122 research outputs found
Visual orbit for the low-mass binary Gliese 22 AC from speckle interferometry
Based on 14 data points obtained with near-infrared speckle interferometry
and covering an almost entire revolution, we present a first visual orbit for
the low-mass binary system Gliese 22 AC. The quality of the orbit is largely
improved with respect to previous astrometric solutions. The dynamical system
mass is 0.592 +- 0.065 solar masses, where the largest part of the error is due
to the Hipparcos parallax. A comparison of this dynamical mass with
mass-luminosity relations on the lower main sequence and theoretical
evolutionary models for low-mass objects shows that both probably underestimate
the masses of M dwarfs. A mass estimate for the companion Gliese 22 C indicates
that this object is a very low-mass star with a mass close to the hydrogen
burning mass limit.Comment: Accepted by Astronomy and Astrophysics, 6 pages, 2 figure
Prospect relativity: how choice options influence decision under risk.
In many theories of decision under risk (e.g., expected utility theory, rank-dependent utility theory, and prospect theory), the utility of a prospect is independent of other options in the choice set. The experiments presented here show a large effect of the available options, suggesting instead that prospects are valued relative to one another. The judged certainty equivalent for a prospect is strongly influenced by the options available. Similarly, the selection of a preferred prospect is strongly influenced by the prospects available. Alternative theories of decision under risk (e.g., the stochastic difference model, multialternative decision field theory, and range frequency theory), where prospects are valued relative to one another, can provide an account of these context effects
Target selection for the SUNS and DEBRIS surveys for debris discs in the solar neighbourhood
Debris discs - analogous to the Asteroid and Kuiper-Edgeworth belts in the
Solar system - have so far mostly been identified and studied in thermal
emission shortward of 100 um. The Herschel space observatory and the SCUBA-2
camera on the James Clerk Maxwell Telescope will allow efficient photometric
surveying at 70 to 850 um, which allow for the detection of cooler discs not
yet discovered, and the measurement of disc masses and temperatures when
combined with shorter wavelength photometry. The SCUBA-2 Unbiased Nearby Stars
(SUNS) survey and the DEBRIS Herschel Open Time Key Project are complimentary
legacy surveys observing samples of ~500 nearby stellar systems. To maximise
the legacy value of these surveys, great care has gone into the target
selection process. This paper describes the target selection process and
presents the target lists of these two surveys.Comment: 67 pages with full tables, 7 figures, accepted to MNRA
New neighbours. III. 21 new companions to nearby dwarfs, discovered with adaptive optics
We present some results of a CFHT adaptive optics search for companions to
nearby dwarfs. We identify 21 new components in solar neighbourhood systems, of
which 13 were found while surveying a volume-limited sample of M dwarfs within
12pc. We are obtaining complete observations for this subsample, to derive
unbiased multiplicity statistics for the very-low-mass disk population.
Additionally, we resolve for the first time 6 known spectroscopic or
astrometric binaries, for a total of 27 newly resolved companions. A fair
fraction of the new binaries has favourable parameters for accurate mass
determinations. The newly resolved companion of Gl120.1C had an apparent
spectroscopic minimum mass in the brown-dwarf range (Duquennoy & Mayor 1991)
and it contributed to the statistical evidence that a few percent of solar type
stars might have close-in brown-dwarf companions. We find that Gl~120.1C
actually is an unrecognised double-lined spectroscopic pair. Its
radial-velocity amplitude had therefore been strongly underestimated by
Duquennoy & Mayor, and it does not truly belong to their sample of single-lined
systems with minimum spectroscopic mass below the substellar limit. We also
present the first direct detection of Gl~494B, an astrometric brown-dwarf
candidate. Its luminosity does straddle the substellar limit, and it is a brown
dwarf if its age is less than 300Myr. A few more years of observations will
ascertain its mass and status from first principles.Comment: Accepted by Astronomy & Astrophysic
Positioning aquatic animals with acoustic transmitters
Geolocating aquatic animals with acoustic tags has been ongoing for decades, relying on the detection of acoustic signals at multiple receivers with known positions to calculate a 2D or 3D position, and ultimately recreate the path of an aquatic animal from detections at fixed stations.This method of underwater geolocation is evolving with new software and hardware options available to help investigators design studies and calculate positions using solvers based predominantly on time-difference-of-arrival and time-of-arrival.We provide an overview of the considerations necessary to implement positioning in aquatic acoustic telemetry studies, including how to design arrays of receivers, test performance, synchronize receiver clocks and calculate positions from the detection data. We additionally present some common positioning algorithms, including both the free open-source solvers and the 'black-box' methods provided by some manufacturers for calculating positions.This paper is the first to provide a comprehensive overview of methods and considerations for designing and implementing better positioning studies that will support users, and encourage further knowledge advances in aquatic systems
The relationship between time perspective and self-regulation: A protocol for a meta-analytical review
Introduction
Both theoretical and empirical evidence
suggests that time perspective is likely to inluence
self-regulatory processes and outcomes. Despite the
theoretical and practical signiicance of such relations, the
relationship between time perspective and self-regulatory
processes and outcomes across different measures,
samples and life domains, including health, has yet to be
explored.
Methods and analysis
The proposed review will develop
a taxonomy for classifying measures according to the selfregulatory
process, ability or outcome that they are likely
to relect. Electronic scientiic databases will be searched,
along with relevant conference abstract booklets and
citation lists. Additionally, a call for unpublished data will
be submitted to relevant bodies. To be eligible for inclusion,
studies must include a measure of time perspective
and a measure of at least one self-regulatory process,
ability and/ or outcome. Eligibility will not be restricted by
publication date, language, type of sample or setting. The
bivariate correlations will be extracted (or calculated) and
submitted to a random-effects meta-analysis. The sampleweighted
average effect size, heterogeneity, risk of bias
and publication bias will be calculated, and the effects of
categorical and continuous moderator variables on the
effect sizes will be determined.
Ethics and dissemination
The proposed meta-analysis
will synthesise previously conducted research; thus,
ethical approval is not required. The indings will be
submitted for publication in an international peer-reviewed
journal and reported as part of the irst author’s
PhD thesis. The indings will also be disseminated to the
research community and, where appropriate, to other
interested parties through presentations at relevant
academic and non-academic conferences
Further Defining Spectral Type "Y" and Exploring the Low-mass End of the Field Brown Dwarf Mass Function
We present the discovery of another seven Y dwarfs from the Wide-field
Infrared Survey Explorer (WISE). Using these objects, as well as the first six
WISE Y dwarf discoveries from Cushing et al., we further explore the transition
between spectral types T and Y. We find that the T/Y boundary roughly coincides
with the spot where the J-H colors of brown dwarfs, as predicted by models,
turn back to the red. Moreover, we use preliminary trigonometric parallax
measurements to show that the T/Y boundary may also correspond to the point at
which the absolute H (1.6 um) and W2 (4.6 um) magnitudes plummet. We use these
discoveries and their preliminary distances to place them in the larger context
of the Solar Neighborhood. We present a table that updates the entire stellar
and substellar constituency within 8 parsecs of the Sun, and we show that the
current census has hydrogen-burning stars outnumbering brown dwarfs by roughly
a factor of six. This factor will decrease with time as more brown dwarfs are
identified within this volume, but unless there is a vast reservoir of cold
brown dwarfs invisible to WISE, the final space density of brown dwarfs is
still expected to fall well below that of stars. We also use these new Y dwarf
discoveries, along with newly discovered T dwarfs from WISE, to investigate the
field substellar mass function. We find that the overall space density of
late-T and early-Y dwarfs matches that from simulations describing the mass
function as a power law with slope -0.5 < alpha < 0.0; however, a power-law may
provide a poor fit to the observed object counts as a function of spectral type
because there are tantalizing hints that the number of brown dwarfs continues
to rise from late-T to early-Y. More detailed monitoring and characterization
of these Y dwarfs, along with dedicated searches aimed at identifying more
examples, are certainly required.Comment: 91 pages, 15 figures, accepted for publication in The Astrophysical
Journa
The HARPS search for southern extra-solar planets XXXI. The M-dwarf sample
(Abridged) Searching for planets around stars with different masses probes
the outcome of planetary formation for different initial conditions. This
drives observations of a sample of 102 southern nearby M dwarfs, using a
fraction of our guaranteed time on the ESO/HARPS spectrograph (Feb. 11th, 2003
to Apr. 1st 2009). This paper makes available the sample's time series,
presents their precision and variability. We apply systematic searches and
diagnostics to discriminate whether the observed Doppler shifts are caused by
stellar surface inhomogeneities or by the radial pull of orbiting planets. We
recover the planetary signals corresponding to 9 planets already announced by
our group (Gl176b, Gl581b, c, d & e, Gl674b, Gl433b, Gl 667Cb and c). We
present radial velocities that confirm GJ 849 hosts a Jupiter-mass planet, plus
a long-term radial-velocity variation. We also present RVs that precise the
planetary mass and period of Gl 832b. We detect long-term RV changes for Gl
367, Gl 680 and Gl 880 betraying yet unknown long-period companions. We
identify candidate signals in the radial-velocity time series and demonstrate
they are most probably caused by stellar surface inhomogeneities. Finally, we
derive a first estimate of the occurrence of M-dwarf planets as a function of
their minimum mass and orbital period. In particular, we find that giant
planets (m sin i = 100-1,000 Mearth) have a low frequency (e.g. f<1% for P=1-10
d and f=0.02^{+0.03}_{-0.01} for P=10-100 d), whereas super-Earths (m sin i =
1-10 Mearth) are likely very abundant (f=0.36^{+0.25}_{-0.10} for P=1-10 d and
f=0.35^{+0.45}_{-0.11} for P=10-100 d). We also obtained
eta_earth=0.41^{+0.54}_{-0.13}, the frequency of habitable planets orbiting M
dwarfs (1<m sin i<10 Mearth). For the first time, eta_earth is a direct measure
and not a number extrapolated from the statistic of more massive and/or
shorter-period planets.Comment: 77p, >100 figures, submitted to A&A, typo corrected in conclusio
Comment letters to the National Commission on Commission on Fraudulent Financial Reporting, 1987 (Treadway Commission) Vol. 1
https://egrove.olemiss.edu/aicpa_sop/1661/thumbnail.jp
A genomic catalog of Earth’s microbiomes
The reconstruction of bacterial and archaeal genomes from shotgun metagenomes has enabled insights into the ecology and evolution of environmental and host-associated microbiomes. Here we applied this approach to >10,000 metagenomes collected from diverse habitats covering all of Earth’s continents and oceans, including metagenomes from human and animal hosts, engineered environments, and natural and agricultural soils, to capture extant microbial, metabolic and functional potential. This comprehensive catalog includes 52,515 metagenome-assembled genomes representing 12,556 novel candidate species-level operational taxonomic units spanning 135 phyla. The catalog expands the known phylogenetic diversity of bacteria and archaea by 44% and is broadly available for streamlined comparative analyses, interactive exploration, metabolic modeling and bulk download. We demonstrate the utility of this collection for understanding secondary-metabolite biosynthetic potential and for resolving thousands of new host linkages to uncultivated viruses. This resource underscores the value of genome-centric approaches for revealing genomic properties of uncultivated microorganisms that affect ecosystem processes
- …