481 research outputs found
Light Elements and Cosmic Rays in the Early Galaxy
We derive constraints on the cosmic rays responsible for the Be and part of
the B observed in stars formed in the early Galaxy: the cosmic rays cannot be
accelerated from the ISM; their energy spectrum must be relatively hard (the
bulk of the nuclear reactions should occur at 30 MeV/nucl); and only
10 erg/SNII in high metallicity, accelerated particle kinetic energy
could suffice to produce the Be and B. The reverse SNII shock could accelerate
the particles.Comment: 5 pages LATEX using paspconf.sty file with one embedded eps figure
using psfig. In press, Proc. Goddard High Resolution Spectrograph Symposium,
PASP, 199
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Precision Fe Kalpha and Fe Kbeta Line Spectroscopy of the Seyfert 1.9 Galaxy NGC 2992 with Suzaku
We present detailed time-averaged X-ray spectroscopy in the 0.5--10 keV band
of the Seyfert~1.9 galaxy NGC 2992 with the Suzaku X-ray Imaging Spectrometers
(XIS). We model the complex continuum in detail. There is an Fe K line emission
complex that we model with broad and narrow lines and we show that the
intensities of the two components are decoupled at a confidence level >3sigma.
The broad Fe K line has an EW of 118 (+32,-61) eV and could originate in an
accretion disk (with inclination angle greater than ~30 degrees). The narrow Fe
Kalpha line has an EW of 163 (+47,-26) eV and is unresolved FWHM <4090 km/s)
and likely originates in distant matter. The absolute flux in the narrow line
implies that the column density out of the line-of-sight could be much higher
than measured in the line-of-sight, and that the mean (historically-averaged)
continuum luminosity responsible for forming the line could be a factor of
several higher than that measured from the data. We also detect the narrow Fe
Kbeta line with a high signal-to-noise ratio and describe a new robust method
to constrain the ionization state of Fe responsible for the Fe Kalpha and Fe
Kbeta lines that does not require any knowledge of possible gravitational and
Doppler energy shifts affecting the line energies. For the distant
line-emitting matter (e.g. the putative obscuring torus) we deduce that the
predominant ionization state is lower than Fe VIII (at 99% confidence),
conservatively taking into account residual calibration uncertainties in the
XIS energy scale and theoretical and experimental uncertainties in the Fe K
fluorescent line energies. From the limits on a possible Compton-reflection
continuum it is likely that the narrow Fe Kalpha and Fe Kbeta lines originate
in a Compton-thin structure.Comment: Abstract is abridged. Accepted for publication in the Suzaku special
issue of PASJ (November 2006). 18 pages, 6 figure
A survey of weather information possessed by thirty-two pupils randomly selected from sixth and eleventh grades and from special classes
Thesis (Ed.M.)--Boston Universit
Factors influencing the hooking mortality of walleyes caught by recreational anglers on Mille Lacs,
Abstract.-Recent implementation of size-based regulations in recreational fisheries for walleye Sander vitreus have led to more released walleyes and presumably to more losses of released fish. We conducted this study to estimate hooking mortality in Mille Lacs, Minnesota, and to determine factors that influence the survival of released walleyes. Volunteers and Minnesota Department of Natural Resources employees sampled walleyes with common angling methods in 2003 and 2004 on Mille Lacs (n ¼ 1,246). Simple hooking mortality rates ranged from 0% (95% confidence interval ¼ 0-1.8%; n ¼ 204) in May, when lake water temperatures were less than 208C, to 12.2% (9.2-15.9%; n ¼ 392) in the July-August period, when lake water temperatures were at least 208C. We used logistic regression within generalized linear or additive models to determine influential variables. Hooking mortality was most associated with water temperature, bleeding, fish length, hook location, and fish floating upon release. Mortality increased as the water warmed above 188C and was higher for fish that bled at temperatures less than 248C but similar for both bleeding and nonbleeding fishes at temperatures of 248C or more. Fish hooked in the throat or stomach died at higher rates than fish hooked in the jaw, inner mouth, or gills and those that were externally foul-hooked, especially when they were smaller. Although fish of medium length (300-600 mm) were more likely to be deep hooked, they died less frequently than walleyes of other lengths. Cutting the line did not significantly improve survival in deeply hooked fish. Mortality was similar between live bait jigs and live bait regular hooks. Most observed hooking mortality was caused by damage to major internal organs. Hooking mortality is minimized when anglers fish in cool water, use active fishing methods, and catch medium-length walleyes
Oxygen ion dynamics in the Earth's ring current: Van Allen probes observations
Oxygen (O+) enhancements in the inner magnetosphere are often observed during geomagnetically active times, such as geomagnetic storms. In this study, we quantitatively examine the difference in ring current dynamics with and without a substantial O+ ion population based on almost 6 years of Van Allen Probes observations. Our results have not only confirmed previous finding of the role of O+ ions to the ring current but also found that abundant O+ ions are always present during large storms when sym-H < -60 nT without exception, whilst having the pressure ratio () between O+ and proton (H+) larger than 0.8 and occasionally even larger than 1 when L < 3. Simultaneously, the pressure anisotropy decreases with decreasing sym-H and increasing L shell. The pressure anisotropy decrease during the storm main phase is likely related to the pitch angle isotropization processes. In addition, we find that increases during the storm main phase and then decreases during the storm recovery phase, suggesting faster buildup and decay of O+ pressure compared to H+ ions, which are probably associated with some species dependent source and/or energization as well as loss processes in the inner magnetosphere.Accepted manuscrip
Study of EMIC wave excitation using direct ion measurements
With data from Van Allen Probes, we investigate electromagnetic ion cyclotron (EMIC) wave excitation using simultaneously observed ion distributions. Strong He band waves occurred while the spacecraft was moving through an enhanced density region. We extract from helium, oxygen, proton, and electron mass spectrometer measurement the velocity distributions of warm heavy ions as well as anisotropic energetic protons that drive wave growth through the ion cyclotron instability. Fitting the measured ion fluxes to multiple sinm-type distribution functions, we find that the observed ions make up about 15% of the total ions, but about 85% of them are still missing. By making legitimate estimates of the unseen cold (below ∼2 eV) ion composition from cutoff frequencies suggested by the observed wave spectrum, a series of linear instability analyses and hybrid simulations are carried out. The simulated waves generally vary as predicted by linear theory. They are more sensitive to the cold O+ concentration than the cold He+ concentration. Increasing the cold O+ concentration weakens the He band waves but enhances the O band waves. Finally, the exact cold ion composition is suggested to be in a range when the simulated wave spectrum best matches the observed one
Suzaku wide-band X-ray Spectroscopy of the Seyfert 2 AGN in NGC 4945
Suzaku observed a nearby Seyfert 2 galaxy NGC4945, which hosts one of the
brightest active galactic nuclei above 20 keV. Combining data from the X-ray
CCD camera (XIS) and the Hard X-ray Detector (HXD), the AGN intrinsic nuclear
emission and its reprocessed signals were observed simultaneously. The
intrinsic emission is highly obscured with an absorbing column of cm, and was detectable only above keV. The
spectrum below 10 keV is dominated by reflection continuum and emission lines
from neutral/ionized material. Along with a neutral iron K line, a
neutral iron K and a neutral nickel K line were detected for the
first time from this source. The neutral lines and the cold reflection
continuum are consistent with both originating in the same location. The
Compton down-scattered shoulder in the neutral Fe-K line is
in flux of the narrow core, which confirms that the line originates from
reflection rather than transmission. The weakness of the Compton shoulder also
indicates that the reflector is probably seen nearly edge-on. Flux of the
intrinsic emission varied by a factor of within ks, which
requires the obscuring material to be geometrically thin. Broadband spectral
modeling showed that the solid angle of the neutral reflector is less than a
few . All this evidence regarding the reprocessed
signals suggests that a disk-like absorber/reflector is viewed from a near
edge-on angle.Comment: 11 pages, 11 figure
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