151 research outputs found
Late-Time Photometry of Type Ia Supernova SN 2012cg Reveals the Radioactive Decay of Co
Seitenzahl et al. (2009) have predicted that roughly three years after its
explosion, the light we receive from a Type Ia supernova (SN Ia) will come
mostly from reprocessing of electrons and X-rays emitted by the radioactive
decay chain , instead of positrons from the
decay chain that dominates the SN light at
earlier times. Using the {\it Hubble Space Telescope}, we followed the light
curve of the SN Ia SN 2012cg out to days after maximum light. Our
measurements are consistent with the light curves predicted by the contribution
of energy from the reprocessing of electrons and X-rays emitted by the decay of
Co, offering evidence that Co is produced in SN Ia explosions.
However, the data are also consistent with a light echo mag fainter
than SN 2012cg at peak. Assuming no light-echo contamination, the mass ratio of
Ni and Ni produced by the explosion, a strong constraint on any
SN Ia explosion model, is , roughly twice Solar. In
the context of current explosion models, this value favors a progenitor white
dwarf with a mass near the Chandrasekhar limit.Comment: Updated to reflect the final version published by ApJ. For a video
about the paper, see https://youtu.be/t3pUbZe8wq
Exotic Axions
We show that axion phenomenology may be significantly different than
conventionally assumed in theories which exhibit late phase transitions (below
the QCD scale). In such theories one can find multiple pseudoscalars with
axion-like couplings to matter, including a string scale axion, whose decay
constant far exceeds the conventional cosmological bound. Such theories have
several dark matter candidates.Comment: 5 pages, 1 figure, References adde
Erupting Dwarf Novae in the Large Magellanic Cloud
We report the first likely detections of erupting Dwarf Novae (DN) in an
external galaxy: the Large Magellanic Cloud. Six candidates were isolated from
approximately a million stars observed every second night over 11 nights with
the CTIO 8K x 8K Mosaic2 CCD imager. Artificial dwarf nova and completeness
tests suggest that we are seeing only the brightest of the LMC DN, probably SS
Cygni-like CVs, but possibly SU UMa-type cataclysmics undergoing
superoutbursts. We derive crude but useful limits on the LMC DN surface
density, and on the number of DN in the LMC. Many thousands of cataclysmic
variables in the Magellanic Clouds can be discovered and characterized with 8
meter class telescopes.Comment: Accepted for publication in AJ, 28 pages, 9 figures total, Figures 1
and 8 are supplied separately in jpeg forma
Entanglement and the Thermodynamic Arrow of Time
We discuss quantum entanglement in the context of the thermodynamic arrow of
time. We review the role of correlations in entropy-decreasing events and prove
that the occurrence of a transformation between two thermodynamic states
constitutes a new type of entanglement witness, one not defined as a separating
plane in state space between separable and entangled states, but as a physical
process dependent on the local initial properties of the states. Extending work
by Partovi, we consider a general entangled multipartite system that allows
large reversals of the thermodynamic arrow of time. We describe a hierarchy of
arrows that arises from the different correlations allowed in a quantum state
and examine these features in the context of Maxwell's Demon. We examine in
detail the case of three qubits, and also propose some simple experimental
demonstrations possible with small numbers of qubits.Comment: 10 pages with 9 figure
Environment as a Witness: Selective Proliferation of Information and Emergence of Objectivity in a Quantum Universe
We study the role of the information deposited in the environment of an open
quantum system in course of the decoherence process. Redundant spreading of
information -- the fact that some observables of the system can be
independently ``read-off'' from many distinct fragments of the environment --
is investigated as the key to effective objectivity, the essential ingredient
of ``classical reality''. This focus on the environment as a communication
channel through which observers learn about physical systems underscores
importance of quantum Darwinism -- selective proliferation of information about
``the fittest states'' chosen by the dynamics of decoherence at the expense of
their superpositions -- as redundancy imposes the existence of preferred
observables. We demonstrate that the only observables that can leave multiple
imprints in the environment are the familiar pointer observables singled out by
environment-induced superselection (einselection) for their predictability.
Many independent observers monitoring the environment will therefore agree on
properties of the system as they can only learn about preferred observables. In
this operational sense, the selective spreading of information leads to
appearance of an objective ``classical reality'' from within quantum substrate.Comment: New figures, to appear in PR
Erupting Cataclysmic Variable Stars in the Nearest Globular Cluster, NGC 6397: Intermediate Polars?
NGC 6397 is the closest globular cluster, and hence the ideal place to search
for faint stellar populations such as cataclysmic variables (CVs). HST and
Chandra observers have identified nine certain and likely CVs in this nearby
cluster, including several magnetic CV candidates. We have combined our recent
UV imagery with archival HST images of NGC 6397 to search for new CV candidates
and especially to look for dwarf nova-like eruptive events. We find remarkable
and somewhat unexpected dwarf nova-like eruptions of the two well-known
cataclysmic systems CV2 and CV3. These two objects have been claimed to be {\it
magnetic} CVs, as indicated by their helium emission-line spectra. Magnetic
fields in CVs are usually expected to prevent the disk instability that leads
to dwarf nova eruptions. In fact, most field magnetic CVs are observed to not
undergo eruptions. Our observations of the dwarf nova eruptions of CV2 and CV3
can be reconciled with these objects' HeII emission lines if both objects are
infrequently-erupting intermediate polars, similar to EX Hya. If this is the
case for most globular cluster CVs then we can reconcile the many X-ray and UV
bright CV candidates seen by Chandra and HST with the very small numbers of
erupting dwarf novae observed in cluster cores.Comment: 12 pages, 3 figures. Accepted for publication in The Astronomical
Journal. Two additional authors adde
Real time approach to tunneling in open quantum systems: decoherence and anomalous diffusion
Macroscopic quantum tunneling is described using the master equation for the
reduced Wigner function of an open quantum system at zero temperature. Our
model consists of a particle trapped in a cubic potential interacting with an
environment characterized by dissipative and normal and anomalous diffusion
coefficients. A representation based on the energy eigenfunctions of the
isolated system, i.e. the system uncoupled to the environment, is used to write
the reduced Wigner function, and the master equation becomes simpler in that
representation. The energy eigenfunctions computed in a WKB approximation
incorporate the tunneling effect of the isolated system and the effect of the
environment is described by an equation that it is in many ways similar to a
Fokker-Planck equation. Decoherence is easily identified from the master
equation and we find that when the decoherence time is much shorter than the
tunneling time the master equation can be approximated by a Kramers like
equation describing thermal activation due to the zero point fluctuations of
the quantum environment. The effect of anomalous diffusion can be dealt with
perturbatively and its overall effect is to inhibit tunneling.Comment: 25 pages, 1 figur
Far-ultraviolet investigation into the galactic globular cluster M30 (NGC 7099): II. Potential X-ray counterparts and variable sources
We present a far-ultraviolet (FUV) study of the globular cluster M30 (NGC
7099). The images were obtained using the Advanced Camera for Surveys (ACS/SBC,
F150LP, FUV) and the Wide Field Planetary Camera 2 (WFPC2, F300W, UV) on board
the Hubble Space Telescope (HST). We compare the catalogue of FUV objects to
ten known X-ray sources and find six confident matches of two cataclysmic
variables (CVs), one RS CVn, one red giant with strong FUV emission and two
sources only detected in the FUV. We also searched for variable sources in our
dataset and found a total of seven blue stragglers (BSs), four horizontal
branch (HB) stars, five red giant branch stars, 28 main sequence stars and four
gap objects that demonstrated variability. One BS star is a known W-UMa contact
binary, one of the gap objects is a known CV identified in this work to be a
dwarf nova, and the three other gap sources are weak variables. The periods and
positions of two of the variable HB stars match them to two previously known RR
Lyrae variables of types RRab and RRc.Comment: 13 pages, 12 figures, accepted for publication to MNRA
- …