Algorithm for Removing Secondary Lines Blended with Balmer Lines in Synthetic Spectra of Massive Stars

We consider the Orion Nebula (M 42) within a project aimed at studying the interaction between massive stars and their surrounding ISM. This is an H ii region ionized by θ1 Ori C, one of the four massive stars in the Trapezium Cluster. θ1 Ori C has the earliest spectral type (O7Vp) among them, emitting an ionizing flux several orders of magnitude larger than those of the other stars. We present a spectral analysis of the Trapezium Cluster stars to determine their stellar parameters. We use spectra between 4250 – 4750 Å and compare them with synthetic spectra obtained by means of an updated version of fastwind that includes an approximated treatment of metal-line blanketing.

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Problems in abundance determination from UV spectra of hot supergiants

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310000578 ◽

2009 ◽

Vol 5 (S265) ◽

pp. 211-212

Author(s):

M. Sarta Deković ◽

D. Kotnik-Karuza ◽

T. Jurkić ◽

D. Dominis Prester

Keyword(s):

High Resolution ◽

Massive Stars ◽

Uv Spectra ◽

Parallel Model ◽

Synthetic Spectra ◽

Abundance Determination

AbstractWe present measurements of equivalent widths of the UV, presumably photospheric lines: C III 1247 Å, N III 1748 Å, N III 1752 Å, N IV 1718 Å and He II 1640 Å in high-resolution IUE spectra of 24 galactic OB supergiants. Equivalent widths measured from the observed spectra have been compared with their counterparts in the Tlusty NLTE synthetic spectra. We discuss possibilities of static plan-parallel model to reproduce observed UV spectra of hot massive stars and possible reasons why observations differ from the model so much.

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Lyman continuum leakage versus quenching with the James Webb Space Telescope: the spectral signatures of quenched star formation activity in reionization-epoch galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/sty1061 ◽

2018 ◽

Vol 479 (1) ◽

pp. 368-376 ◽

Cited By ~ 4

Author(s):

Christian Binggeli ◽

Erik Zackrisson ◽

Kristiaan Pelckmans ◽

Rubén Cubo ◽

Hannes Jensen ◽

...

Keyword(s):

Star Formation ◽

Formation Rate ◽

Classification Algorithm ◽

Space Telescope ◽

Spectral Signatures ◽

Synthetic Spectra ◽

Lyman Continuum ◽

James Webb Space Telescope ◽

Star Formation Activity ◽

Balmer Lines

ABSTRACT In this paper, we study the effects of a recent drop in star formation rate (SFR) on the spectra of epoch of reionization (EoR) galaxies, and the resulting degeneracy with the spectral features produced by extreme Lyman continuum leakage. In order to study these effects in the wavelength range relevant for the upcoming James Webb Space Telescope (JWST), we utilize synthetic spectra of simulated EoR galaxies from cosmological simulations together with synthetic spectra of partially quenched mock galaxies. We find that rapid declines in the SFR of EoR galaxies could seriously affect the applicability of methods that utilize the equivalent width of Balmer lines and the ultraviolet spectral slope to assess the escape fraction of EoR galaxies. In order to determine if the aforementioned degeneracy can be avoided by using the overall shape of the spectrum, we generate mock NIRCam observations and utilize a classification algorithm to identify galaxies that have undergone quenching. We find that while there are problematic cases, JWST/NIRCam or NIRSpec should be able to reliably identify galaxies with redshifts z∼ 7 that have experienced a significant decrease in the SFR (by a factor of 10–100) in the past 50–100 Myr with a success rate ${\gtrsim } 85\,{per\,cent}$. We also find that uncertainties in the dust-reddening effects on EoR galaxies significantly affect the performance of the results of the classification algorithm. We argue that studies that aim to characterize the dust extinction law most representative in the EoR would be extremely useful.

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The Evaluation of the Balmer Merging Effects in Different Chromospheric Solar Flare Models

International Astronomical Union Colloquium ◽

10.1017/s0252921100154508 ◽

1989 ◽

Vol 104 (2) ◽

pp. 345-348

Author(s):

A. Falchi ◽

R. Falciani ◽

L.A. Smaldone ◽

G.P. Tozzi

Keyword(s):

Solar Flare ◽

Impulsive Phase ◽

Theoretical Models ◽

Semiempirical Model ◽

The Best Approximation ◽

Synthetic Spectra ◽

Self Consistent ◽

Balmer Lines ◽

Very High ◽

Chromospheric Flare

AbstractSynthetic spectra computed svith semiempirical and theoretical models of the flare atmosphere are discussed. Stark profile of the Dahner lines ( n ≥ 6) and the Balmer continuum have been computed according to Donati-Falchi et al., (1985). A semiempirical model in between the F2 and F3 models proposed by Avrett et al., (1986) might represent a good approximation of the atmosphere of a flare during the impusive phase. Among the theoretical models proposed by Ricchiazzi (1982), the model, indicated as 1073, with very high coronal pressure (Po = 1000 dyne cm–2) probably represents the best approximation of the emission observed during the impulsive phase of a chromospheric flare. Continuum and Balmer lines ought to be measured and interpreted on the same time for a self-consistent diagnostic of the chromospheric modification.

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Polarimetric Observations of Red Variables: A Study of Gas and Particle Interactions

International Astronomical Union Colloquium ◽

10.1017/s0252921100073668 ◽

1979 ◽

Vol 46 ◽

pp. 386-408 ◽

Cited By ~ 2

Author(s):

G. V. Coyne ◽

I. S. McLean

Keyword(s):

Wavelength Dependence ◽

Stellar Atmosphere ◽

Molecular Absorption ◽

Absorption Bands ◽

Absorption And Emission ◽

Mira Variables ◽

Stellar Photosphere ◽

Regular Variable ◽

Red Supergiants ◽

Balmer Lines

AbstractIn recent years the wavelength, dependence of the polarization in a number of Mira variables, semi-regular variables and red supergiants has been measured with resolutions between 0.3 and 300 A over the range 3300 to 11000 A. Variations are seen across molecular absorption bands, especially TiO bands, and across atomic absorption and emission lines, especially the Balmer lines. In most cases one can ignore or it is possible to eliminate the effects due to interstellar polarization, so that one can study the polarization mechanisms operating in the stellar atmosphere and environment. The stars Omicron Ceti. (Mira), V CVn (semi-regular variable) and Mu Cephei (M2 la), in addition to other stars similar to them, will be discussed in some detail.Models to explain the observed polarization consider that the continuum flux is polarized either by electron, molecular and/or grain scattering or by temperature variations and/or geometrical asymmetries over the stellar photosphere. This polarized radiation is affected by atomic and molecular absorption and emission processes at various geometric depths in the stellar atmosphere and envelope. High resolution spectropolarimetry promises, therefore, to be a power-rul tool for studying stratification effects in these stars.

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