151 research outputs found
Forming the first planetary systems: debris around Galactic thick disc stars
The thick disc contains stars formed within the first Gyr of Galactic
history, and little is known about their planetary systems. The Spitzer MIPS
instrument was used to search 11 of the closest of these old low-metal stars
for circumstellar debris, as a signpost that bodies at least as large as
planetesimals were formed. A total of 22 thick disc stars has now been
observed, after including archival data, but dust is not found in any of the
systems. The data rule out a high incidence of debris among star systems from
early in the Galaxy's formation. However, some stars of this very old
population do host giant planets, at possibly more than the general incidence
among low-metal Sun-like stars. As the Solar System contains gas giants but
little cometary dust, the thick disc could host analogue systems that formed
many Gyr before the Sun.Comment: accepted by MNRAS Letters; 5 pages, 4 figure
Metallicities and ages of stellar populations at a high Galactic latitude field
We present an analysis of data from the Selected Area SA 141. By
applying recalibrated methods of measuring ultraviolet excess (UVX), we
approximate abundances and absolute magnitudes for 368 stars over 1.3 square
degrees out to distances over 10 kpc. With the density distribution constrained
from our previous photometric parallax investigations and with sufficient
accounting for the metallicity bias in the UVX method, we are able to compare
the vertical abundance distribution to those measured in previous studies. We
find that the abundance distribution has an underlying uniform component
consistent with previous spectroscopic results that posit a monometallic thick
disk and halo with abundances of = 0.8 and 1.4, respectively.
However, there are a number of outlying data points that may indicate
contamination by more metal-rich halo streams. The absence of vertical
abundance gradients in the Galactic stellar populations and the possible
presence of interloping halo streams would be consistent with expectations from
merger models of Galaxy formation. We find that our UVX method has limited
sensitivity in exploring the metallicity distribution of the distant Galactic
halo, owing to the poor constraint on the properties of very metal-poor
stars. The derivation of metallicities from broadband photometry remains
fundamentally sound for the exploration of the halo but is in need of both
improved calibration and superior data.Comment: 11 pages, 11 figures, accepted for publication in MNRAS Journa
Ultracool dwarf benchmarks with \emph{Gaia} primaries
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We explore the potential of \emph{Gaia} for the field of benchmark ultracool/brown dwarf companions, and present the results of an initial search for metal-rich/metal-poor systems. A simulated population of resolved ultracool dwarf companions to \emph{Gaia} primary stars is generated and assessed. Of order 24,000 companions should be identifiable outside of the Galactic plane (deg) with large-scale ground- and space-based surveys including late M, L, T, and Y types. Our simulated companion parameter space covers , , and , with systems required to have a false alarm probability 0.6\, kau}\,Peer reviewedFinal Accepted Versio
A catalog of chromospherically active binary stars (third edition)
Chromospherically Active Binaries (CAB) catalogue have been revised and
updated. With 203 new identifications, the number of CAB stars is increased to
409. Catalogue is available in electronic format where each system has various
number of lines (sub-orders) with a unique order number. Columns contain data
of limited number of selected cross references, comments to explain
peculiarities and position of the binarity in case it belongs to a multiple
system, classical identifications (RS CVn, BY Dra), brightness and colours,
photometric and spectroscopic data, description of emission features (Ca II
H&K, , UV, IR), X-Ray luminosity, radio flux, physical quantities
and orbital information, where each basic entry are referenced so users can go
original sources.Comment: 5 pages, including 2 figures and 3 tables, accepted for publication
in MNRA
Discovery of the benchmark metal poor T8 dwarf BD+01 2920B
We have searched the WISE first data release for widely separated (<10,000AU)
late T dwarf companions to Hipparcos and Gliese stars. We have discovered a new
binary system containing a K-band suppressed T8p dwarf WISEP J1423+0116 and the
mildly metal poor ([Fe/H]=-0.38+-0.06) primary BD+01 2920 (Hip 70319), a G1
dwarf at a distance of 17.2pc. This new benchmark has Teff=680+-55K and a mass
of 20-50 Mjup. Its spectral properties are well modelled except for known
discrepancies in the Y and K bands. Based on the well determined metallicity of
its companion, the properties of BD+01 2920B imply that the currently known T
dwarfs are dominated by young low-mass objects. We also present an accurate
proper motion for the T8.5 dwarf WISEP J075003.84+272544.8.Comment: MNRAS, accepted 2012 January 1
Risk profiles and one-year outcomes of patients with newly diagnosed atrial fibrillation in India: Insights from the GARFIELD-AF Registry.
BACKGROUND: The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is an ongoing prospective noninterventional registry, which is providing important information on the baseline characteristics, treatment patterns, and 1-year outcomes in patients with newly diagnosed non-valvular atrial fibrillation (NVAF). This report describes data from Indian patients recruited in this registry. METHODS AND RESULTS: A total of 52,014 patients with newly diagnosed AF were enrolled globally; of these, 1388 patients were recruited from 26 sites within India (2012-2016). In India, the mean age was 65.8 years at diagnosis of NVAF. Hypertension was the most prevalent risk factor for AF, present in 68.5% of patients from India and in 76.3% of patients globally (P < 0.001). Diabetes and coronary artery disease (CAD) were prevalent in 36.2% and 28.1% of patients as compared with global prevalence of 22.2% and 21.6%, respectively (P < 0.001 for both). Antiplatelet therapy was the most common antithrombotic treatment in India. With increasing stroke risk, however, patients were more likely to receive oral anticoagulant therapy [mainly vitamin K antagonist (VKA)], but average international normalized ratio (INR) was lower among Indian patients [median INR value 1.6 (interquartile range {IQR}: 1.3-2.3) versus 2.3 (IQR 1.8-2.8) (P < 0.001)]. Compared with other countries, patients from India had markedly higher rates of all-cause mortality [7.68 per 100 person-years (95% confidence interval 6.32-9.35) vs 4.34 (4.16-4.53), P < 0.0001], while rates of stroke/systemic embolism and major bleeding were lower after 1 year of follow-up. CONCLUSION: Compared to previously published registries from India, the GARFIELD-AF registry describes clinical profiles and outcomes in Indian patients with AF of a different etiology. The registry data show that compared to the rest of the world, Indian AF patients are younger in age and have more diabetes and CAD. Patients with a higher stroke risk are more likely to receive anticoagulation therapy with VKA but are underdosed compared with the global average in the GARFIELD-AF. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01090362
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