202 research outputs found
SS433's jet trace from ALMA imaging and Global Jet Watch spectroscopy: evidence for post-launch particle acceleration
We present a comparison of Doppler-shifted H-alpha line emission observed by
the Global Jet Watch from freshly-launched jet ejecta at the nucleus of the
Galactic microquasar SS433 with subsequent ALMA imaging at mm-wavelengths of
the same jet ejecta. There is a remarkable similarity between the
transversely-resolved synchrotron emission and the prediction of the jet trace
from optical spectroscopy: this is an a priori prediction not an a posteriori
fit, confirming the ballistic nature of the jet propagation. The mm-wavelength
of the ALMA polarimetry is sufficiently short that the Faraday rotation is
negligible and therefore that the observed E-vector directions are accurately
orthogonal to the projected local magnetic field. Close to the nucleus the
B-field vectors are perpendicular to the direction of propagation. Further out
from the nucleus, the B-field vectors that are coincident with the jet instead
become parallel to the ridge line; this occurs at a distance where the jet
bolides are expected to expand into one another. X-ray variability has also
been observed at this location; this has a natural explanation if shocks from
the expanding and colliding bolides cause particle acceleration. In regions
distinctly separate from the jet ridge line, the fractional polarisation
approaches the theoretical maximum for synchrotron emission.Comment: To appear in ApJ Letter
Classical Nova Carinae 2018: Discovery of circumbinary iron and oxygen
We present time-lapse spectroscopy of a classical nova explosion commencing 9
days after discovery. These data reveal the appearance of a transient feature
in Fe II and [O I]. We explore different models for this feature and conclude
that it is best explained by a circumbinary disc shock-heated following the
classical nova event. Circumbinary discs may play an important role in novae in
accounting for the absorption systems known as THEA, the transfer of angular
momentum, and the possible triggering of the nova event itself
GG Carinae: Discovery of orbital phase dependent 1.583-day periodicities in the B[e] supergiant binary
GG Carinae is a binary whose primary component is a B[e] supergiant. Using
photometric data from TESS, ASAS, OMC, and ASAS-SN, and spectroscopic data from
the Global Jet Watch to study visible He\,I, Fe\,II and Si\,II emission lines,
we investigate the short-period variations which are exhibited in GG Car. We
find a hitherto neglected periodicity of \,days that is
present in both its photometry and the radial velocities of its emission lines,
alongside variability at the well-established 31-day orbital period. We
find that the amplitudes of the shorter-period variations in both photometry
and some of the emission lines are modulated by the orbital phase of the
binary, such that the short-period variations have largest amplitudes when the
binary is at periastron. There are no significant changes in the phases of the
short-period variations over the orbital period. We investigate potential
causes of the 1.583-day variability, and find that the observed period agrees
well with the expected period of the f-mode of the primary given its mass
and radius. We propose that the primary is periodically pulled out of
hydrostatic equilibrium by the quadrupolar tidal forces when the components are
near periastron in the binary's eccentric orbit () and the primary
almost fills its Roche lobe. This causes an oscillation at the f-mode
frequency which is damped as the distance between the components increases.Comment: Accepted for publication in MNRAS. 14 pages, 14 figure
Molecular States of Electrons: Emission of Single Molecules in Self-Organized InP/GaInP Quantum Dots
Global Phase Diagram of nu = 2 Quantum Hall Bilayers in Tilted Magnetic Field
We consider a bilayer quantum Hall system at total filling fraction nu=2 in
tilted magnetic field allowing for charge imbalance as well as tunneling
between the two layers. Using an "unrestricted Hartree Fock," previously
discussed by Burkov and MacDonald (Phys Rev B 66 115323 2002), we examine the
zero temperature global phase diagrams that would be accessed experimentally by
changing the in-plane field and the bias voltage between the layers while
keeping the tunneling between the two layers fixed. In accordance with previous
work, we find symmetric and ferromagnetic phases as well as a first order
transition between two canted phases with spontaneously broken U(1) symmetry.
We find that these two canted phases are topologically connected in the phase
diagram and, reminiscent of a first order liquid-gas transition, the first
order transition line between these two phases ends in a quantum critical
point. We develop a physical picture of these two phases and describe in detail
the physics of the transition
Tracing the colliding winds of Carinae in He I
Carinae is an extremely luminous and energetic colliding-wind binary.
The combination of its orbit and orientation, with respect to our line of
sight, enables direct investigation of the conditions and geometry of the
colliding winds. We analyse optical He I 5876 and 7065 \unicode{x212B} line
profiles from the Global Jet Watch observatories covering the last 1.3 orbital
periods. The sustained coverage throughout apastron reveals the distinct
dynamics of the emitting versus absorbing components: the emission lines follow
orbital velocities whilst one of the absorption lines is detected only around
apastron () and exhibits velocities that deviate
substantially from the orbital motion. To interpret these deviations, we
conjecture that this He I absorption component is formed in the post-shock
primary wind, and is only detected when our line of sight intersects with the
shock cone formed by the collision of the two winds. We formulate a geometrical
model for the colliding winds in terms of a hyperboloid in which the opening
angle and location of its apex are parameterised in terms of the ratio of the
wind momentum of the primary star to that of companion. We fit this geometrical
model to the absorption velocities, finding results that are concordant with
the panchromatic observations and simulations of Carinae. The model
presented here is an extremely sensitive probe of the exact geometry of the
wind momentum balance of binary stars, and can be extended to probe the
latitudinal dependence of mass loss.Comment: 14 pages, 10 figures, accepted for publication in MNRA
Fast deep reinforcement learning using online adjustments from the past
We propose Ephemeral Value Adjusments (EVA): a means of allowing deep
reinforcement learning agents to rapidly adapt to experience in their replay
buffer. EVA shifts the value predicted by a neural network with an estimate of
the value function found by planning over experience tuples from the replay
buffer near the current state. EVA combines a number of recent ideas around
combining episodic memory-like structures into reinforcement learning agents:
slot-based storage, content-based retrieval, and memory-based planning. We show
that EVAis performant on a demonstration task and Atari games.Comment: Accepted at NIPS 201
Scientific Reification
In the Embodied Earth installation, part of the Art and Light Exhibition held 15-30 August 2015 in the HD Skinner Annex of the Otago Museum in Dunedin, the viewer sensorially experiences lightning strikes in synchronicity with actual terrestrial lightning events occurring over a large swathe of the Earth’s surface via a live data stream. Viewers face a large projection screen on which they can see themselves in silhouette. My design intends the viewer to don a haptic jacket and move freely, as a live data stream, translated into animated lightning flashes, tracks the viewer’s screen position, appearing to strike the wearer’s upper body. In association with with the visual cue, the viewer would feel a strong vibration at the point of apparent lightning contact, concurrent with a synchronised subwoofer signal that pulsates their body with a short burst of low-frequency sound
- …