1,379 research outputs found
M Giants with IGRINS II. Chemical Evolution of Fluorine at High Metallicities
The origin and evolution of fluorine in the Milky Way galaxy is still in
debate. In particular, the increase of the [F/Fe] in metal-rich stars found
from near-IR HF-lines is challenging to explain theoretically. We determine the
fluorine abundances from 50 M giants in the solar neighbourhood spanning a
broad range of metallicities (-0.9<[Fe/H]<0.25 dex). These stars are cool
enough to have an array of HF lines in the K band. We observed the stars with
the IGRINS and investigate each of ten HF molecular lines in detail. Based on a
detailed line-by-line analysis of ten HF lines, we find that the R19, R18 and
R16 lines should primarily be used for abundance analysis. The R15, R14 and R13
lines can also be used, but the trends based on these lines show increasing
dependencies with the stellar parameters. The strongest HF lines, namely R12,
R11, R9 and R7 should be avoided since the abundances from them show
significant trends with the stellar parameters, and a high sensitivity to
variations in the microturbulence, especially for coolest metal-rich stars.
This leads to a huge scatter and high fluorine abundances for supersolar
metallicity stars, not seen in the trends from the weaker lines for the same
stars. When estimating the final mean fluorine abundance trend versus
metallicity, we neglect the fluorine abundances from the four strongest lines
(R7, R9, R11 and R12) for all stars and use only those derived from R16, R18,
and R19 for the coolest metal-rich stars. We confirm the flat trend of [F/Fe]
found in other studies in the metallicity range of -1.0<[Fe/H]<0.0. We also
find a slight enhancement at supersolar metallicities (0<[Fe/H]<0.15) but we
cannot confirm the upward trend seen at [Fe/H]>0.25. We need more observations
of M giants at super solar metallicities with a spectrometer like IGRINS to
confirm if the metal-rich fluorine abundance upturn is real or not.Comment: 11 pages, 6 figures, Accepted for publication in A&
Interpretation of AIRS Data in Thin Cirrus Atmospheres Based on a Fast Radiative Transfer Model
A thin cirrus cloud thermal infrared radiative transfer model has been developed for application to cloudy
satellite data assimilation. This radiation model was constructed by combining the Optical Path Transmittance
(OPTRAN) model, developed for the speedy calculation of transmittances in clear atmospheres, and
a thin cirrus cloud parameterization using a number of observed ice crystal size and shape distributions.
Numerical simulations show that cirrus cloudy radiances in the 800â1130-cm^(-1) thermal infrared window are
sufficiently sensitive to variations in cirrus optical depth and ice crystal size as well as in ice crystal shape
if appropriate habit distribution models are selected a priori for analysis. The parameterization model has
been applied to the Atmospheric Infrared Sounder (AIRS) on board the Aqua satellite to interpret clear
and thin cirrus spectra observed in the thermal infrared window. Five clear and 29 thin cirrus cases at
nighttime over and near the Atmospheric Radiation Measurement program (ARM) tropical western Pacific
(TWP) Manus Island and Nauru Island sites have been chosen for this study. A X^2-minimization program
was employed to infer the cirrus optical depth and ice crystal size and shape from the observed AIRS
spectra. Independent validation shows that the AIRS-inferred cloud parameters are consistent with those
determined from collocated ground-based millimeter-wave cloud radar measurements. The coupled thin
cirrus radiative transfer parameterization and OPTRAN, if combined with a reliable thin cirrus detection
scheme, can be effectively used to enhance the AIRS data volume for data assimilation in numerical
weather prediction models
Chemical Abundances Of Open Clusters From High-Resolution Infrared Spectra. I. NGC 6940
We present near-infrared spectroscopic analysis of 12 red giant members of
the Galactic open cluster NGC 6940. High-resolution (R45000) and high
signal-to-noise ratio (S/N > 100) near-infrared H and K band spectra were
gathered with the Immersion Grating Infrared Spectrograph (IGRINS) on the 2.7m
Smith Telescope at McDonald Observatory. We obtained abundances of H-burning
(C, N, O), (Mg, Si, S, Ca), light odd-Z (Na, Al, P, K), Fe-group
(Sc, Ti, Cr, Fe, Co, Ni) and neutron-capture (Ce, Nd, Yb) elements. We report
the abundances of S, P, K, Ce, and Yb in NGC 6940 for the first time. Many OH
and CN features in the H band were used to obtain O and N abundances. C
abundances were measured from four different features: CO molecular lines in
the K band, high excitation C I lines present in both near-infrared and
optical, CH and bands in the optical region. We have also determined
ratios from the R-branch band heads of first overtone (2-0) and
(3-1) (2-0) lines near 23440
\overset{\lower.5em\circ}{\mathrm{A}} and (3-1) lines at about
23730 \overset{\lower.5em\circ}{\mathrm{A}}. We have also investigated the HF
feature at 23358.3 \overset{\lower.5em\circ}{\mathrm{A}}, finding solar
fluorine abundances without ruling out a slight enhancement. For some elements
(such as the group), IGRINS data yield more internally
self-consistent abundances. We also revisited the CMD of NGC 6940 by
determining the most probable cluster members using Gaia DR2. Finally, we
applied Victoria isochrones and MESA models in order to refine our estimates of
the evolutionary stages of our targets.Comment: 16 pages, 10 figure
Strong Nebular Line Ratios in the Spectra of z~2-3 Star-forming Galaxies: First Results from KBSS-MOSFIRE
We present initial results of a deep near-IR spectroscopic survey covering
the 15 fields of the Keck Baryonic Structure Survey (KBSS) using MOSFIRE on the
Keck 1 telescope, focusing on a sample of 251 galaxies with redshifts 2.0< z <
2.6, star-formation rates 2 < SFR < 200 M_sun/yr, and stellar masses 8.6 <
log(M*/M_sun) < 11.4, with high-quality spectra in both H- and K-band
atmospheric windows. We show unambiguously that the locus of z~2.3 galaxies in
the "BPT" nebular diagnostic diagram exhibits a disjoint, yet similarly tight,
relationship between the ratios [NII]6585/Halpha and [OIII]/Hbeta as compared
to local galaxies. Using photoionization models, we argue that the offset of
the z~2.3 locus relative to z~ 0 is explained by a combination of harder
ionizing radiation field, higher ionization parameter, and higher N/O at a
given O/H than applies to most local galaxies, and that the position of a
galaxy along the z~2.3 star-forming BPT locus is surprisingly insensitive to
gas-phase oxygen abundance. The observed nebular emission line ratios are most
easily reproduced by models in which the net ionizing radiation field resembles
a blackbody with effective temperature T_eff = 50000-60000 K and N/O close to
the solar value at all O/H. We critically assess the applicability of
commonly-used strong line indices for estimating gas-phase metallicities, and
consider the implications of the small intrinsic scatter in the empirical
relationship between excitation-sensitive line indices and stellar mass (i.e.,
the "mass-metallicity" relation), at z~2.3.Comment: 41 pages, 25 figures, accepted for publication in the Astrophysical
Journal. Version with full-resolution figures available at
http://www.astro.caltech.edu/~ccs/mos_bpt_submit.pd
A Candidate Young Massive Planet in Orbit around the Classical T Tauri Star CI Tau
The ~2 Myr old classical T Tauri star CI Tau shows periodic variability in
its radial velocity (RV) variations measured at infrared (IR) and optical
wavelengths. We find that these observations are consistent with a massive
planet in a ~9-day period orbit. These results are based on 71 IR RV
measurements of this system obtained over 5 years, and on 26 optical RV
measurements obtained over 9 years. CI Tau was also observed photometrically in
the optical on 34 nights over ~one month in 2012. The optical RV data alone are
inadequate to identify an orbital period, likely the result of star spot and
activity induced noise for this relatively small dataset. The infrared RV
measurements reveal significant periodicity at ~9 days. In addition, the full
set of optical and IR RV measurements taken together phase coherently and with
equal amplitudes to the ~9 day period. Periodic radial velocity signals can in
principle be produced by cool spots, hot spots, and reflection of the stellar
spectrum off the inner disk, in addition to resulting from a planetary
companion. We have considered each of these and find the planet hypothesis most
consistent with the data. The radial velocity amplitude yields an Msin(i) of
~8.1 M_Jup; in conjunction with a 1.3 mm continuum emission measurement of the
circumstellar disk inclination from the literature, we find a planet mass of
~11.3 M_Jup, assuming alignment of the planetary orbit with the disk.Comment: 61 pages, 13 figures, accepted for publication in The Astrophysical
Journa
Cues and knowledge structures used by mental-health professionals when making risk assessments
Background: Research into mental-health risks has tended to focus on epidemiological approaches and to consider pieces of evidence in isolation. Less is known about the particular
factors and their patterns of occurrence that influence cliniciansâ risk judgements in practice.
Aims: To identify the cues used by clinicians to make risk judgements and to explore how these combine within cliniciansâ psychological representations of suicide, self-harm, self-neglect, and harm to others.
Method: Content analysis was applied to semi-structured interviews conducted with 46 practitioners from various mental-health disciplines, using mind maps to represent the
hierarchical relationships of data and concepts.
Results: Strong consensus between experts meant their knowledge could be integrated into a single hierarchical structure for each risk. This revealed contrasting emphases between data and concepts underpinning risks, including: reflection and forethought for suicide; motivation
for self-harm; situation and context for harm to others; and current presentation for self-neglect.
Conclusions: Analysis of expertsâ risk-assessment knowledge identified influential cues and their relationships to risks. It can inform development of valid risk-screening decision support systems that combine actuarial evidence with clinical expertise
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Development of high-reliability, multikilohertz repetition-rate, fast-discharge components
The two basic components in pulsed-power technology are capacitors and switches. In order to develop these high-voltage components, a unique laboratory has been constructed using state-of-the-art diagnostic and shielding techniques. The laboratory is comprised of three basic systems: charging systems, (2) diagnostic systems, and (3) grounding and shielding systems
Radial Velocity Variability of Field Brown Dwarfs
We present paper six of the NIRSPEC Brown Dwarf Spectroscopic Survey, an analysis of multi-epoch, high-resolution (R ~ 20,000) spectra of 25 field dwarf systems (3 late-type M dwarfs, 16 L dwarfs, and 6 T dwarfs) taken with the NIRSPEC infrared spectrograph at the W. M. Keck Observatory. With a radial velocity (RV) precision of ~2 km s^â1, we are sensitive to brown dwarf companions in orbits with periods of a few years or less given a mass ratio of 0.5 or greater. We do not detect any spectroscopic binary brown dwarfs in the sample. Given our target properties, and the frequency and cadence of observations, we use a Monte Carlo simulation to determine the detection probability of our sample. Even with a null detection result, our 1Ï upper limit for very low mass binary frequency is 18%. Our targets included seven known, wide brown dwarf binary systems. No significant RV variability was measured in our multi-epoch observations of these systems, even for those pairs for which our data spanned a significant fraction of the orbital period. Specialized techniques are required to reach the high precisions sensitive to motion in orbits of very low-mass systems. For eight objects, including six T dwarfs, we present the first published high-resolution spectra, many with high signal to noise, that will provide valuable comparison data for models of brown dwarf atmospheres
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