1,034 research outputs found
Disk-Like Structure in the Semi-Regular Pulsating Star, X Her
The author reports a result of an interferometric observation of the
semiragular pulsating star with an unusual narrow molecular line profile, X
Her, in the CO J=1-0 line with the Berkeley-Illinois-Maryland array. In the CO
spectrum, a double-component profile (including narrow and broad components) is
seen as reported by previous observations. The narrow component consists of two
spiky peaks. The spatial structure of the board component shows bipolar shape,
and that of the narrow component shows an elliptical/spherical shape. The two
peaks in the narrow component show a systematic difference in the integrated
intensity map. The kinematical and geometrical properties of the narrow
component are reminiscent of a Keplerian rotating disk with the central mass of
0.9 M_sun, though an interpretation by an expansion disk seems to be more
natural. A secondary bipolar flow instead of the disk cannot be fully excluded
as an interpretation of the narrow line.Comment: 12 pages, 4 figues, accepted for publication in Ap
Mass loss rates of a sample of irregular and semiregular M-type AGB-variables
We have determined mass loss rates and gas expansion velocities for a sample
of 69 M-type irregular (IRV; 22 objects) and semiregular (SRV; 47 objects)
AGB-variables using a radiative transfer code to model their circumstellar CO
radio line emission. We believe that this sample is representative for the mass
losing stars of this type. The (molecular hydrogen) mass loss rate distribution
has a median value of 2.0E-7 solar masses per year. M-type IRVs and SRVs with a
mass loss rate in excess of 5E-7 solar masses per year must be very rare, and
among these mass losing stars the number of sources with mass loss rates below
a few 10E-8 solar masses per year must be small. We find no significant
difference between the IRVs and the SRVs in terms of their mass loss
characteristics. Among the SRVs the mass loss rate shows no dependence on the
period. Likewise the mass loss rate shows no correlation with the stellar
temperature. The gas expansion velocity distribution has a median of 7.0 km/s.
The mass loss rate and the gas expansion velocity correlate well, a result in
line with theoretical predictions for an optically thin, dust-driven wind. In
general, the model produces line profiles which acceptably fit the observed
ones.
We have compared the results of this M-star sample with a similar C-star
sample analysed in the same way. The mass loss rate characteristics are very
similar for the two samples. On the contrary, the gas expansion velocity
distributions are clearly different. In particular, the number of low-velocity
sources is much higher in the M-star sample. We found no example of the sharply
double-peaked CO line profile, which is evidence of a large, detached CO-shell,
among the M-stars. About 10% of the C-stars show this phenomenon.Comment: 16 pages, 11 figures, accepted by A&
Uncertainty about the impact of social decisions increases prosocial behaviour
Uncertainty about how our choices will affect others infuses social life. Past research suggests uncertainty has a negative effect on prosocialbehaviour by enabling people to adopt self-serving narratives about their actions. We show that uncertainty does not always promote selfishness. We introduce a distinction between two types of uncertainty that have opposite effects on prosocial behaviour. Previous work focused on outcome uncertainty (uncertainty about whether or not a decision will lead to a particular outcome). However, as soon as peopleâs decisions might have negative consequences for others, there is also impact uncertainty (uncertainty about how othersâ well-being will be impacted by the negative outcome). Consistent with past research, we found decreased prosocial behaviour under outcome uncertainty. In contrast, prosocial behaviour was increased under impact uncertainty in incentivized economic decisions and hypothetical decisions about infectious disease threats. Perceptions of social norms paralleled the behavioural effects. The effect of impact uncertainty on prosocial behaviour did not depend on the individuation of others or the mere mention of harm, and was stronger when impact uncertainty was made more salient. Our findings offer insights into communicating uncertainty, especially in contexts where prosocial behaviour is paramount, such as responding to infectious disease threats
The census of interstellar complex organic molecules in the Class I hot corino of SVS13-A
We present the first census of the interstellar Complex Organic Molecules
(iCOMs) in the low-mass Class I protostar SVS13-A, obtained by analysing data
from the IRAM-30m Large Project ASAI (Astrochemical Surveys At IRAM). They
consist of an high-sensitivity unbiased spectral survey at the 1mm, 2mm and 3mm
IRAM bands. We detected five iCOMs: acetaldehyde (CHCHO), methyl formate
(HCOOCH), dimethyl ether (CHOCH), ethanol (CHCHOH) and
formamide (NHCHO). In addition we searched for other iCOMs and ketene
(HCCO), formic acid (HCOOH) and methoxy (CHO), whose only ketene was
detected. The numerous detected lines, from 5 to 37 depending on the species,
cover a large upper level energy range, between 15 and 254 K. This allowed us
to carry out a rotational diagram analysis and derive rotational temperatures
between 35 and 110 K, and column densities between and
cm on the 0."3 size previously determined by
interferometric observations of glycolaldehyde. These new observations clearly
demonstrate the presence of a rich chemistry in the hot corino towards SVS13-A.
The measured iCOMs abundances were compared to other Class 0 and I hot corinos,
as well as comets, previously published in the literature. We find evidence
that (i) SVS13-A is as chemically rich as younger Class 0 protostars, and (ii)
the iCOMs relative abundances do not substantially evolve during the
protostellar phase.Comment: 24 pages, MNRAS in pres
Modelling CO emission from Mira's wind
We have modelled the circumstellar envelope of {\it o} Ceti (Mira) using new
observational constraints. These are obtained from photospheric light scattered
in near-IR vibrational-rotational lines of circumstellar CO molecules at 4.6
micron: absolute fluxes, the radial dependence of the scattered intensity, and
two line ratios. Further observational constraints are provided by ISO
observations of far-IR emission lines from highly excited rotational states of
the ground vibrational state of CO, and radio observations of lines from
rotational levels of low excitation of CO. A code based on the Monte-Carlo
technique is used to model the circumstellar line emission.
We find that it is possible to model the radio and ISO fluxes, as well as the
highly asymmetric radio-line profiles, reasonably well with a spherically
symmetric and smooth stellar wind model. However, it is not possible to
reproduce the observed NIR line fluxes consistently with a `standard model' of
the stellar wind. This is probably due to incorrectly specified conditions of
the inner regions of the wind model, since the stellar flux needs to be larger
than what is obtained from the standard model at the point of scattering, i.e.,
the intermediate regions at approximately 100-400 stellar radii (2"-7") away
from the star. Thus, the optical depth in the vibrational-rotational lines from
the star to the point of scattering has to be decreased. This can be
accomplished in several ways. For instance, the gas close to the star (within
approximately 2") could be in such a form that light is able to pass through,
either due to the medium being clumpy or by the matter being in radial
structures (which, further out, developes into more smooth or shell-like
structures).Comment: 18 pages, 3 figures, accepted for publication in Ap
Probing isotopic ratios at z = 0.89: molecular line absorption in front of the quasar PKS 1830-211
With the Plateau de Bure interferometer, we have measured the C, N, O and S
isotopic abundance ratios in the arm of a spiral galaxy with a redshift of
0.89. The galaxy is seen face-on according to HST images. Its bulge intercepts
the line of sight to the radio-loud quasar PKS 1830-211, giving rise at mm
wavelengths to two Einstein images located each behind a spiral arm. The arms
appear in absorption in the lines of several molecules, giving the opportunity
to study the chemical composition of a galaxy only a few Gyr old. The isotopic
ratios in this spiral galaxy differ markedly from those observed in the Milky
Way. The O/O and N/N ratios are low, as one would
expect from an object too young to let low mass stars play a major role in the
regeneration of the gas.Comment: accepted in A&
Lognormal scale invariant random measures
In this article, we consider the continuous analog of the celebrated
Mandelbrot star equation with lognormal weights. Mandelbrot introduced this
equation to characterize the law of multiplicative cascades. We show existence
and uniqueness of measures satisfying the aforementioned continuous equation;
these measures fall under the scope of the Gaussian multiplicative chaos theory
developed by J.P. Kahane in 1985 (or possibly extensions of this theory). As a
by product, we also obtain an explicit characterization of the covariance
structure of these measures. We also prove that qualitative properties such as
long-range independence or isotropy can be read off the equation.Comment: 31 pages; Probability Theory and Related Fields (2012) electronic
versio
Exact and explicit probability densities for one-sided Levy stable distributions
We study functions g_{\alpha}(x) which are one-sided, heavy-tailed Levy
stable probability distributions of index \alpha, 0< \alpha <1, of fundamental
importance in random systems, for anomalous diffusion and fractional kinetics.
We furnish exact and explicit expression for g_{\alpha}(x), 0 \leq x < \infty,
satisfying \int_{0}^{\infty} exp(-p x) g_{\alpha}(x) dx = exp(-p^{\alpha}),
p>0, for all \alpha = l/k < 1, with k and l positive integers. We reproduce all
the known results given by k\leq 4 and present many new exact solutions for k >
4, all expressed in terms of known functions. This will allow a 'fine-tuning'
of \alpha in order to adapt g_{\alpha}(x) to a given experimental situation.Comment: 4 pages, 3 figures and 1 tabl
Motivations underpinning honeybee management practices: A Q methodology study with UK beekeepers
This is the final version. Available on open access from Springer via the DOI in this recordBeekeepers are central to pollinator health. For policymakers and beekeeping organisations to develop widely accepted strategies to sustain honeybee populations alongside wild pollinators, a structured understanding of beekeeper motivations is essential. UK beekeepers are increasing in number, with diverse management styles despite calls for coordinated practice to manage honeybee health. Our Q methodology study in Cornwall, UK, indicated five beekeeping perspectives; conventional hobbyists, natural beekeepers, black bee farmers, new-conventional hobbyists and pragmatic bee farmers. Motivations can be shared across perspectives but trade-offs (notably between economic, social responsibility and ideological motivations) result in differing practices, some of which counter 'official' UK advice and may have implications for pollinator health and competition. Honeybee conservation emerged as a key motivator behind non-conventional practices, but wild pollinator conservation was not prioritised by most beekeepers in practice. Q methodology has the potential to facilitate non-hierarchical collaboration and conceptualisation of sustainable beekeeping, moving towards co-production of knowledge to influence policy.Halpin Trus
A multifractal random walk
We introduce a class of multifractal processes, referred to as Multifractal
Random Walks (MRWs). To our knowledge, it is the first multifractal processes
with continuous dilation invariance properties and stationary increments. MRWs
are very attractive alternative processes to classical cascade-like
multifractal models since they do not involve any particular scale ratio. The
MRWs are indexed by few parameters that are shown to control in a very direct
way the multifractal spectrum and the correlation structure of the increments.
We briefly explain how, in the same way, one can build stationary multifractal
processes or positive random measures.Comment: 5 pages, 4 figures, uses RevTe
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