2,096 research outputs found
Bayesian analysis of ages, masses, and distances to cool stars with non-LTE spectroscopic parameters
For studies of Galactic evolution, the accurate characterization of stars in
terms of their evolutionary stage and population membership is of fundamental
importance. A standard approach relies on extracting this information from
stellar evolution models but requires the effective temperature, surface
gravity, and metallicity of a star obtained by independent means. In previous
work, we determined accurate effective temperatures and non-LTE logg and [Fe/H]
(NLTE-Opt) for a large sample of metal-poor stars, -3<[Fe/H]<-0.5, selected
from the RAVE survey. As a continuation of that work, we derive here their
masses, ages, and distances using a Bayesian scheme and GARSTEC stellar tracks.
For comparison, we also use stellar parameters determined from the widely-used
1D LTE excitation-ionization balance of Fe (LTE-Fe). We find that the latter
leads to systematically underestimated stellar ages, by 10-30%, but
overestimated masses and distances. Metal-poor giants suffer from the largest
fractional distance biases of 70%. Furthermore, we compare our results with
those released by the RAVE collaboration for the stars in common (DR3, Zwitter
et al. 2010, Seibert et al. 2011). This reveals -400 to +400 K offsets in
effective temperature, -0.5 to 1.0 dex offsets in surface gravity, and 10 to
70% in distances. The systematic trends strongly resemble the correlation we
find between the NLTE-Opt and LTE-Fe parameters, indicating that the RAVE DR3
data may be affected by the physical limitations of the 1D LTE synthetic
spectra. Our results bear on any study, where spectrophotometric distances
underlie stellar kinematics. In particular, they shed new light on the debated
controversy about the Galactic halo origin raised by the SDSS/SEGUE
observations.Comment: 13 pages and 15 figures. Accepted for publication in MNRA
The hunt for the Milky Way's accreted disc
The Milky Way is expected to host an accreted disc of stars and dark matter.
This forms as massive >1:10 mergers are preferentially dragged towards the disc
plane by dynamical friction and then tidally shredded. The accreted disc likely
contributes only a tiny fraction of the Milky Way's thin and thick stellar
disc. However, it is interesting because: (i) its associated `dark disc' has
important implications for experiments hoping to detect a dark matter particle
in the laboratory; and (ii) the presence or absence of such a disc constrains
the merger history of our Galaxy. In this work, we develop a chemo-dynamical
template to hunt for the accreted disc. We apply our template to the
high-resolution spectroscopic sample from Ruchti et al. (2011), finding at
present no evidence for accreted stars. Our results are consistent with a
quiescent Milky Way with no >1:10 mergers since the disc formed and a
correspondingly light `dark disc'. However, we caution that while our method
can robustly identify accreted stars, our incomplete stellar sample makes it
more challenging to definitively rule them out. Larger unbiased stellar samples
will be required for this.Comment: 14 pages; 8 figures; 1 table. Accepted for publication in MNRA
Non-local thermodynamic equilibrium stellar spectroscopy with 1D and 3D models - II. Chemical properties of the Galactic metal-poor disc and the halo
From exploratory studies and theoretical expectations it is known that
simplifying approximations in spectroscopic analysis (LTE, 1D) lead to
systematic biases of stellar parameters and abundances. These biases depend
strongly on surface gravity, temperature, and, in particular, for LTE vs.
non-LTE (NLTE) on metallicity of the stars. Here we analyse the [Mg/Fe] and
[Fe/H] plane of a sample of 326 stars, comparing LTE and NLTE results obtained
using 1D hydrostatic models and averaged models. We show that compared to
the NLTE benchmark, all other three methods display increasing biases
towards lower metallicities, resulting in false trends of [Mg/Fe] against
[Fe/H], which have profound implications for interpretations by chemical
evolution models. In our best NLTE model, the halo and disc stars show a
clearer behaviour in the [Mg/Fe] - [Fe/H] plane, from the knee in abundance
space down to the lowest metallicities. Our sample has a large fraction of
thick disc stars and this population extends down to at least [Fe/H] ~ -1.6
dex, further than previously proven. The thick disc stars display a constant
[Mg/Fe] ~ 0.3 dex, with a small intrinsic dispersion in [Mg/Fe] that suggests
that a fast SN Ia channel is not relevant for the disc formation. The halo
stars reach higher [Mg/Fe] ratios and display a net trend of [Mg/Fe] at low
metallicities, paired with a large dispersion in [Mg/Fe]. These indicate the
diverse origin of halo stars from accreted low-mass systems to
stochastic/inhomogeneous chemical evolution in the Galactic halo.Comment: 15 pages, accepted for publication in Ap
unveiling systematic biases in the 1d lte excitation-ionization balance of fe for fgk stars: A novel approach to determination of stellar parameters
We present a comprehensive analysis of different techniques available for the spectroscopic analysis of FGK stars and provide a recommended methodology which efficiently estimates accurate stellar atmospheric parameters for large samples of stars. Our analysis includes a simultaneous equivalent width analysis of Fe I and Fe II spectral lines, and for the first time, utilizes on-the-fly non-local thermodynamic equilibrium (NLTE) corrections of individual Fe I lines. We further investigate several temperature scales, finding that estimates from Balmer line measurements provide the most accurate effective temperatures at all metallicities. We apply our analysis to a large sample of both dwarf and giant stars selected from the Radial Velocity Experiment (RAVE) survey. We then show that the difference between parameters determined by our method and that by the standard 1D LTE excitation-ionization balance of Fe reveals substantial systematic biases: up to 400 K in effective temperature, 1.0 dex in surface gravity and 0.4 dex in metallicity for stars with [Fe/H] -2.5. This has large implications for the study of the stellar populations in the Milky Wa
The RAVE survey: constraining the local Galactic escape speed
We report new constraints on the local escape speed of our Galaxy. Our analysis is based on a sample of high-velocity stars from the RAVE survey and two previously published data sets. We use cosmological simulations of disc galaxy formation to motivate our assumptions on the shape of the velocity distribution, allowing for a significantly more precise measurement of the escape velocity compared to previous studies. We find that the escape velocity lies within the range 498 < vesc < 608 km s−1 (90 per cent confidence), with a median likelihood of 544 km s−1. The fact that v2esc is significantly greater than 2v2circ (where vcirc= 220 km s−1 is the local circular velocity) implies that there must be a significant amount of mass exterior to the solar circle, that is, this convincingly demonstrates the presence of a dark halo in the Galaxy. We use our constraints on vesc to determine the mass of the Milky Way halo for three halo profiles. For example, an adiabatically contracted NFW halo model results in a virial mass of 1.42+1.14−0.54× 1012 M⊙ and virial radius of (90 per cent confidence). For this model the circular velocity at the virial radius is 142+31−21 km s−1. Although our halo masses are model dependent, we find that they are in good agreement with each othe
The sixth data release of the Radial Velocity Experiment (RAVE). I. Survey description, spectra and radial velocities
The Radial Velocity Experiment (RAVE) is a magnitude-limited (9<I<12)
spectroscopic survey of Galactic stars randomly selected in the southern
hemisphere. The RAVE medium-resolution spectra (R~7500) cover the Ca-triplet
region (8410-8795A). The 6th and final data release (DR6 or FDR) is based on
518387 observations of 451783 unique stars. RAVE observations were taken
between 12 April 2003 and 4 April 2013. Here we present the genesis, setup and
data reduction of RAVE as well as wavelength-calibrated and flux-normalized
spectra and error spectra for all observations in RAVE DR6. Furthermore, we
present derived spectral classification and radial velocities for the RAVE
targets, complemented by cross matches with Gaia DR2 and other relevant
catalogs. A comparison between internal error estimates, variances derived from
stars with more than one observing epoch and a comparison with radial
velocities of Gaia DR2 reveals consistently that 68% of the objects have a
velocity accuracy better than 1.4 km/s, while 95% of the objects have radial
velocities better than 4.0 km/s. Stellar atmospheric parameters, abundances and
distances are presented in subsequent publication. The data can be accessed via
the RAVE Web (http://rave-survey.org) or the Vizier database.Comment: 32 pages, 11 figures, accepted for publication to A
CERT1 mutations perturb human development by disrupting sphingolipid homeostasis
Neural differentiation, synaptic transmission, and action potential propagation depend on membrane sphingolipids, whose metabolism is tightly regulated. Mutations in the ceramide transporter CERT (CERT1), which is involved in sphingolipid biosynthesis, are associated with intellectual disability, but the pathogenic mechanism remains obscure. Here, we characterize 31 individuals with de novo missense variants in CERT1. Several variants fall into a previously uncharacterized dimeric helical domain that enables CERT homeostatic inactivation, without which sphingolipid production goes unchecked. The clinical severity reflects the degree to which CERT autoregulation is disrupted, and inhibiting CERT pharmacologically corrects morphological and motor abnormalities in a Drosophila model of the disease, which we call ceramide transporter (CerTra) syndrome. These findings uncover a central role for CERT autoregulation in the control of sphingolipid biosynthetic flux, provide unexpected insight into the structural organization of CERT, and suggest a possible therapeutic approach for patients with CerTra syndrome.This work was supported by the National Institute of Neurological Disorders and Stroke (NINDS), NIH (R01NS109858, to VAG); the Paul A. Marks Scholar Program at the Columbia University Vagelos College of Physicians and Surgeons (to VAG); a TIGER grant from the TAUB Institute at the Columbia Vagelos College of Physicians and Scientists (to VAG); the Swiss National Science Foundation (SNF 31003A-179371, to TH); the European Joint Program on Rare Diseases (EJP RD+SNF 32ER30-187505, to TH); the Swiss Cancer League (KFS-4999-02-2020, to GD); the EPFL institutional fund (to GD); the Kristian Gerhard Jebsen Foundation (to GD); the Swiss National Science Foundation (SNSF) (310030_184926, to GD); the Swiss Foundation for Research on Muscle Disease (FSRMM, to MAL); the Natural Science and Engineering Research Council of Canada (Discovery Grant 2020-04241, to JEB); the Italian Ministry of Health Young Investigator Grant (GR-2011-02347754, to EL); the Fondazione Istituto di Ricerca Pediatrica – Città della Speranza (18-04, to EL); the Wroclaw Medical University (SUB.E160.21.004, to RS); the National Science Centre, Poland (2017/27/B/NZ5/0222, to RS); Telethon Undiagnosed Diseases Program (TUDP) (GSP15001); the Temple Street Foundation/Children’s Health Foundation Ireland (RPAC 19-02, to IK); the Deutsche Forschungsgemeinschaft (DFG) (PO2366/2–1, to BP); the Instituto de Salud Carlos III, Spain (to ELM, EBS, and BMD); the National Natural Science Foundation of China (81871079 and 81730036, to HG and KX); and the National Institutes of Diabetes and Digestive and Kidney Diseases (NIDDK), NIH (R01 DK115574, to SSC).The DEFIDIAG study is funded by grants from the French Ministry of Health in the framewok of the national French initiative for genomic medicine. The funders were not involved in the study design, data acquisition, analysis, or writing of the manuscript. Funding for the DECIPHER project was provided by Wellcome. The DDD study presents independent research commissioned by the Health Innovation Challenge Fund (grant number HICF-1009-003), a parallel funding partnership between Wellcome and the Department of Health, and the Wellcome Sanger Institute (grant number WT098051). The views expressed in this publication are those of the author(s) and not necessarily those of Wellcome or the Department of Health. The study has UK Research Ethics Committee approval (10/H0305/83, granted by the Cambridge South REC, and GEN/284/12, granted by the Republic of Ireland REC). The research team acknowledges the support of the National Institute for Health Research, through the Comprehensive Clinical Research Network.S
Penilaian Kinerja Keuangan Koperasi di Kabupaten Pelalawan
This paper describe development and financial performance of cooperative in District Pelalawan among 2007 - 2008. Studies on primary and secondary cooperative in 12 sub-districts. Method in this stady use performance measuring of productivity, efficiency, growth, liquidity, and solvability of cooperative. Productivity of cooperative in Pelalawan was highly but efficiency still low. Profit and income were highly, even liquidity of cooperative very high, and solvability was good
Juxtaposing BTE and ATE – on the role of the European insurance industry in funding civil litigation
One of the ways in which legal services are financed, and indeed shaped, is through private insurance arrangement. Two contrasting types of legal expenses insurance contracts (LEI) seem to dominate in Europe: before the event (BTE) and after the event (ATE) legal expenses insurance. Notwithstanding institutional differences between different legal systems, BTE and ATE insurance arrangements may be instrumental if government policy is geared towards strengthening a market-oriented system of financing access to justice for individuals and business. At the same time, emphasizing the role of a private industry as a keeper of the gates to justice raises issues of accountability and transparency, not readily reconcilable with demands of competition. Moreover, multiple actors (clients, lawyers, courts, insurers) are involved, causing behavioural dynamics which are not easily predicted or influenced.
Against this background, this paper looks into BTE and ATE arrangements by analysing the particularities of BTE and ATE arrangements currently available in some European jurisdictions and by painting a picture of their respective markets and legal contexts. This allows for some reflection on the performance of BTE and ATE providers as both financiers and keepers. Two issues emerge from the analysis that are worthy of some further reflection. Firstly, there is the problematic long-term sustainability of some ATE products. Secondly, the challenges faced by policymakers that would like to nudge consumers into voluntarily taking out BTE LEI
Search for stop and higgsino production using diphoton Higgs boson decays
Results are presented of a search for a "natural" supersymmetry scenario with gauge mediated symmetry breaking. It is assumed that only the supersymmetric partners of the top-quark (stop) and the Higgs boson (higgsino) are accessible. Events are examined in which there are two photons forming a Higgs boson candidate, and at least two b-quark jets. In 19.7 inverse femtobarns of proton-proton collision data at sqrt(s) = 8 TeV, recorded in the CMS experiment, no evidence of a signal is found and lower limits at the 95% confidence level are set, excluding the stop mass below 360 to 410 GeV, depending on the higgsino mass
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