scholarly journals An Empirical Template Library of Stellar Spectra for a Wide Range of Spectral Classes, Luminosity Classes, and Metallicities Using SDSS BOSS Spectra

2017 ◽  
Vol 230 (2) ◽  
pp. 16 ◽  
Author(s):  
Aurora Y. Kesseli ◽  
Andrew A. West ◽  
Mark Veyette ◽  
Brandon Harrison ◽  
Dan Feldman ◽  
...  
Keyword(s):  
Stellar Spectra ◽  
Wide Range ◽  
Template Library

scholarly journals Double and Multiple Star Speckle Observations at the 6-m Telescope

1992 ◽  
Vol 135 ◽  
pp. 469-476
Author(s):  
I.I. Balega ◽  
Y.Y. Balega ◽  
V.A. Vasyuk ◽  
J.J. McManus
Keyword(s):  
Binary Stars ◽  
Photon Counting ◽  
Speckle Interferometry ◽  
Spectroscopic Binaries ◽  
Multiple Star ◽  
Stellar Spectra ◽  
Ss 433 ◽  
Composite Spectra ◽  
Wide Range ◽  
Single Aperture

During the last 15 years more than 9,000 speckle interferometric measurements of binary stars have been collected using large optical telescopes (McAlister & Hartkopf 1988). Among them a significant contribution to the world speckle data has been made by the 6-m telscope near Zelenchuk. Up to now this instrument provides the maximal spatial resolution for single–aperture telescopes. First speckle images of the binary Capella were recorded at the telescope in 1977 (Balega & Tikhonov 1977), but we spent 5 more years to create special television techniques for photon counting and digital means for image processing before we started the regular interferometric program of binary observations in the wide range of stellar magnitudes. At first, the measurements were conducted in cooperation with French astronomers from the Centre d’Etudes et de Recherches Geodynamiques et Astronomiques using the optical camera and the television detector developed by Blazit et al. (1977). Since 1983 our equipment has been in use. The program of observations was oriented upon the traditional problems of multiple star speckle interferometry:1.Determination of stellar distances and masses for different types of binaries whose orbital elements can be derived. This includes already known fast visual and astrometric pairs with undetermined orbits, spectroscopic binaries that can be resolved directly, and newly discovered interferometric pairs which show fast orbital motion. The main attention was devoted to the late–type dwarfs in the vicinity of the Sun.2.Search for the secondary components whose existence could explain anomalies of stellar spectra or photometry (stars with composite spectra, occultation binaries, etc.)3.Study of unusual binaries (symbiotic stars, binaries with relativistic components, such as SS 433, etc.)

scholarly journals Meghnad Saha, 1893-1956

1960 ◽  
Vol 5 ◽  
pp. 216-236 ◽  
Keyword(s):  
Nuclear Physics ◽  
Direct Consequence ◽  
Stellar Atmospheres ◽  
Thermal Ionization ◽  
Active Member ◽  
Radio Waves ◽  
Indian Government ◽  
Stellar Spectra ◽  
National Planning ◽  
Wide Range

The name of Professor Meghnad Saha would always remain associated with the theory of thermal ionization and its application to the interpretation of stellar spectra in terms of the physical conditions prevailing in the stellar atmospheres. The theory had all the simplicity and inevitableness which usually characterize a fundamental and epochal contribution. It was almost a direct consequence of the recognition that the laws of thermodynamics and the kinetic theory of gases can be extended to a gas of free electrons. Apart from astrophysics, the theory later found numerous other important applications, such as, to mention some of them, in the study of the ionosphere, conductivity of flames, electric arcs and explosion phenomena. Saha’s researches in astrophysics and physics extended over a wide range of subjects. At one time or the other he worked on stellar spectra, thermal ionization, selective radiation pressure, spectroscopy, molecular dissociation, propagation of radio waves in the ionosphere, solar corona, radio emission from the sun, beta radioactivity, and the age of the rocks. Besides physics he took a keen interest, at times almost bordering on the professional, in ancient history and archaeology. He was a devoted and inspiring teacher, and he gave his time generously to his students. He organized active schools of research at Allahabad and Calcutta; and in establishing the Institute of Nuclear Physics at Calcutta, in building the laboratories of the Indian Association for the Cultivation of Science, and in founding academies of sciences in India, his role throughout was of the utmost importance. He, more than anyone else, was responsible in starting the monthly journal Science and Culture , and he was its editor for many years. He was from the beginning a member of the Council of Scientific and Industrial Research constituted by the Indian Government in 1942, and member (or chairman) of several of the research and other committees of the Council. He was the Chairman of the Council’s Indian Calendar Reform Committee. He was an elected independent member of the Indian Parliament. He took the keenest interest in problems of national planning, particularly in relation to science and industry. He was an active member of the National Planning Committee appointed by the Indian National Congress in 1938 with Jawaharlal Nehru as chairman. In his criticism of things and men, Saha was fearless and trenchant, and he was motivated by a deep earnestness and sincerely, though often tenaciously, held convictions. His memory and versatility were amazing. He was extremely simple, almost austere, in his habits and personal needs. Outwardly, he sometimes gave the impression of being remote, matter of fact, and even harsh, but once the outer shell was broken, one invariably found in him a person of extreme warmth, deep humanity, sympathy and understanding; and though almost altogether unmindful of his own personal comforts, he was extremely solicitous in the case of others. It was not in his nature to placate others. He was a man of undaunted spirit, resolute determination, untiring energy and dedication. On 16 February 1956, on his way to the Office of the Planning Commission in New Delhi, he succumbed to a sudden heart-attack (some hundred yards from the Office of the Commission) and at the age of sixty-two, a career superb in science and great in its promotion and dissemination was tragically closed.

scholarly journals QUETZAL - an open source C++ template library for coalescence-based environmental demogenetic models inference

2017 ◽  
Author(s):  
Arnaud Becheler ◽  
Camille Coron ◽  
Stéphane Dupas
Keyword(s):  
Population Growth ◽  
Open Source ◽  
Approximate Bayesian Computation ◽  
Changing Environment ◽  
Implementation Framework ◽  
Computation Techniques ◽  
Wide Range ◽  
Template Library ◽  
And Migration ◽  
Approximate Bayesian

1AbstractThe purpose of this article is to introduce an implementation framework enabling us, using available genetic samples, to understand and foresee the behavior of species living in a fragmented and temporally changing environment. To this aim, we first present a model of coalescence which is conditioned to environment, through an explicit modeling of population growth and migration. The parameters of this model can be infered using Approximate Bayesian Computation techniques, which supposes that the considered model can be efficiently simulated. We next present Quetzal, a C++ library composed of reusable generic components and designed to efficiently implement a wide range of coalescence-based environmental demogenetic models.

LAMOST-Subaru exploration of chemical relics of first stars

2017 ◽  
Vol 13 (S334) ◽  
pp. 21-24
Author(s):  
Haining Li ◽  
Wako Aoki ◽  
Gang Zhao ◽  
Takuma Suda ◽  
Satoshi Honda ◽  
...  
Keyword(s):  
Mass Star ◽  
Chemical Abundances ◽  
Homogeneous Sample ◽  
First Stars ◽  
Joint Project ◽  
Stellar Spectra ◽  
Chemical Enrichment ◽  
Chemical Signatures ◽  
Wide Range ◽  
Low Mass

AbstractVery metal-poor (VMP) stars preserve chemical signatures of early generations of stars, and are crutial to understand the early nucleosynthesis and first stars. Millions of stellar spectra obtained by LAMOST provide an unprecedented chance to enlarge the currently limited VMP star sample. Since 2014, a joint project on searching for VMP stars has been conducted based on the LAMOST survey and Subaru follow-up observations. So far, the project has obtained chemical abundances for about 250 VMP stars and a number of chemically interesting objects, e.g., three ultra metal-poor stars with [Fe/H] ~ − 4.0, a dozen Li-rich VMP stars distributed in a wide range of evolutionary stages. Statistics of the large homogeneous sample of VMP stars will be of great interest and importance to probe the chemical enrichment in the early Galaxy and low-mass star evolution.

scholarly journals Assessing the performance of LTE and NLTE synthetic stellar spectra in a machine learning framework

2020 ◽  
Vol 498 (3) ◽  
pp. 3817-3834 ◽  
Author(s):  
Spencer Bialek ◽  
Sébastien Fabbro ◽  
Kim A Venn ◽  
Nripesh Kumar ◽  
Teaghan O’Briain ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Rotational Velocity ◽  
Chemical Abundances ◽  
Stellar Spectra ◽  
Learning Framework ◽  
Accuracy And Precision ◽  
Wide Range ◽  
Parameter Ranges ◽  
Spectral Libraries ◽  
Temperature Surface

ABSTRACT In the current era of stellar spectroscopic surveys, synthetic spectral libraries are the basis for the derivation of stellar parameters and chemical abundances. In this paper, we compare the stellar parameters determined using five popular synthetic spectral grids (INTRIGOSS, FERRE, AMBRE, PHOENIX, and MPIA/1DNLTE) with our convolutional neural network (CNN, StarNet). The stellar parameters are determined for six physical properties (effective temperature, surface gravity, metallicity, [α/Fe], radial velocity, and rotational velocity) given the spectral resolution, signal-to-noise ratio, and wavelength range of optical FLAMES-UVES spectra from the Gaia-ESO Survey. Both CNN modelling and epistemic uncertainties are incorporated through training an ensemble of networks. StarNet training was also adapted to mitigate differences between the synthetic grids and observed spectra by augmenting with realistic observational signatures (i.e. resolution matching, wavelength sampling, Gaussian noise, zeroing flux values, rotational and radial velocities, continuum removal, and masking telluric regions). Using the FLAMES-UVES spectra for FGK-type dwarfs and giants as a test set, we quantify the accuracy and precision of the stellar label predictions from StarNet. We find excellent results over a wide range of parameters when StarNet is trained on the MPIA/1DNLTE synthetic grid, and acceptable results over smaller parameter ranges when trained on the 1DLTE grids. These tests also show that our CNN pipeline is highly adaptable to multiple simulation grids.

scholarly journals ATHOS: On-the-fly stellar parameter determination of FGK stars based on flux ratios from optical spectra

2018 ◽  
Vol 619 ◽  
pp. A134 ◽  
Author(s):  
Michael Hanke ◽  
Camilla J. Hansen ◽  
Andreas Koch ◽  
Eva K. Grebel
Keyword(s):  
Large Scale ◽  
Training Sample ◽  
Optical Spectra ◽  
Parameter Determination ◽  
Analysis Tool ◽  
Stellar Spectra ◽  
Wide Range ◽  
Iron Abundance ◽  
Analytical Relations

The rapidly increasing number of stellar spectra obtained by existing and future large-scale spectroscopic surveys feeds a demand for fast and efficient tools for the spectroscopic determination of fundamental stellar parameters. Such tools should not only comprise customized solutions for one particular survey or instrument, but, in order to enable cross-survey comparability, they should also be capable of dealing with spectra from a variety of spectrographs, resolutions, and wavelength coverages. To meet these ambitious specifications, we developed ATHOS (A Tool for HOmogenizing Stellar parameters), a fundamentally new analysis tool that adopts easy-to-use, computationally inexpensive analytical relations tying flux ratios (FRs) of designated wavelength regions in optical spectra to the stellar parameters effective temperature (T eff), iron abundance ([Fe/H]), and surface gravity (log g). Our T eff estimator is based on FRs from nine pairs of wavelength ranges around the Balmer lines Hβ and Hα, while for [Fe/H] and log g we provide 31 and 11 FRs, respectively, which are spread between ∼4800 Å and ∼6500 Å; a region covered by most optical surveys. The analytical relations employing these FRs were trained on N = 124 real spectra of a stellar benchmark sample that covers a large parameter space of T eff ≈ 4000–6500 K (spectral types F to K), [Fe/H] ≈ −4.5 to 0.3 dex, and log g ≈ 1–5 dex, which at the same time reflects ATHOS’ range of applicability. We find accuracies of 97 K for T eff, 0.16 dex for [Fe/H], and 0.26 dex for log g, which are merely bounded by finite uncertainties in the training sample parameters. ATHOS’ internal precisions can be better by up to 70%. We tested ATHOS on six independent large surveys spanning a wide range of resolutions (R = λ/Δ λ ≈ 2000–52 000), amongst which are the Gaia-ESO and the SDSS/SEGUE surveys. The exceptionally low execution time (< 30 ms per spectrum per CPU core) together with a comparison to the literature parameters showed that ATHOS can successfully achieve its main objectives, in other words fast stellar parametrization with cross-survey validity, high accuracy, and high precision. These are key to homogenize the output from future surveys, such as 4MOST or WEAVE.

scholarly journals A collection of model stellar spectra for spectral types B to early-M

2018 ◽  
Vol 618 ◽  
pp. A25 ◽  
Author(s):  
C. Allende Prieto ◽  
L. Koesterke ◽  
I. Hubeny ◽  
M. A. Bautista ◽  
P. S. Barklem ◽  
...  
Keyword(s):  
High Resolution ◽  
Interstellar Medium ◽  
Effective Temperature ◽  
Molecular Data ◽  
Chemical Compositions ◽  
Wavelength Interval ◽  
Atmospheric Parameters ◽  
Stellar Spectra ◽  
Synthetic Spectra ◽  
Wide Range

Context. Models of stellar spectra are necessary for interpreting light from individual stars, planets, integrated stellar populations, nebulae, and the interstellar medium. Aims. We provide a comprehensive and homogeneous collection of synthetic spectra for a wide range of atmospheric parameters and chemical compositions. Methods. We compile atomic and molecular data from the literature. We adopt the largest and most recent set of ATLAS9 model atmospheres, and use the radiative code ASSϵT. Results. The resulting collection of spectra is made publicly available at medium and high-resolution (R ≡ λ/δλ = 10 000, 100 000 and 300 000) spectral grids, which include variations in effective temperature between 3500 K and 30 000 K, surface gravity (0 ≤ log g ≤ 5), and metallicity (−5 ≤ [Fe/H] ≤ +0:5), spanning the wavelength interval 120–6500 nm. A second set of denser grids with additional dimensions, [α/Fe] and micro-turbulence, are also provided (covering 200–2500 nm). We compare models with observations for a few representative cases.

Some problems of objective-prism spectra classification

1966 ◽  
Vol 24 ◽  
pp. 51-52
Author(s):  
E. K. Kharadze ◽  
R. A. Bartaya
Keyword(s):  
Short Wave ◽  
High Quality ◽  
Stellar Spectra ◽  
Objective Prism

The unique 70-cm meniscus-type telescope of the Abastumani Astrophysical Observatory supplied with two objective prisms and the seeing conditions characteristic at Mount Kanobili (Abastumani) permit us to obtain stellar spectra of a high quality. No additional design to improve the “climate” immediately around the telescope itself is being applied. The dispersions and photographic magnitude limits are 160 and 660Å/mm, and 12–13, respectively. The short-wave end of spectra reaches 3500–3400Å.

Recent Applications of High Resolution Electron Microscopy to Crystalline Arrays of Virus Particles

1978 ◽  
Vol 36 (3) ◽  
pp. 470-482 ◽  
Author(s):  
R.W. Horne
Keyword(s):  
Electron Microscopy ◽  
Image Processing ◽  
Analytical Techniques ◽  
Staining Technique ◽  
High Resolution Electron Microscopy ◽  
Optical Diffraction ◽  
Full Potential ◽  
Virus Particles ◽  
Resolution Electron ◽  
Wide Range

The technique of surrounding virus particles with a neutralised electron dense stain was described at the Fourth International Congress on Electron Microscopy, Berlin 1958 (see Home & Brenner, 1960, p. 625). For many years the negative staining technique in one form or another, has been applied to a wide range of biological materials. However, the full potential of the method has only recently been explored following the development and applications of optical diffraction and computer image analytical techniques to electron micrographs (cf. De Hosier & Klug, 1968; Markham 1968; Crowther et al., 1970; Home & Markham, 1973; Klug & Berger, 1974; Crowther & Klug, 1975). These image processing procedures have allowed a more precise and quantitative approach to be made concerning the interpretation, measurement and reconstruction of repeating features in certain biological systems.

Microfabrication research at the National Submicron Facility

1983 ◽  
Vol 41 ◽  
pp. 86-89
Author(s):  
E.D. Wolf
Keyword(s):  
Integrated Circuits ◽  
Particle Physics ◽  
High Speed ◽  
New Technology ◽  
High Energy ◽  
High Energy Particle ◽  
New Science ◽  
Wide Range ◽  
Intermediate Domain ◽  
Circuit Function

Most microelectronics devices and circuits operate faster, consume less power, execute more functions and cost less per circuit function when the feature-sizes internal to the devices and circuits are made smaller. This is part of the stimulus for the Very High-Speed Integrated Circuits (VHSIC) program. There is also a need for smaller, more sensitive sensors in a wide range of disciplines that includes electrochemistry, neurophysiology and ultra-high pressure solid state research. There is often fundamental new science (and sometimes new technology) to be revealed (and used) when a basic parameter such as size is extended to new dimensions, as is evident at the two extremes of smallness and largeness, high energy particle physics and cosmology, respectively. However, there is also a very important intermediate domain of size that spans from the diameter of a small cluster of atoms up to near one micrometer which may also have just as profound effects on society as “big” physics.

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