1,827 research outputs found
s/alpha/Fe Abundance Ratios in Halo Field Stars: Is there a Globular Cluster Connection?
We try to understand the s- and r-process elements vs Ti/Fe plots derived by
Jehin et al. (1999) for mildly metal-poor stars within the framework of the
analytical semi-empirical models for these elements by Pagel & Tautvaisiene
(1995, 1997). Jehin et al. distinguished two Pop II subgroups: IIa with
alpha/Fe and s-elements/Fe increasing together, which they attribute to pure
SNII activity, and IIb with constant alpha/Fe and a range in s/Fe which they
attribute to a prolonged accretion phase in parent globular clusters. However,
their sample consists mainly of thick-disk stars with only 4 clear halo
members, of which two are `anomalous' in the sense defined by Nissen & Schuster
(1997). Only the remaining two halo stars (and one in Nissen & Schuster's
sample) depart significantly from Y/Ti (or s/alpha) ratios predicted by our
model.Comment: 6 pages, 5 figures To appear in: Roma-Trieste Workshop 1999: `The
Chemical Evolution of the Milky Way: Stars vs Clusters', Vulcano Sept. 1999.
F. Giovanelli & F. Matteucci (eds), Kluwer, Dordrech
The Metallicity of the Red Giant Branch in the Disk of NGC 6822
Deep J, H, and K' images obtained with the Canada-France-Hawaii Telescope
adaptive optics system are used to investigate the metallicity of red giant
branch (RGB) stars in three fields in the disk of the Local Group dwarf
irregular galaxy NGC 6822. The slope of the RGB on the (K, J-K) color-magnitude
diagrams indicates that = -1.0 +/- 0.3. The locus of the RGB is bluer
than that of globular clusters with the same RGB slope, by an amount that is
consistent with the majority of RGB stars in these fields having an age near 3
Gyr. It is demonstrated that if RGB stars in NGC 6822 are this young then the
metallicity computed from the RGB slope may be ~ 0.05 dex too low.Comment: 19 pages of text; 10 figures; to appear in the PAS
Corn: Signed, Constant-Time Communication
Recent advances in cacheable technology and unstable theory have paved the way for lambda calculus. In this position paper, we verify the evaluation of hierarchical databases, demonstrates the unproven importance of hardware and architecture. In this work, we propose a novel algorithm for the deployment of Markov models (Corn), confirming that architecture and e-commerce are mostly incompatible
A Bayesian Estimate of the Primordial Helium Abundance
We introduce a new statistical method to estimate the primordial helium
abundance, Y_p from observed abundances in a sample of galaxies which have
experienced stellar helium enrichment. Rather than using linear regression on
metal abundance we construct a likelihood function using a Bayesian prior,
where the key assumption is that the true helium abundance must always exceed
the primordial value. Using a sample of measurements compiled from the
literature we find estimates of Y_p between 0.221 and 0.236, depending on the
specific subsample and prior adopted, consistent with previous estimates either
from a linear extrapolation of the helium abundance with respect to
metallicity, or from the helium abundance of the lowest metallicity HII region,
I Zw 18. We also find an upper limit which is insensitive to the specific
subsample or prior, and estimate a model-independent bound Y_p < 0.243 at 95%
confidence, favoring a low cosmic baryon density and a high primordial
deuterium abundance. The main uncertainty is not the model of stellar
enrichment but possible common systematic biases in the estimate of Y in each
individual HII region.Comment: 14 pages, latex, 3 ps figure
Modeling microbial dormancy in soils
Dormancy is a very effective trait of microorganisms in soil to cope with varying environmental conditions (e.g. substrate availability or moisture) that leads to a graded, switch-like microbial response to fluctuations in environmental parameters. Microbial dormancy strategies vary from rapid to delayed response to environmental change and the activation from dormant to active state is typically faster than the transition to dormant state (Blagodatskaya, E., & Kuzyakov, Y. 2013). Dormancy is typically represented in models by explicitly considering active and dormant biomass pools or by introducing a physiological state variable that describes the active fraction of the total biomass. Existing modeling approaches mainly differ in the description of the transformation process between active and dormant states and disregard the classification into active, potentially active and dormant microbial states. The growth rate, death rates and the transition rate from active to dormant state are represented by generic functions. The question arises of gauging the sensitivity of model predictions for the temporal evolution of active and dormant bacteria not only to perturbations in constants of proportionality (parameter sensitivity), but to perturbations in uncertain or assumed expressions (functional sensitivity). Instead of postulating a particular description, the functional form of the transition function can be tested by fitting a type of free-form function as a linear combination of shape functions to the experimental dataset used in Wang et al. 2014. Depending on the form of the transition function, we observe that simple SOM turnover models show qualitatively different dynamical behavior. We aim to generalize existing modeling approaches to account for diversity in dormancy strategies and to understand which strategies for transiting between dormant and active states are favoured under which environmental conditions
The oxygen abundance calibrations and N/O abundance ratios of ~40,000 SDSS star-forming galaxies
Using a large sample of 38,478 star-forming galaxies selected from the Second
Data Release of the Sloan Digital Sky Survey database (SDSS-DR2), we derive
analytical calibrations for oxygen abundances from several
metallicity-sensitive emission-line ratios: [N II]/H_alpha, [O III]/[N II], [N
II]/[O II], [N II]/[S II], [S II]/H_alpha, and [O III]/H_beta. This consistent
set of strong-line oxygen abundance calibrations will be useful for future
abundance studies. Among these calibrations, [N II]/[O II] is the best for
metal-rich galaxies due to its independence on ionization parameter and low
scatter. Dust extinction must be considered properly at first. These
calibrations are more suitable for metal-rich galaxies (8.4<12+log(O/H)<9.3),
and for the nuclear regions of galaxies. The observed relations are consistent
with those expected from the photoionization models of Kewley & Dopita (2002).
However, most of the observational data spread in a range of ionization
parameter q from 1*10^7 to 8*10^7 cm s^{-1}, corresponding to logU= -3.5 to
-2.5, narrower than that suggested by the models. We also estimate the (N/O)
abundance ratios of this large sample of galaxies, and these are consistent
with the combination of a "primary" and a dominant "secondary" components of
nitrogen.Comment: 17 pages, 10 figures, 1 table. ApJ in pres
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