21,020 research outputs found
Efficient least-squares basket-weaving
We report on a novel method to solve the basket-weaving problem.
Basket-weaving is a technique that is used to remove scan-line patterns from
single-dish radio maps. The new approach applies linear least-squares and works
on gridded maps from arbitrarily sampled data, which greatly improves
computational efficiency and robustness. It also allows masking of bad data,
which is useful for cases where radio frequency interference is present in the
data. We evaluate the algorithms using simulations and real data obtained with
the Effelsberg 100-m telescope.Comment: 11 pages, 11 figures, accepted by A&
The Carbon footprint of B[e] supergiants
We report on the first detection of C enhancement in two B[e]
supergiants in the Large Magellanic Cloud. Stellar evolution models predict the
surface abundance in C to strongly increase during main-sequence and
post-main sequence evolution of massive stars. However, direct identification
of chemically processed material on the surface of B[e] supergiants is hampered
by their dense, disk-forming winds, hiding the stars. Recent theoretical
computations predict the detectability of enhanced C via the molecular
emission in CO arising in the circumstellar disks of B[e] supergiants.
To test this potential method and to unambiguously identify a post-main
sequence B[e]SG by its CO emission, we have obtained high-quality
-band spectra of two known B[e] supergiants in the Large Magellanic Cloud,
using the Very Large Telescope's Spectrograph for INtegral Field Observation in
the Near-Infrared (VLT/SINFONI). Both stars clearly show the CO band
emission, whose strength implies a strong enhancement of C, in agreement
with theoretical predictions. This first ever direct confirmation of the
evolved nature of B[e] supergiants thus paves the way to the first
identification of a Galactic B[e] supergiant.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
The Stellar Populations of Praesepe and Coma Berenices
We present the results of a stellar membership survey of the nearby open
clusters Praesepe and Coma Berenices. We have combined archival survey data
from the SDSS, 2MASS, USNOB1.0, and UCAC-2.0 surveys to compile proper motions
and photometry for ~5 million sources over 300 deg^2. Of these sources, 1010
stars in Praesepe and 98 stars in Coma Ber are identified as candidate members
with probability >80%; 442 and 61 are identified as high-probability candidates
for the first time. We estimate that this survey is >90% complete across a wide
range of spectral types (F0 to M5 in Praesepe, F5 to M6 in Coma Ber). We have
also investigated the stellar mass dependence of each cluster's mass and radius
in order to quantify the role of mass segregation and tidal stripping in
shaping the present-day mass function and spatial distribution of stars.
Praesepe shows clear evidence of mass segregation across the full stellar mass
range; Coma Ber does not show any clear trend, but low number statistics would
mask a trend of the same magnitude as in Praesepe. The mass function for
Praesepe (t~600 Myr; M~500 Msun) follows a power law consistent with that of
the field present-day mass function, suggesting that any mass-dependent tidal
stripping could have removed only the lowest-mass members (<0.15 Msun). Coma
Ber, which is younger but much less massive (t~400 Myr; M~100 Msun), follows a
significantly shallower power law. This suggests that some tidal stripping has
occurred, but the low-mass stellar population has not been strongly depleted
down to the survey completeness limit (~0.12 Msun).Comment: Accepted to AJ; 14 pages, 10 figures, 5 tables + 2 online-only table
Disk tracing for B[e] supergiants in the Magellanic Clouds
B[e] supergiants are evolved massive stars with a complex circumstellar
environment. A number of important emission features probe the structure and
the kinematics of the circumstellar material. In our survey of Magellanic Cloud
B[e] supergiants we focus on the [OI] and [CaII] emission lines, which we
identified in four more objects.Comment: 2 pages; 1 figure; submitted to the proceedings of the Physics of
Evolved Stars - A conference dedicated to the memory of Olivier Chesneau,
Nice, France, June 8-12, 201
A Brief Interpretation of Summer Flounder, Paralichthys dentatus, Movements and Stock Structure with New Tagging Data on Juveniles
Summer flounder, Paralichthys dentatus, are managed as a single stock along the Atlantic coast from the U.S.– Canada border to the southern border of North Carolina. Justification of the single-stock approach is based on lack of genetic evidence for multiple stocks and the difficulty presented by managing the species from Cape Hatteras to the U.S.–Canada border. In this review, we present an interpretation of various morphometric, meristic, biochemical, and tagging studies, published and unpublished, that indicate the presence of two, or possibly three, distinct stocks in the management area. In addition, we have included new data from a tagging study that was conducted on juveniles from Virginia that aids in defining the stock(s) north of Cape Hatteras. Summer flounder, overfished for the past two decades, is recovering, and reconsideration of proposed stock structure could have direct implications for management policy decisions
BTZ Black Hole with Chern-Simons and Higher Derivative Terms
The entropy of a BTZ black hole in the presence of gravitational Chern-Simons
terms has previously been analyzed using Euclidean action formalism. In this
paper we treat the BTZ solution as a two dimensional black hole by regarding
the angular coordinate as a compact direction, and use Wald's Noether charge
method to calculate the entropy of this black hole in the presence of higher
derivative and gravitational Chern-Simons terms. The parameters labelling the
black hole solution can be determined by extremizing an entropy function whose
value at the extremum gives the entropy of the black hole.Comment: LaTeX file, 11 page
Local unitary equivalence and entanglement of multipartite pure states
The necessary and sufficient conditions for the equivalence of arbitrary
n-qubit pure quantum states under Local Unitary (LU) operations derived in [B.
Kraus Phys. Rev. Lett. 104, 020504 (2010)] are used to determine the different
LU-equivalence classes of up to five-qubit states. Due to this classification
new parameters characterizing multipartite entanglement are found and their
physical interpretation is given. Moreover, the method is used to derive
examples of two n-qubit states (with n>2 arbitrary) which have the properties
that all the entropies of any subsystem coincide, however, the states are
neither LU-equivalent nor can be mapped into each other by general local
operations and classical communication
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