bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical differences and similarities among the kinematically selected thick disk, inner halo and outer halo stars
Authors: Ishigaki Miho N. , Aoki Wako , Chiba Masashi 
Published: January 2014

AbstractChemical diversity among metal-poor stars in the old stellar components in the Milky Way (MW), namely the thick disk and stellar halo, provides clues to understanding the early chemodynamical evolution of our Galaxy. We present our results on a homogeneous chemical abundance analysis for nearby metal-poor stars likely belonging to the MW thick disk, inner and outer stellar halos. Abundances of alpha, sodium, iron-peak and neutron-capture elements in the sample stars have been estimated using high-resolution (R 50000) spectra obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. The derived abundances are used to examine differences and similarities in elemental abundance ratios among the kinematically defined thick disk, inner and outer halo subsamples in the metallicity range of −3.3 < [Fe/H] < −0.5. We show that, in the metallicity range of [Fe/H] < −2, the three subsamples are similar in most of the elemental abundances. On the other hand, in the higher metallicities, particularly in [Fe/H] > −1.5, the thick disk and the inner/outer halo subsamples show systematically different abundance ratios for some elements including alpha, sodium, zinc and europium. A modest difference in the sodium and zinc abundances between the inner- and outer halo subsamples is also identified. The observed distinct abundances of some elements among the three subsamples implies that their constituent stars originally formed in progenitor systems that have experienced different star formation and chemical enrichment histories.
MilkyWay@home: Harnessing volunteer computers to constrain dark matter in the Milky Way
Authors: Newberg Heidi Jo , Newby Matthew , Desell Travis , Magdon-Ismail Malik , Szymanski Boleslaw , Varela Carlos 
Published: January 2014

AbstractMilkyWay@home is a volunteer computing project that allows people from every country in the world to volunteer their otherwise idle processors to Milky Way research. Currently, more than 25,000 people (150,000 since November 9, 2007) contribute about half a PetaFLOPS of computing power to our project. We currently run two types of applications: one application fits the spatial density profile of tidal streams using statistical photometric parallax, and the other application finds the N-body simulation parameters that produce tidal streams that best match the measured density profile of known tidal streams. The stream fitting application is well developed and is producing published results. The Sagittarius dwarf leading tidal tail has been fit, and the algorithm is currently running on the trailing tidal tail and bifurcated pieces. We will soon have a self-consistent model for the density of the smooth component of the stellar halo and the largest tidal streams. The N-body application has been implemented for fitting dwarf galaxy progenitor properties only, and is in the testing stages. We use an Earth-Mover Distance method to measure goodness-of-fit for density of stars along the tidal stream. We will add additional spatial dimensions as well as kinematic measures in a piecemeal fashion, with the eventual goal of fitting the orbit and parameters of the Milky Way potential (and thus the density distribution of dark matter) using multiple tidal streams.
Stellar yields for chemical evolution modelling
Authors: Karakas Amanda I. 
Published: January 2014

AbstractStellar yields are a key ingredient in chemical evolution models. Stars with masses as low as 0.9M⊙, which have an age less than that of our Galaxy at low metallicity, can contribute to the chemical evolution of elements. Stars less than about 8–10M⊙ experience recurrent mixing events that can significantly change the surface composition of the envelope. Evolved stars are observed with surface enrichment in carbon, nitrogen, fluorine, and heavy elements synthesized by the slow neutron capture process (the s-process). These stars release their nucleosynthesis products through stellar outflows or winds, in contrast to massive stars that explode as core-collapse supernovae. Here I review stellar yields for stars up to 10M⊙, including a brief discussion of their uncertainties and shortcomings. Finally, I discuss efforts by various groups to address these issues and to provide homogeneous yields for low and intermediate-mass stars covering a broad range of metallicities.
Supernova Yields for Chemical Evolution Modeling
Authors: Nomoto Ken'ichi , Suzuki Tomoharu 
Published: January 2014

AbstractWe review the recent results of the nucleosynthesis yields of massive stars. We examine how those yields are affected by some hydrodynamical effects during the supernova explosions, namely, explosion energies from those of hypernovae to faint supernovae, mixing and fallback of processed materials, asphericity, etc. Those parameters in the supernova nucleosynthesis models are constrained from observational data of supernovae and metal-poor stars. The elemental abundance patterns observed in extremely metal-poor stars show some peculiarities relative to the solar abundance pattern, which suggests the important contributions of hypernovae and faint supernovae in the early chemical enrichment of galaxies. These constraints on supernova nucleosynthesis are taken into account in the latest yield table for chemical evolution modeling.
Stream-orbit misalignment & a new algorithm for constraining the Galactic potential with streams
Authors: Sanders Jason L. , Binney James 
Published: January 2014

AbstractIn general, a tidal stream is misaligned with the orbit of its progenitor. Here we present the formation of tidal streams in angle-action space to discuss the effect of this misalignment on orbit-fitting algorithms for constraining the Galactic potential. We close by presenting and testing an alternative algorithm which more fully accounts for the dynamics of streams by using the angle-action formalism.
Action-space clustering of tidal streams to map the Galactic potential
Authors: Sanderson Robyn E. , Helmi Amina , Hogg David W. 
Published: January 2014

AbstractGiven a parametrized model of the Galactic potential, the best-fit parameters can be obtained by maximizing the Kullback-Leibler divergence of the action distribution of a set of stars initially clustered in action space (e.g. stars in tidal streams). This method will allow us to map the Milky Way's gravitational potential by simultaneously fitting multiple tidal streams without requiring stream membership information. With 20 streams of at least 20 stars each, including observational errors consistent with predictions for Gaia, this technique recovers the input potential parameters to a precision of 10-60% and an accuracy of 10%. With all the observed streams in our mock stellar halo (about 40) that fit the error criteria, the precision improves to 10%.
How can star formation be sustained?
Authors: Fraternali Filippo 
Published: January 2014

AbstractThere is overwhelming evidence that the Milky Way has formed its stars at a relatively constant rate throughout the Hubble time. This implies that its stock of cold gas was not in place since the beginning but it has been acquired slowly through gas accretion. The gas accretion must have been at low metallicity in order to reconcile the metallicities observed in the disc with the predictions of chemical evolution models. But how does this gas accretion take place? I review the current evidence of gas accretion into the Milky Way and similar galaxies through the infall of cold gas clouds and satellites. The conclusion from these studies is that the infalling gas at high column densities observed in HI emission is a least one order of magnitude below the value required to sustain star formation, thus accretion must come from a different channel. The likely reservoir for gas accretion is the cosmological corona of virial-temperature gas in which every galaxy must be embedded. At the interface between the disc and the corona the cold high-metallicity disc gas and the hot coronal medium must mix efficiently and this mixing causes the cooling and accretion of the lower corona. I show how this mechanism reproduces the kinematics of the neutral extraplanar gas in the Milky Way and other nearby galaxies and the ionised high-velocity clouds observed in HST spectra. I conclude with the speculation that the loss in efficiency of the disc-corona interaction is the ultimate cause for the evolution of disc galaxies towards the red sequence.
LSS-GAC – A LAMOST Spectroscopic Survey of the Galactic Anti-center
Authors: Liu X.-W. , Yuan H.-B. , Huo Z.-Y. , Deng L.-C. , Hou J.-L. , Zhao Y.-H. , Zhao G. , Shi J.-R. , Luo A.-L. , Xiang M.-S. , Zhang H.-H. , Huang Y. , Zhang H.-W. 
Published: January 2014

AbstractAs a major component of the LAMOST Galactic surveys, the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) will survey a significant volume of the Galactic thin/thick disks and halo in a contiguous sky area of ~3,400 sq.deg., centered on the Galactic anti-center (|b| ≤ 30°, 150 ≤ l ≤ 210°), and obtain λλ3800–9000 low resolution (R ~1,800) spectra for a statistically complete sample of ≳ 3 M stars of all colors, uniformly and randomly selected from (r, g - r) and (r, r - i) Hess diagrams obtained from a CCD imaging photometric survey of ~5,400 sq.deg. with the Xuyi 1.04/1.20 m Schmidt Telescope, ranging from r = 14.0 to a limiting magnitude of r = 17.8 (18.5 for limited fields). The survey will deliver spectral classification, radial velocity (Vr) and stellar parameters (effective temperature (Teff), surface gravity (log g) and metallicity [Fe/H]) for millions of Galactic stars. Together with Gaia which will provide accurate distances and tangential velocities for a billion stars, the LSS-GAC will yield a unique data set to study the stellar populations, chemical composition, kinematics and structure of the disks and their interface with the halo, identify streams of debris of tidally disrupted dwarf galaxies and clusters, probe the gravitational potential and dark matter distribution, map the 3D distribution of interstellar dust extinction, search for rare objects (e.g. extremely metal-poor or hyper-velocity stars), and ultimately advance our understanding of the assemblage of the Milky Way and other galaxies and the origin of regularity and diversity of their properties.The survey was initiated in the fall of 2012 and expected to complete in the spring of 2017. Hitherto, about 0.4 M spectra of S/N(λ7450) ≥ 10 per pixel have been accumulated. In addition, bright nights have been used to target stars brighter than 14 mag and have so far generated over 0.4 M spectra, yielding an excellent sample of local stars to probe the solar neighborhood. LSP3, a set of pipelines tailored to the need of LSS-GAC, for spectral flux-calibration, and radial velocity and stellar parameter determinations, have been developed at Peking University, based on packages developed for the SDSS and those at the National Astronomical Observatories of Chinese Academy of Sciences. Comparisons of multi-epoch observations, with the SDSS results, as well as applying the pipelines to open and globular clusters show that LSP3 has achieved a precision of 5 km s−1, 110 K, 0.15 dex and 0.15 dex for Vr, Teff, log g and [Fe/H], respectively. The data are publicly available, subject to regulations of the LAMOST data policy, and begin to yield scientific results. The potential of LSS-GAC and power of existing data are illustrated with examples of selected problems.
The Sun. A typical star in the solar neighborhood?
Authors: Meléndez Jorge 
Published: January 2014

AbstractThe Sun is used as the fundamental standard in chemical abundance studies, thus it is important to know whether the solar abundance pattern is representative of the solar neighborhood. Albeit at low precision (0.05 – 0.10 dex) the Sun seems to be a typical solar-metallicity disk star, at high precision (0.01 dex) its abundance pattern seems abnormal when compared to solar twins. The Sun shows a deficiency of refractory elements that could be due to the formation of terrestrial planets. The formation of giant planets may also introduce a signature in the chemical composition of stars. We discuss both planet signatures and also the enhancement of neutron-capture elements in the solar twin 18 Sco.
Abundance analysis of three metal poor stars: CS 22166-0030, CS 22186-0005, and CS 30344-0033
Authors: Çalışkan Şeyma , Caffau Elisabetta , Bonifacio Piercarlo , Sbordone Luca , Albayrak Berahitdin 
Published: January 2014

AbstractWe present the abundance analysis of three very metal poor stars, CS 22166-0030 ([Fe/H]=−2.96), CS 22186-0005 ([Fe/H]=−2.70), and CS 30344-0033 ([Fe/H]=−2.90). Our study is based on high resolution spectra which were obtained from SARG (on TNG), HARPS (on 3.6m), and UVES (on VLT) spectrographs and one-dimensional ATLAS9 model atmospheres. We derived the abundances for 2, 9, and 16 atomic species in the spectrum of CS 22166-0030, CS 22186-0005, and CS 30344-0033, respectively. The Na and Mg abundances of CS 22166-0030 are highly under-abundant with respect to the solar values. The abundance patterns of CS 22186-0005 and CS 30344-0033 are consistent with the other halo stars within abundance uncertainties.
Influence of Departures from LTE on Oxygen Abundance Determination in the Atmospheres of A – K stars
Authors: Sitnova Tatyana , Mashonkina Lyudmila , Zhao Gang , Ryabchikova Tatiana , Pakhomov Yury 
Published: January 2014

AbstractSolar oxygen abundance is a key parameter for the studies of solar physics. Oxygen abundances of cool stars with different metallicities are important for understanding the galactic chemical evolution. We present non-LTE calculations for O I with the classical plane-parallel (1D) model atmospheres for a set of stellar parameters corresponding to stars of spectral types from A to K. Non-LTE leads to strengthening the O I lines, and the difference between the non-LTE and LTE abundances (non-LTE correction) is negative. The departures from LTE grow toward higher effective temperature and lower surface gravity. In the entire temperature range and log g = 4, the non-LTE correction does not exceed 0.05 dex in absolute value for lines of O I in the visible spectral range. The non-LTE corrections are significantly larger for the infrared O I 7771-5, 8446 Å lines and reach an order of magnitude for A-type stars. To differentiate the effects of inelastic collisions with electrons and neutral hydrogen atoms on the statistical equilibrium (SE) of O I, we derived the oxygen abundance for the five well studied A-type stars. For each star, non-LTE largely removes the difference between the infrared and visible lines found in LTE. In the case of cool stars (Sun and Procyon), inelastic collisions with H I affect the SE of O I, and agreement between the abundances from different lines is achieved when using the Drawin's formalism for collisional rates calculations. The solar mean oxygen abundance from the six lines is ϵ = 8.74 ± 0.05, when using the MAFAGS-OS solar model atmosphere and ϵ = 8.78 ± 0.03, when applying the 3D corrections taken from the literature. The non-LTE abundances of oxygen are derived for the sample of cool dwarfs with various metallicities on high-resolution spectra observed in the Lick observatory.
The Correction of Fiber Throughput Variation due to Focal Ratio Degradation
Authors: Chen Jianjun , Bai Zhongrui , Li Guangwei , Zhang Haotong 
Published: January 2014

AbstractThe focal ratio degradation (FRD) of optical fibers is a major source causing light loss to astronomical multi-fibre instruments like LAMOST (Oliveira, A. C, et al. 2005). The effects of stress and twist during mounting and rotation of the fibers could change the FRD for individual fibers (Clayton 1989), which means that the transmission efficiency of each individual fiber will vary. We investigate such throughput variation among LAMOST fibers and its relevance to the intensity of sky emission lines (Garstang 1989) over the full wavelength coverage. On the basis of the work, we present an approach to correct the varied fiber throughput by measuring the strength of the sky emission lines as the secondary throughput correction.
Fiber Positioning Test
Authors: Dong Yiqiao , Zhang Haotong , Bai Zhongrui , Yuan Hailong , Lei Yajuan 
Published: January 2014

AbstractWith the concern that observed flux is very sensitive upon fiber positions, we develop a novel approach measuring the error of fiber positions in this work. More specifically, we compute two orthogonal groups of the flux ratio before and after moving the fiber a few arcseconds, and correct the system coordinate transformation based on the computed fiber position error.
Strontium in the era of Gaia and LAMOST
Authors: Hansen Camilla J. , Caffau Elisabetta , Bergemann Maria 
Published: January 2014

AbstractThe formation and evolution of the heavy neutron-capture elements (Z > 37) are to date not well understood. Therefore, abundance and galactic chemical evolution (GCE) studies of these heavy elements may carry key information to this open question. Strontium (Sr) is one of the two heavy elements (Sr and Ba) that show intrinsically very strong absorption lines even in extremely metal-poor stars (and remains detectable at low spectral resolution). Hence, the 4077 Å Sr II line provides a unique insight into the behaviour of heavy neutron-capture elements at all metallicities and resolutions. Here the focus is on strontium, its 3D and NLTE (non-local thermodynamic equilibrium) corrections, as well as chemical evolution.
The methods for searching hypervelocity star candidates from the SDSS
Authors: Li Yinbi , Luo Ali , Zhao Gang , Lu Youjun 
Published: January 2014

AbstractHyper-velocity stars are believed to be ejected out from the Galactic center through dynamical interactions of (binary) stars with the central massive black hole(s). In this paper, we firstly select F and G type main sequence stars from about 370,000 stellar spectra of DR7. Then, we select 369 high velocity stars from main sequence samples using the radial velocity distribution. Finally, we find 13 possible unbound hyper-velocity star candidates from the 369 high velocity stars.
The photometric system of the Nanshan One-meter Wide field Telescope
Authors: Liu Jinzhong , Zhang Yu , Feng Guojie , Bai Chunhai 
Published: January 2014

AbstractA one-meter wide field astronomical telescope with Alt-Az mount, putting in work at prime focus with field corrector, is located at the Nanshan site of Xinjiang Astronomical Observatory. The Nanshan One meter Wide-field Telescope (hereafter NOWT) provides excellent optical quality, pointing accuracy and tracking accuracy. The main scientific goals of NOWT are supernovae, gamma-ray bursts, novae, variable stars, and active galactic nuclei. It is worthwhile to point out that the sky background at the Nanshan is a classic optical site.
The stellar metallicity distribution of the Galaxy from the BATC survey
Authors: Peng Xiyan , Du Cuihua , Wu Zhenyu , Ma Jun , Zhou Xu 
Published: January 2014

AbstractUsing ~2200 BATC main sequence (MS) stars which include SDSS stellar atmospheric parameters, we develop the polynomial photometric calibration method to evaluate the stellar effective temperature and metallicity for BATC data. This calibration method has been applied to about 160 000 MS stars. The mean stellar metallicity smoothly decreases from −0.65 to −0.78 dex in the interval 0.5 < |Z| ≤ 2 kpc. Metallicity distributions in the halo and the thick disk seem invariant with the distance from the Galactic plane.
The SED Machine - Fast classification of transient objects
Authors: Ritter Andreas , Konidaris N. , Ngeow C. C. , Quimby R. , Ben-Ami S. 
Published: January 2014

AbstractThe field of time-domain astronomy is expected to enjoy a golden age during this decade. However, the traditional method for the classification of transient candidates using spectra obtained with medium- to large-aperture telescopes is extremely time consuming and struggling to keep up with the discovery rate. The Spectral Energy Distribution (SED) Machine uses a new approach in order to overcome this shortcoming.
Relations of stellar mass and electron temperature-based metallicity of star-forming galaxies in wide mass range
Authors: Shi Weibin , Liang Yanchun , Hammer Francois 
Published: January 2014

AbstractWe gather a sample of both metal-rich and low metallicity galaxies. Both of them have oxygen abundances estimated from electron temperature (Te). They spread in a wide stellar mass range from 106M⊙ to 1011M⊙. Then, a consistent relation of stellar mass and metallicity are derived from them for such wide range of stellar masses. This relation also shows clearly the discrepancy of Te-based oxygen abundances from those derived from the strong-line method.
Measuring Stellar Radial Velocity using Markov Chain Monte Carlo(MCMC) Method
Authors: Song Yihan , Luo Ali , Zhao Yongheng 
Published: January 2014

AbstractStellar radial velocity is estimated by using template fitting and Markov Chain Monte Carlo(MCMC) methods. This method works on the LAMOST stellar spectra. The MCMC simulation generates a probability distribution of the RV. The RV error can also computed from distribution.
Error Analysis of SDSS/LAMOST Stellar Radial Velocity Measurement
Authors: Wang Fengfei , Luo Ali , Zhang Haotong 
Published: January 2014

AbstractWe select super high quality spectra of spectral type A, F, G, K, M stars from SDSS C DR7. We mix our spectra with noise and then measure their radial velocity. The analysis shows that the accuracy of K, M type stars is much better than A, F stars. With our relationship between the signal-to-noise and accuracy of radial velocity measurement of different spectral type, we provide a good reference for stellar study related to radial velocity.
Spin-Orbit Angles as a Probe to Orbital Evolution
Authors: Triaud A. H. M. J. , Cameron A. Collier , Queloz D. , Anderson D. R. , Brown D. J. A. , Smalley B. , Bouchy F. , Lendl M. , Gillon M. 
Published: January 2014

AbstractWe observed with HARPS, the Rossiter-McLaughlin effect for 40 of the 75 transiting hot Jupiters discovered in the Southern Hemisphere by WASP. Our observations reveal a wide distribution in orbital inclinations indicative of past dynamical interactions. Our data also demonstrate the important effect produced by tidal interactions in shaping the spin–orbit (β) angle distribution. We briefly present and interpret the data we collected in a series of graphs.