72 research outputs found
Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo*; A new classification scheme based on Sr and Ba
Carbon-enhanced metal-poor (CEMP) stars span a wide range of stellar
populations, from bona fide second-generation stars to later forming stars that
provide excellent probes of, e.g., binary mass transfer. Here we analyse 11
metal-poor stars of which 10 are CEMP stars. Based on high signal-to-noise
(SNR) X-Shooter spectra, we derive abundances of 20 elements (C, N, O, Na, Mg,
Ca, Sc, Ti, Cr, Mn, Fe, Ni, Sr, Y, Ba, La, Ce, Pr, Nd, Eu). From the high SNR
spectra, we trace the chemical contribution of the rare earth elements (REE)
from various production sites, finding a preference for metal-poor low-mass AGB
stars of 1.5Mo in CEMP-s stars, while CEMP-r/s stars may indicate a more
massive AGB contribution (2-5Mo). A contribution from the r-process - possibly
from neutron star mergers (NSM), is also detectable in the REE abundances,
especially in the CEMP-r/s. Combining spectra with Gaia DR2 astrometric data
indicates that all but one star in our sample (and most literature stars)
belong to the Galactic halo. They exhibit a median orbital eccentricity of 0.7,
and are found on both pro- and retrograde orbits. The orbital parameters of
CEMP-no and CEMP4s stars are remarkably similar in the 98 stars we study. A
special CEMP-no star, with very low Sr and Ba content, possesses the most
eccentric orbit among the stars in our sample, passing close to the Galactic
centre. Finally, we propose an improved scheme to sub-classify the CEMP stars,
making use of the SrBa ratio, which can also be used to separate very
metal-poor stars from CEMP stars in 93 stars in the metallicity range
[Fe/H]. The Sr/Ba ratio can also be used for distinguishing
CEMP-s,-r/s and -no stars. The Sr/Ba ratio is also a powerful astro-nuclear
indicator, as AGB stars exhibit very different Sr/Ba ratios, compared to fast
rotating massive stars and NSM, and it is fairly unbiased by NLTE and 3D
corrections.(abridged)Comment: 15 pages, 4 pages appendix, 11 figures, accepted for publication in
A&
Chemical homogeneity of wide binary system: An approach from Near-Infrared spectroscopy
Wide binaries, with separations between two stars from a few AU to more than
several thousand AU, are valuable objects for various research topics in
Galactic astronomy. As the number of newly reported wide binaries continues to
increase, studying the chemical abundances of their component stars becomes
more important. We conducted high-resolution near-infrared (NIR) spectroscopy
for six pairs of wide binary candidates using the Immersion Grating Infrared
Spectrometer (IGRINS) at the Gemini-South telescope. One pair was excluded from
the wide binary samples due to a significant difference in radial velocity
between its component stars, while the remaining five pairs exhibited
homogeneous properties in 3D motion and chemical composition among the pair
stars. The differences in [Fe/H] ranged from 0.00 to 0.07 dex for these wide
binary pairs. The abundance differences between components are comparable to
the previous results from optical spectroscopy for other samples. In addition,
when combining our data with literature data, it appears that the variation of
abundance differences increases in wide binaries with larger separations.
However, the SVO2324 and SVO3206 showed minimal differences in most elements
despite their large separation, supporting the concept of multiple formation
mechanisms depending on each wide binary. This study is the first approach to
the chemical properties of wide binaries based on NIR spectroscopy. Our results
further highlight that NIR spectroscopy is an effective tool for stellar
chemical studies based on equivalent measurements of chemical abundances from
the two stars in each wide binary system.Comment: 16 pages, 9 figures, accepted for publication in A
The haloes and environments of nearby galaxies (HERON) -- III. A 45 kpc spiral structure in the GLSB galaxy UGC 4599
We use a 0.7-m telescope in the framework of the Halos and Environments of
Nearby Galaxies (HERON) survey to probe low surface brightness structures in
nearby galaxies. One of our targets, UGC 4599, is usually classified as an
early-type galaxy surrounded by a blue ring making it a potential Hoag's Object
analog. Prior photometric studies of UGC 4599 were focused on its bright core
and the blue ring. However, the HERON survey allows us to study its faint
extended regions. With an eight hour integration, we detect an extremely faint
outer disk with an extrapolated central surface brightness of
mag arcsec down to 31 mag arcsec and a
scale length of 15 kpc. We identify two distinct spiral arms of pitch angle
~6{\deg} surrounding the ring. The spiral arms are detected out to ~45 kpc in
radius and the faint disk continues to ~70 kpc. These features are also seen in
the GALEX FUV and NUV bands, in a deep u-band image from the 4.3m Lowell
Discovery Telescope (which reveals inner spiral structure emerging from the
core), and in HI. We compare this galaxy to ordinary spiral and elliptical
galaxies, giant low surface brightness (GLSB) galaxies, and Hoag's Object
itself using several standard galaxy scaling relations. We conclude that the
pseudobulge and disk properties of UGC 4599 significantly differ from those of
Hoag's Object and of normal galaxies, pointing toward a GLSB galaxy nature and
filamentary accretion of gas to generate its outer disk.Comment: 17 pages, 14 figures, accepted for publication in MNRA
Blanco DECam Bulge Survey (BDBS) IV: Metallicity Distributions and Bulge Structure from 2.6 Million Red Clump Stars
We present photometric metallicity measurements for a sample of 2.6 million
bulge red clump stars extracted from the Blanco DECam Bulge Survey (BDBS).
Similar to previous studies, we find that the bulge exhibits a strong vertical
metallicity gradient, and that at least two peaks in the metallicity
distribution functions appear at b < -5. We can discern a metal-poor ([Fe/H] ~
-0.3) and metal-rich ([Fe/H] ~ +0.2) abundance distribution that each show
clear systematic trends with latitude, and may be best understood by changes in
the bulge's star formation/enrichment processes. Both groups exhibit asymmetric
tails, and as a result we argue that the proximity of a star to either peak in
[Fe/H] space is not necessarily an affirmation of group membership. The
metal-poor peak shifts to lower [Fe/H] values at larger distances from the
plane while the metal-rich tail truncates. Close to the plane, the metal-rich
tail appears broader along the minor axis than in off-axis fields. We also
posit that the bulge has two metal-poor populations -- one that belongs to the
metal-poor tail of the low latitude and predominantly metal-rich group, and
another belonging to the metal-poor group that dominates in the outer bulge. We
detect the X-shape structure in fields with |Z| > 0.7 kpc and for stars with
[Fe/H] > -0.5. Stars with [Fe/H] < -0.5 may form a spheroidal or "thick bar"
distribution while those with [Fe/H] > -0.1 are strongly concentrated near the
plane.Comment: 26 pages, 22 figures, accepted for publication in MNRAS; the full
data table is very long so only a stub table has been provided here; the full
electronic table will be provided through MNRAS upon publication, but early
access to the full table will be granted upon request to the author
RR Lyrae Stars Belonging to the Candidate Globular Cluster Patchick 99
Patchick 99 is a candidate globular cluster located in the direction of the
Galactic bulge, with a proper motion almost identical to the field and extreme
field star contamination. A recent analysis suggests it is a low-luminosity
globular cluster with a population of RR Lyrae stars. We present new spectra of
stars in and around Patchick 99, targeting specifically the 3 RR Lyrae stars
associated with the cluster as well as the other RR Lyrae stars in the field. A
sample of 53 giant stars selected from proper motions and a position on CMD are
also observed. The three RR Lyrae stars associated with the cluster have
similar radial velocities and distances, and two of the targeted giants also
have radial velocities in this velocity regime and [Fe/H] metallicities that
are slightly more metal-poor than the field. Therefore, if Patchick 99 is a
bonafide globular cluster, it would have a radial velocity of -92+/-10 km s-1,
a distance of 6.7+/-0.4 kpc (as determined from the RR Lyrae stars), and an
orbit that confines it to the inner bulge.Comment: Accepted to The Astrophysical Journal Letters. Replaced due to a typo
in the titl
The Milky Way Bulge extra-tidal star survey: BH 261 (AL 3)
The Milky Way Bulge extra-tidal star survey (MWBest) is a spectroscopic
survey with the goal of identifying stripped globular cluster stars from inner
Galaxy clusters. In this way, an indication of the fraction of metal-poor bulge
stars that originated from globular clusters can be determined. We observed and
analyzed stars in and around BH 261, an understudied globular cluster in the
bulge. From seven giants within the tidal radius of the cluster, we measured an
average heliocentric radial velocity of = -61 +- 2.6 km/s with a radial
velocity dispersion of \sigma = 6.1 +- 1.9 km/s. The large velocity dispersion
may have arisen from tidal heating in the cluster's orbit about the Galactic
center, or because BH 261 has a high dynamical mass as well as a high
mass-to-light ratio. From spectra of five giants, we measure an average
metallicity of = -1.1 +- 0.2 dex. We also spectroscopically confirm an
RR Lyrae star in BH 261, which yields a distance to the cluster of 7.1 +-
0.4~kpc. Stars with 3D velocities and metallicities consistent with BH 261
reaching to ~0.5 degrees from the cluster are identified. A handful of these
stars are also consistent with the spatial distribution of that potential
debris from models focussing on the most recent disruption of the cluster.Comment: accepted for publication in The Astronomical Journa
Chemical abundances of metal-poor RR Lyrae stars in the Magellanic Clouds
We present for the first time a detailed spectroscopic study of chemical
element abundances of metal-poor RR Lyrae stars in the Large and Small
Magellanic Cloud (LMC and SMC). Using the MagE echelle spectrograph at the 6.5m
Magellan telescopes, we obtain medium resolution (R ~ 2000 - 6000) spectra of
six RR Lyrae stars in the LMC and three RR Lyrae stars in the SMC. These stars
were chosen because their previously determined photometric metallicities were
among the lowest metallicities found for stars belonging to the old populations
in the Magellanic Clouds. We find the spectroscopic metallicities of these
stars to be as low as [Fe/H]_{spec} = -2.7dex, the lowest metallicity yet
measured for any star in the Magellanic Clouds. We confirm that for metal-poor
stars, the photometric metallicities from the Fourier decomposition of the
lightcurves are systematically too high compared to their spectroscopic
counterparts. However, for even more metal-poor stars below [Fe/H]_{phot} <
-2.8dex this trend is reversed and the spectroscopic metallicities are
systematically higher than the photometric estimates. We are able to determine
abundance ratios for ten chemical elements, which extend the abundance
measurements of chemical elements for RR Lyrae stars in the Clouds beyond
[Fe/H] for the first time. For the overall [alpha/Fe] ratio, we obtain an
overabundance of 0.36dex, which is in very good agreement with results from
metal-poor stars in the Milky Way halo as well as from the metal-poor tail in
dwarf spheroidal galaxies. Comparing the abundances with those of the stars in
the Milky Way halo we find that the abundance ratios of stars of both
populations are consistent with another. Therefore we conclude that from a
chemical point of view early contributions from Magellanic-type galaxies to the
formation of the Galactic halo as claimed in cosmological models are plausible.Comment: accepted for publication in AJ, 19 pages, 12 figure
Dissecting the Shared Genetic Architecture of Suicide Attempt, Psychiatric Disorders, and Known Risk Factors
Background Suicide is a leading cause of death worldwide, and nonfatal suicide attempts, which occur far more frequently, are a major source of disability and social and economic burden. Both have substantial genetic etiology, which is partially shared and partially distinct from that of related psychiatric disorders. Methods We conducted a genome-wide association study (GWAS) of 29,782 suicide attempt (SA) cases and 519,961 controls in the International Suicide Genetics Consortium (ISGC). The GWAS of SA was conditioned on psychiatric disorders using GWAS summary statistics via multitrait-based conditional and joint analysis, to remove genetic effects on SA mediated by psychiatric disorders. We investigated the shared and divergent genetic architectures of SA, psychiatric disorders, and other known risk factors. Results Two loci reached genome-wide significance for SA: the major histocompatibility complex and an intergenic locus on chromosome 7, the latter of which remained associated with SA after conditioning on psychiatric disorders and replicated in an independent cohort from the Million Veteran Program. This locus has been implicated in risk-taking behavior, smoking, and insomnia. SA showed strong genetic correlation with psychiatric disorders, particularly major depression, and also with smoking, pain, risk-taking behavior, sleep disturbances, lower educational attainment, reproductive traits, lower socioeconomic status, and poorer general health. After conditioning on psychiatric disorders, the genetic correlations between SA and psychiatric disorders decreased, whereas those with nonpsychiatric traits remained largely unchanged. Conclusions Our results identify a risk locus that contributes more strongly to SA than other phenotypes and suggest a shared underlying biology between SA and known risk factors that is not mediated by psychiatric disorders.Peer reviewe
Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU
Contains fulltext :
172380.pdf (publisher's version ) (Open Access
Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network
Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects
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