1,569 research outputs found
Magnetometer Surveys: Attempts and Issues in Locating a 1948 Private Water Well on the Shore of Lac Sault Dore, Price County, Wisconsin
Two different magnetometer surveys in northern Wisconsin during the summers of 1997 and 2010, using two different Geometrics magnetometers, a proton precession G-816 unit and a cesium vapor G-858 unit, in an attempt to locate a surface-target position of, and depth to, an abandoned 1948 private water well, successfully targeted the suspect surface position and the depth to the well head spike. Both surveys detected 400-gamma anomalies and estimated the depth to the spike at 2 meters. A land owner, private family photograph taken in 1951, was used to compare the anomaly’s position to the actual surface position of the well. Two, one meter deep pits were hand dug in 2004, in an attempt to excavate, remove and replace the well spike; however, the attempt was not successful due to large trees, roots, and available equipment. For aesthetic reasons, the land owners were reluctant to cut the trees down at that time in order to continue excavation. After the 2010, magnetometer survey, a second excavation attempt was not made, and no future excavation attempts are planned at this time
Coronal X-ray emission from an intermediate-age brown dwarf
We report the X-ray detection of the brown dwarf (BD) companion TWA 5B in a
Myr old pre-main sequence binary system. We clearly resolve the
faint companion (35 photons) separated from the X-ray luminous primary by 2
arcsec in a {\it Chandra} ACIS image. TWA 5B shows a soft X-ray spectrum with a
low plasma temperature of only 0.3 keV and a constant flux during the 3 hour
observation, of which the characteristics are commonly seen in the solar
corona. The X-ray luminosity is 4 erg s (0.1--10 keV
band) or .
Comparing these properties to both younger and older BDs, we discuss the
evolution of the X-ray emission in BDs. During their first few Myr, they
exhibit high levels of X-ray activity as seen in higher mass pre-main sequence
stars. The level in TWA 5B is still high at Myr in while has already substantially cooled
Quiescent X-ray emission from an evolved brown dwarf ?
I report on the X-ray detection of Gl569Bab. During a 25ksec Chandra
observation the binary brown dwarf is for the first time spatially separated in
X-rays from the flare star primary Gl569A. Companionship to Gl569A constrains
the age of the brown dwarf pair to ~300-800 Myr. The observation presented here
is only the second X-ray detection of an evolved brown dwarf. About half of the
observing time is dominated by a large flare on Gl569Bab, the remainder is
characterized by weak and non-variable emission just above the detection limit.
This emission -- if not related to the afterglow of the flare -- represents the
first detection of a quiescent corona on a brown dwarf, representing an
important piece in the puzzle of dynamos in the sub-stellar regime.Comment: to appear in ApJ
A Chandra Observation of a TW Hydrae Association Brown Dwarf
We present Chandra observations of the young brown dwarf 2MASSW
J1207334-393254, which is a probable member of the TW Hya association. Although
this substellar object has strong H alpha emission, it has no detected X Ray
flux in a fifty kilosecond ACIS-S observation. We place a conservative upper
limit of 1.2 x 10^{26} erg/sec on its X-ray luminosity. We compare our M8
target to the similar mass object TWA 5B, which has weaker H alpha emission but
strong X-ray emission. We argue our results are consistent with the notion that
2MASSW J1207334-393254 is interacting with a disk.Comment: ApJ Letter, in pres
A Search for Radio Emission at the Bottom of the Main Sequence and Beyond
We have used the VLA to conduct a deep search for 3.6 cm radio emission from
nearby very low mass stars and brown dwarfs. The Gudel-Benz relation is used to
predict radio luminosities for some very low mass stars and candidate brown
dwarfs with measured X-ray fluxes. The predicted radio fluxes are quite small,
whereas the measured radio flux from the brown dwarf candidate Rho Oph GY 31 is
relatively strong. In light of our new observations, this object remains an
anomaly. We present upper limits for our measured radio fluxes at 3.6 cm for
our targets.Comment: 10 pages, no figures. Accepted for publication in A
First optical images of circumstellar dust surrounding the debris disk candidate HD 32297
Near-infrared imaging with the Hubble Space Telescope recently revealed a
circumstellar dust disk around the A star HD 32297. Dust scattered light is
detected as far as 400 AU radius and the linear morphology is consistent with a
disk ~10 degrees away from an edge-on orientation. Here we present the first
optical images that show the dust scattered light morphology from 560 to 1680
AU radius. The position angle of the putative disk midplane diverges by 31
degrees and the color of dust scattering is most likely blue. We associate HD
32297 with a wall of interstellar gas and the enigmatic region south of the
Taurus molecular cloud. We propose that the extreme asymmetries and blue disk
color originate from a collision with a clump of interstellar material as HD
32297 moves southward, and discuss evidence consistent with an age of 30 Myr or
younger.Comment: 5 pages; Accepted for publication in ApJ Letter
Spontaneous charge carrier localization in extended one-dimensional systems
Charge carrier localization in extended atomic systems has been described
previously as being driven by disorder, point defects or distortions of the
ionic lattice. Here we show for the first time by means of first-principles
computations that charge carriers can spontaneously localize due to a purely
electronic effect in otherwise perfectly ordered structures. Optimally-tuned
range-separated density functional theory and many-body perturbation
calculations within the GW approximation reveal that in trans-polyacetylene and
polythiophene the hole density localizes on a length scale of several
nanometers. This is due to exchange-induced translational symmetry breaking of
the charge density. Ionization potentials, optical absorption peaks, excitonic
binding energies and the optimally-tuned range parameter itself all become
independent of polymer length as it exceeds the critical localization scale.
Moreover, lattice disorder and the formation of a polaron result from the
charge localization in contrast to the traditional view that lattice
distortions precede charge localization. Our results can explain experimental
findings that polarons in conjugated polymers form instantaneously after
exposure to ultrafast light pulses.Comment: 5 pages, 4 figure
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