49 research outputs found
Chemical Abundances in the Secondary Star in the Black Hole Binary A0620-00
Using a high resolution spectrum of the secondary star in the black hole
binary A0620-00, we have derived the stellar parameters and veiling caused by
the accretion disk in a consistent way. We have used a chi^2 minimization
procedure to explore a grid of 800 000 LTE synthetic spectra computed for a
plausible range of both stellar and veiling parameters. Adopting the best model
parameters found, we have determined atmospheric abundances of Fe, Ca, Ti, Ni
and Al. The Fe abundance of the star is [Fe/H]=0.14 +- 0.20. Except for Ca, we
found the other elements moderately over-abundant as compared with stars in the
solar neighborhood of similar iron content. Taking into account the small
orbital separation, the mass transfer rate and the mass of the convection zone
of the secondary star, a comparison with element yields in supernova explosion
models suggests a possible explosive event with a mass cut comparable to the
current mass of the compact object. We have also analyzed the Li abundance,
which is unusually high for a star of this spectral type and relatively low
mass.Comment: 32 pages, 5 tables and 11 figures, uses rotate.st
Oxygen abundances in unevolved metal-poor stars from near-UV OH lines
We have performed a detailed oxygen abundance analysis of 23 metal-poor
(-3.0<[Fe/H]<-0.3) unevolved halo stars and one giant through the OH bands in
the near UV, using high-resolution echelle spectra. Oxygen is found to be
overabundant with respect to iron in these stars, with the [O/Fe] ratio
increasing from 0.6 to 1 between [Fe/H]=-1.5 and -3.0. The behavior of the
oxygen overabundance with respect to [Fe/H] is similar to that seen in previous
works based on OI IR triplet data (Abia and Rebolo 1989; Tomkin et al. 1992;
Cavallo, Pilachowski, and Rebolo 1997). Contrary to the previously accepted
picture, our oxygen abundances, derived from low-excitation OH lines, agree
well with those derived from high-excitation lines of the triplet. For nine
stars in common with Tomkin et al. we obtain a mean difference of 0.00+/-0.11
dex with respect to the abundances determined from the triplet using the same
stellar parameters and model photospheres. For four stars in our sample we have
found measurements of the [OI] 6300 A line in the literature, from which we
derive oxygen abundances consistent (average difference 0.09 dex) with those
based on OH lines, showing that the long standing controversy between oxygen
abundances from forbidden and permitted lines in metal-poor unevolved stars can
be resolved. Our new oxygen abundances show a smooth extension of the
Edvardsson et al.'s (1993) [O/Fe] versus metallicity curve to much lower
abundances, with a slope -0.31+/- 0.11 (taking into account the error bars in
both oxygen abundances and metallicities) in the range -3<[Fe/H]<-1.Comment: 17 pages, 8 figures, 3 table
The First Extrasolar Planet Discovered with a New Generation High Throughput Doppler Instrument
We report the detection of the first extrasolar planet, ET-1 (HD 102195b),
using the Exoplanet Tracker (ET), a new generation Doppler instrument. The
planet orbits HD 102195, a young star with solar metallicity that may be part
of the local association. The planet imparts radial velocity variability to the
star with a semiamplitude of m s and a period of 4.11 days.
The planetary minimum mass () is .Comment: 42 pages, 11 figures and 5 tables, Accepted for publication in Ap
THz emission from Fe/Pt spintronic emitters with L1-FePt alloyed interface
Recent developments in nanomagnetism and spintronics have enabled the use of
ultrafast spin physics for terahertz (THz) emission. Spintronic THz emitters,
consisting of ferromagnetic FM / non-magnetic (NM) thin film heterostructures,
have demonstrated impressive properties for the use in THz spectroscopy and
have great potential in scientific and industrial applications. In this work,
we focus on the impact of the FM/NM interface on the THz emission by
investigating Fe/Pt bilayers with engineered interfaces. In particular, we
intentionally modify the Fe/Pt interface by inserting an ordered L1-FePt
alloy interlayer. Subsequently, we establish that a Fe/L1-FePt (2\,nm)/Pt
configuration is significantly superior to a Fe/Pt bilayer structure, regarding
THz emission amplitude. The latter depends on the extent of alloying on either
side of the interface. The unique trilayer structure opens new perspectives in
terms of material choices for the next generation of spintronic THz emitters
Enhanced lithium depletion in Sun-like stars with orbiting planets
The surface abundance of lithium on the Sun is 140 times less than
protosolar, yet the temperature at the base of the surface convective zone is
not hot enough to burn Li. A large range of Li abundances in solar type stars
of the same age, mass and metallicity is observed, but theoretically difficult
to understand. An earlier suggestion that Li is more depleted in stars with
planets was weakened by the lack of a proper comparison sample of stars without
detected planets. Here we report Li abundances for an unbiased sample of
solar-analogue stars with and without detected planets. We find that the
planet-bearing stars have less than 1 per cent of the primordial Li abundance,
while about 50 per cent of the solar analogues without detected planets have on
average 10 times more Li. The presence of planets may increase the amount of
mixing and deepen the convective zone to such an extent that the Li can be
burned.Comment: 13 pages, 2 figure
Growth in non-Laplacian fields
We develop a formal method for assigning rules to lattice-based walkers which allows the modeling of irreversible growth in systems governed by non-Laplacian partial differential equations. The method is used to study diffusive growth in finite concentration fields. Good agreement with analytic results is obtained. The method is subsequently applied to study electrochemical deposition and investigate the interplay between the electrostatic and diffusion fields. We examine the effect of a local (nonuniform) flow field on deposition on a substrate
A compositional link between rocky exoplanets and their host stars
Stars and planets both form by accreting material from a surrounding disk.
Because they grow from the same material, theory predicts that there should be
a relationship between their compositions. In this study, we search for a
compositional link between rocky exoplanets and their host stars. We estimate
the iron-mass fraction of rocky exoplanets from their masses and radii and
compare it with the compositions of their host stars, which we assume reflect
the compositions of the protoplanetary disks. We find a correlation (but not a
1:1 relationship) between these two quantities, with a slope of >4, which we
interpret as being attributable to planet formation processes. Super-Earths and
super-Mercuries appear to be distinct populations with differing compositions,
implying differences in their formation processes.Comment: Authors' version of the manuscript. Published in Scienc
Oxygen in the Very Early Galaxy
Oxygen abundances in a sample of ultra-metal-poor subdwarfs have been derived
from measurements of the oxygen triplet at 7771--5 A and OH lines in the near
UV performed in high-resolution and high signal-to-noise spectra obtained with
WHT/UES, KeckI/HIRES, and VLT/UVES. Our Fe abundances were derived in LTE and
then corrected for NLTE effects following Thevenin and Idiart (1999). The new
oxygen abundances confirm previous findings for a progressive linear rise in
the oxygen-to-iron ratio with a slope -0.33+-0.02 from solar metallicity to
[Fe/H] -3. A slightly higher slope would be obtained if the Fe NLTE corrections
were not considered. Below [Fe/H]= -2.5 our stars show [O/Fe] ratios as high as
~ 1.17 (G64-12), which can be interpreted as evidence for oxygen overproduction
in the very early epoch of the formation of the halo, possibly associated with
supernova events with very massive progenitor stars. We show that the arguments
against this linear trend given by Fulbright and Kraft (1999), based on the LTE
Fe analysis of two metal-poor stars cannot be sustained when an NLTE analysis
is performed. Using 1-D models our analysis of three oxygen indicators
available for BD +23 3130 gives consistent abundances within 0.16 dex and
average [O/Fe] ratio of 0.91.Comment: 45 pages, 11 figures, accepted for publication in The Astrophysical
Journa
The global burden of adolescent and young adult cancer in 2019 : a systematic analysis for the Global Burden of Disease Study 2019
Background In estimating the global burden of cancer, adolescents and young adults with cancer are often overlooked, despite being a distinct subgroup with unique epidemiology, clinical care needs, and societal impact. Comprehensive estimates of the global cancer burden in adolescents and young adults (aged 15-39 years) are lacking. To address this gap, we analysed results from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019, with a focus on the outcome of disability-adjusted life-years (DALYs), to inform global cancer control measures in adolescents and young adults. Methods Using the GBD 2019 methodology, international mortality data were collected from vital registration systems, verbal autopsies, and population-based cancer registry inputs modelled with mortality-to-incidence ratios (MIRs). Incidence was computed with mortality estimates and corresponding MIRs. Prevalence estimates were calculated using modelled survival and multiplied by disability weights to obtain years lived with disability (YLDs). Years of life lost (YLLs) were calculated as age-specific cancer deaths multiplied by the standard life expectancy at the age of death. The main outcome was DALYs (the sum of YLLs and YLDs). Estimates were presented globally and by Socio-demographic Index (SDI) quintiles (countries ranked and divided into five equal SDI groups), and all estimates were presented with corresponding 95% uncertainty intervals (UIs). For this analysis, we used the age range of 15-39 years to define adolescents and young adults. Findings There were 1.19 million (95% UI 1.11-1.28) incident cancer cases and 396 000 (370 000-425 000) deaths due to cancer among people aged 15-39 years worldwide in 2019. The highest age-standardised incidence rates occurred in high SDI (59.6 [54.5-65.7] per 100 000 person-years) and high-middle SDI countries (53.2 [48.8-57.9] per 100 000 person-years), while the highest age-standardised mortality rates were in low-middle SDI (14.2 [12.9-15.6] per 100 000 person-years) and middle SDI (13.6 [12.6-14.8] per 100 000 person-years) countries. In 2019, adolescent and young adult cancers contributed 23.5 million (21.9-25.2) DALYs to the global burden of disease, of which 2.7% (1.9-3.6) came from YLDs and 97.3% (96.4-98.1) from YLLs. Cancer was the fourth leading cause of death and tenth leading cause of DALYs in adolescents and young adults globally. Interpretation Adolescent and young adult cancers contributed substantially to the overall adolescent and young adult disease burden globally in 2019. These results provide new insights into the distribution and magnitude of the adolescent and young adult cancer burden around the world. With notable differences observed across SDI settings, these estimates can inform global and country-level cancer control efforts. Copyright (C) 2021 The Author(s). Published by Elsevier Ltd.Peer reviewe
ARDD 2020: from aging mechanisms to interventions
Aging is emerging as a druggable target with growing interest from academia, industry and investors. New technologies such as artificial intelligence and advanced screening techniques, as well as a strong influence from the industry sector may lead to novel discoveries to treat age-related diseases. The present review summarizes presentations from the 7th Annual Aging Research and Drug Discovery (ARDD) meeting, held online on the 1st to 4th of September 2020. The meeting covered topics related to new methodologies to study aging, knowledge about basic mechanisms of longevity, latest interventional strategies to target the aging process as well as discussions about the impact of aging research on society and economy. More than 2000 participants and 65 speakers joined the meeting and we already look forward to an even larger meeting next year. Please mark your calendars for the 8th ARDD meeting that is scheduled for the 31st of August to 3rd of September, 2021, at Columbia University, USA