Hydrogen infrared recombination lines as a diagnostic tool for the geometry of the circumstellar material of hot stars

Lenorzer, A.; Koter, A. de; Waters, L.B.F.M.

doi:10.1051/0004-6361:20020322

Cited by 29 publications

(86 citation statements)

References 14 publications

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“…We see a general trend that the Be stars in the upper right part of the diagram are those with the largest IR excess. As Lenorzer et al (2002b) point out, in optically thick disks, the line flux ratio will be given by the product of the line source function ratio and the ratio of projected radiating surfaces. We expect that in very dense environments both these ratios will approach unity, so that the ratios for Be stars with dense disks will appear in the upper right part of the diagram near ðlog½Hu14=Pfγ ; log½Hu14=Brα Þ ¼ ð0; 0Þ, the same region where stars with large IR excesses are plotted.…”

Section: Discussionmentioning

confidence: 99%

Spectral Energy Distributions of Be and Other Massive Stars

Touhami¹,

Richardson²,

Gies³

et al. 2010

Publications of the Astronomical Society of the Pacific

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ABSTRACT. We present spectrophotometric data from 0.4 μm to 4.2 μm for bright, northern sky, Be stars and several other types of massive stars. Our goal is to use these data with ongoing high-angular-resolution interferometric observations to model the density structure and sky orientation of the gas surrounding these stars. We also present a montage of the Hα and near-infrared emission lines that form in Be star disks. We find that a simplified measurement of the IR excess flux appears to be correlated with the strength of emission lines from high level transitions of hydrogen. This suggests that the near-IR continuum and upper level line fluxes both form in the inner part of the disk, close to the star.

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Section: Discussionmentioning

confidence: 99%

Spectral Energy Distributions of Be and Other Massive Stars

Touhami¹,

Richardson²,

Gies³

et al. 2010

Publications of the Astronomical Society of the Pacific

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“…Although this implies an additional diagnostic potential (see Lenorzer et al 2002b), it does require spectra of sufficient quality, both in terms of signal-to-noise and spectral resolution, in order to capitalize on this. Also, α, β, and γ lines are stonger than their counterparts in the Balmer series in the optical.…”

Section: Diagnosticsmentioning

confidence: 99%

Modeling the near-infrared lines of O-type stars

Lenorzer

Mokiem

Koter

et al. 2004

A&A

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Abstract. We use a grid of 30 line-blanketed unified stellar photosphere and wind models for O-type stars; computed with the code  in order to evaluate its potential in the near-infrared spectral domain. The grid includes dwarfs, giants and supergiants. We analyse the equivalent width behaviour of the 20 strongest lines of hydrogen and helium in spectral windows that can be observed using ground-based instrumentation and compare the results with observations. Our main findings are that: i) He /He  line ratios in the J, H and K bands correlate well with the optical ratio employed in spectral classification, and can therefore be used to determine the spectral type; ii) in supergiant stars the transition from the stellar photosphere to the wind follows a shallower density gradient than the standard approach followed in our models, which can be mimicked by adopting a lower gravity in our prescription of the density stratification; iii) the Brγ line poses a number of peculiar problems which might partly be related to wind clumping; and iv) the Brα line is an excellent mass-loss indicator. For the first and last item we provide quantitative calibrations.

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“…5 we will use the overall SED to further constrain the circumstellar environment. Lenorzer et al (2002a) recently developed a tool to investigate the geometry of the circumstellar material around hot stars. A diagram using hydrogen lines from different series, all observable in the L -band, allows one to separate sources in which the circumstellar material is distributed roughly spherically (e.g.…”

Section: Radio Slopementioning

confidence: 99%

The peculiar circumstellar environment of NGC 2024 IRS2

Lenorzer¹,

Bik²,

Koter³

et al. 2004

A&A

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Abstract. We re-examine the nature of NGC 2024 IRS2 in light of the recent discovery of the late O-type star, IRS2b, located 5 from IRS2. Using L-band spectroscopy, we set a lower limit of A V = 27.0 mag on the visual extinction towards IRS2. Arguments based on the nature of the circumstellar material, favor an A V of 31.5 mag. IRS2 is associated with the UCH region G206.543-16.347 and the infrared source IRAS 05393-0156. We show that much of the mid-infrared emission towards IRS2, as well as the far infrared emission peaking at ∼100 µm, do not originate in the direct surroundings of IRS2, but instead from an extended molecular cloud. Using new K-, L-and L -band spectroscopy and a comprehensive set of infrared and radio continuum measurements from the literature, we apply diagnostics based on the radio slope, the strength of the infrared hydrogen recombination lines, and the presence of CO band-heads to constrain the nature and spatial distribution of the circumstellar material of IRS2. Using simple gaseous and/or dust models of prescribed geometry, we find strong indications that the infrared flux originating in the circumstellar material of IRS2 is dominated by emission from a dense gaseous disk with a radius of about 0.6 AU. At radio wavelengths the flux density distribution is best described by a stellar wind recombining at a radius of about 100 AU. Although NGC 2024 IRS2 shares many similarities with BN-like objects, we do not find evidence for the presence of a dust shell surrounding this object. Therefore, IRS2 is likely more evolved.

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Hydrogen infrared recombination lines as a diagnostic tool for the geometry of the circumstellar material of hot stars

Cited by 29 publications

References 14 publications

Spectral Energy Distributions of Be and Other Massive Stars

Spectral Energy Distributions of Be and Other Massive Stars

Modeling the near-infrared lines of O-type stars

The peculiar circumstellar environment of NGC 2024 IRS2

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