96 research outputs found
ESO Imaging Survey. The Stellar Catalogue in the Chandra Deep Field South
(abridged) Stellar catalogues in five passbands (UBVRI) over an area of
approximately 0.3 deg^2, comprising about 1200 objects, and in seven passbands
(UBVRIJK) over approximately 0.1 deg^2, comprising about 400 objects, in the
direction of the Chandra Deep Field South are presented.
The 90% completeness level of the number counts is reached at approximately U
= 23.8, B = 24.0, V = 23.5, R = 23.0, I = 21.0, J = 20.5, K = 19.0.
A scheme is presented to select point sources from these catalogues, by
combining the SExtractor parameter CLASS_STAR from all available passbands.
Probable QSOs and unresolved galaxies are identified by using the previously
developed \chi^2-technique (Hatziminaoglou et al 2002), that fits the overall
spectral energy distributions to template spectra and determines the best
fitting template.
The observed number counts, colour-magnitude diagrams, colour-colour diagrams
and colour distributions are presented and, to judge the quality of the data,
compared to simulations based on the predictions of a Galactic Model convolved
with the estimated completeness functions and the error model used to describe
the photometric errors of the data.
The resulting stellar catalogues and the objects identified as likely QSOs
and unresolved galaxies with coordinates, observed magnitudes with errors and
assigned spectral types by the -technique are presented and are
publicly available.Comment: Paper as it will appear in print. Complete figures and tables can be
obtained from: http://www.eso.org/science/eis/eis_pub/eis_pub.html. Astronomy
& Astrophysics, accepted for publicatio
G\"odel Incompleteness and the Black Hole Information Paradox
Semiclassical reasoning suggests that the process by which an object
collapses into a black hole and then evaporates by emitting Hawking radiation
may destroy information, a problem often referred to as the black hole
information paradox. Further, there seems to be no unique prediction of where
the information about the collapsing body is localized. We propose that the
latter aspect of the paradox may be a manifestation of an inconsistent
self-reference in the semiclassical theory of black hole evolution. This
suggests the inadequacy of the semiclassical approach or, at worst, that
standard quantum mechanics and general relavity are fundamentally incompatible.
One option for the resolution for the paradox in the localization is to
identify the G\"odel-like incompleteness that corresponds to an imposition of
consistency, and introduce possibly new physics that supplies this
incompleteness. Another option is to modify the theory in such a way as to
prohibit self-reference. We discuss various possible scenarios to implement
these options, including eternally collapsing objects, black hole remnants,
black hole final states, and simple variants of semiclassical quantum gravity.Comment: 14 pages, 2 figures; revised according to journal requirement
Precision Astrometry of a Sample of Speckle Binaries and Multiples with the Adaptive Optics Facilities at the Hale and Keck II Telescopes
Using the adaptive optics facilities at the 200-in Hale and 10-m Keck II, we
observed in the near infrared a sample of 12 binary and multiple stars and one
open cluster. We used the near diffraction limited images of these systems to
measure the relative separations and position angles between their components.
In this paper, we investigate and correct for the influence of the differential
chromatic refraction and chip distortions on our relative astrometric
measurements. Over one night, we achieve an astrometric precision typically
well below 1 miliarcsecond and occasionally as small as 40 microarcseconds.
Such a precision is in principle sufficient to astrometrically detect planetary
mass objects around the components of nearby binary and multiple stars. Since
we have not had sufficiently large data sets for the observed sample of stars
to detect planets, we provide the limits to planetary mass objects based on the
obtained astrometric precision.Comment: 18 pages, 8 figures, 9 tables, to appear in MNRA
Two-year outcomes in de novo renal transplant recipients receiving everolimus-facilitated calcineurin inhibitor reduction regimen from TRANSFORM study
TRANSFORM was a 24-month, prospective, open-label trial in 2037 de novo renal transplant recipients (RTxRs) randomized (1:1) within 24 hours of transplantation to receive everolimus (EVR) with reduced-exposure calcineurin inhibitor (EVR+rCNI) or mycophenolate with standard-exposure CNI (MPA+sCNI). Consistent with previously reported 12-month findings, noninferiority of the EVR+rCNI regimen for the primary endpoint of treated biopsy-proven acute rejection (tBPAR) or estimated glomerular filtration rate (eGFR) <50 mL/min/1.73 m2 was achieved at Month 24 (47.9% vs 43.7%; difference = 4.2%; 95% confidence interval [CI] = -0.3, 8.7; P = 0.006). Mean eGFR was stable up to Month 24 (52.6 vs 54.9 mL/min/1.73m2 ) in both arms. The incidence of de novo donor-specific antibodies (dnDSA) was lower in the EVR+rCNI arm (12.3% vs 17.6%) among on-treatment patients. Although discontinuation rates due to adverse events were higher with EVR+rCNI (27.2% vs 15.0%), rates of cytomegalovirus (2.8% vs 13.5%) and BK virus (5.8% vs 10.3%) infections were lower. Cytomegalovirus infection rates were significantly lower with EVR+rCNI even in the D+/R- high-risk group (P<0.0001). In conclusion, the EVR+rCNI regimen offers comparable efficacy and graft function with low tBPAR and dnDSA rates and significantly lower incidence of viral infections relative to standard-of-care up to 24 months. This article is protected by copyright. All rights reserved
Gas Accretion and Galactic Chemical Evolution: Theory and Observations
This chapter reviews how galactic inflows influence galaxy metallicity. The
goal is to discuss predictions from theoretical models, but particular emphasis
is placed on the insights that result from using models to interpret
observations. Even as the classical G-dwarf problem endures in the latest round
of observational confirmation, a rich and tantalizing new phenomenology of
relationships between , , SFR, and gas fraction is emerging both in
observations and in theoretical models. A consensus interpretation is emerging
in which star-forming galaxies do most of their growing in a quiescent way that
balances gas inflows and gas processing, and metal dilution with enrichment.
Models that explicitly invoke this idea via equilibrium conditions can be used
to infer inflow rates from observations, while models that do not assume
equilibrium growth tend to recover it self-consistently. Mergers are an overall
subdominant mechanism for delivering fresh gas to galaxies, but they trigger
radial flows of previously-accreted gas that flatten radial gas-phase
metallicity gradients and temporarily suppress central metallicities. Radial
gradients are generically expected to be steep at early times and then
flattened by mergers and enriched inflows of recycled gas at late times.
However, further theoretical work is required in order to understand how to
interpret observations. Likewise, more observational work is needed in order to
understand how metallicity gradients evolve to high redshifts.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springer. 29 pages, 2 figure
Search for nearby stars among proper motion stars selected by optical-to-infrared photometry III. Spectroscopic distances of 322 NLTT stars
Distance estimates based on low-resolution spectroscopy and Two Micron All
Sky Survey (2MASS) J magnitudes are presented for a large sample of 322 nearby
candidates from Luyten's NLTT catalogue. Mainly relatively bright (typically 7
< K_s < 11) and red high proper motion stars have been selected according to
their 2MASS magnitudes and optical-to-infrared colours (+1 < R-K_s < +7). Some
LHS stars previously lacking spectroscopy have also been included. We have
classified the majority of the objects as early-M dwarfs (M2-M5). More than 70%
of our targets turned out to lie within the 25 pc horizon of the catalogue of
nearby stars, with 50 objects placed within 15 pc and 8 objects being closer
than 10 pc. Three objects in the 10 pc sample have no previously published
spectral type: LP 876-10 (M4), LP 870-65 (M4.5), and LP 869-26 (M5). A large
fraction of the objects in our sample (57%) have independent distance
estimates, mainly by the recent efforts of Reid and collaborators. Our distance
determinations are generally in good agreement with theirs. 11 rather distant
(d > 100 pc) objects have also been identified, including a probable halo, but
relatively hot (T_eff = 13000 K) white dwarf (LHS 1200) and 10 red dwarfs with
extremely large tangential velocities (250 < v_t < 1150 km/s). Altogether,
there are 11 red dwarfs (including one within 70 pc) with tangential velocities
larger than about 250 km/s. All these objects are suspected to be in fact
subdwarfs, if so, their distances would be only about half of our original
estimates. The three most extreme objects in that respect are the K and early M
dwarfs LP 323-168, LHS 5343 and LP 552-21 with corrected distances between 180
pc and 400 pc and resulting tangential velocities still larger than about 400
km/s.Comment: 19 pages, 14 Figures, complete Table 1 available on request from the
first author, paper accepted by Astronomy and Astrophysic
An integrated framework for assessing coastal community vulnerability across cultures, oceans and scales.
Coastal communities are some of the most at-risk populations with respect to climate change impacts. It is therefore important to determine the vulnerability of such communities to co-develop viable adaptation options. Global efforts to address this issue include international scientific projects, such as Global Learning for Local Solutions (GULLS), which focuses on five fast warming regions of the southern hemisphere and aims to provide an understanding of the local scale processes influencing community vulnerability that can then be up-scaled to regional, country and global levels. This paper describes the development of a new social and ecological vulnerability framework which integrates exposure, sensitivity and adaptive capacity with the social livelihoods and food security approaches. It also measures community flexibility to understand better the adaptive capacity of different levels of community organization. The translation of the conceptual framework to an implementable method is described and its application in a number of “hotspot” countries, where ocean waters are warming faster than the rest of the world, is presented. Opportunities for cross-cultural comparisons to uncover similarities and differences in vulnerability and adaptation patterns among the study’s coastal communities, which can provide accelerated learning mechanisms to other coastal regions, are highlighted. The social and ecological framework and the associated survey approach allow for future integration of local-level vulnerability data with ecological and oceanographic models
Extremely faint high proper motion objects from SDSS stripe 82 - Optical classification spectroscopy of about 40 new objects
(abridged) Deep multi-epoch Sloan Digital Sky Survey data in a 275 square
degrees area along the celestial equator (SDSS stripe 82 = S82) allowed us to
search for extremely faint () objects with proper motions larger than
0.14 arcsec/yr. We classify 38 newly detected objects with low-resolution
optical spectroscopy using FORS1 @ ESO VLT. All 22 previously known L dwarfs in
S82 have been detected in our high proper motion survey. However, 11 of the
known L dwarfs have smaller proper motions (0.010.14 arcsec/yr).
Although S82 was already one of the best investigated sky regions with respect
to L and T dwarfs, we are able to classify 13 new L dwarfs. We have also found
eight new M7.5-M9.5 dwarfs. Four new cool white dwarfs (CWDs) discovered by us
are about 1-2 mag fainter than those previously detected in SDSS data. All new
L-type, late-M and CWD objects show thick disk and halo kinematics. There are
13 objects, mostly with uncertain proper motions, which we initially classified
as mid-M dwarfs. Among them we have found 9 with an alternative subdwarf
classification (sdM7 or earlier types), whereas we have not found any new
spectra resembling the known ultracool (sdM7) subdwarfs. Some M subdwarf
candidates have been classified based on spectral indices with large
uncertainties. We failed to detect new nearby ( pc) L dwarfs, probably
because the S82 area was already well-investigated before. With our survey we
have demonstrated a higher efficiency in finding Galactic halo CWDs than
previous searches. The space density of halo CWDs is according to our results
about 1.5-3.0 10 pc.Comment: 19 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
Melanesian mtDNA Complexity
Melanesian populations are known for their diversity, but it has been hard to grasp the pattern of the variation or its underlying dynamic. Using 1,223 mitochondrial DNA (mtDNA) sequences from hypervariable regions 1 and 2 (HVR1 and HVR2) from 32 populations, we found the among-group variation is structured by island, island size, and also by language affiliation. The more isolated inland Papuan-speaking groups on the largest islands have the greatest distinctions, while shore dwelling populations are considerably less diverse (at the same time, within-group haplotype diversity is less in the most isolated groups). Persistent differences between shore and inland groups in effective population sizes and marital migration rates probably cause these differences. We also add 16 whole sequences to the Melanesian mtDNA phylogenies. We identify the likely origins of a number of the haplogroups and ancient branches in specific islands, point to some ancient mtDNA connections between Near Oceania and Australia, and show additional Holocene connections between Island Southeast Asia/Taiwan and Island Melanesia with branches of haplogroup E. Coalescence estimates based on synonymous transitions in the coding region suggest an initial settlement and expansion in the region at ∼30–50,000 years before present (YBP), and a second important expansion from Island Southeast Asia/Taiwan during the interval ∼3,500–8,000 YBP. However, there are some important variance components in molecular dating that have been overlooked, and the specific nature of ancestral (maternal) Austronesian influence in this region remains unresolved
Decision making under catastrophic risk and learning: the case of the possible collapse of the West Antarctic Ice Sheet
- …