4,372 research outputs found
Uniaxial stress flips the natural quantization axis of a quantum dot for integrated quantum photonics
Gravitational lensing by wave dark matter halos
Wave Dark Matter (WaveDM) has recently gained attention as a viable candidate
to account for the dark matter content of the Universe. In this paper we
explore the extent to which dark matter halos in this model, and under what
conditions, are able to reproduce strong lensing systems. First, we
analytically explore the lensing properties of the model -- finding that a pure
WaveDM density profile, a soliton profile, produces a weaker lensing effect
than other similar cored profiles. Then we analyze models with a soliton
embedded in an NFW profile, as has been found in numerical simulations of
structure formation. We use a benchmark model with a boson mass of
, for which we see that there is a bi-modality in the
contribution of the external NFW part of the profile, and actually some of the
free parameters associated with it are not well constrained. We find that for
configurations with boson masses -- , a range of
masses preferred by dwarf galaxy kinematics, the soliton profile alone can fit
the data but its size is incompatible with the luminous extent of the lens
galaxies. Likewise, boson masses of the order of , which
would be consistent with Lyman- constraints and consist of more compact
soliton configurations, necessarily require the NFW part in order to reproduce
the observed Einstein radii. We then conclude that lens systems impose a
conservative lower bound and that the NFW envelope around the
soliton must be present to satisfy the observational requirements.Comment: 26 pages, 7 figures, Publishe
The pre-main sequence spectroscopic binary UZ Tau East: improved orbital parameters and accretion phase dependence
We present radial-velocity measurements obtained using high- and
intermediate-resolution spectroscopic observations of the classical T Tauri
star UZ Tau East obtained from 1994 to 1996. We also provide measurements of
H equivalent widths and optical veiling. Combining our radial-velocity
data with those recently reported by Prato et al. (2002), we improve the
orbital elements for this spectroscopic binary. The orbital period is
18.9790.007 days and the eccentricity is e=0.14. We find variability in
the H emission and veiling, signposts of accretion, but at periastron
passage the accretion is not as clearly enhanced as in the case of the binary
DQ Tau. The difference in the behaviour of these two binaries is consistent
with the hydrodynamical models of accretion from circumbinary disks because UZ
Tau East has lower eccentricity than DQ Tau. It seems that enhanced periastron
accretion may occur only in systems with very high eccentricity (e0.5).Comment: accepted for publication in A&
A possible third component in the L dwarf binary system DENIS-P J020529.0-115925 discovered with the Hubble Space Telescope
We present results showing that the multiple system DENIS-P J020529.0-115925
is likely to be a triple system of brown dwarfs. The secondary of this
previously known binary system shows a clear elongation on six images obtained
at six different epochs. Significant residuals remain after PSF subtraction on
these images, characteristic of multiplicity, and indicating that the secondary
is probably a double itself. Dual-PSF fitting shows that the shape of the
secondary is consistent with that of a binary system. These measurements show
that the probability that DENIS-P J020529.0-115925 is a triple system is very
high. The photometric and spectroscopic properties of the system are consistent
with the presence of three components with spectral types L5, L8 and T0.Comment: 15 pages, 3 tables, 6 figures, accepted for publication in AJ. High
resolution version available at
ftp://ftp.mpe.mpg.de/people/hbouy/publications/denis0205.ps.g
Discovery of very nearby ultracool dwarfs from DENIS
We report new spectroscopic results, obtained with UKIRT/CGS4, of a sample of
14 candidate ultracool dwarfs selected from the DENIS (Deep Near-Infrared
Survey of the Southern Sky) database. A further object, selected from the 2MASS
Second Incremental Release, was observed at a later epoch with the same
instrument. Six objects are already known in the literature; we re-derive their
properties. A further four prove to be very nearby (~10 pc) mid-to-late
L-dwarfs, three unknown hitherto, two of which are almost certainly substellar.
These findings increase the number of L-dwarfs known within ~10 pc by ~25%. The
remainder of the objects discussed here are early L or very late M-type dwarfs
lying between ~45 and 15 pc and are also new to the literature. Spectral types
have been derived by direct comparison with J-,H- and K- band spectra of known
template ultracool dwarfs given by Leggett et al.
(ftp://ftp.jach.hawaii.edu/pub/ukirt/skl/dL.spectra/) For the known objects, we
generally find agreement to within ~1 subclass with previously derived spectral
types. Distances are determined from the most recent M_J vs. spectral type
calibrations, and together with our derived proper motions yield kinematics for
most targets consistent with that expected for the disk population; for three
probable late M-dwarfs, membership of a dynamically older population is
postulated. The very nearby L-type objects discussed here are of great interest
for future studies of binarity and parallaxes.Comment: 4 pages, 2 figures, accepted in A&A Letter
The entangling side of the Unruh-Hawking effect
We show that the Unruh effect can create net quantum entanglement between
inertial and accelerated observers depending on the choice of the inertial
state. This striking result banishes the extended belief that the Unruh effect
can only destroy entanglement and furthermore provides a new and unexpected
source for finding experimental evidence of the Unruh and Hawking effects.Comment: 4 pages, 4 figures. Added Journal referenc
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