scholarly journals The Te[N ii]–Te[O iii] temperature relation in H ii regions and the reliability of strong-line methods

2020 ◽  
Vol 497 (1) ◽  
pp. 672-686
Author(s):  
K Z Arellano-Córdova ◽  
M Rodríguez
Keyword(s):  
High Resolution ◽  
Direct Method ◽  
Strong Line ◽  
Temperature Sensitive ◽  
H Ii Regions ◽  
Temperature Relation ◽  
Degree Of Ionization ◽  
Sensitive Line ◽  
The One

ABSTRACT We use a sample of 154 observations of 124 H ii regions that have measurements of both Te[O iii] and Te[N ii], compiled from the literature, to explore the behaviour of the Te[O iii]–Te[N ii] temperature relation. We confirm that the relation depends on the degree of ionization and present a new set of relations for two different ranges of this parameter. We study the effects introduced by our temperature relations and four other available relations in the calculation of oxygen and nitrogen abundances. We find that our relations improve slightly on the results obtained with the previous ones. We also use a sample of 26 deep, high-resolution spectra to estimate the contribution of blending to the intensity of the temperature-sensitive line [O iii] λ4363, and we derive a relation to correct Te[O iii] for this effect. With our sample of 154 spectra, we analyse the reliability of the R, S, O3N2, N2, ONS, and C strong-line methods by comparing the metallicity obtained with these methods with the one implied by the direct method. We find that the strong-line methods introduce differences that reach ∼0.2 dex or more, and that these differences depend on O/H, N/O, and the degree of ionization.

The Culgoora Magnetograph

1971 ◽  
Vol 43 ◽  
pp. 24-29 ◽  
Author(s):  
J. V. Ramsay ◽  
R. G. Giovanelli ◽  
H. R. Gillett
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Angular Resolution ◽  
Field Of View ◽  
Large Field ◽  
Sensitive Line ◽  
The One ◽  
The Magnetic Field

The magnetograph is based on a high-resolution filter which serves in place of a spectrograph, except that a reasonably large field of view (one-quarter of the Sun's diameter) can be observed at the one instant. Observations are made by obtaining filtergrams of opposite circular polarizations simultaneously in the wing of a magnetically sensitive line. Exposure times are about 0.3 s, the angular resolution of the magnetic field is about 2 arc s, closest frame repetition rates about 8 s. The filtergrams are processed subsequently by photographic or television subtraction. Semiautomatic photographic and/or TV subtractions yield magnetograms suitable for cinematographic projection though the subtractions are not yet as perfect as those obtained by individual subtraction.

scholarly journals Bar effect on gas-phase abundance gradients. I. Data sample and chemical abundances

2020 ◽  
Vol 500 (2) ◽  
pp. 2359-2379 ◽  
Author(s):  
A Zurita ◽  
E Florido ◽  
F Bresolin ◽  
E Pérez-Montero ◽  
I Pérez
Keyword(s):  
Emission Line ◽  
Gas Phase ◽  
Direct Method ◽  
Structural Parameters ◽  
Companion Paper ◽  
Strong Line ◽  
H Ii Regions ◽  
Chemical Abundances ◽  
The Galaxy ◽  
H Ii Region

ABSTRACT Studies of gas-phase radial metallicity profiles in spirals published in the last decade have diminished the importance of galactic bars as agents that mix and flatten the profiles, contradicting results obtained in the 1990s. We have collected a large sample of 2831 published H ii region emission-line fluxes in 51 nearby galaxies, including objects both with and without the presence of a bar, with the aim of revisiting the issue of whether bars affect the radial metal distribution in spirals. In this first paper of a series of two, we present the galaxy and the H ii region samples. The methodology is homogeneous for the whole data sample and includes the derivation of H ii region chemical abundances, structural parameters of bars and discs, galactocentric distances, and radial abundance profiles. We have obtained O/H and N/O abundance ratios from the Te-based (direct) method for a subsample of 610 regions, and from a variety of strong-line methods for the whole H ii region sample. The strong-line methods have been evaluated in relation to the Te-based one from both a comparison of the derived O/H and N/O abundances for individual H ii regions and a comparison of the abundance gradients derived from both methodologies. The median value and the standard deviation of the gradient distributions depend on the abundance method, and those based on the O3N2 indicator tend to flatten the steepest profiles, reducing the range of observed gradients. A detailed analysis and discussion of the derived O/H and N/O radial abundance gradients and y-intercepts for barred and unbarred galaxies is presented in the companion Paper II. The whole H ii region catalogue including emission-line fluxes, positions, and derived abundances is made publicly available on the CDS VizieR facility, together with the radial abundance gradients for all galaxies.

scholarly journals Exploring chemical homogeneity in dwarf galaxies: a VLT-MUSE study of JKB 18

2020 ◽  
Vol 495 (3) ◽  
pp. 2564-2581 ◽  
Author(s):  
Bethan L James ◽  
Nimisha Kumari ◽  
Andrew Emerick ◽  
Sergey E Koposov ◽  
Kristen B W McQuinn ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
Large Scale ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Direct Method ◽  
Mixing Time ◽  
Strong Line ◽  
H Ii Regions ◽  
Chemical Abundances ◽  
Chemical Homogeneity

ABSTRACT Deciphering the distribution of metals throughout galaxies is fundamental in our understanding of galaxy evolution. Nearby, low-metallicity, star-forming dwarf galaxies, in particular, can offer detailed insight into the metal-dependent processes that may have occurred within galaxies in the early Universe. Here, we present VLT/MUSE observations of one such system, JKB 18, a blue diffuse dwarf galaxy with a metallicity of only 12 + log(O/H)=7.6 ± 0.2 (∼0.08 Z⊙). Using high spatial resolution integral-field spectroscopy of the entire system, we calculate chemical abundances for individual H ii regions using the direct method and derive oxygen abundance maps using strong-line metallicity diagnostics. With large-scale dispersions in O/H, N/H, and N/O of ∼0.5–0.6 dex and regions harbouring chemical abundances outside this 1σ distribution, we deem JKB 18 to be chemically inhomogeneous. We explore this finding in the context of other chemically inhomogeneous dwarf galaxies and conclude that neither the accretion of metal-poor gas, short mixing time-scales or self-enrichment from Wolf–Rayet stars are accountable. Using a galaxy-scale, multiphase, hydrodynamical simulation of a low-mass dwarf galaxy, we find that chemical inhomogeneities of this level may be attributable to the removal of gas via supernovae and the specific timing of the observations with respect to star formation activity. This study not only draws attention to the fact that dwarf galaxies can be chemically inhomogeneous, but also that the methods used in the assessment of this characteristic can be subject to bias.

scholarly journals Chemical abundances in active galaxies

2020 ◽  
Vol 496 (2) ◽  
pp. 2191-2203 ◽  
Author(s):  
Sophia R Flury ◽  
Edward C Moran
Keyword(s):  
Direct Method ◽  
Flux Ratio ◽  
Single Equation ◽  
Sloan Digital Sky Survey ◽  
H Ii Regions ◽  
Chemical Abundances ◽  
Temperature Relation ◽  
Oxygen Abundance ◽  
Star Forming ◽  
Liner Galaxies

ABSTRACT The Sloan Digital Sky Survey (SDSS) has proved to be a powerful resource for understanding the physical properties and chemical composition of star-forming galaxies in the local Universe. The SDSS population of active galactic nuclei (AGNs) remains as of yet less explored in this capacity. To extend the rigorous study of H ii regions in the SDSS to AGNs, we adapt methods for computing direct-method chemical abundances for application to the narrow-line regions (NLR) of AGNs. By accounting for triply ionized oxygen, we are able to more completely estimate the total oxygen abundance. We find a strong correlation between electron temperature and oxygen abundance due to collisional cooling by metals. Furthermore, we find that nitrogen and oxygen abundances in AGNs are strongly correlated. From the metal–temperature relation and the coupling of nitrogen and oxygen abundances, we develop a new, empirically and physically motivated method for determining chemical abundances from the strong emission lines commonly employed in flux-ratio diagnostic diagrams (BPT diagrams). Our approach, which for AGNs reduces to a single equation based on the BPT line ratios, consistently recovers direct-method abundances over a 1.5 dex range in oxygen abundance with an rms uncertainty of 0.18 dex. We have determined metallicities for thousands of AGNs in the SDSS, and in the process have discovered an ionization-related discriminator for Seyfert and LINER galaxies.

scholarly journals Spatially resolved direct method metallicity in a high-redshift analogue local galaxy: temperature structure impact on metallicity gradients

2020 ◽  
Author(s):  
Alex J Cameron ◽  
Tiantian Yuan ◽  
Michele Trenti ◽  
David C Nicholls ◽  
Lisa J Kewley
Keyword(s):  
Direct Method ◽  
High Redshift ◽  
Direct Methods ◽  
Spectroscopic Studies ◽  
Strong Line ◽  
H Ii Regions ◽  
Temperature Structure ◽  
Spatially Resolved ◽  
Systematic Effects ◽  
Gradient Measurements

Abstract We investigate how H ii region temperature structure assumptions affect “direct-method” spatially-resolved metallicity observations using multispecies auroral lines in a galaxy from the SAMI Galaxy Survey. SAMI609396B, at redshift z = 0.018, is a low-mass galaxy in a minor merger with intense star formation, analogous to conditions at high redshifts. We use three methods to derive direct metallicities and compare with strong-line diagnostics. The spatial metallicity trends show significant differences among the three direct methods. Our first method is based on the commonly used electron temperature Te([O iii]) from the [O iii]λ4363 auroral line and a traditional Te([O ii]) – Te([O iii]) calibration. The second method applies a recent empirical correction to the O+ abundance from the [O iii]/[O ii] strong-line ratio. The third method infers the Te([O ii]) from the [S ii]λλ4069,76 auroral lines. The first method favours a positive metallicity gradient along SAMI609396B, whereas the second and third methods yield flattened gradients. Strong-line diagnostics produce mostly flat gradients, albeit with unquantified contamination from shocked regions. We conclude that overlooked assumptions about the internal temperature structure of H ii regions in the direct method can lead to large discrepancies in metallicity gradient studies. Our detailed analysis of SAMI609396B underlines that high-accuracy metallicity gradient measurements require a wide array of emission lines and improved spatial resolutions in order to properly constrain excitation sources, physical conditions, and temperature structures of the emitting gas. Integral-field spectroscopic studies with future facilities such as JWST/NIRSpec and ground-based ELTs will be crucial in minimising systematic effects on measured gradients in distant galaxies.

A Simple Real-Space Channelling Theory for Electron Diffraction and HREM

1990 ◽  
Vol 48 (1) ◽  
pp. 64-65
Author(s):  
D. Van Dyck
Keyword(s):  
High Resolution ◽  
Electron Diffraction ◽  
Direct Method ◽  
Real Space ◽  
Zone Axis ◽  
Phase Object ◽  
High Resolution Images ◽  
The Many ◽  
Analytical Expressions ◽  
Electron Wavefunction

The computation of the many beam dynamical electron diffraction amplitudes or high resolution images can only be done numerically by using rather sophisticated computer programs so that the physical insight in the diffraction progress is often lost. Furthermore, it is not likely that in this way the inverse problem can be solved exactly, i.e. to reconstruct the structure of the object from the knowledge of the wavefunction at its exit face, as is needed for a direct method [1]. For this purpose, analytical expressions for the electron wavefunction in real or reciprocal space are much more useful. However, the analytical expressions available at present are relatively poor approximations of the dynamical scattering which are only valid either for thin objects ((weak) phase object approximation, thick phase object approximation, kinematical theory) or when the number of beams is very limited (2 or 3). Both requirements are usually invalid for HREM of crystals. There is a need for an analytical expression of the dynamical electron wavefunction which applies for many beam diffraction in thicker crystals. It is well known that, when a crystal is viewed along a zone axis, i.e. parallel to the atom columns, the high resolution images often show a one-to-one correspondence with the configuration of columns provided the distance between the columns is large enough and the resolution of the instrument is sufficient. This is for instance the case in ordered alloys with a column structure [2,3]. From this, it can be suggested that, for a crystal viewed along a zone axis with sufficient separation between the columns, the wave function at the exit face does mainly depend on the projected structure, i.e. on the type of atom columns. Hence, the classical picture of electrons traversing the crystal as plane-like waves in the directions of the Bragg beams which historically stems from the X-ray diffraction picture, is in fact misleading.

The studies on highly concentrated complex dispersions of gold nanoparticles and temperature-sensitive nanogels and their application as new blood-vessel-embolic materials with high-resolution angiography

2014 ◽  
Vol 2 (36) ◽  
pp. 6044-6053 ◽  
Author(s):  
Yingying Ma ◽  
Jiangshan Wan ◽  
Kun Qian ◽  
Shinan Geng ◽  
Nijun He ◽  
...  
Keyword(s):  
Gold Nanoparticles ◽  
High Resolution ◽  
Blood Vessel ◽  
Au Nanoparticles ◽  
Blood Pool ◽  
Temperature Sensitive ◽  
Colloid Stability ◽  
Blood Pool Imaging ◽  
Embolic Materials

High colloid stability of highly concentrated Au nanoparticles (GNPs) for use in blood-pool imaging was achieved, using p(N-isopropylacrylamide-co-butyl methylacrylate) nanogels.

scholarly journals BRRNet: A Fully Convolutional Neural Network for Automatic Building Extraction From High-Resolution Remote Sensing Images

2020 ◽  
Vol 12 (6) ◽  
pp. 1050 ◽  
Author(s):  
Zhenfeng Shao ◽  
Penghao Tang ◽  
Zhongyuan Wang ◽  
Nayyer Saleem ◽  
Sarath Yam ◽  
...  
Keyword(s):  
Remote Sensing ◽  
High Resolution ◽  
Input Image ◽  
Economic Forecast ◽  
Building Extraction ◽  
Remote Sensing Images ◽  
Global Features ◽  
Prediction Module ◽  
Deep Learning Network ◽  
The One

Building extraction from high-resolution remote sensing images is of great significance in urban planning, population statistics, and economic forecast. However, automatic building extraction from high-resolution remote sensing images remains challenging. On the one hand, the extraction results of buildings are partially missing and incomplete due to the variation of hue and texture within a building, especially when the building size is large. On the other hand, the building footprint extraction of buildings with complex shapes is often inaccurate. To this end, we propose a new deep learning network, termed Building Residual Refine Network (BRRNet), for accurate and complete building extraction. BRRNet consists of such two parts as the prediction module and the residual refinement module. The prediction module based on an encoder–decoder structure introduces atrous convolution of different dilation rates to extract more global features, by gradually increasing the receptive field during feature extraction. When the prediction module outputs the preliminary building extraction results of the input image, the residual refinement module takes the output of the prediction module as an input. It further refines the residual between the result of the prediction module and the real result, thus improving the accuracy of building extraction. In addition, we use Dice loss as the loss function during training, which effectively alleviates the problem of data imbalance and further improves the accuracy of building extraction. The experimental results on Massachusetts Building Dataset show that our method outperforms other five state-of-the-art methods in terms of the integrity of buildings and the accuracy of complex building footprints.

scholarly journals Small Galactic Nebulae

1987 ◽  
Vol 115 ◽  
pp. 191-192
Author(s):  
Yervant Terzian ◽  
Kenneth C. Turner
Keyword(s):  
High Resolution ◽  
Planetary Nebula ◽  
Physical Parameters ◽  
H Ii Regions ◽  
Radio Observations ◽  
Cluster Emission ◽  
Active Star ◽  
Star Forming ◽  
Cometary Nebula ◽  
Significant Flux

We have performed high resolution VLA radio observations for several small H II regions, including the cluster emission nebulae S258, S255, S257, and S256. The region (PP56) between S255 and S257 at λ2 cm reveals significant flux structure close to OH, H2O and infrared emitting sources as shown in Figure 1. The flux densities and positions are indicated in Table 1. Observations of the cometary nebula PP59 (S269) also reveal similar characteristics as shown in Figure 2. These regions are considered to be active star-forming clouds. The cometary nebula PP40 was also observed and we note that its physical parameters are very similar to those of a typical planetary nebula.

scholarly journals Radio and X-ray Study of SNRs in the Magellanic Clouds

1999 ◽  
Vol 192 ◽  
pp. 104-107
Author(s):  
M.D. Filipović ◽  
W. Pietsch ◽  
G. L. White ◽  
F. Haberl ◽  
L. Staveley-Smith ◽  
...  
Keyword(s):  
High Resolution ◽  
Supernova Remnants ◽  
Magellanic Clouds ◽  
Radio Continuum ◽  
H Ii Regions ◽  
Complete Sample ◽  
X Ray ◽  
Compact Array

We present our high-resolution radio-continuum and X-ray study of supernova remnants (SNRs) in the Magellanic Clouds (MCs). These investigations are based on Australia Telescope Compact Array (ATCA) radio-continuum and ROSAT X-ray observations. Our main aim is to study a complete sample of the MC SNRs and H II regions.

Sign in / Sign up

Export Citation Format

Share Document