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

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