1,020 research outputs found
NICMOS Imaging of the Host Galaxies of z ~ 2 - 3 Radio-Quiet Quasars
We have made a deep NICMOS imaging study of a sample of 5 z ~ 2 - 3
radio-quiet quasars with low absolute nuclear luminosities, and we have
detected apparent host galaxies in all of these. Most of the hosts have
luminosities approximately equal to present-day L*, with a range from 0.2 L* to
about 4 L*. These host galaxies have magnitudes and sizes consistent with those
of the Lyman break galaxies at similar redshifts and at similar rest
wavelengths, but are about two magnitudes fainter than high-z powerful radio
galaxies. The hosts of our high-z sample are comparable to or less luminous
than the hosts of the low-z RQQs with similar nuclear absolute magnitudes.
However, the high z galaxies are more compact than the hosts of the low z
quasars, and probably have only 10 - 20% of the stellar mass of their low-z
counterparts. Application of the M(bulge)/M(BH) relation found for present-day
spheroids to the stellar masses implied for the high z host galaxies would
indicate that they contain black holes with masses around 10^8 Msolar.
Comparison to their nuclear magnitudes implies accretion rates that are near or
at the Eddington limit. Although these high z hosts already contain
supermassive black holes, the galaxies will need to grow significantly to
evolve into present-day L* galaxies. These results are basically consistent
with theoretical predictions for the hierarchical buildup of the galaxy host
and its relation to the central supermassive black hole.Comment: 25 pages, 13 figures, accepted for publication in Ap
Static Black Hole Solutions without Rotational Symmetry
We construct static black hole solutions that have no rotational symmetry.
These arise in theories, including the standard electroweak model, that include
charged vector mesons with mass . In such theories, a magnetically
charged Reissner-Nordstrom black hole with horizon radius less than a critical
value of the order of is classically unstable against the development
of a nonzero vector meson field just outside the horizon, indicating the
existence of static black hole solutions with vector meson hair. For the case
of unit magnetic charge, spherically symmetric solutions of this type have
previously been studied. For other values of the magnetic charge, general
arguments show that any new solution with hair cannot be spherically symmetric.
In this paper we develop and apply a perturbative scheme (which may have
applicability in other contexts) for constructing such solutions in the case
where the Reissner-Nordstrom solution is just barely unstable. For a few low
values of the magnetic charge the black holes retain a rotational symmetry
about a single axis, but this axial symmetry disappears for higher charges.
While the vector meson fields vanish exponentially fast at distances greater
than , the magnetic field and the metric have higher multipole
components that decrease only as powers of the distance from the black hole.Comment: 42 pages, phyzzx. 4 figures (PostScript, 1.7 MB when uncompressed)
available by email from the Authors on reques
Genetic diversity and virulence variability in Diplodia mutila isolates from symptomatic grapevines in New Zealand: Virulence and genetic diversity of Diplodia mutila
Genetic diversity and virulence variability of Diplodia mutila isolates recovered from grapevines in New Zealand were investigated. The universally primed PCR (UP-PCR) and vegetative compatibility group (VCG) methods were used to investigate the genetic diversity. Pathogenicity tests with âSauvignon Blancâ detached shoots and potted vines were used to determine the virulence diversity. UP-PCR analysis determined eight genetic groups of D. mutila with 70% of the population within one group. Phylogenetic analysis also determined that New Zealand isolates were more closely related to Australian isolates than Californian isolates. Vegetative compatibility grouping analysis placed the isolates into three VCG groups, with 57% of isolates belonging to all three VCGs. Vegetative compatibility reactions were observed among isolates, but this was not correlated with the genetic clustering. Virulence assays proved that all isolates tested were pathogenic on grapevine stems. Differences in necrotic lesions lengths caused by D. mutila isolates were identified, indicating different virulence levels among isolates, however, no relationship was found between the genetic groups and the virulence. The results of the study indicated movement of D. mutila isolates between nurseries, vineyards, and other sources in New Zealand. This information will inform control strategies to limit the further spread of this pathogen into vineyards in the same region or new regions
Propagule and soil type affects the pathogenicity of Ilyonectria and Dactylonectria spp., the causal agents of black foot disease of grapevines
Black foot disease of grapevines is a significant economic issue for the viticulture industry worldwide. The disease is mainly associated with soil borne pathogen species within the genera Dactylonectria and Ilyonectria. The aim of this study was to determine the pathogenicity of different pathogen propagules, including chlamydospores, conidia and mycelium, to grapevine rootstocks grown in soil. A combination of nine isolates belonging to Dactylonectria and Ilyonectria genera, representative of the fungal species associated with black foot disease in New Zealand were used to inoculate grapevines in a field experiment. In the second experiment, the pathogenicity of the different propagules was assessed in different soil types, clay loam, silt loam and sandy loam soils. In the field experiment, chlamydospores and conidia resulted in higher disease incidence and severity at 0 cm above the grapevine stem base compared with mycelium. At 5 cm above the stem base, chlamydospores caused the greatest disease incidence compared with the other two propagules. Propagule type had no effect on shoot and root dry weights. In the pot experiment, soil type affected disease incidence and severity, with clay loam soil resulting in significantly greater disease incidence and severity than silt loam or sandy loam soils. Disease severity at 0 cm above the stem base was significantly higher with conidial inoculations compared with chlamydospore inoculations irrespective of soil type. Root dry weights were also affected with heavier roots from plants grown in sandy loam compared with silt loam and clay loam soils, however, shoot dry weight was greater in clay loam and sandy loam compared with silt loam soils. The results of the study confirmed that all propagule types were able to infect grapevine rootstocks when planted in inoculated soil and showed that although the pathogens were capable of infecting the rootstocks in all soil types, disease level was higher in the heavier clay loam soil. It is therefore recommended that growers either avoid planting in such soils or apply strategies to improve drainage and soil aeration
Solar Absorption in Cloudy Atmospheres
The theoretical computations used to compute spectral absorption of solar radiation are discussed. Radiative properties relevant to the cloud absorption problem are presented and placed in the context of radiative forcing. Implications for future measuring programs and the effect of horizontal inhomogeneities are discussed
High-Resolution Infrared Spectroscopy of the Brown Dwarf Epsilon Indi Ba
We report on the analysis of high-resolution infrared spectra of the newly
discovered brown dwarf Epsilon Indi Ba. This is the closest known brown dwarf
to the solar system, with a distance of 3.626 pc. Spectra covering the ranges
of 2.308-2.317 microns and 1.553-1.559 microns were observed at a spectral
resolution of R=50,000 with the Phoenix spectrometer on the Gemini South
telescope. The physical paramters of effective temperature and surface gravity
are derived by comparison to model spectra calculated from atmospheres computed
using unified cloudy models. An accurate projected rotational velocity is also
derived.Comment: 9 pages, 3 figures. Astrophysical Journal Letters, in pres
Perturbation theory for self-gravitating gauge fields I: The odd-parity sector
A gauge and coordinate invariant perturbation theory for self-gravitating
non-Abelian gauge fields is developed and used to analyze local uniqueness and
linear stability properties of non-Abelian equilibrium configurations. It is
shown that all admissible stationary odd-parity excitations of the static and
spherically symmetric Einstein-Yang-Mills soliton and black hole solutions have
total angular momentum number , and are characterized by
non-vanishing asymptotic flux integrals. Local uniqueness results with respect
to non-Abelian perturbations are also established for the Schwarzschild and the
Reissner-Nordstr\"om solutions, which, in addition, are shown to be linearly
stable under dynamical Einstein-Yang-Mills perturbations. Finally, unstable
modes with are also excluded for the static and spherically
symmetric non-Abelian solitons and black holes.Comment: 23 pages, revtex, no figure
Aldebaran's angular diameter: how well do we know it?
The bright, well-known K5 giant Aldebaran, alpha Tau, is probably the star
with the largest number of direct angular diameter determinations, achieved
over a long time by several authors using various techniques. In spite of this
wealth of data, or perhaps as a direct result of it, there is not a very good
agreement on a single angular diameter value. This is particularly unsettling
if one considers that Aldebaran is also used as a primary calibrator for some
angular resolution methods, notably for optical and infrared long baseline
interferometry. Directly connected to Aldebaran's angular diameter and its
uncertainties is its effective temperature, which also has been used for
several empirical calibrations. Among the proposed explanations for the
elusiveness of an accurate determination of the angular diameter of Aldebaran
are the possibility of temporal variations as well as a possible dependence of
the angular diameter on the wavelength. We present here a few, very accurate
new determinations obtained by means of lunar occultations and long baseline
interferometry. We derive an average value of 19.96+-0.03 milliarcseconds for
the uniform disk diameter. The corresponding limb-darkened value is 20.58+-0.03
milliarcseconds, or 44.2+-0.9 R(sun). We discuss this result, in connection
with previous determinations and with possible problems that may affect such
measurements.Comment: 8 pages, 4 figures, accepted for publication in A&
Ultrahigh-temperature microwave annealing of Alâș- and Pâș-implanted 4H-SiC
In this work, an ultrafast solid-state microwaveannealing has been performed, in the temperature range of 1700â2120°C on Alâș- and Pâș-implanted 4H-SiC. The solid-state microwave system used in this study is capable of raising the SiC sample temperatures to extremely high values, at heating rates of âŒ600°Câs. The samples were annealed for 5â60s in a pure nitrogen ambient. Atomic force microscopy performed on the annealed samples indicated a smooth surface with a rms roughness of 1.4nm for 5Ă5ÎŒmÂČ scans even for microwaveannealing at 2050°C for 30s. Auger sputter profiling revealed a <7nm thick surface layer composed primarily of silicon, oxygen, and nitrogen for the samples annealed in Nâ, at annealing temperatures up to 2100°C. X-ray photoelectron spectroscopy revealed that this surface layer is mainly composed of silicon oxide and silicon nitride. Secondary ion mass spectrometry depth profiling confirmed almost no dopant in diffusion after microwaveannealing at 2100°C for 15s. However, a sublimation of âŒ100nm of the surface SiC layer was observed for 15sannealing at 2100°C. Rutherford backscattering spectra revealed a lattice damage-free SiC material after microwaveannealing at 2050°C for 15s, with scattering yields near the virgin SiC material. Van der PauwâHall measurements have revealed sheet resistance values as low as 2.4kΩâ⥠for Alâș-implanted material annealed at 2100°C for 15s and 14Ωâ⥠for the P+-implanted material annealed at 1950°C for 30s. The highest electron and hole mobilities measured in this work were 100 and 6.8cm2/Vs, respectively, for the Pâș- and Alâș-implanted materials.The GMU work is supported by Army Research Of-
fice Dr. Prater under Grant No. W911NF-04-1-0428 and a
subcontract from LT Technologies under NSF SBIR Grant
No. 0539321
Resolving Vega and the inclination controversy with CHARA/MIRC
Optical and infrared interferometers definitively established that the
photometric standard Vega (alpha Lyrae) is a rapidly rotating star viewed
nearly pole-on. Recent independent spectroscopic analyses could not reconcile
the inferred inclination angle with the observed line profiles, preferring a
larger inclination. In order to resolve this controversy, we observed Vega
using the six-beam Michigan Infrared Combiner on the Center for High Angular
Resolution Astronomy Array. With our greater angular resolution and dense
(u,v)-coverage, we find Vega is rotating less rapidly and with a smaller
gravity darkening coefficient than previous interferometric results. Our models
are compatible with low photospheric macroturbulence and also consistent with
the possible rotational period of ~0.71 days recently reported based on
magnetic field observations. Our updated evolutionary analysis explicitly
incorporates rapid rotation, finding Vega to have a mass of 2.15+0.10_-0.15
Msun and an age 700-75+150 Myrs, substantially older than previous estimates
with errors dominated by lingering metallicity uncertainties
(Z=0.006+0.003-0.002).Comment: Accepted for publication in ApJ Letter
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