6,113 research outputs found
Evidence of Multiple r-Process Sites in the Early Galaxy: New Observations of CS 22892-052
First results are reported of a new abundance study of neutron-capture
elements in the ultra-metal-poor (UMP; [Fe/H] = -3.1) halo field giant star CS
22892-052. Using new high resolution, high signal-to-noise spectra, abundances
of more than 30 neutron-capture elements (Z>30) have been determined. Six
elements in the 40<Z<56 domain (Nb, Ru, Rh, Pd, Ag and Cd) have been detected
for the first time in a UMP star. Abundances are also derived for three of the
heaviest stable elements (Os, Ir, and Pb). A second transition of thorium,
Th{4086}, confirms the abundance deduced from the standard Th{4019} line, and
an upper limit to the abundance of uranium is established from the absence of
the U{3859} line. As found in previous studies, the abundances of the heavier
(Z>=56) stable neutron-capture elements in CS 22892-052 match well the scaled
solar system r-process abundance distribution. From the observed Th abundance,
an average age of ~= 16 +/- 4 Gyr is derived for cs22892-052, consistent with
the lower age limit of ~= 11 Gyr derived from the upper limit on the U
abundance. The concordance of scaled solar r-process and CS 22892-052
abundances breaks down for the lighter neutron-capture elements, supporting
previous suggestions that different r-process production sites are responsible
for lighter and heavier neutron-capture elements.Comment: To be published in the Astrophysical Journal Letter
The Herschel Virgo Cluster Survey XVI: a cluster inventory
Herschel FIR observations are used to construct Virgo cluster galaxy
luminosity functions and to show that the cluster lacks the very bright and the
numerous faint sources detected in field galaxy surveys. The far-infrared SEDs
are fitted to obtain dust masses and temperatures and the dust mass function.
The cluster is over dense in dust by about a factor of 100 compared to the
field. The same emissivity (beta) temperature relation applies for different
galaxies as that found for different regions of M31. We use optical and HI data
to show that Virgo is over dense in stars and atomic gas by about a factor of
100 and 20 respectively. Metallicity values are used to measure the mass of
metals in the gas phase. The mean metallicity is about 0.7 solar and 50% of the
metals are in the dust. For the cluster as a whole the mass density of stars in
galaxies is 8 times that of the gas and the gas mass density is 130 times that
of the metals. We use our data to consider the chemical evolution of the
individual galaxies, inferring that the measured variations in effective yield
are due to galaxies having different ages, being affected to varying degrees by
gas loss. Four galaxy scaling relations are considered: mass-metallicity,
mass-velocity, mass-star formation rate and mass-radius - we suggest that
initial galaxy mass is the prime driver of a galaxy's ultimate destiny.
Finally, we use X-ray observations and galaxy dynamics to assess the dark and
baryonic matter content compared to the cosmological model
Fluctuating Elastic Rings: Statics and Dynamics
We study the effects of thermal fluctuations on elastic rings. Analytical
expressions are derived for correlation functions of Euler angles, mean square
distance between points on the ring contour, radius of gyration, and
probability distribution of writhe fluctuations. Since fluctuation amplitudes
diverge in the limit of vanishing twist rigidity, twist elasticity is essential
for the description of fluctuating rings. We find a crossover from a small
scale regime in which the filament behaves as a straight rod, to a large scale
regime in which spontaneous curvature is important and twist rigidity affects
the spatial configurations of the ring. The fluctuation-dissipation relation
between correlation functions of Euler angles and response functions, is used
to study the deformation of the ring by external forces. The effects of inertia
and dissipation on the relaxation of temporal correlations of writhe
fluctuations, are analyzed using Langevin dynamics.Comment: 43 pages, 9 Figure
Probing highly obscured, self-absorbed galaxy nuclei with vibrationally excited HCN
We present high resolution (0."4) IRAM PdBI and ALMA mm and submm
observations of the (ultra) luminous infrared galaxies ((U)LIRGs)
IRAS17208-0014, Arp220, IC860 and Zw049.057 that reveal intense line emission
from vibrationally excited (=1) J=3-2 and 4-3 HCN. The emission is
emerging from buried, compact (r<17-70 pc) nuclei that have very high implied
mid-infrared surface brightness L kpc.
These nuclei are likely powered by accreting supermassive black holes (SMBHs)
and/or hot (>200 K) extreme starbursts. Vibrational, =1, lines of HCN
are excited by intense 14 micron mid-infrared emission and are excellent probes
of the dynamics, masses, and physical conditions of (U)LIRG nuclei when H
column densities exceed cm. It is clear that these lines open
up a new interesting avenue to gain access to the most obscured AGNs and
starbursts. Vibrationally excited HCN acts as a proxy for the absorbed
mid-infrared emission from the embedded nuclei, which allows for reconstruction
of the intrinsic, hotter dust SED. In contrast, we show strong evidence that
the ground vibrational state (=0), J=3-2 and 4-3 rotational lines of HCN
and HCO fail to probe the highly enshrouded, compact nuclear regions owing
to strong self- and continuum absorption. The HCN and HCO line profiles are
double-peaked because of the absorption and show evidence of non-circular
motions - possibly in the form of in- or outflows. Detections of vibrationally
excited HCN in external galaxies are so far limited to ULIRGs and early-type
spiral LIRGs, and we discuss possible causes for this. We tentatively suggest
that the peak of vibrationally excited HCN emission is connected to a rapid
stage of nuclear growth, before the phase of strong feedback.Comment: 13 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Domestication as innovation : the entanglement of techniques, technology and chance in the domestication of cereal crops
The origins of agriculture involved pathways of domestication in which human behaviours and plant genetic adaptations were entangled. These changes resulted in consequences that were unintended at the start of the process. This paper highlights some of the key innovations in human behaviours, such as soil preparation, harvesting and threshing, and how these were coupled with genetic ‘innovations’ within plant populations. We identify a number of ‘traps’ for early cultivators, including the needs for extra labour expenditure on crop-processing and soil fertility maintenance, but also linked gains in terms of potential crop yields. Compilations of quantitative data across a few different crops for the traits of nonshattering and seed size are discussed in terms of the apparently slow process of domestication, and parallels and differences between different regional pathways are identified. We highlight the need to bridge the gap between a Neolithic archaeobotanical focus on domestication and a focus of later periods on crop-processing activities and labour organization. In addition, archaeobotanical data provide a basis for rethinking previous assumptions about how plant genetic data should be related to the origins of agriculture and we contrast two alternative hypotheses: gradual evolution with low selection pressure versus metastable equilibrium that prolonged the persistence of ‘semi-domesticated’ populations. Our revised understanding of the innovations involved in plant domestication highlight the need for new approaches to collecting, modelling and integrating genetic data and archaeobotanical evidence
Wetland succession in a permafrost collapse: interactions between fire and thermokarst
To determine the influence of fire and thermokarst in a boreal landscape, we investigated peat cores within and adjacent to a permafrost collapse feature on the Tanana River Floodplain of Interior Alaska. Radioisotope dating, diatom assemblages, plant macrofossils, charcoal fragments, and carbon and nitrogen content of the peat profile indicate ~600 years of vegetation succession with a transition from a terrestrial forest to a sedge-dominated wetland over 100 years ago, and to a <i>Sphagnum</i>-dominated peatland in approximately 1970. The shift from sedge to <i>Sphagnum</i>, and a decrease in the detrended tree-ring width index of black spruce trees adjacent to the collapse coincided with an increase in the growing season temperature record from Fairbanks. This concurrent wetland succession and reduced growth of black spruce trees indicates a step-wise ecosystem-level response to a change in regional climate. In 2001, fire was observed coincident with permafrost collapse and resulted in lateral expansion of the peatland. These observations and the peat profile suggest that future warming and/or increased fire disturbance could promote permafrost degradation, peatland expansion, and increase carbon storage across this landscape; however, the development of drought conditions could reduce the success of both black spruce and <i>Sphagnum</i>, and potentially decrease the long-term ecosystem carbon storage
CDW photogrammetry of low relief fluvial features: accuracy and implications for reach-scale sediment budgeting
Effects of hydrological events on morphological evolution of a fluvial system.
This study quantifies morphological evolution of the Dez River, Iran, from 1955 to 2016. The approach uses a sequence of Landsat images, aerial photos, and topographic maps. In addition, the hydrological data including average daily discharge and yearly maximum discharge at the Dezful hydrological station for the period (1955-2016) were used. The study reach was divided into 48 meander loops from upstream to downstream. Active channel width (w) was determined at 10 m intervals and changes assessed along the study reach of the Dez River. Morphological indices including sinuosity index; straight meander length; centerline flow length; erosion area; erodible length channel migration; centerline elongation; and radius of curvature were calculated in the reach. Results showed that the study reach of the Dez River changed dramatically in response to major floods, although the general trend is towards a narrowing of active channel width by 38% in the period 1955-2016. Results show that most of the meander loops in the study area extended and expanded. Between 1989 and 1995, all types of meander change were observed. There was a direct correlation between the frequency of hydrological events (flood days) bigger than 2-years return period and elongation of bends
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