19,776 research outputs found
A dynamical and kinematical model of the Galactic stellar halo and possible implications for galaxy formation scenarios
We re-analyse the kinematics of the system of blue horizontal branch field
(BHBF) stars in the Galactic halo (in particular the outer halo), fitting the
kinematics with the model of radial and tangential velocity dispersions in the
halo as a function of galactocentric distance r proposed by Sommer-Larsen,
Flynn & Christensen (1994), using a much larger sample (almost 700) of BHBF
stars. The basic result is that the character of the stellar halo velocity
ellipsoid changes markedly from radial anisotropy at the sun to tangential
anisotropy in the outer parts of the Galactic halo (r greater than approx 20
kpc). Specifically, the radial component of the stellar halo's velocity
ellipsoid decreases fairly rapidly beyond the solar circle, from approx 140 +/-
10 km/s at the sun, to an asymptotic value of 89 +/- 19 km/s at large r. The
rapid decrease in the radial velocity dispersion is matched by an increase in
the tangential velocity dispersion, with increasing r.
Our results may indicate that the Galaxy formed hierarchically (partly or
fully) through merging of smaller subsystems - the 'bottom-up' galaxy formation
scenario, which for quite a while has been favoured by most theorists and
recently also has been given some observational credibility by HST observations
of a potential group of small galaxies, at high redshift, possibly in the
process of merging to a larger galaxy (Pascarelle et al 1996).Comment: Latex, 16 pages. 2 postscript figures. Submitted to the Astrophysical
Journal. also available at http://astro.utu.fi/~cflynn/outerhalo.htm
Low-energy enhancement of magnetic dipole radiation
Magnetic dipole strength functions have been deduced from averages of a large
number of transition strengths calculated within the shell model for the
nuclides Zr, Mo, Mo, and Mo. An enhancement of
strength toward low transition energy has been found for all nuclides
considered. Large strengths appear for transitions between close-lying
states with configurations including proton as well as neutron high- orbits
that re-couple their spins and add up their magnetic moments coherently. The
strength function deduced from the calculated transition strengths is
compatible with the low-energy enhancement found in (He,He') and
experiments. The present work presents for the first time an
explanation of the experimental findings
Use of the VAD technique and measurements of momentum flux in the stratosphere at Aercibo, part 4.3A
The Arecibo 430-MHz radar was used in the velocity-azimuth display (VAD) mode to obtain radial velocity measurements at 16 azimuth directions from which the three-dimensional wind field and momentum flux can be calculated. The radar was operated on a nearly continuous basis for a seven-day period in May of 1982 and the elapsed time between start and finish of a VAD scan was approximately 35 minutes. Radial velocities were measured in the upper troposphere and lower stratosphere (6-24 km) with at height resolution of 150 meters at a zenith angle of 15 deg. Vertical and horizontal velocities are calculated from the sums and differences, respectively, of radial velocity pairs, i.e., at azimuth directions AZ and AZ + 180 degrees. Momentum flux at a particular azimuth is calculated by taking the difference between the square of radial velocities at AZ and AZ + 180 degrees. It should be noted that measurements of radial velocity pairs are not simultaneous but are time delayed by approximately 15-25 minutes. This period, the time required to rotate the antenna feed and take measurements at AZ and AZ + 180 deg, effectively limits sampling of velocities and momentum fluxes to longer period gravity waves and planetary waves
Computer and photogrammetric general land use study of central north Alabama
The object of this report is to acquaint potential users with two computer programs, developed at NASA, Marshall Space Flight Center. They were used in producing a land use survey and maps of central north Alabama from Earth Resources Technology Satellite (ERTS) digital data. The report describes in detail the thought processes and analysis procedures used from the initiation of the land use study to its completion, as well as a photogrammetric study that was used in conjunction with the computer analysis to produce similar land use maps. The results of the land use demonstration indicate that, with respect to computer time and cost, such a study may be economically and realistically feasible on a statewide basis
Investigation on the influence of nematophagous fungi as feed additive on nematode infection risk of sheep and goats on pasture
Gastrointestinal nematodes in small ruminants cause high economic losses. Thus on most farms anthelmintic treatment is required. In response to increasing problems with anthelmintic resistance, biological control, for example the use of nematophagous fungi, has received significant attention. The aim of this study was to investigate the effect of Duddingtonia flagrans orally applied to small ruminants on natural infection with gastrointestinal nematodes in a field study in Northern Germany.
20 goats and 20 sheep were fed daily for 3 months with 5x105 spores of D. flagrans per kg bodyweight. Differences in body weight, faecal egg count and larval development in faeces and on pasture in comparison with same-sized control groups were analysed. After 3 months the control goats showed significantly higher mean faecal egg count than the fungus-fed group. No significant difference was found between the two sheep groups. The maximum in larval reduction in faeces was 81.3 % in the sheep groups and 67.9 % in the goat groups (not significant). At the end of the study the body weight gain in the fungus-treated groups was 1.7 kg higher in goats and 0.7 kg higher in sheep than in the control groups (not significant). Regarding the first-year-grazing goats only, the bodyweights revealed significant differences (p<0.05). No statistically significant differences were observed in pasture larval counts.
In the study presented here, no clear effect of fungus could be observed. A modified feeding regimen, perhaps with permanent release boluses or feed blocks, may improve the efficacy. Furthermore, it seems that climatic conditions during the study period could have influenced the results and displayed how sensitive the fungus application may be on such parameters
Surveying the Inner Halo of the Galaxy with 2MASS-Selected Horizontal Branch Candidates
We use 2MASS photometry to select blue horizontal branch (BHB) candidates
covering the sky |b|>15 deg. A 12.5<J<15.5 sample of BHB stars traces the thick
disk and inner halo to d<9 kpc, with a density comparable to that of M giant
stars. We base our sample selection strategy on the Century Survey Galactic
Halo Project, a survey that provides a complete, spectroscopically-identified
sample of blue stars to a similar depth as the 2MASS catalog. We show that a
-0.20<(J-H)_0<0.10, -0.10<(H-K)_0<0.10 color-selected sample of stars is 65%
complete for BHB stars, and is composed of 47% BHB stars. We apply this
photometric selection to the full 2MASS catalog, and see no spatial
overdensities of BHB candidates at high Galactic latitude |b|>50 deg. We insert
simulated star streams into the data and conclude that the high Galactic
latitude BHB candidates are consistent with having no ~5 deg wide star stream
with density greater than 0.33 objects deg^-2 at the 95% confidence level. The
absence of structure suggests there have been no major accretion events in the
inner halo in the last few Gyr. However, at low Galactic latitudes a two-point
angular correlation analysis reveals structure on angular scales <1 deg. This
structure is apparently associated with stars in the thick disk, and has a
physical scale of 10-100 pc. Interestingly, such structures are expected by
cosmological simulations that predict the majority of the thick disk may arise
from accretion and disruption of satellite mergers.Comment: 11 pages, including figures. Accepted by AJ with minor revision
Faint Fuzzy Star Clusters in NGC1023 as Remnants of Merged Star Cluster Complexes
In the lenticular galaxy NGC1023 a third population of globular clusters
(GCs), called faint fuzzies (FFs), was discovered next to the blue and red GC
populations by Larsen & Brodie. While these FFs have colors comparable to the
red population, the new population is fainter, larger (R_eff > 7 pc) and, most
importantly, shows clear signs of co-rotation with the galactic disk of
NGC1023. We present N-body simulations verifying the hypothesis that these
disk-associated FFs are related to the young massive cluster complexes (CCs)
observed by Bastian et. al in M51, who discovered a mass-radius relation for
these CCs. Our models have an initial configuration based on the observations
from M51 and are placed on various orbits in a galactic potential derived for
NGC1023. All computations end up with a stable object containing 10 to 60% of
the initial CC mass after an integration time of 5 Gyr. A conversion to visual
magnitudes demonstrates that the resulting objects cover exactly the observed
range for FFs. Moreover, the simulated objects show projected half-mass radii
between 3.6 and 13.4 pc, in good agreement with the observed FF sizes. We
conclude that objects like the young massive CCs in M51 are likely progenitors
of the FFs observed in NGC1023.Comment: Accepted for publication in Ap
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