1,302 research outputs found
Economic evaluation of the eradication program for bovine viral diarrhea in the Swiss dairy sector
The aim of this study was to conduct an economic evaluation of the BVD eradication program in the Swiss dairy sector. The situation before the start of the program (herd-level prevalence: 20%) served as a baseline scenario. Production models for three dairy farm types were used to estimate gross margins as well as net production losses and expenditures caused by BVD. The total economic benefit was estimated as the difference in disease costs between the baseline scenario and the implemented eradication program and was compared to the total eradication costs in a benefit-cost analysis. Data on the impact of BVD virus (BVDV) infection on animal health, fertility and production parameters were obtained empirically in a retrospective epidemiological case-control study in Swiss dairy herds and complemented by literature. Economic and additional production parameters were based on benchmarking data and published agricultural statistics. The eradication costs comprised the cumulative expenses for sampling and diagnostics. The economic model consisted of a stochastic simulation in @Risk for Excel with 20,000 iterations and was conducted for a time period of 14 years (2008â2021)
No Increase of the Red-Giant-Branch Tip Luminosity Toward the Center of M31
We present observations with the Hubble Space Telescope Wide Field Planetary
Camera 2 of three fields centered on super-metal-rich globular clusters in the
bulge of M31. Our (I,V-I) color-magnitude diagrams reach as faint as I ~ 26.5
mag and clearly reveal the magnitude of the first ascent red giant branch (RGB)
tip. We find that the apparent I magnitude of the RGB tip does not become
brighter near the center of M31 as concluded by previous investigators. Our
observations and artificial star experiments presented in this study strongly
support the idea that previous very bright stars were likely the result of
spurious detections of blended stars due to crowding in lower resolution
images. On the contrary, our observations indicate that, at a mean projected
galactocentric distance of 1.1 kpc, the RGB tip is some 1.3 magnitudes fainter
than it is at 7 kpc. An analysis of this difference in RGB tip magnitude
suggests that the M31 bulge stellar population has a mean metallicity close to
that of the Sun.Comment: Accepted for publication in ApJ, June 20, 1999 issu
A Consistent Picture Emerges: A Compact X-ray Continuum Emission Region in the Gravitationally Lensed Quasar SDSS J0924+0219
We analyze the optical, UV, and X-ray microlensing variability of the lensed
quasar SDSS J0924+0219 using six epochs of Chandra data in two energy bands
(spanning 0.4-8.0 keV, or 1-20 keV in the quasar rest frame), 10 epochs of
F275W (rest-frame 1089A) Hubble Space Telescope data, and high-cadence R-band
(rest-frame 2770A) monitoring spanning eleven years. Our joint analysis
provides robust constraints on the extent of the X-ray continuum emission
region and the projected area of the accretion disk. The best-fit half-light
radius of the soft X-ray continuum emission region is between 5x10^13 and 10^15
cm, and we find an upper limit of 10^15 cm for the hard X-rays. The best-fit
soft-band size is about 13 times smaller than the optical size, and roughly 7
GM_BH/c^2 for a 2.8x10^8 M_sol black hole, similar to the results for other
systems. We find that the UV emitting region falls in between the optical and
X-ray emitting regions at 10^14 cm < r_1/2,UV < 3x10^15 cm. Finally, the
optical size is significantly larger, by 1.5*sigma, than the theoretical
thin-disk estimate based on the observed, magnification-corrected I-band flux,
suggesting a shallower temperature profile than expected for a standard disk.Comment: Replaced with accepted version to Ap
The redshift of the gravitationally lensed radio source PKS1830-211
We report on the spectroscopic identification and the long awaited redshift
measurement of the heavily obscured, gravitationally lensed radio source PKS
1830-211, which was first observed as a radio Einstein ring. The NE component
of the doubly imaged core is identified, in our infrared spectrum covering the
wavelength range 1.5-2.5 microns, as an impressively reddened quasar at
z=2.507. Our redshift measurement, together with the recently measured time
delay (Lovell et al.), means that we are a step closer to determining the
Hubble constant from this lens. Converting the time delay into the Hubble
constant by using existing models leads to high values for the Hubble constant.
Since the lensing galaxy lies very close to the center of the lensed ring,
improving the error bars on the Hubble constant will require not only a more
precise time delay measurement, but also very precise astrometry of the whole
system.Comment: 11 pages, 2 figures, Accepted ApJ
Ages and Metallicities of Young Globular Clusters in the Merger Remnant NGC 7252
UV-to-visual spectra of eight young star clusters in the merger remnant and
protoelliptical galaxy NGC 7252, obtained with the Blanco 4-m telescope on
Cerro Tololo, are presented. These clusters lie at projected distances of 3-15
kpc from the center and move with a velocity dispersion of 140+/-35 km/s in the
line of sight. Seven of the clusters show strong Balmer absorption lines in
their spectra [EW(H-beta)= 6-13 Angstrom], while the eighth lies in a giant HII
region and shows no detectable absorption features.
Based on comparisons with model-cluster spectra by Bruzual & Charlot (1996)
and Bressan, Chiosi, & Tantalo (1996), six of the absorption-line clusters have
ages in the range of 400-600 Myr, indicating that they formed early on during
the recent merger. These clusters are globular clusters as judged by their
small effective radii and ages corresponding to ~100 core crossing times. The
one emission-line object is <10 Myr old and may be a nascent globular cluster
or an OB association.
The mean metallicities measured for three clusters are solar to within
+/-0.15 dex, suggesting that the merger of two likely Sc galaxies in NGC 7252
formed a globular-cluster system with a bimodal metallicity distribution. Since
NGC 7252 itself shows the characteristics of a 0.5-1 Gyr old protoelliptical,
its second-generation solar-metallicity globulars provide direct evidence that
giant ellipticals with bimodal globular-cluster systems can form through major
mergers of gas-rich disk galaxies.Comment: 34 pages, incl. 6 figures in EPS format, AAS LaTeX, to be published
in AJ, Vol. 116, Nov. 199
An XMM-Newton observation of the globular cluster Omega Centauri
We report on a deep XMM-Newton EPIC observation of the globular cluster Omega
Cen performed on August 13th, 2001. We have detected 11 and 27 faint X-ray
sources in the core and half mass radii, searching down to a luminosity of 1.3
x 10^{31} erg s^{-1} in the 0.5-5 keV range. Most sources have bolometric X-ray
luminosities between ~ 10^{31}-10^{32} erg s^{-1}. We present the color-color
and hardness-intensity diagrams of the source sample, as well as high-quality
EPIC spectra of the brightest objects of the field; including the two candidate
Cataclysmic Variables (CVs) in the core and the quiescent neutron star low-mass
X-ray binary candidate. The spectra of the latter objects fully support their
previous classification. We show that the bulk of sources are hard and
spectrally similar to CVs. The lack of soft faint sources might be related to
the absence of millisecond pulsars in the cluster. The XMM-Newton observations
reveal the presence of an excess of sources well outside the core of the
cluster where several RS CVn binaries have already been found. We have also
analyzed a publicly available Chandra ACIS-I observation performed on January
24-25th, 2000, to improve the XMM-Newton source positions and to search for
source intensity variations between the two data sets. 63 XMM-Newton sources
have a Chandra counterpart, and 15 sources within the half-mass radius have
shown time variability. Overall, the general properties of the faint X-ray
sources in Omega Cen suggest that they are predominantly CVs and active
binaries (RS CVn or BY Dra).Comment: 21 pages, 2 color figures, 8 B&W figures. Accepted for publication in
Astronomy and Astrophysic
The low-mass Initial Mass Function in the 30 Doradus starburst cluster
We present deep Hubble Space Telescope (HST) NICMOS 2 F160W band observations
of the central 56*57" (14pc*14.25pc) region around R136 in the starburst
cluster 30 Dor (NGC 2070) located in the Large Magellanic Cloud. Our aim is to
derive the stellar Initial Mass Function (IMF) down to ~1 Msun in order to test
whether the IMF in a massive metal-poor cluster is similar to that observed in
nearby young clusters and the field in our Galaxy. We estimate the mean age of
the cluster to be 3 Myr by combining our F160W photometry with previously
obtained HST WFPC2 optical F555W and F814W band photometry and comparing the
stellar locus in the color-magnitude diagram with main sequence and pre-main
sequence isochrones. The color-magnitude diagrams show the presence of
differential extinction and possibly an age spread of a few megayears. We
convert the magnitudes into masses adopting both a single mean age of 3 Myr
isochrone and a constant star formation history from 2 to 4 Myr. We derive the
IMF after correcting for incompleteness due to crowding. The faintest stars
detected have a mass of 0.5 Msun and the data are more than 50% complete
outside a radius of 5 pc down to a mass limit of 1.1 Msun for 3 Myr old
objects. We find an IMF of dN/dlog(M) M^(-1.20+-0.2) over the mass range
1.1--20 Msun only slightly shallower than a Salpeter IMF. In particular, we
find no strong evidence for a flattening of the IMF down to 1.1 Msun at a
distance of 5 pc from the center, in contrast to a flattening at 2 Msun at a
radius of 2 pc, reported in a previous optical HST study. We examine several
possible reasons for the different results. If the IMF determined here applies
to the whole cluster, the cluster would be massive enough to remain bound and
evolve into a relatively low-mass globular cluster.Comment: Accepted in ApJ. Abstract abridge
Massive perturbers and the efficient merger of binary massive black holes
We show that dynamical relaxation in the aftermath of a galactic merger and
the ensuing formation and decay of a binary massive black hole (MBH), are
dominated by massive perturbers (MPs) such as giant molecular clouds or
clusters. MPs accelerate relaxation by orders of magnitude relative to 2-body
stellar relaxation alone, and efficiently scatter stars into the binary MBH's
orbit. The 3-body star-binary MBH interactions shrink the binary MBH to the
point where energy losses from the emission of gravitational waves (GW) lead to
rapid coalescence. We model this process based on observed and simulated MP
distributions and take into account the decreased efficiency of the star-binary
MBH interaction due to acceleration in the galactic potential. We show that
mergers of gas-rich galactic nuclei lead to binary MBH coalescence well within
the Hubble time. Moreover, lower-mass binary MBHs (<10^8 Msun) require only a
few percent of the typical gas mass in a post-merger nucleus to coalesce in a
Hubble time. The fate of a binary MBH in a gas poor galactic merger is less
certain, although massive stellar structures (e.g. clusters, stellar rings)
could likewise lead to efficient coalescence. These coalescence events are
observable by their strong GW emission. MPs thus increase the cosmic rate of
such GW events, lead to a higher mass deficit in the merged galactic core and
suppress the formation of triple MBH systems and the resulting ejection of MBHs
into intergalactic space.Comment: 14 pages, 4 figures, 3 tables. More detailed explanations and changes
in structure. Section on hypervelocity stars moved to another paper (in
preparation). Results and conclusions unchanged. Accepted to Ap
Dietary plasticity linked to divergent growth trajectories in a critically endangered sea turtle
Foraging habitat selection and diet quality are key factors that influence individual fitness and meta-population dynamics through effects on demographic rates. There is growing evidence that sea turtles exhibit regional differences in somatic growth linked to alternative dispersal patterns during the oceanic life stage. Yet, the role of habitat quality and diet in shaping somatic growth rates is poorly understood. Here, we evaluate whether diet variation is linked to regional growth variation in hawksbill sea turtles (Eretmochelys imbricata), which grow significantly slower in Texas, United States versus Florida, United States, through novel integrations of skeletal growth, gastrointestinal content (GI), and bulk tissue and amino acid (AA)-specific stable nitrogen (ÎŽ15N) and carbon (ÎŽ13C) isotope analyses. We also used AA ÎŽ15N ÎŁV values (heterotrophic bacterial re-synthesis index) and ÎŽ13C essential AA (ÎŽ13CEAA) fingerprinting to test assumptions about the energy sources fueling hawksbill food webs regionally. GI content analyses, framed within a global synthesis of hawksbill dietary plasticity, revealed that relatively fast-growing hawksbills stranded in Florida conformed with assumptions of extensive spongivory for this species. In contrast, relatively slow-growing hawksbills stranded in Texas consumed considerable amounts of non-sponge invertebrate prey and appear to forage higher in the food web as indicated by isotopic niche metrics and higher AA ÎŽ15N-based trophic position estimates internally indexed to baseline nitrogen isotope variation. However, regional differences in estimated trophic position may also be driven by unique isotope dynamics of sponge food webs. AA ÎŽ15N ÎŁV values and ÎŽ13CEAA fingerprinting indicated minimal bacterial re-synthesis of organic matter (ÎŁVâ<â2) and that eukaryotic microalgae were the primary energy source supporting hawksbill food webs. These findings run contrary to assumptions that hawksbill diets predominantly comprise high microbial abundance sponges expected to primarily derive energy from bacterial symbionts. Our findings suggest alternative foraging patterns could underlie regional variation in hawksbill growth rates, as divergence from typical sponge prey might correspond with increased energy expenditure and reduced foraging success or diet quality. As a result, differential dispersal patterns may infer substantial individual and population fitness costs and represent a previously unrecognized challenge to the persistence and recovery of this critically endangered species
The Quasar Pair Q 1634+267 A, B and the Binary QSO vs. Dark Lens Hypotheses
Deep HST/NICMOS H (F160W) band observations of the z=1.96 quasar pair Q
1634+267A,B reveal no signs of a lens galaxy to a 1 sigma threshold of
approximately 22.5 mag. The minimum luminosity for a normal lens galaxy would
be a 6L_* galaxy at z > 0.5, which is 650 times greater than our detection
threshold. Our observation constrains the infrared mass-to-light ratio of any
putative, early-type, lens galaxy to (M/L)_H > 690h_65 (1200h_65) for
Omega_0=0.1 (1.0) and H_0=65h_65 km/s/Mpc. We would expect to detect a galaxy
somewhere in the field because of the very strong Mg II absorption lines at
z=1.1262 in the Q 1634+267 A spectrum, but the HST H-band, I-band (F785LP) and
V-band (F555W) images require that any associated galaxy be very under-luminous
less than 0.1 L^*_H (1.0 L^*_I) if it lies within less than 40 h^{-1} (100
h^{-1}) kpc from Q 1634+267 A,B.
While the large image separation (3.86 arcsec) and the lack of a lens galaxy
strongly favor interpreting Q 1634+267A,B as a binary quasar system, the
spectral similarity remains a puzzle. We estimate that at most 0.06% of
randomly selected quasar pairs would have spectra as similar to each other as
the spectra of Q 1634+267 A and B. Moreover, spectral similarities observed for
the 14 quasar pairs are significantly greater than would be expected for an
equivalent sample of randomly selected field quasars. Depending on how strictly
we define similarity, we estimate that only 0.01--3% of randomly drawn samples
of 14 quasar pairs would have as many similar pairs as the observational
sample.Comment: 24 pages, including 4 figures, LaTex, ApJ accepted, comments from the
editor included, minor editorial change
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