutral current event rates at the
Sudbury Neutrino Observatory (SNO) are estimated. The implications of the
various scenarios for the Boron neutrino energy spectrum and BOREXINO are
briefly discussed. The consequences of MSW-induced solar neutrino depletion
within the Exact Parity Model differ in interesting ways from the standard
and cases. The physical causes of
these differences are determined.Comment: 43 pages, 8 figures, RevTeX; to appear in Phys. Rev. D, accepted
versio
Special and Differential Treatment in the WTO: Why, When and How?
This paper analyses to which extent domestic institutions affect trade flows. We use two complementary approaches, one focusing on the size of total trade flows and one focusing on bilateral trade patterns (gravity equation). Besides, we control for two other domestic policy variables: trade policy and domestic infrastructure. We find that the quality of institutions has a positive and significant impact on a country's level of openness. Domestic tariffs have no statistically significant impact on their own, but do affect total trade flows when combined with good institutions. Domestic institutions also have a positive and significant impact on bilateral trade flows, but the parameter of our institution variables is reduced by almost a half and may turn insignificant when the quality of domestic infrastructure is included in the regression