1,108 research outputs found
Population Synthesis in the Blue IV: Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations
[Abridged] We present new model predictions for 16 Lick absorption line
indices from Hdelta through Fe5335, and UBV colors for single stellar
populations (SPs) with ages ranging between 1 and 15 Gyr, [Fe/H] ranging from
-1.3 to +0.3, and variable abundance ratios. We develop a method to estimate
mean ages and abundances of Fe, C, N, Mg, and Ca that explores the sensitivity
of the various indices to those parameters. When applied to high-S/N Galactic
cluster data, the models match the clusters' elemental abundances and ages with
high precision. Analyzing stacked SDSS spectra of early-type galaxies brighter
than Lstar, we find mean luminosity-weighted ages of the order of ~ 8 Gyr and
iron abundances slightly below solar. Abundance ratios, [X/Fe], are higher than
solar, and correlate positively with galaxy luminosity. Nitrogen is the element
whose abundance correlates the most strongly with luminosity, which seems to
indicate secondary enrichment. This result may impose a lower limit of 50-200
Myr to the time-scale of star formation in early-type galaxies. Unlike in the
case of clusters, in galaxies bluer Balmer lines yield younger ages than Hbeta.
This age discrepancy is stronger for lower luminosity galaxies. We examine four
scenarios to explain this trend. The most likely is the presence of small
amounts of a young/intermediate-age SP component. Two-component models provide
a better match to the data when the mass fraction of the young component is a
few %. This result implies that star formation has been extended in early-type
galaxies, and more so in less massive galaxies, lending support to the
``downsizing'' scenario. It also implies that SP synthesis models are capable
of constraining not only the mean ages of SPs in galaxies, but also their age
spread.Comment: To appear in the Astrophysical Journal Supplement Series. 55 Pages,
using emulateapj5.sty. Full version, containing all (enlarged) figures can be
found at http://www.astro.virginia.edu/~rps7v/Models/ms.pdf . A number of
useful tables in the Appendix can be obtained in advance of publication by
request to the autho
Bounds for the time to failure of hierarchical systems of fracture
For years limited Monte Carlo simulations have led to the suspicion that the
time to failure of hierarchically organized load-transfer models of fracture is
non-zero for sets of infinite size. This fact could have a profound
significance in engineering practice and also in geophysics. Here, we develop
an exact algebraic iterative method to compute the successive time intervals
for individual breaking in systems of height in terms of the information
calculated in the previous height . As a byproduct of this method,
rigorous lower and higher bounds for the time to failure of very large systems
are easily obtained. The asymptotic behavior of the resulting lower bound leads
to the evidence that the above mentioned suspicion is actually true.Comment: Final version. To appear in Phys. Rev. E, Feb 199
Impact of fertiliser, water table, and warming on celery yield and CO2 and CH4 emissions from fenland agricultural peat
Peatlands are globally important areas for carbon preservation; although covering only 3% of global land area, they store 30% of total soil carbon. Lowland peat soils can also be very productive for agriculture, but their cultivation requires drainage as most crops are intolerant of root-zone anoxia. This leads to the creation of oxic conditions in which organic matter becomes vulnerable to mineralisation. Given the demand for high quality agricultural land, 40% of the UK's peatlands have been drained for agricultural use.
In this study we present the outcomes of a controlled environment experiment conducted on agricultural fen peat to examine possible trade-offs between celery growth (an economically important crop on the agricultural peatlands of eastern England) and emissions of greenhouse gases (carbon dioxide (CO2) and methane (CH4)) at different temperatures (ambient and ambient +5 °C), water table levels (−30 cm, and −50 cm below the surface), and fertiliser use.
Raising the water table from −50 cm to −30 cm depressed yields of celery, and at the same time decreased the entire ecosystem CO2 loss by 31%. A 5 °C temperature increase enhanced ecosystem emissions of CO2 by 25% and increased celery dry shoot weight by 23% while not affecting the shoot fresh weight. Fertiliser addition increased both celery yields and soil respiration by 22%. Methane emissions were generally very low and not significantly different from zero.
Our results suggest that increasing the water table can lower emissions of greenhouse gases and reduce the rate of peat wastage, but reduces the productivity of celery. If possible, the water table should be raised to −30 cm before and after cultivation, and only decreased during the growing season, as this would reduce the overall greenhouse gas emissions and peat loss, potentially not affecting the production of vegetable crops
Probabilistic Approach to Time-Dependent Load-Transfer Models of Fracture
A probabilistic method for solving time-dependent load-transfer models of
fracture is developed. It is applicable to any rule of load redistribution,
i.e, local, hierarchical, etc. In the new method, the fluctuations are
generated during the breaking process (annealed randomness) while in the usual
method, the random lifetimes are fixed at the beginning (quenched disorder).
Both approaches are equivalent.Comment: 13 pages, 4 figures. To appear in Phys.Rev.
Line-profile tomography of exoplanet transits -- II. A gas-giant planet transiting a rapidly-rotating A5 star
Most of our knowledge of extrasolar planets rests on precise radial-velocity
measurements, either for direct detection or for confirmation of the planetary
origin of photometric transit signals. This has limited our exploration of the
parameter space of exoplanet hosts to solar- and later-type, sharp-lined stars.
Here we extend the realm of stars with known planetary companions to include
hot, fast-rotating stars. Planet-like transits have previously been reported in
the lightcurve obtained by the SuperWASP survey of the A5 star HD15082
(WASP-33; V=8.3, v sin i = 86 km/sec). Here we report further photometry and
time-series spectroscopy through three separate transits, which we use to
confirm the existence of a gas giant planet with an orbital period of 1.22d in
orbit around HD15082. From the photometry and the properties of the planet
signal travelling through the spectral line profiles during the transit we
directly derive the size of the planet, the inclination and obliquity of its
orbital plane, and its retrograde orbital motion relative to the spin of the
star. This kind of analysis opens the way to studying the formation of planets
around a whole new class of young, early-type stars, hence under different
physical conditions and generally in an earlier stage of formation than in
sharp-lined late-type stars. The reflex orbital motion of the star caused by
the transiting planet is small, yielding an upper mass limit of 4.1 Jupiter
masses on the planet. We also find evidence of a third body of sub-stellar mass
in the system, which may explain the unusual orbit of the transiting planet. In
HD 15082, the stellar line profiles also show evidence of non-radial
pulsations, clearly distinct from the planetary transit signal. This raises the
intriguing possibility that tides raised by the close-in planet may excite or
amplify the pulsations in such stars.Comment: 9 pages, 6 figures, accepted for publication in MNRA
A genomewide scan for Attention-Deficit/Hyperactivity Disorder in an extended sample: Suggestive linkage on 17p11
Attention-deficit/hyperactivity disorder (ADHD [MIM 143465]) is a common, highly heritable neurobehavioral disorder of childhood onset, characterized by hyperactivity, impulsivity, and/or inattention. As part of an ongoing study of the genetic etiology of ADHD, we have performed a genomewide linkage scan in 204 nuclear families comprising 853 individuals and 270 affected sibling pairs (ASPs). Previously, we reported genomewide linkage analysis of a “first wave” of these families composed of 126 ASPs. A follow-up investigation of one region on 16p yielded significant linkage in an extended sample. The current study extends the original sample of 126 ASPs to 270 ASPs and provides linkage analyses of the entire sample, using polymorphic microsatellite markers that define an ∼10-cM map across the genome. Maximum LOD score (MLS) analysis identified suggestive linkage for 17p11 (MLS=2.98) and four nominal regions with MLS values >1.0, including 5p13, 6q14, 11q25, and 20q13. These data, taken together with the fine mapping on 16p13, suggest two regions as highly likely to harbor risk genes for ADHD: 16p13 and 17p11. Interestingly, both regions, as well as 5p13, have been highlighted in genomewide scans for autism
Spectroscopically resolving the Algol triple system
Algol (β Persei) is the prototypical semidetached eclipsing binary and a hierarchical triple system. From 2006 to 2010 we obtained 121 high-resolution and high signal-to-noise ratio échelle spectra of this object. Spectral disentangling yields the individual spectra of all three stars, and greatly improved elements both the inner and outer orbits. We find masses of M_A = 3.39 ± 0.06 M⊙, M_B = 0.770 ± 0.009 M⊙ and M_C = 1.58 ± 0.09 M⊙. The disentangled spectra also give the light ratios between the components in the B and V bands. Atmospheric parameters for the three stars are determined, including detailed elemental abundances for Algol A and Algol C. We find the following effective temperatures: T_A = 12 550 ± 120 K, T_B = 4900 ± 300 K and T_C = 7550 ± 250 K. The projected rotational velocities are v_A sin i_A = 50.8 ± 0.8 km/s, v_B sin i_B = 62 ± 2 km/s and v_C sin i_C = 12.4 ± 0.6 km/s. This is the first measurement of the rotational velocity for Algol B, and confirms that it is synchronous with the orbital motion. The abundance patterns of components A and C are identical to within the measurement errors, and are basically solar. They can be summarized as mean metal abundances: [M/H]_A = −0.03 ± 0.08 and [M/H]_C = 0.04 ± 0.09. A carbon deficiency is confirmed for Algol A, with tentative indications for a slight overabundance of nitrogen. The ratio of their abundances is (C/N)_A = 2.0 ± 0.4, half of the solar value of (C/N)⊙ = 4.0 ± 0.7. The new results derived in this study, including detailed abundances and metallicities, will enable tight constraints on theoretical evolutionary models for this complex system
Wave propagation in linear electrodynamics
The Fresnel equation governing the propagation of electromagnetic waves for
the most general linear constitutive law is derived. The wave normals are found
to lie, in general, on a fourth order surface. When the constitutive
coefficients satisfy the so-called reciprocity or closure relation, one can
define a duality operator on the space of the two-forms. We prove that the
closure relation is a sufficient condition for the reduction of the fourth
order surface to the familiar second order light cone structure. We finally
study whether this condition is also necessary.Comment: 13 pages. Phys. Rev. D, to appea
Minimizing follow-up for space-based transit surveys using full lightcurve analysis
One of the biggest challenges facing large transit surveys is the elimination
of false-positives from the vast number of transit candidates. We investigate
to what extent information from the lightcurves can identify blend scenarios
and eliminate them as planet candidates, to significantly decrease the amount
of follow-up observing time required to identify the true exoplanet systems. If
a lightcurve has a sufficiently high signal-to-noise ratio, a distinction can
be made between the lightcurve of a stellar binary blended with a third star
and the lightcurve of a transiting exoplanet system. We perform simulations to
determine what signal-to-noise level is required to make the distinction
between blended and non-blended systems as function of transit depth and impact
parameter. Subsequently we test our method on real data from the first IRa01
field observed by the CoRoT satellite, concentrating on the 51 candidates
already identified by the CoRoT team. About 70% of the planet candidates in the
CoRoT IRa01 field are best fit with an impact parameter of b>0.85, while less
than 15% are expected in this range considering random orbital inclinations. By
applying a cut at b<0.85, meaning that ~15% of the potential planet population
would be missed, the candidate sample decreases from 41 to 11. The lightcurves
of 6 of those are best fit with such low host star densities that the
planet-to-star size ratii imply unrealistic planet radii of R>2RJup. Two of the
five remaining systems, CoRoT1b and CoRoT4b, have been identified as planets by
the CoRoT team, for which the lightcurves alone rule out blended light at 14%
(2sigma) and 31% (2sigma). We propose to use this method on the Kepler database
to study the fraction of real planets and to potentially increase the
efficiency of follow-up.Comment: 13 pages, 11 figures, 2 tables. Accepted for publication in A&
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