9,829 research outputs found
Microwave soil moisture measurements and analysis
An effort to develop a model that simulates the distribution of water content and of temperature in bare soil is documented. The field experimental set up designed to acquire the data to test this model is described. The microwave signature acquisition system (MSAS) field measurements acquired in Colby, Kansas during the summer of 1978 are pesented
Star Formation Histories of Nearby Elliptical Galaxies. II. Merger Remnant Sample
This work presents high spectroscopic observations of a sample of six
suspected merger remnants, selected primarily on the basis of H{\sc i} tidal
debris detections. Single stellar population analysis of these galaxies
indicates that their ages, metallicities, and -enhancement ratios are
consistent with those of a representative sample of nearby elliptical galaxies.
The expected stellar population of a recent merger remnant, young age combined
with low [/Fe], is not seen in any H{\sc i}-selected galaxy. However,
one galaxy (NGC~2534), is found to deviate from the -plane in the sense
expected for a merger remnant. Another galaxy (NGC~7332), selected by other
criteria, best matches the merger remnant expectations.Comment: 12 pages, 10 figures, accepted by A
The AKARI 2.5-5 Micron Spectra of Luminous Infrared Galaxies in the Local Universe
We present AKARI 2.5-5um spectra of 145 local luminous infrared galaxies in
the Great Observatories All-sky LIRG Survey. In all of the spectra, we measure
the line fluxes and EQWs of the polycyclic aromatic hydrocarbon (PAH) at 3.3um
and the hydrogen recombination line Br-alpha, with apertures matched to the
slit sizes of the Spitzer spectrograph and with an aperture covering ~95% of
the total flux in the AKARI 2D spectra. The star formation rates (SFRs) derived
from Br-alpha measured in the latter aperture agree well with SFRs(LIR), when
the dust extinction correction is adopted based on the 9.7um absorption
feature. Together with the Spitzer spectra, we are able to compare the 3.3 and
6.2um PAH features, the two most commonly used near/mid-IR indicators of
starburst (SB) or active galactic nucleus (AGN) dominated galaxies. We find
that the 3.3 and 6.2um PAH EQWs do not follow a linear correlation and at least
1/3 of galaxies classified as AGN-dominated using 3.3um PAH are classified as
starbursts based on 6.2um PAH. These galaxies have a bluer continuum slope than
galaxies that are indicated to be SB-dominated by both PAH features. The bluer
continuum emission suggests that their continuum is dominated by stellar
emission rather than hot dust. We also find that the median Spitzer spectra of
these sources are remarkably similar to the pure SB-dominated sources indicated
by high PAH EQWs in both 3.3 and 6.2um. We propose a revised SB/AGN diagnostic
diagram using 2-5um data. We also use the AKARI and Spitzer spectra to examine
the performance of our new diagnostics and to estimate 3.3um PAH fluxes using
the JWST photometric bands in 0<z<5. Of the known PAH features and mid-IR high
ionization emission lines used as SB/AGN indicators, only the 3.3um PAH feature
is observable with JWST at z>3.5, because the rest of the features at longer
wavelengths fall outside the JWST wavelength coverage.Comment: 13 pages (without appendices), 12 figures, Accepted for publication
in A&
Radiation-Hydrodynamic Simulations of Collapse and Fragmentation in Massive Protostellar Cores
We simulate the early stages of the evolution of turbulent, virialized,
high-mass protostellar cores, with primary attention to how cores fragment, and
whether they form a small or large number of protostars. Our simulations use
the Orion adaptive mesh refinement code to follow the collapse from ~0.1 pc
scales to ~10 AU scales, for durations that cover the main fragmentation phase,
using three-dimensional gravito-radiation hydrodynamics. We find that for a
wide range of initial conditions radiation feedback from accreting protostars
inhibits the formation of fragments, so that the vast majority of the collapsed
mass accretes onto one or a few objects. Most of the fragmentation that does
occur takes place in massive, self-shielding disks. These are driven to
gravitational instability by rapid accretion, producing rapid mass and angular
momentum transport that allows most of the gas to accrete onto the central star
rather than forming fragments. In contrast, a control run using the same
initial conditions but an isothermal equation of state produces much more
fragmentation, both in and out of the disk. We conclude that massive cores with
observed properties are not likely to fragment into many stars, so that, at
least at high masses, the core mass function probably determines the stellar
initial mass function. Our results also demonstrate that simulations of massive
star forming regions that do not include radiative transfer, and instead rely
on a barotropic equation of state or optically thin heating and cooling curves,
are likely to produce misleading results.Comment: 23 pages, 18 figures, emulateapj format. Accepted to ApJ. This
version has minor typo fixes and small additions, no significant changes.
Resolution of images severely degraded to fit within size limit. Download the
full paper from http://www.astro.princeton.edu/~krumholz/recent.htm
Creep motion in a granular pile exhibiting steady surface flow
We investigate experimentally granular piles exhibiting steady surface flow.
Below the surface flow, it has been believed exisitence of a `frozen' bulk
region, but our results show absence of such a frozen bulk. We report here that
even the particles in deep layers in the bulk exhibit very slow flow and that
such motion can be detected at an arbitrary depth. The mean velocity of the
creep motion decays exponentially with depth, and the characteristic decay
length is approximately equal to the particle-size and independent of the flow
rate. It is expected that the creep motion we have seeen is observable in all
sheared granular systems.Comment: 3 pages, 4 figure
EPIC 219217635: A Doubly Eclipsing Quadruple System Containing an Evolved Binary
We have discovered a doubly eclipsing, bound, quadruple star system in the
field of K2 Campaign 7. EPIC 219217635 is a stellar image with that
contains an eclipsing binary (`EB') with d and a second EB with
d. We have obtained followup radial-velocity (`RV')
spectroscopy observations, adaptive optics imaging, as well as ground-based
photometric observations. From our analysis of all the observations, we derive
good estimates for a number of the system parameters. We conclude that (1) both
binaries are bound in a quadruple star system; (2) a linear trend to the RV
curve of binary A is found over a 2-year interval, corresponding to an
acceleration, cm s; (3) small
irregular variations are seen in the eclipse-timing variations (`ETVs')
detected over the same interval; (4) the orbital separation of the quadruple
system is probably in the range of 8-25 AU; and (5) the orbital planes of the
two binaries must be inclined with respect to each other by at least
25. In addition, we find that binary B is evolved, and the cooler and
currently less massive star has transferred much of its envelope to the
currently more massive star. We have also demonstrated that the system is
sufficiently bright that the eclipses can be followed using small ground-based
telescopes, and that this system may be profitably studied over the next decade
when the outer orbit of the quadruple is expected to manifest itself in the ETV
and/or RV curves.Comment: Accepted for publication in MNRA
Beam Profile Measurements and Simulations of the PETRA Laser-Wire
The Laser-wire will be an essential diagnostic tool at the International
Linear Collider. It uses a finely focussed laser beam to measure the transverse
profile of electron bunches by detecting the Compton-scattered photons (or
degraded electrons) downstream of where the laser beam intersects the electron
beam. Such a system has been installed at the PETRA storage ring at DESY, which
uses a piezo-driven mirror to scan the laser-light across the electron beam.
Lat- est results of experimental data taking are presented and compared to
detailed simulations using the Geant4 based program BDSIM.Comment: 3 pagesm 4 figures. Submitted as a conference paper for the Particle
Accelerator Conference 2005 (PAC05
Neutron-proton analyzing power at 12 MeV and inconsistencies in parametrizations of nucleon-nucleon data
We present the most accurate and complete data set for the analyzing power
Ay(theta) in neutron-proton scattering. The experimental data were corrected
for the effects of multiple scattering, both in the center detector and in the
neutron detectors. The final data at En = 12.0 MeV deviate considerably from
the predictions of nucleon-nucleon phase-shift analyses and potential models.
The impact of the new data on the value of the charged pion-nucleon coupling
constant is discussed in a model study.Comment: Six pages, four figures, one table, to be published in Physics
Letters
Massive Star Cluster Formation and Destruction in Luminous Infrared Galaxies in GOALS
We present the results of a {\it Hubble Space Telescope} ACS/HRC FUV, ACS/WFC
optical study into the cluster populations of a sample of 22 Luminous Infrared
Galaxies in the Great Observatories All-Sky LIRG Survey. Through integrated
broadband photometry we have derived ages and masses for a total of 484 star
clusters contained within these systems. This allows us to examine the
properties of star clusters found in the extreme environments of LIRGs relative
to lower luminosity star-forming galaxies in the local Universe. We find that
by adopting a Bruzual \& Charlot simple stellar population (SSP) model and
Salpeter initial mass function, the age distribution of clusters declines as
, consistent with the age distribution derived
for the Antennae Galaxies, and interpreted as evidence for rapid cluster
disruption occuring in the strong tidal fields of merging galaxies. The large
number of young clusters identified in the sample also
suggests that LIRGs are capable of producing more high-mass clusters than what
is observed to date in any lower luminosity star-forming galaxy in the local
Universe. The observed cluster mass distribution of is consistent with the canonical -2 power law used to describe the
underlying initial cluster mass function (ICMF) for a wide range of galactic
environments. We interpret this as evidence against mass-dependent cluster
disruption, which would flatten the observed CMF relative to the underlying
ICMF distribution.Comment: 63 pages, 58 Figures, 56 Tables, Accepted for publication in Ap
- …