We present new ultra-metal-poor stars parameters with Fe/H < −4.0 based on line-by-line non-local thermodynamic equilibrium (NLTE) abundances using an up-to-date iron model atom with a new recipe for ...non-elastic hydrogen collision rates. We study the departures from LTE in their atmospheric parameters and show that they can grow up to ∼1.00 dex in Fe/H, ∼150 K in and ∼0.5 dex in log g toward the lowest metallicities. Accurate NLTE atmospheric stellar parameters, in particular Fe/H being significantly higher, are the first step to eventually providing full NLTE abundance patterns that can be compared with Population III supernova nucleosynthesis yields to derive properties of the first stars. Overall, this maximizes the potential of these likely second-generation stars to investigate the early universe and how the chemical elements were formed.
Abstract
Precise fundamental atmospheric stellar parameters and abundance determination of individual elements in stars are important for all stellar population studies. Non–local thermodynamic ...equilibrium (non-LTE; hereafter NLTE) models are often important for such high precision, however, can be computationally complex and expensive, which renders the models less utilized in spectroscopic analyses. To alleviate the computational burden of such models, we developed a robust 1D, NLTE fundamental atmospheric stellar parameter derivation tool,
LOTUS
, to determine the effective temperature
T
eff
, surface gravity
log
g
, metallicity Fe/H, and microturbulent velocity
v
mic
for FGK-type stars, from equivalent width (EW) measurements of Fe
i
and Fe
ii
lines. We utilize a generalized curve of growth method to take into account the EW dependencies of each Fe
i
and Fe
ii
line on the corresponding atmospheric stellar parameters. A global differential evolution optimization algorithm is then used to derive the fundamental parameters. Additionally,
LOTUS
can determine precise uncertainties for each stellar parameter using a Markov Chain Monte Carlo algorithm. We test and apply
LOTUS
on a sample of benchmark stars, as well as stars with available asteroseismic surface gravities from the K2 survey, and metal-poor stars from the Gaia-ESO and
R
-Process Alliance surveys. We find very good agreement between our NLTE-derived parameters in
LOTUS
to nonspectroscopic values on average within
T
eff
= ±30 K, and
log
g
= ±0.10 dex for benchmark stars. We provide open access of our code, as well as of the interpolated precomputed NLTE EW grids available on Github
(the software is available on GitHub
3
3
https://github.com/Li-Yangyang/LOTUS
under an MIT License, and version 0.1.1 (as the persistent version) is archived in Zenodo) and documentation with working examples on the
Readthedocs
book.
Abstract
We present observational evidence that an aspherical supernova explosion could have occurred in the first stars in the early universe. Our results are based on the first determination of a ...Zn abundance in a
Hubble Space Telescope
/Cosmic Origins Spectrograph high-resolution UV spectrum of a hyper-metal-poor (HMP) star, HE 1327−2326, with
. We determine Zn/Fe = 0.80 ± 0.25 from a UV Zn
i
line at 2138 Å, detected at 3.4
σ
. Yields of a 25
M
⊙
aspherical supernova model with artificially modified densities exploding with
E
= 5 × 10
51
erg best match the entire abundance pattern of HE 1327−2326. Such high-entropy hypernova explosions are expected to produce bipolar outflows, which could facilitate the external enrichment of small neighboring galaxies. This has already been predicted by theoretical studies of the earliest star-forming minihalos. Such a scenario would have significant implications for the chemical enrichment across the early universe, as HMP carbon-enhanced metal-poor (CEMP) stars such as HE 1327−2326 might have formed in such externally enriched environments.
We present the first detailed chemical abundance study of the ultra-faint dwarf galaxy Tucana II, based on high-resolution Magellan/MIKE spectra of four red giant stars. The metallicities of these ...stars range from Fe/H = -3.2 to -2.6, and all stars are low in neutron-capture abundances (Sr/Fe and Ba/Fe < -1). However, a number of anomalous chemical signatures are present. One star is relatively metal-rich (Fe/H = -2.6) and shows Na, alpha, Sc/Fe < 0, suggesting an extended star formation history with contributions from AGB stars and SNe Ia. Two stars with Fe/H < -3 are mildly carbon-enhanced (C/Fe ~ 0.7) and may be consistent with enrichment by faint supernovae, if such supernovae can produce neutron-capture elements. A fourth star with Fe/H = -3 is carbon-normal, and exhibits distinct light element abundance ratios from the carbon-enhanced stars. This carbon-normal star implies that at least two distinct nucleosynthesis sources, both possibly associated with Population III stars, contributed to the early chemical enrichment of this galaxy. Despite its very low luminosity, Tucana II shows a diversity of chemical signatures that preclude it from being a simple "one-shot" first galaxy yet still provide a window into star and galaxy formation in the early universe.
Abstract
Extensive progress has recently been made in our understanding of heavy-element production via the
r
-process in the universe, specifically with the first observed neutron star binary merger ...(NSBM) event associated with the gravitational-wave signal detected by LIGO, GW170817. The chemical abundance patterns of metal-poor
r
-process-enhanced stars provide key evidence for the dominant site(s) of the
r
-process and whether NSBMs are sufficiently frequent or prolific
r
-process sources to be responsible for the majority of
r
-process material in the universe. We present atmospheric stellar parameters (using a nonlocal thermodynamic equilibrium analysis) and abundances from a detailed analysis of 141 metal-poor stars carried out as part of the
R
-Process Alliance (RPA) effort. We obtained high-resolution “snapshot” spectroscopy of the stars using the MIKE spectrograph on the 6.5 m Magellan Clay telescope at Las Campanas Observatory in Chile. We find 10 new highly enhanced
r
-II (with Eu/Fe > +1.0), 62 new moderately enhanced
r
-I (+0.3 < Eu/Fe ≤ +1.0), and 17 new limited-
r
(Eu/Fe < +0.3) stars. Among those, we find 17 new carbon-enhanced metal-poor (CEMP) stars, of which five are CEMP-no. We also identify one new
s
-process-enhanced (Ba/Eu > +0.5) and five new
r
/
s
(0.0 < Ba/Eu < +0.5) stars. In the process, we discover a new ultra-metal-poor (UMP) star at Fe/H = −4.02. One of the
r
-II stars shows a deficit in
α
and Fe-peak elements, typical of dwarf galaxy stars. Our search for
r
-process-enhanced stars by RPA efforts has already roughly doubled the known
r
-process sample.
This paper presents the detailed abundances and r-process classifications of 126 newly identified metal-poor stars as part of an ongoing collaboration, the R-Process Alliance. The stars were ...identified as metal-poor candidates from the RAdial Velocity Experiment (RAVE) and were followed up at high spectral resolution (R ∼ 31,500) with the 3.5 m telescope at Apache Point Observatory. The atmospheric parameters were determined spectroscopically from Fe i lines, taking into account non-LTE corrections and using differential abundances with respect to a set of standards. Of the 126 new stars, 124 have Fe/H < −1.5, 105 have Fe/H < −2.0, and 4 have Fe/H < −3.0. Nine new carbon-enhanced metal-poor stars have been discovered, three of which are enhanced in r-process elements. Abundances of neutron-capture elements reveal 60 new r-I stars (with +0.3 ≤ Eu/Fe ≤ +1.0 and Ba/Eu < 0) and 4 new r-II stars (with Eu/Fe > +1.0). Nineteen stars are found to exhibit a "limited-r" signature (Sr/Ba > +0.5, Ba/Eu < 0). For the r-II stars, the second- and third-peak main r-process patterns are consistent with the r-process signature in other metal-poor stars and the Sun. The abundances of the light, , and Fe-peak elements match those of typical Milky Way (MW) halo stars, except for one r-I star that has high Na and low Mg, characteristic of globular cluster stars. Parallaxes and proper motions from the second Gaia data release yield UVW space velocities for these stars that are consistent with membership in the MW halo. Intriguingly, all r-II and the majority of r-I stars have retrograde orbits, which may indicate an accretion origin.
Brivanib is a selective dual inhibitor of vascular endothelial growth factor and fibroblast growth factor receptors implicated in tumorigenesis and angiogenesis in hepatocellular carcinoma (HCC). An ...unmet medical need persists for patients with HCC whose tumors do not respond to sorafenib or who cannot tolerate it. This multicenter, double-blind, randomized, placebo-controlled trial assessed brivanib in patients with HCC who had been treated with sorafenib.
In all, 395 patients with advanced HCC who progressed on/after or were intolerant to sorafenib were randomly assigned (2:1) to receive brivanib 800 mg orally once per day plus best supportive care (BSC) or placebo plus BSC. The primary end point was overall survival (OS). Secondary end points included time to progression (TTP), objective response rate (ORR), and disease control rate based on modified Response Evaluation Criteria in Solid Tumors (mRECIST) and safety.
Median OS was 9.4 months for brivanib and 8.2 months for placebo (hazard ratio HR, 0.89; 95.8% CI, 0.69 to 1.15; P = .3307). Adjusting treatment effect for baseline prognostic factors yielded an OS HR of 0.81 (95% CI, 0.63 to 1.04; P = .1044). Exploratory analyses showed a median time to progression of 4.2 months for brivanib and 2.7 months for placebo (HR, 0.56; 95% CI, 0.42 to 0.76; P < .001), and an mRECIST ORR of 10% for brivanib and 2% for placebo (odds ratio, 5.72). Study discontinuation due to treatment-related adverse events (AEs) occurred in 61 brivanib patients (23%) and nine placebo patients (7%). The most frequent treatment-related grade 3 to 4 AEs for brivanib included hypertension (17%), fatigue (13%), hyponatremia (11%), and decreased appetite (10%).
In patients with HCC who had been treated with sorafenib, brivanib did not significantly improve OS. The observed benefit in the secondary outcomes of TTP and ORR warrants further investigation.
Abstract
We present a nearly complete rapid neutron-capture process (
r
-process) chemical inventory of the metal-poor (Fe/H = −1.46 ± 0.10)
r
-process-enhanced (Eu/Fe = +1.32 ± 0.08) halo star HD ...222925. This abundance set is the most complete for any object beyond the solar system, with a total of 63 metals detected and seven with upper limits. It comprises 42 elements from 31 ≤
Z
≤ 90, including elements rarely detected in
r
-process-enhanced stars, such as Ga, Ge, As, Se, Cd, In, Sn, Sb, Te, W, Re, Os, Ir, Pt, and Au. We derive these abundances from an analysis of 404 absorption lines in ultraviolet spectra collected using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope and previously analyzed optical spectra. A series of appendices discusses the atomic data and quality of fits for these lines. The
r
-process elements from Ba to Pb, including all elements at the third
r
-process peak, exhibit remarkable agreement with the solar
r
-process residuals, with a standard deviation of the differences of only 0.08 dex (17%). In contrast, deviations among the lighter elements from Ga to Te span nearly 1.4 dex, and they show distinct trends from Ga to Se, Nb through Cd, and In through Te. The
r
-process contribution to Ga, Ge, and As is small, and Se is the lightest element whose production is dominated by the
r
-process. The lanthanide fraction, log
X
La
= −1.39 ± 0.09, is typical for
r
-process-enhanced stars and higher than that of the kilonova from the GW170817 neutron-star merger event. We advocate adopting this pattern as an alternative to the solar
r
-process-element residuals when confronting future theoretical models of heavy-element nucleosynthesis with observations.
Abstract
We derive dynamical parameters for a large sample of 446
r
-process-enhanced (RPE) metal-poor stars in the halo and disk systems of the Milky Way, based on data releases from the
R
-Process ...Alliance, supplemented by additional literature samples. This sample represents more than a 10-fold increase in size relative to that previously considered by Roederer et al. and, by design, covers a larger range of
r
-process-element enrichment levels. We test a number of clustering analysis methods on the derived orbital energies and other dynamical parameters for this sample, ultimately deciding on application of the
HDBSCAN
algorithm, which obtains 30 individual chemodynamically tagged groups (CDTGs); 21 contain between 3 and 5 stars, and 9 contain between 6 and 12 stars. Even though the clustering was performed solely on the basis of their dynamical properties, the stars in these CDTGs exhibit
statistically significant similarities
in their metallicity (Fe/H), carbonicity (C/Fe), and neutron-capture element ratios (Sr/Fe, Ba/Fe, and Eu/Fe). These results demonstrate that the RPE stars in these CDTGs have likely experienced common chemical-evolution histories, presumably in their parent satellite galaxies or globular clusters, prior to being disrupted into the Milky Way’s halo. We also confirm the previous claim that the orbits of the RPE stars preferentially exhibit pericentric distances that are substantially lower than the present distances of surviving ultrafaint dwarf and canonical dwarf spheroidal galaxies, consistent with the disruption hypothesis. The derived dynamical parameters for several of our CDTGs indicate their association with previously known substructures, dynamically tagged groups, and RPE groups.
Abstract Our understanding of early-type galaxies (ETGs) has grown in the past decade with the advance of full-spectrum fitting techniques used to infer the properties of the stellar populations that ...make up the galaxy. We present ages, central velocity dispersions, and abundance ratios relative to Fe of C, N, O, Mg, Si, Ca, Ti, Cr, Mn, Co, Ni, Cu, Sr, Ba, and Eu, derived using full-spectrum fitting techniques for three ETGs, NGC 2865, NGC 3818, and NGC 4915. Each of these three galaxies were selected because they have optical, disturbed structures (fine structure) that are linked to major merger events that occurred 1, 7, and 6 Gyr ago, respectively. Two of the ETGs, NGC 3818 and NGC 4915, show chemical signatures similar to ETGs without fine structure, which is consistent with a gas-poor merger of elliptical galaxies in which substantial star formation is not expected. For NGC 2865, we find a statistically higher abundance of Ca (an α element) and Cr and Mn (Fe-peak elements). We show that for NGC 2865, a simple gas-rich merger scenario fails to explain the larger abundance ratios compared to ETGs without fine structure. These three ETGs with fine structure exhibit a range of abundances, suggesting ETGs with fine structure can form via multiple pathways and types of galaxy mergers.
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