6,156 research outputs found
The Age, Metallicity and Alpha-Element Abundance of Galactic Globular Clusters from Single Stellar Population Models
Establishing the reliability with which stellar population parameters can be
measured is vital to extragalactic astronomy. Galactic GCs provide an excellent
medium in which to test the consistency of Single Stellar Population (SSP)
models as they should be our best analogue to a homogeneous (single) stellar
population. Here we present age, metallicity and -element abundance
measurements for 48 Galactic globular clusters (GCs) as determined from
integrated spectra using Lick indices and SSP models from Thomas, Maraston &
Korn, Lee & Worthey and Vazdekis et al. By comparing our new measurements to
independent determinations we are able to assess the ability of these SSPs to
derive consistent results -- a key requirement before application to
heterogeneous stellar populations like galaxies.
We find that metallicity determinations are extremely robust, showing good
agreement for all models examined here, including a range of enhancement
methods. Ages and -element abundances are accurate for a subset of our
models, with the caveat that the range of these parameters in Galactic GCs is
limited. We are able to show that the application of published Lick index
response functions to models with fixed abundance ratios allows us to measure
reasonable -element abundances from a variety of models. We also
examine the age-metallicity and [/Fe]-metallicity relations predicted
by SSP models, and characterise the possible effects of varied model horizontal
branch morphology on our overall results.Comment: 22 pages, 19 figures, accepted for publication in MNRA
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Additive and synergistic relations of early mother-child and caregiver-child interactions for predicting later achievement.
This study examines associations between stimulating-responsive social interactions with mothers and nonparental childcare providers during the first 3 years of life and children's vocabulary and mathematics skills through age 15 (N = 1,364). Additive relations were found in which more stimulating-responsive interactions with mothers and with caregivers were linked to higher mathematics achievement in childhood and adolescence. More stimulating-responsive early interactions with mothers were also associated with larger child vocabularies through age 15. Synergistic relations, consistent with the dual-risk hypothesis, also were found. Children whose early interactions with both mothers and caregivers were low in stimulation and responsivity had substantially lower mathematics skills. Implications for early childhood interventions and policies are discussed. (PsycINFO Database Record (c) 2019 APA, all rights reserved)
Searching for Earth-mass planets around Centauri: precise radial velocities from contaminated spectra
This work is part of an ongoing project which aims to detect terrestrial
planets in our neighbouring star system Centauri using the Doppler
method. Owing to the small angular separation between the two components of the
Cen AB binary system, the observations will to some extent be
contaminated with light coming from the other star. We are accurately
determining the amount of contamination for every observation by measuring the
relative strengths of the H- and NaD lines. Furthermore, we have
developed a modified version of a well established Doppler code that is
modelling the observations using two stellar templates simultaneously. With
this method we can significantly reduce the scatter of the radial velocity
measurements due to spectral cross-contamination and hence increase our chances
of detecting the tiny signature caused by potential Earth-mass planets. After
correcting for the contamination we achieve radial velocity precision of for a given night of observations. We have also
applied this new Doppler code to four southern double-lined spectroscopic
binary systems (HR159, HR913, HR7578, HD181958) and have successfully recovered
radial velocities for both components simultaneously.Comment: accepted for publication in the International Journal of Astrobiology
(published by Cambridge University Press); will appear in a revised form,
subsequent to editorial input by Cambridge University Pres
The Weihai Observatory search for close-in planets orbiting giant stars
Planets are known to orbit giant stars, yet there is a shortage of planets
orbiting within ~0.5 AU (P<100 days). First-ascent giants have not expanded
enough to engulf such planets, but tidal forces can bring planets to the
surface of the star far beyond the stellar radius. So the question remains: are
tidal forces strong enough in these stars to engulf all the missing planets? We
describe a high-cadence observational program to obtain precise radial
velocities of bright giants from Weihai Observatory of Shandong University. We
present data on the planet host Beta Gem (HD 62509), confirming our ability to
derive accurate and precise velocities; our data achieve an rms of 7.3 m/s
about the Keplerian orbit fit. This planet-search programme currently receives
~100 nights per year, allowing us to aggressively pursue short-period planets
to determine whether they are truly absent.Comment: Accepted for publication in PAS
Environmental pollutants from the Scott and Shackleton expeditions during the ‘Heroic Age’ of Antarctic exploration
Early explorers to Antarctica built wooden huts and brought huge quantities of supplies and equipment to support their geographical and scientific studies for several years. When the expeditions ended and relief ships arrived, a rapid exodus frequently allowed only essential items to be taken north. The huts and thousands of items were left behind. Fuel depots with unused containers of petroleum products, asbestos materials, and diverse chemicals were also left at the huts. This investigation found high concentrations of polyaromatic hydrocarbons in soils under and around the historic fuel depots, including anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, fluorene, and pyrene, as well as benzo[a]anthracene, benzo[a]pyrene, and fluoranthene, which are recognized carcinogens. Asbestos materials within the huts have been identified and extensive amounts of fragmented asbestos were found littering the ground around the Cape Evans hut. These materials are continually abraded and fragmented as tourists walk over them and the coarse scoria breaks and grinds down the materials. A chemical spill, within the Cape Evans hut, apparently from caustic substances from one of the scientific experiments, has caused an unusual deterioration and defibration on affected woods. Although these areas are important historic sites protected by international treaties, the hazardous waste materials left by the early explorers should be removed and remedial action taken to restore the site to as pristine a condition as possible. Recommendations are discussed for international efforts to study and clean up these areas, where the earliest environmental pollution in Antarctica was produced
Development of a Semi-Automated Tobacco Stripping Machine Utilizing String Trimmers
Conventional stripping of burley tobacco is labor intensive and typically requires 50 to 75 worker hours per acre (wkr•h/acre). The goal of the project was to reduce labor by optimizing leaf removal by string trimmer heads using combinations of strings lengths and motor speeds. In tests conducted on a single grade, all leaves outside the grade were removed by hand. Plants were run through the machine for string lengths of 13, 18, and 23 cm (5, 7, and 9 in.) and associated motor speeds which were monitored and recorded. Stripping efficiencies were calculated for each plant and collectively for each set of four plants. The machine was then tested for three grade stripping efficiency. Particle size analysis tests were run to determine potential losses due to leaf shredding. Efficiencies for single grade testing ranged from 93% to 96% for optimal string length and speed combinations. Stripping three grades by machine resulted in an average of 97% efficiency. Potential losses due to shredding accounted for 5.6% of the total weight mechanically removed. It is believed that this stripping concept, implemented on a full scale four grade basis, could result in savings of at least 45 wkr•h/ha (18 wkr•h/acre)
Carlisle Memorial Volume
Table of Contents:
The Carlisle Family
Life Sketch of Dr. Carlisle - by Dr. Charles Forster Smith
Dr. Carlisle as a Citizen - by Watson B. Duncan
The Wofford Chapel Hour - by Dr. Henry Nelson Snyder
Wofford College and its President Twenty Years Ago - by Dr. Robert A. Law
Dr. Carlisle as a Teacher - by Dr. David Duncan Wallace
Tributes to Dr. Carlislehttps://digitalcommons.wofford.edu/collegebooks/1005/thumbnail.jp
Robust Statistical Detection of Power-Law Cross-Correlation
We show that widely used approaches in statistical physics incorrectly
indicate the existence of power-law cross-correlations between financial stock
market fluctuations measured over several years and the neuronal activity of
the human brain lasting for only a few minutes. While such cross-correlations
are nonsensical, no current methodology allows them to be reliably discarded,
leaving researchers at greater risk when the spurious nature of cross-
correlations is not clear from the unrelated origin of the time series and
rather requires careful statistical estimation. Here we propose a theory and
method (PLCC-test) which allows us to rigorously and robustly test for power-
law cross-correlations, correctly detecting genuine and discarding spurious
cross-correlations, thus establishing meaningful relationships between
processes in complex physical systems. Our method reveals for the first time
the presence of power-law cross-correlations between amplitudes of the alpha
and beta frequency ranges of the human electroencephalogram
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