772 research outputs found
Pollen Nightmare: Elevated Airborne Pollen Levels at Night
High airborne pollen concentrations are generally associated with daylight hours when it is sunny and warm and plants release pollen into the air (AlcĂĄzar et al. 1999; Dahl et al. 2013). In contrast, cooler night-time periods are usually considered to be the time of low-allergy risk. This opinion is often reflected in pollen allergy avoidance strategies presented by the media, where the most commonly repeated recommendation is to stay indoors during the day and plan outdoor activities for the evening. However, there is evidence to suggest that elevated concentrations of airborne pollen might also occur during the evening (e.g. Norris-Hill and Emberlin 1991). So, is the night really a time of low-allergy risk? We present the results of the comparative analysis of pollen concentrations during daytime and night-time hours for five allergenic pollen types (Burbach et al. 2009), i.e. alder (Alnus sp.), birch (Betula sp.), grasses (Poaceae), mugwort (Artemisia sp.) and ragweed (Ambrosia sp.)
Dynamics of the 6.7 and 12.2 GHz methanol masers around Cepheus A HW2
The 6.7 GHz methanol maser is exclusively associated with high-mass star
formation. However, it remains unclear what structures harbour the methanol
masers. Cepheus A is one of the closest regions of massive star formation,
making it an excellent candidate for detailed studies. We determine the
dynamics of maser spots in the high-mass star-forming region Cepheus A in order
to infer where and when the maser emission occurs. Very long baseline
interferometry (VLBI) observations of the 6.7 and 12.2 GHz methanol masers
allows for mapping their spatial and velocity distribution. Phase-referencing
is used to determine the astrometric positions of the maser emission, and
multi-epoch observations can reveal 3D motions. The 6.7 GHz methanol masers are
found in a filamentary structure over ~1350 AU, straddling the waist of the
radio jet HW2. The positions agree well with previous observations of both the
6.7 and 12.2 GHz methanol masers. The velocity field of the maser spots does
not show any sign of rotation, but is instead consistent with an infall
signature. The 12.2 GHz methanol masers are closely associated with the 6.7 GHz
methanol masers, and the parallax that we derive confirms previous
measurements. We show that the methanol maser emission very likely arises in a
shock interface in the equatorial region of Cepheus A HW2 and presents a model
in which the maser emission occurs between the infalling gas and the accretion
disk/process.Comment: 9 pages, 5 figures; accepted for publication in Astronomy and
Astrophysic
Environmental and Parental Influences on Offspring Health and Growth in Great Tits (Parus major)
PMCID: PMC3728352This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Gallavotti-Cohen-Type symmetry related to cycle decompositions for Markov chains and biochemical applications
We slightly extend the fluctuation theorem obtained in \cite{LS} for sums of
generators, considering continuous-time Markov chains on a finite state space
whose underlying graph has multiple edges and no loop. This extended frame is
suited when analyzing chemical systems. As simple corollary we derive in a
different method the fluctuation theorem of D. Andrieux and P. Gaspard for the
fluxes along the chords associated to a fundamental set of oriented cycles
\cite{AG2}.
We associate to each random trajectory an oriented cycle on the graph and we
decompose it in terms of a basis of oriented cycles. We prove a fluctuation
theorem for the coefficients in this decomposition. The resulting fluctuation
theorem involves the cycle affinities, which in many real systems correspond to
the macroscopic forces. In addition, the above decomposition is useful when
analyzing the large deviations of additive functionals of the Markov chain. As
example of application, in a very general context we derive a fluctuation
relation for the mechanical and chemical currents of a molecular motor moving
along a periodic filament.Comment: 23 pages, 5 figures. Correction
Unveiling the origin of X-ray flares in Gamma-Ray Bursts
We present an updated catalog of 113 X-ray flares detected by Swift in the
~33% of the X-ray afterglows of Gamma-Ray Bursts (GRB). 43 flares have a
measured redshift. For the first time the analysis is performed in 4 different
X-ray energy bands, allowing us to constrain the evolution of the flare
temporal properties with energy. We find that flares are narrower at higher
energies: their width follows a power-law relation w~E^{-0.5} reminiscent of
the prompt emission. Flares are asymmetric structures, with a decay time which
is twice the rise time on average. Both time scales linearly evolve with time,
giving rise to a constant rise-to-decay ratio: this implies that both time
scales are stretched by the same factor. As a consequence, the flare width
linearly evolves with time to larger values: this is a key point that clearly
distinguishes the flare from the GRB prompt emission. The flare 0.3-10 keV peak
luminosity decreases with time, following a power-law behaviour with large
scatter: L_{pk}~ t_{pk}^{-2.7}. When multiple flares are present, a global
softening trend is established: each flare is on average softer than the
previous one. The 0.3-10 keV isotropic energy distribution is a log-normal
peaked at 10^{51} erg, with a possible excess at low energies. The flare
average spectral energy distribution (SED) is found to be a power-law with
spectral energy index beta~1.1. These results confirmed that the flares are
tightly linked to the prompt emission. However, after considering various
models we conclude that no model is currently able to account for the entire
set of observations.Comment: MNRAS submitte
First Stars II. Elemental abundances in the extremely metal-poor star CS 22949--037: A diagnostic of early massive supernovae
CS 22949--037 is one of the most metal-poor giants known ([Fe/H]), and it exhibits large overabundances of carbon and nitrogen
(Norris et al.). Using VLT-UVES spectra of unprecedented quality, regarding
resolution and S/N ratio, covering a wide wavelength range (from to 900 nm), we have determined abundances for 21 elements in this star
over a wide range of atomic mass. The major new discovery is an exceptionally
large oxygen enhancement, [O/Fe] , as measured from the [OI] line
at 630.0 nm. We find an enhancement of [N/Fe] of , and a milder
one of [C/Fe] 0.1, similar to those already reported in the
literature. This implies . We also find carbon
isotopic ratios C/C and C/N, close to the equilibrium value of the CN cycle. Lithium is
not detected. Na is strongly enhanced ([Na/Fe] ), while S and K
are not detected. The silicon-burning elements Cr and Mn are underabundant,
while Co and Zn are overabundant ([Zn/Fe]). Zn is measured for the
first time in such an extremely metal-poor star. The abundances of the
neutron-capture elements Sr, Y, and Ba are strongly decreasing with the atomic
number of the element: [Sr/Fe] , [Y/Fe] , and
[Ba/Fe] . Among possible progenitors of CS 22949--037, we discuss
the pair-instability supernovae. Such very massive objects indeed produce large
amounts of oxygen, and have been found to be possible sources of primary
nitrogen. Other scenarios are also discussed. A 30-40 supernova,
with fallback, seems the most likely progenitor for CS 22949--037.Comment: 12 Pages, 10 figures, accepted for publication in Astronomy and
Astrophysic
The two metallicity groups of the globular cluster M22: a chemical perspective
We present a detailed chemical composition analysis of 35 red giant stars in
the globular cluster M22. High resolution spectra for this study were obtained
at five observatories, and analyzed in a uniform manner. We have determined
abundances of representative light proton-capture, alpha, Fe-peak and
neutron-capture element groups. Our aim is to better understand the peculiar
chemical enrichment history of this cluster, in which two stellar groups are
characterized by a different content in iron, neutron capture elements Y, Zr
and Ba, and alpha element Ca. The principal results of this study are: (i)
substantial star-to-star metallicity scatter (-2.0<[Fe/H]<-1.6); (ii)
enhancement of s-process/r-process neutron-capture abundance ratios in a
fraction of giants, positively correlated with metallicity; (iii) sharp
separation between the s-process rich and s-process poor groups by [La/Eu]
ratio; (iv) possible increase of [Cu/Fe] ratios with increasing [Fe/H],
suggesting that this element also has a significant s-process component; and
(v) presence of Na-O and C-N anticorrelations in both the stellar groups.Comment: 26 pages, 19 figures. Accepted for publication in A&
First Stars VIII -- Enrichment of the neutron-capture elements in the early Galaxy
Our aim is to measure accurate, homogeneous neutron-capture element
abundances for the sample of 32 EMP giant stars studied earlier in this series,
including 22 stars with [Fe/H] 3.0. Based on high-resolution, high S/N
spectra from the ESO VLT/UVES, 1D, LTE model atmospheres, and synthetic
spectrum fits, we determine abundances or upper limits for the 16 elements Sr,
Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb in all stars. As
found earlier, [Sr/Fe], [Y/Fe], [Zr/Fe] and [Ba/Fe] are below Solar in the EMP
stars, with very large scatter. However, we find a tight anti-correlation of
[Sr/Ba], [Y/Ba], and [Zr/Ba] with [Ba/H] for [Ba/H] , also
when subtracting the contribution of the main -process as measured by
[Ba/H]. The huge, well-characterised scatter of the [n-capture/Fe] ratios in
our EMP stars is in stark contrast to the negligible dispersion in the
[/Fe] and [Fe-peak/Fe] ratios for the same stars found in Paper V.
These results demonstrate that a second (``weak'' or LEPP) -process
dominates the production of the lighter neutron-capture elements for [Ba/H] . The combination of very consistent [/Fe] and erratic
[n-capture/Fe] ratios indicates that inhomogeneous models for the early
evolution of the halo are needed. Our accurate data provide strong constraints
on future models of the production and mixing of the heavy elements in the
early Galaxy.Comment: 19 pages, 16 figures, A&A accepte
The Origins of Two Classes of Carbon-Enhanced, Metal-Poor Stars
We have compiled composition, luminosity, and binarity information for
carbon-enhanced, metal-poor (CEMP) stars reported by recent studies. We divided
the CEMP star sample into two classes, having high and low abundances,
respectively, of the s-process elements, and consider the abundances of several
isotopes, in particular 12C, 13C, and 14N, as well as the likely evolutionary
stages of each star. Despite the fact that objects in both groups were selected
from the same surveys (primarily the HK survey), without a-priori knowledge of
their s-process element abundances, we identify the following remarkable
difference between the two classes: s-element-rich CEMP (CEMP-s) stars occupy a
wide range of evolutionary states, but do not have a strongly evolved 13C/14N
ratio, whereas s-element-normal CEMP stars (CEMP-no) are found only high up the
first-ascent giant branch, and possess 13C/14N ratios approaching the CN-cycle
equilibrium value. Based on these observational facts, we discuss scenarios of
formation of CEMP stars.Comment: 17 pages, 4 figures, 1 table, ApJ, in pres
Carbon Abundances of Three Carbon-Enhanced Metal-Poor Stars from High-Resolution Gemini-S/bHROS Spectra of the 8727A [C I] Line
We present the results from an analysis of the 8727ang forbidden [C I] line
in high-resolution Gemini-S/bHROS spectra of three CEMP stars. We find the
[C/Fe] ratios based on the [C I] abundances of the two most Fe-rich stars in
our sample (HIP 0507-1653: [Fe/H] = -1.42 and HIP 0054-2542: [Fe/H] = -2.66) to
be in good agreement with previously determined CH and C_2 line-based values.
For the most Fe-deficient star in our sample (HIP 1005-1439: [Fe/H] = -3.08),
however, the [C/Fe] ratio is found to be 0.34 dex lower than the published
molecular-based value. We have carried out 3D local thermodynamic equilibrium
(LTE) calculations for [C I], and the resulting corrections are found to be
modest for all three stars, suggesting that the discrepancy between the [C I]
and molecular-based C abundances of HIP 1005-1439 is due to more severe 3D
effects on the molecular lines. Carbon abundances are also derived from C I
high-excitation lines and are found to be 0.45-0.64 dex higher than the [C
I]-based abundances. Previously published non-LTE C I abundance corrections
bring the [C I] and C I abundances into better agreement; however, targeted
NLTE calculations for CEMP stars are clearly needed. We have also derived the
abundances of N, K, and Fe for each star. The Fe abundances agree well with
previously derived values, and the K abundances are similar to those of
C-normal metal-poor stars. Nitrogen abundances have been derived from resolved
lines of the CN red system. The abundances are found to be approximately 0.44
dex larger than literature values, which have been derived from CN blue bands
near 3880 and 4215 ang. We discuss evidence that suggests that analyses of the
CN blue system bands underestimate the N abundances of metal-poor giants.Comment: Accepted for publication in AJ; 42 pages, 6 figures, 7 table
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