1,350 research outputs found
Sub shot noise phase quadrature measurement of intense light beams
We present a setup to perform sub shot noise measurements of the phase
quadrature for intense pulsed light without the use of a separate local
oscillator. A Mach--Zehnder interferometer with an unbalanced arm length is
used to detect the fluctuations of the phase quadrature at a single side band
frequency. Using this setup, the non--separability of a pair of quadrature
entangled beams is demonstrated experimentally.Comment: 9 pages, 2 figures, accepted for publication in Optics Letter
Accurate masses and radii of normal stars: modern results and applications
This paper presents and discusses a critical compilation of accurate,
fundamental determinations of stellar masses and radii. We have identified 95
detached binary systems containing 190 stars (94 eclipsing systems, and alpha
Centauri) that satisfy our criterion that the mass and radius of both stars be
known to 3% or better. To these we add interstellar reddening, effective
temperature, metal abundance, rotational velocity and apsidal motion
determinations when available, and we compute a number of other physical
parameters, notably luminosity and distance. We discuss the use of this
information for testing models of stellar evolution. The amount and quality of
the data also allow us to analyse the tidal evolution of the systems in
considerable depth, testing prescriptions of rotational synchronisation and
orbital circularisation in greater detail than possible before. The new data
also enable us to derive empirical calibrations of M and R for single (post-)
main-sequence stars above 0.6 M(Sun). Simple, polynomial functions of T(eff),
log g and [Fe/H] yield M and R with errors of 6% and 3%, respectively.
Excellent agreement is found with independent determinations for host stars of
transiting extrasolar planets, and good agreement with determinations of M and
R from stellar models as constrained by trigonometric parallaxes and
spectroscopic values of T(eff) and [Fe/H]. Finally, we list a set of 23
interferometric binaries with masses known to better than 3%, but without
fundamental radius determinations (except alpha Aur). We discuss the prospects
for improving these and other stellar parameters in the near future.Comment: 56 pages including figures and tables. To appear in The Astronomy and
Astrophysics Review. Ascii versions of the tables will appear in the online
version of the articl
The Banana Project. III. Spin-orbit Alignment in the Long-period Eclipsing Binary NY Cephei
Binaries are not always neatly aligned. Previous observations of the DI Her
system showed that the spin axes of both stars are highly inclined with respect
to one another and the orbital axis. Here we report on a measurement of the
spin-axis orientation of the primary star of the NY Cep system, which is
similar to DI Her in many respects: it features two young early-type stars (~6
Myr, B0.5V+B2V), in an eccentric and relatively long-period orbit (e=0.48,
P=15.d3). The sky projections of the rotation vector and the spin vector are
well-aligned (beta_p = 2 +- 4 degrees), in strong contrast to DI Her. Although
no convincing explanation has yet been given for the misalignment of DI Her,
our results show that the phenomenon is not universal, and that a successful
theory will need to account for the different outcome in the case of NY Cep.Comment: accepted for publication in Ap
The Hubble Space Telescope Treasury Program on the Orion Nebula Cluster
The Hubble Space Telescope (HST) Treasury Program on the Orion Nebula Cluster
has used 104 orbits of HST time to image the Great Orion Nebula region with the
Advanced Camera for Surveys (ACS), the Wide-Field/Planetary Camera 2 (WFPC2)
and the Near Infrared Camera and Multi Object Spectrograph (NICMOS) instruments
in 11 filters ranging from the U-band to the H-band equivalent of HST. The
program has been intended to perform the definitive study of the stellar
component of the ONC at visible wavelengths, addressing key questions like the
cluster IMF, age spread, mass accretion, binarity and cirumstellar disk
evolution. The scanning pattern allowed to cover a contiguous field of
approximately 600 square arcminutes with both ACS and WFPC2, with a typical
exposure time of approximately 11 minutes per ACS filter, corresponding to a
point source depth AB(F435W) = 25.8 and AB(F775W)=25.2 with 0.2 magnitudes of
photometric error. We describe the observations, data reduction and data
products, including images, source catalogs and tools for quick look preview.
In particular, we provide ACS photometry for 3399 stars, most of them detected
at multiple epochs, WFPC2 photometry for 1643 stars, 1021 of them detected in
the U-band, and NICMOS JH photometry for 2116 stars. We summarize the early
science results that have been presented in a number of papers. The final set
of images and the photometric catalogs are publicly available through the
archive as High Level Science Products at the STScI Multimission Archive hosted
by the Space Telescope Science Institute.Comment: Accepted for publication on the Astrophysical Journal Supplement
Series, March 27, 201
Call to adopt a nominal set of astrophysical parameters and constants to improve the accuracy of fundamental physical properties of stars
The increasing precision of astronomical observations of stars and stellar
systems is gradually getting to a level where the use of slightly different
values of the solar mass, radius and luminosity, as well as different values of
fundamental physical constants, can lead to measurable systematic differences
in the determination of basic physical properties. An equivalent issue with an
inconsistent value of the speed of light was resolved by adopting a nominal
value that is constant and has no error associated with it. Analogously, we
suggest that the systematic error in stellar parameters may be eliminated by:
(1) replacing the solar radius Rsun and luminosity Lsun by the nominal values
that are by definition exact and expressed in SI units: 1 RnomSun = 6.95508 x
10^8 m and 1 LnomSun = 3.846 x 10^{26} W; (2) computing stellar masses in terms
of Msun by noting that the measurement error of the product G.Msun is 5 orders
of magnitude smaller than the error in G; (3) computing stellar masses and
temperatures in SI units by using the derived values Msun(2010) = 1.988547 x
10^{30} kg and Tsun(2010) = 5779.57 K; and (4) clearly stating the reference
for the values of the fundamental physical constants used. We discuss the need
and demonstrate the advantages of such a paradigm shift.Comment: 6 pages, 3 table
Einstein-Podolsky-Rosen-like correlation on a coherent-state basis and inseparability of two-mode Gaussian states
The strange property of the Einstein-Podolsky-Rosen (EPR) correlation between
two remote physical systems is a primitive object on the study of quantum
entanglement. In order to understand the entanglement in canonical
continuous-variable systems, a pair of the EPR-like uncertainties is an
essential tool. Here, we consider a normalized pair of the EPR-like
uncertainties and introduce a state-overlap to a classically correlated mixture
of coherent states. The separable condition associated with this state-overlap
determines the strength of the EPR-like correlation on a coherent-state basis
in order that the state is entangled. We show that the coherent-state-based
condition is capable of detecting the class of two-mode Gaussian entangled
states. We also present an experimental measurement scheme for estimation of
the state-overlap by a heterodyne measurement and a photon detection with a
feedforward operation.Comment: 9 pages, 5 figures. A part of the materials in Sec. VI B of previous
versions was moved into another paper: Journal of Atomic, Molecular, and
Optical Physics, 2012, 854693 (2012).
http://www.hindawi.com/journals/jamop/2012/854693
- …