4,068 research outputs found
Submillimeter observations of OH and CH in M42
The (sup 2) pi sub 1/2 (J = 3/2 to 1/2) transitions of OH at 163.12 and 163.40 micro m have been detected and upper limits have been obtained for the (sup 2) pi sub 3/2 (J = 3/2 to 1/2) transitions of CH at 149.09 and 149.39 micro m, in observations of the Kleinmann-Low Nebula of Orion. All four flux levels lie between 1 and 1.2 x 10 to the 17th power/sq.cm. The OH lines are bright when compared to the lower, (sup 2) pi sub 3/2 (J = 5/2 to 3/2) fluxes reported and imply that the 119 micro m emission observed is partially self-absorbed. The combined results provide strong constraints. Taken together with existing data on molecular hydrogen and CO and recent data on other OH transition, they suggest OH emission from post-shock regions at temperatures T approx 1000 k, densities approx. 7 x 10 to the 6th powr/cu cm N sub OH approx 80/cu cm optically thick for the (sup 2) pi sub 3/2 (J = 5/2 to 3/2), 119 micro m but only partially self-absorbing in the (J = 7/2 to 3/2), 84 micro m transitions over a Doppler velocity bandwidth of 30 km/sec. The OH column density is N sub OH approx 4 x 10 to the 16th powr/sq cm. in the emitting regions which occupy a fraction of approx 0.1 of a 1' x 1' field of view centered on the Becklin-Neugebauer source. The CO (J = 31 to 30), 84 micro m transition appears to lie sufficiently close to one of the 84 micro m OH line components to be partially absorbed as well, through a Bowen-type mechanism
Processes governing development of ecotoxicity in clayey and silty soils incubated with olive mill wast water under different temperature and humidity conditions
Olive oil production generates olive mill wastewater (OMW) with a high content in nutrients and phenolic substances. Its application to soil could be a cost-effective solution for recycling. However, the degree of toxic effects of OMW on soil biota is widely unknown and has to be considered when searching for adisposal strategy.
The objective of this study was to understand the degradation process of OMW organic matter and its influence on toxic effects as well as soil properties. We hypothesized that OMW toxicity decreases with degradation of its phenolic components. A higher soil biological activity was expected to increase degradation.
We incubated a clayey soil and a silty soil with OMW for 60 days under conditions typical for this region in order to simulate the application during various seasons (winter, spring, summer dry, summer wet). Soil respiration, pH, electrical conductivity, total phenolic content as well as anion and cation content, specific ultraviolet absorbance at 254 nm and dissolved organic carbon were measured at ten points of time during incubation. Soils and methanolic soil extracts were tested for ecotoxicity using Lepidium sativum germination and Folsomia candida egg hatching rate.
The degradation and transformation of OMW-organic matter was stronger under warm and humid conditions than under cold and dry conditions. It was furthermore enhanced in the clayey soil compared to the silty soil. Most severe ecotoxicological effects were found under summer dry conditions while spring as well as summer wet conditions led to a fast recovery of both germination and hatching. However, the silty soil did not recover to preapplication levels. In the clayey soil, germination parameter were higher than in control after around 30 days suggesting a fertilizing effect. Effects in methanol extracts were higher in all soils and climatic scenarios. Therefore, remobilization of OMW derived toxic compounds has to be considered on a long-term scale. Egg hatching as most sensitive life-cycle parameter of Folsomia candida showed also the same relation to climatic conditions and soil type but was more robust to OMW compared to Lepidium sativum.
Environmental conditions as well as soil type are key factors determining degradation of OMW organic matter and OMW derived ecotoxicity. Therefore, spring application (warm and wet) of OMW seems to be a compromise with regard to OMW recycling, OMW occurrence in winter and farmer considerations
--PhotoZ: Photometric Redshifts by Inverting the Tolman Surface Brightness Test
Surface brightness is a fundamental observational parameter of galaxies. We
show, for the first time in detail, how it can be used to obtain photometric
redshifts for galaxies, the -PhotoZ method.
We demonstrate that the Tolman surface brightness relation, , is a powerful tool for determining galaxy redshifts from
photometric data.
We develop a model using and a color percentile (ranking) measure to
demonstrate the -PhotoZ method. We apply our method to a set of galaxies
from the SHELS survey, and demonstrate that the photometric redshift accuracy
achieved using the surface brightness method alone is comparable with the best
color-based methods.
We show that the -PhotoZ method is very effective in determining the
redshift for red galaxies using only two photometric bands. We discuss the
properties of the small, skewed, non-gaussian component of the error
distribution.
We calibrate from the SDSS to redshift, and tabulate the
result, providing a simple, but accurate look up table to estimate the redshift
of distant red galaxies.Comment: Accepted for publication in the Astronomical Journa
First exit times of solutions of stochastic differential equations driven by multiplicative Levy noise with heavy tails
In this paper we study first exit times from a bounded domain of a gradient
dynamical system perturbed by a small multiplicative
L\'evy noise with heavy tails. A special attention is paid to the way the
multiplicative noise is introduced. In particular we determine the asymptotics
of the first exit time of solutions of It\^o, Stratonovich and Marcus canonical
SDEs.Comment: 19 pages, 2 figure
Free-Free Spectral Energy Distributions of Hierarchically Clumped HII Regions
In an effort to understand unusual power-law spectral slopes observed in some
hypercompact HII regions, we consider the radio continuum energy distribution
from an ensemble of spherical clumps. An analytic expression for the free-free
emission from a single spherical clump is derived. The radio continuum slope
(with F_\nu \nu^\alpha) is governed by the population of clump optical depths
N(tau), such that (a) at frequencies where all clumps are thick, a continuum
slope of +2 is found, (b) at frequencies where all clumps are optically thin, a
flattened slope of -0.11 is found, and (c) at intermediate frequencies, a
power-law segment of significant bandwidth with slopes between these two
limiting values can result. For the ensemble distribution, we adopt a power-law
distribution N(tau) tau^{-\gamma}, and find that significant power-law segments
in the SED with slopes from +2 to -0.11 result only for a relatively restricted
range of values of 1 to 2. Further, a greater range of clump optical
depths for this distribution leads to a wider bandwidth over which the
intermediate power-law segment exists. The model is applied to the source
W49N-B2 with an observed slope of \alphab +0.9, but that may be turning over to
become optically thin around 2 mm. An adequate fit is found in which most
clumps are optically thin and there is little shadowing of rearward clumps by
foreground clumps (i.e., the geometrical covering factor C<<1). The primary
insight gained from our study is that in the Rayleigh-Jeans limit for the
Planck function that applies for the radio band, it is the distribution in
optical depth of the clump population that is solely responsible for setting
the continuum shape, with variations in the size and temperature of clumps
serving to modulate the level of free-free emission.Comment: Astrophysical Journal, in pres
The Instability Strip for Pre--Main-Sequence Stars
We investigate the pulsational properties of Pre--Main-Sequence (PMS) stars
by means of linear and nonlinear calculations. The equilibrium models were
taken from models evolved from the protostellar birthline to the ZAMS for
masses in the range 1 to 4 solar masses. The nonlinear analysis allows us to
define the instability strip of PMS stars in the HR diagram. These models are
used to constrain the internal structure of young stars and to test
evolutionary models. We compare our results with observations of the best case
of a pulsating young star, HR~5999, and we also identify possible candidates
for pulsational variability among known Herbig Ae/Be stars which are located
within or close to the instability strip boundaries.Comment: 14 pages, three postscript figures, accepted for publication on the
Astrophysical Journal Letter
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