400 research outputs found
Polarization Profiles of Scattered Emission Lines. II. Upstream Dust Scattering in the HH 1 Jet
Detailed comparisons are made between observations of scattered light
upstream of the head of the HH~1 jet and predictions of simple scattering
models. It is shown that, in order to unambiguously determine the velocity of
the head of the jet (bow shock) with respect to the upstream dust, existing
spectroscopic observations are insufficient and that spectropolarimetric
observations of the scattered light are necessary. Such an independent measure
of the bow shock velocity is important in order to test ``multiple outflow''
theories of Herbig-Haro jets. It is also shown 2that the scattering dust must
have a very forward-throwing scattering phase function
(\langle\cos\theta\rangle\msim 0.7) and slight evidence is found for a
dust-gas ratio that is higher than average.Comment: 11 pages, uuencoded compressed postscript (including 9 figures),
accepted for publication in Ap.J., IAUNAM_contrib.#34
Evidence for polar jets as precursors of polar plume formation
Observations from the Hinode/XRT telescope and STEREO/SECCHI/EUVI are
utilized to study polar coronal jets and plumes. The study focuses on the
temporal evolution of both structures and their relationship. The data sample,
spanning April 7-8 2007, shows that over 90% of the 28 observed jet events are
associated with polar plumes. EUV images (STEREO/SECCHI) show plume haze rising
from the location of approximately 70% of the polar X-ray (Hinode/XRT) and EUV
jets, with the plume haze appearing minutes to hours after the jet was
observed. The remaining jets occurred in areas where plume material previously
existed causing a brightness enhancement of the latter after the jet event.
Short-lived, jet-like events and small transient bright points are seen (one at
a time) at different locations within the base of pre-existing long-lived
plumes. X-ray images also show instances (at least two events) of
collimated-thin jets rapidly evolving into significantly wider plume-like
structures that are followed by the delayed appearance of plume haze in the
EUV. These observations provide evidence that X-ray jets are precursors of
polar plumes, and in some cases cause brightenings of plumes. Possible
mechanisms to explain the observed jet and plume relationship are discussed.Comment: 10 pages, 4 figures, accepted as APJ Lette
Seething Horizontal Magnetic Fields in the Quiet Solar Photosphere
The photospheric magnetic field outside of active regions and the network has
a ubiquitous and dynamic line-of-sight component that strengthens from disk
center to limb as expected for a nearly horizontal orientation. This component
shows a striking time variation with an average temporal rms near the limb of
1.7 G at ~3" resolution. In our moderate resolution observations the nearly
horizontal component has a frequency variation power law exponent of -1.4 below
1.5 mHz and is spatially patchy on scales up to ~15 arcsec. The field may be a
manifestation of changing magnetic connections between eruptions and evolution
of small magnetic flux elements in response to convective motions. It shows no
detectable latitude or longitude variations.Comment: 7 pages, 6 figures, submitted to ApJ letters, quality of figures
significantly degraded here by compression requirement
A Keck High Resolution Spectroscopic Study of the Orion Nebula Proplyds
We present the results of spectroscopy of four bright proplyds in the Orion
Nebula obtained at a velocity resolution of 6 km/s. After careful isolation of
the proplyd spectra from the confusing nebular radiation, the emission line
profiles are compared with those predicted by realistic dynamic/photoionization
models of the objects. The spectral line widths show a clear correlation with
ionization potential, which is consistent with the free expansion of a
transonic, ionization-stratified, photoevaporating flow. Fitting models of such
a flow simultaneously to our spectra and HST emission line imaging provides
direct measurements of the proplyd size, ionized density and outflow velocity.
These measurements confirm that the ionization front in the proplyds is
approximately D-critical and provide the most accurate and robust estimate to
date of the proplyd mass loss rate. Values of 0.7E-6 to 1.5E-6 Msun/year are
found for our spectroscopic sample, although extrapolating our results to a
larger sample of proplyds implies that 0.4E-6 Msun/year is more typical of the
proplyds as a whole. In view of the reported limits on the masses of the
circumstellar disks within the proplyds, the length of time that they can have
been exposed to ionizing radiation should not greatly exceed 10,000 years - a
factor of 30 less than the mean age of the proplyd stars. We review the various
mechanisms that have been proposed to explain this situation, and conclude that
none can plausibly work unless the disk masses are revised upwards by a
substantial amount.Comment: 23 pages, 8 figures, uses emulateapj.sty, accepted for publication in
The Astronomical Journal (scheduled November 1999
Video Relay Service for Deaf people using WebRTC
This paper reports on an experimental open
source video relay service prototype that helps Deaf people
communicate with hearing people by accessing a third party
sign language interpreter on a mobile device. Deaf people are
disadvantaged in many ways when communicating with the
hearing world in real world scenarios, such as hospital visits
and in cases of emergency. When possible, Deaf people can
enlist the assistance of a family member, community worker or
sign language interpreter to assist with such scenarios, however
this assistance is pre-arranged and Deaf people would prefer
on-the-fly assistance. Our application will assist Deaf people to
contact any available sign language interpreter to facilitate
communication between the Deaf person and a hearing person
using a split screen model, effectively creating a three-way
conversation between the Deaf person, the hearing person and
the sign language interpreter. The prototype was developed
using the WebRTC platform, with JavaScript for browser
operability and hardware platform independence. Our hope is
that the research can be used to persuade mobile network
operators of the need for free or heavily discounted data
connection to relay services for Deaf mobile customers
Thiel Embalming:Quantifying histological changes in skeletal muscle and tendon and investigating the role of boric acid
Estimating Electric Fields from Vector Magnetogram Sequences
Determining the electric field (E-field) distribution on the Sun's
photosphere is essential for quantitative studies of how energy flows from the
Sun's photosphere, through the corona, and into the heliosphere. This E-field
also provides valuable input for data-driven models of the solar atmosphere and
the Sun-Earth system. We show how Faraday's Law can be used with observed
vector magnetogram time series to estimate the photospheric E-field, an
ill-posed inversion problem. Our method uses a "poloidal-toroidal
decomposition" (PTD) of the time derivative of the vector magnetic field. The
PTD solutions are not unique; the gradient of a scalar potential can be added
to the PTD E-field without affecting consistency with Faraday's Law. We present
an iterative technique to determine a potential function consistent with ideal
MHD evolution; but this E-field is also not a unique solution to Faraday's Law.
Finally, we explore a variational approach that minimizes an energy functional
to determine a unique E-field, similar to Longcope's "Minimum Energy Fit". The
PTD technique, the iterative technique, and the variational technique are used
to estimate E-fields from a pair of synthetic vector magnetograms taken from an
MHD simulation; and these E-fields are compared with the simulation's known
electric fields. These three techniques are then applied to a pair of vector
magnetograms of solar active region NOAA AR8210, to demonstrate the methods
with real data.Comment: 41 pages, 10 figure
Can Protostellar Jets Drive Supersonic Turbulence in Molecular Clouds?
Jets and outflows from young stellar objects are proposed candidates to drive
supersonic turbulence in molecular clouds. Here, we present the results from
multi-dimensional jet simulations where we investigate in detail the energy and
momentum deposition from jets into their surrounding environment and quantify
the character of the excited turbulence with velocity probability density
functions. Our study include jet--clump interaction, transient jets, and
magnetised jets. We find that collimated supersonic jets do not excite
supersonic motions far from the vicinity of the jet. Supersonic fluctuations
are damped quickly and do not spread into the parent cloud. Instead subsonic,
non-compressional modes occupy most of the excited volume. This is a generic
feature which can not be fully circumvented by overdense jets or magnetic
fields. Nevertheless, jets are able to leave strong imprints in their cloud
structure and can disrupt dense clumps. Our results question the ability of
collimated jets to sustain supersonic turbulence in molecular clouds.Comment: 33 pages, 18 figures, accepted by ApJ, version with high resolution
figures at:
http://www.ita.uni-heidelberg.de/~banerjee/publications/jet_paper.pd
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