scholarly journals New line-blanketed model atmospheres and their impact on synthesis models

2003 ◽  
Vol 212 ◽  
pp. 604-611
Author(s):  
Linda J. Smith ◽  
Richard P.F. Norris ◽  
Paul A. Crowther
Keyword(s):  
Model Atmosphere ◽  
Evolutionary Synthesis ◽  
H Ii Regions ◽  
Single Star ◽  
New Model ◽  
New Models ◽  
Low Metallicity ◽  
H Ii Region ◽  
Basic Code ◽  
Photo Ionization

A new grid of ionizing fluxes for O-type and Wolf-Rayet stars is presented for use with evolutionary synthesis codes and analyses of single star H ii regions. A total of 230 expanding, non-LTE, line-blanketed model atmospheres have been calculated for five metallicities (0.05, 0.2, 0.4, 1 and 2 Z⊙). We have used the wm-basic code of Pauldrach et al. (2001) for O-type stars and the cmfgen code of Hillier & Miller (1998) for WR stars. The stellar wind parameters are scaled with metallicity for both O-type and WR stars. The ionizing fluxes of the new models, incorporated into the evolutionary synthesis code STARBURST99 (Leitherer et al. 1999), are compared with the predictions of the original starburst99 and Schaerer & Vacca (1998) for an instantaneous burst. We find large changes in the output ionizing fluxes as a function of age, especially below the He+ edge. In contrast to previous studies, nebular He ii λ4686 will be at, or just below, the detection limit in low metallicity starbursts during the WR phase. The new models have lower fluxes in the He i continuum for Z ≥ 0.4 Z⊙ and ages ≤ 7 Myr because of the increased line-blanketing. The accuracy of the new model atmosphere grid is tested by constructing photo-ionization models for an H ii region where the ionizing flux is provided by an instantaneous burst. The new models occupy the same region in nebular diagnostic diagrams as the observational data of Bresolin et al. (1999), particularly during the WR phase. The new model grid and updated starburst99 code can be downloaded from http://www.star.ucl.ac.uk/starburst.

scholarly journals Photo-ionization models of NGC 2363 and their implications

1999 ◽  
Vol 193 ◽  
pp. 487-488
Author(s):  
Valentina Luridiana ◽  
Manuel Peimbert ◽  
Claus Leitherer
Keyword(s):  
Observational Data ◽  
Emission Spectra ◽  
Temperature Fluctuations ◽  
High Mass ◽  
Observational Constraints ◽  
Stellar Cluster ◽  
A Value ◽  
Low Metallicity ◽  
H Ii Region ◽  
Photo Ionization

We compute photo-ionization models for the giant extragalactic H II region NGC 2363, and compare them with optical observational data. We focus on the following observational constraints: F(Hβ), Ne, EW(Hβ), and the ratios of I(λ 5007), I(λ 4363), I(λ 3727), I(λ 6300), I(λ 6720) and I(λ 4686) relative to I(Hβ). We discuss the variations of the emission spectra obtained with different input parameters. We show that low metallicity models (Z = 0.10Z⊙) cannot reproduce the observed features of the spectrum, and that the disagreement can be satisfactorily overcome by allowing for spatial temperature fluctuations in the nebula. Accordingly, we show that the metallicity of NGC 2363 has most probably been underestimated, and that a value of Z ≃ 0.25 Z⊙ is in better agreement with the observational data than the usually adopted value Z≃0.10Z⊙. We also derive values for the slope and the high mass end of the IMF, as well as the age of the stellar cluster.

scholarly journals A new opacity-sampling model atmosphere program for arbitrary abundances

1996 ◽  
Vol 176 ◽  
pp. 523-526 ◽  
Author(s):  
Robert L. Kurucz
Keyword(s):  
Surface Flux ◽  
Model Atmosphere ◽  
Molecular Data ◽  
High Resolution Spectrum ◽  
H Ii Regions ◽  
Cd Rom ◽  
Lower Energy Level ◽  
Spectrum Synthesis ◽  
H Ii Region ◽  
Treat All

I have developed a new opacity-sampling version of my model atmosphere program called ATLAS12. It recognizes more than 1000 atomic and molecular species, each in up to 10 isotopic forms. It can treat all ions of the elements up through Zn and the first 5 ions of heavier elements up through Es. The elemental and isotopic abundances are treated as variables with depth. At present ATLAS12 reads atomic line data from Kurucz CD-ROM 1 and diatomic molecular data from Kurucz CD-ROM 15. For each line the wavelength, identification, lower energy level, gf, radiative, Stark, and van der Waals damping constants are packed into 16 bytes. At each wavelength point in a frequency integration the Voigt profiles of all the significant nearby lines are computed and summed. The H, He, and auto-ionizing lines are treated with the appropriate profile functions.The fluxes predicted by ATLAS12 are not accurate in intermediate or narrow bandpass intervals because the sample size is too small. A special stripped version of the spectrum synthesis program SYNTHE is used to generate the surface flux for the converged model using the line data on CD-ROMs 1 and 15. That high resolution spectrum can be used directly or can be instrumentally broadened to compare to low resolution observations.ATLAS12 can be used to produce improved models for Am and Ap stars. It should be very useful for investigating diffusion effects in atmospheres. It can be used to model exciting stars for H II regions with abundances consistent with those of the H II region. These programs and line files will be distributed on CD-ROMs.

scholarly journals Deuterium Balmer Emission from Nebulae

2000 ◽  
Vol 198 ◽  
pp. 238-239
Author(s):  
Guillaume Hébrard ◽  
Daniel Péquignot ◽  
Alfred Vidal-Madjar ◽  
Jeremy R. Walsh ◽  
Roger Ferlet
Keyword(s):  
Optical Spectroscopy ◽  
Molecular Cloud ◽  
Planetary Nebula ◽  
H Ii Regions ◽  
Orion Nebula ◽  
Excitation Mechanism ◽  
Upper Limit ◽  
Balmer Lines ◽  
Low Metallicity ◽  
H Ii Region

We report on the detection and first identification of the deuterium Balmer lines dα and dβ, observed in emission in the Orion Nebula (M 42). The excitation mechanism is UV fluorescence from the Lyman(D i) lines at the interface between the H ii region and the molecular cloud. These lines may open the possibility to measure D/H in galactic H ii regions and, e.g., low-metallicity extragalactic H ii regions, using optical spectroscopy. Fluorescence provides an extremely sensitive way to detect deuterium. Thus, the non-detection of dα and dβ in the planetary nebula NGC 6572 leads to the stringent upper limit (D/H)ngc 6572 less than the order of 1 × 10−7.

The primordial helium abundance determination using multicomponent photoionization modelling of low-metallicity H II regions

2018 ◽  
Vol 8 (1) ◽  
pp. 16-23
Author(s):  
I. Koshmak ◽  
B. Melekh
Keyword(s):  
Chemical Compositions ◽  
H Ii Regions ◽  
Helium Abundance ◽  
Rotating Stars ◽  
Chemical Abundances ◽  
Free Expansion ◽  
Outer Component ◽  
Low Metallicity ◽  
H Ii Region ◽  
Primordial Helium

The method for the multicomponent photoionization modelling (MPhM) of low-metallicity H II regions surrounding the starburst region was developed. The internal structure of the H II region has been determined using the evolutionary modelling of the superwind bubble surrounding the star-forming region. Models of Chevalier and Clegg (1985) and Weaver et al. (1977) have been used to determine the radial distribution of the gas density, the velocity of gas layers, and the temperature within internal components (the region of the superwind free expansion and the cavity, respectively). The chemical abundances in region of the superwind free expansion were obtained from the evolutionary population synthesis with including of rotating stars. The chemical abundances within cavity were defined by averaging over mass the chemical compositions of mixture of the abundances of gas from superwind and ones within outer component, because of gas evaporation from external component into the cavity. External components of our models describe a high-density, thin shell of gas formed by superwind shock and a typical undisturbed hydrodynamically H II region, respectively. Evolutionary grids of multicomponent low-metallicity models are calculated. A comparative analysis of the results of their calculation with the observed data has been carried out. The ionic abundances averaged over modelling volume as well as chemical composition assumed in models were used to derive the new expressions for ionization-correction factors that were used to redetermine the chemical compositions of 88 H II regions in blue compact dwarf galaxies. It must be noticed that we used for this propose the ionic abundances obtained by Izotov et al. (2007). In result the primordial helium abundance and its enrichment during stellar chemical evolution of matter were determined.

scholarly journals Massive star population in circumnuclear star-forming regions

2003 ◽  
Vol 212 ◽  
pp. 537-538
Author(s):  
Mar Álvarez-Álvarez ◽  
Ángeles I. Díaz ◽  
Marcelo Castellanos
Keyword(s):  
Massive Star ◽  
Stellar Populations ◽  
H Ii Regions ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Spectrophotometric Data ◽  
H Ii Region ◽  
Formation And Evolution ◽  
Photo Ionization

Due to their high luminosity, the importance of understanding the massive star formation and evolution of giant Hii regions has become more and more evident in the last few years. A mayor scenario where giant H ii regions form and develop are the very inner parts of some galaxies. These bursts frequently are arranged in a ring-like pattern. We present a study of the stellar populations and gas physical conditions in circumnuclear star-forming regions (CNSFR) based on broad- and narrow-band photometry and spectrophotometric data, which have been analyzed with the use of evolutionary population synthesis and photo-ionization models. It is found that most CNSFRs show composite stellar populations of slightly different ages. They seem to have the highest abundances found in H ii region-like objects, showing also N/O overabundances and S/O underabundaces by a factor of about three. Also, CNSFRs as a class segregate from the disk H ii region family, clustering around higher ionizing temperatures.

New Algorithm for Modeling of Bronchial Trees

2012 ◽  
Vol 17 (4) ◽  
pp. 179-190
Author(s):  
Kacper Pluta ◽  
Marcin Janaszewski ◽  
Michał Postolski
Keyword(s):  
Quantitative Analysis ◽  
3D Model ◽  
Ct Images ◽  
Basic Algorithm ◽  
New Model ◽  
Comparison Of Results ◽  
Basic Model ◽  
New Models ◽  
Bronchial Tubes

Abstract The article presents new conception of 3D model of human bronchial tubes, which represents bronchial tubes extracted from CT images of the chest. The new algorithm which generates new model is an extension of the algorithm (basic algorithm) proposed by Hiroko Kitaoka, Ryuji Takaki and Bela Suki. The basic model has been extended by geometric deformations of branches and noise which occur in bronchial trees extracted from CT images. The article presents comparison of results obtained with the use of the new algorithm and the basic one. Moreover, the discussion of usefulness of generated new models for testing of algorithms for quantitative analysis of bronchial tubes based on CT images is also included.

scholarly journals On the Nature of R 136, the Central Object of 30 Dor. A Comparison by the Galactic Cluster NGC 3603

1984 ◽  
Vol 108 ◽  
pp. 257-258
Author(s):  
Michael Rosa ◽  
Jorge Melnick ◽  
Preben Grosbol
Keyword(s):  
Core Region ◽  
H Ii Regions ◽  
Central Object ◽  
The Core ◽  
Dominant Component ◽  
Galactic Cluster ◽  
H Ii Region

The massive H II region NGC 3603 is the closest galactic counterpart to the giant LMC nebula 30 Dor. Walborn (1973) first compared the ionizing OB/WR clusters of the two H II regions and suggested that R 136, the unresolved luminous WR + 0 type central object of 30 Dor, might be a multiple system like the core region of NGC 3603. Suggestions that the dominant component of R 136, i.e. R 136A, might be either a single or a very few supermassive and superluminous stars (Schmidt-Kaler and Feitzinger 1982, Savage et al. 1983) have recently been disputed by Moffat and Seggewiss (1983) and Melnick (1983), who have presented spectroscopic and photometric evidence to support the hypothesis of an unresolved cluster of stars. We have extended Walborn's original comparison of the apparent morphology of the two clusters by digital treatment of the images to simulate how the galactic cluster would look like if it were located in the LMC

scholarly journals Three generations of stars: a possible case of triggered star formation

2020 ◽  
Vol 496 (1) ◽  
pp. 870-874
Author(s):  
M B Areal ◽  
A Buccino ◽  
S Paron ◽  
C Fariña ◽  
M E Ortega
Keyword(s):  
Star Formation ◽  
Young Stellar Objects ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Three Generations ◽  
The North ◽  
Western Border ◽  
H Ii Region ◽  
New Generation ◽  
North Western

ABSTRACT Evidence for triggered star formation linking three generations of stars is difficult to assemble, as it requires convincingly associating evolved massive stars with H ii regions that, in turn, would need to present signs of active star formation. We present observational evidence for triggered star formation relating three generations of stars in the neighbourhood of the star LS II +26 8. We carried out new spectroscopic observations of LS II +26 8, revealing that it is a B0 III-type star. We note that LS II +26 8 is located exactly at the geometric centre of a semi-shell-like H ii region complex. The most conspicuous component of this complex is the H ii region Sh2-90, which is probably triggering a new generation of stars. The distances to LS II +26 8 and to Sh2-90 are in agreement (between 2.6 and 3 kpc). Analysis of the interstellar medium on a larger spatial scale shows that the H ii region complex lies on the north-western border of an extended H2 shell. The radius of this molecular shell is about 13 pc, which is in agreement with what an O9 V star (the probable initial spectral type of LS II +26 8 as inferred from evolutive tracks) can generate through its winds in the molecular environment. In conclusion, the spatial and temporal correspondences derived in our analysis enable us to propose a probable triggered star formation scenario initiated by the evolved massive star LS II +26 8 during its main-sequence stage, followed by stars exciting the H ii region complex formed in the molecular shell, and culminating in the birth of young stellar objects around Sh2-90.

How Social Media Offers Opportunities for Growth in the Traditional Media Industry

2019 ◽  
pp. 727-742
Author(s):  
Andrew Duffy
Keyword(s):  
Social Media ◽  
Web 2.0 ◽  
Media Industry ◽  
Traditional Media ◽  
New Model ◽  
New Models

Under threat from social media and interactive Web 2.0, the traditional media industry seeks new models to maintain its viability. This chapter studies both consumers and prospective producers of one genre—travel journalism—to advocate a model that could help arrest the industry's decline and return to growth. It argues that one way forward for traditional media would be a new model of curatorship, in which a professional journalist collaborates with amateur contributors. It suggests that such a hybrid arrangement will be recognisable neither as professional newsroom nor as amateur social media, but a new model with features of both. This offers a way forward so that rather than contributing to the declining fortunes of the traditional media industry, as many journalists fear, social media can instead encourage progress.

scholarly journals SN 2018hti: a nearby superluminous supernova discovered in a metal-poor galaxy

2020 ◽  
Vol 497 (1) ◽  
pp. 318-335 ◽  
Author(s):  
W L Lin ◽  
X F Wang ◽  
W X Li ◽  
J J Zhang ◽  
J Mo ◽  
...  
Keyword(s):  
Formation Rate ◽  
Host Galaxy ◽  
Type I ◽  
Single Star ◽  
Maximum Brightness ◽  
Star Evolution ◽  
Low Metallicity ◽  
Rotating Star ◽  
Larger Sample ◽  
Luminosity Evolution

ABSTRACT SN 2018hti is a Type I superluminous supernova (SLSN I) with an absolute g-band magnitude of −22.2 at maximum brightness, discovered by the Asteroid Terrestrial-impact Last Alert System in a metal-poor galaxy at a redshift of 0.0612. We present extensive photometric and spectroscopic observations of this supernova, covering the phases from ∼−35 d to more than  +340 d from the r-band maximum. Combining our BVgri-band photometry with Swift UVOT optical/ultraviolet photometry, we calculated the peak luminosity as ∼3.5 × 1044 erg s−1. Modelling the observed light curve reveals that the luminosity evolution of SN 2018hti can be produced by an ejecta mass of 5.8 M⊙ and a magnetar with a magnetic field of B = 1.8 × 1013 G having an initial spin period of P0 = 1.8 ms. Based on such a magnetar-powered scenario and a larger sample, a correlation between the spin of the magnetar and the kinetic energy of the ejecta can be inferred for most SLSNe I, suggesting a self-consistent scenario. Like for other SLSNe I, the host galaxy of SN 2018hti is found to be relatively faint (Mg = −17.75 mag) and of low metallicity (Z = 0.3 Z⊙), with a star formation rate of 0.3 M⊙ yr−1. According to simulation results of single-star evolution, SN 2018hti could originate from a massive, metal-poor star with a zero-age main sequence (ZAMS) mass of 25–40 M⊙, or from a less massive rotating star with MZAMS ≈ 16–25 M⊙. For the case of a binary system, its progenitor could also be a star with $M_\mathrm{ZAMS} \gtrsim 25\, \mathrm{ M}_\odot$.

Sign in / Sign up

Export Citation Format

Share Document