Carbon Monoxide Fundamental Bands in Late-Type Stars. III. Chromosphere or CO-mosphere?

Wiedemann, G.; Ayres, Thomas R.; Jennings, D. E.; Saar, S. H.

doi:10.1086/173859

Cited by 54 publications

(62 citation statements)

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“…", arguing that in the internetwork regions, the temperature rise is merely an artifact of time-averaged modeling, with evanescent pulses of high temperatures occurring from periodic heating by wave dissipation. This view is supported by the presence of cool CO 4.7 m emission at chromospheric heights, the amusingly named CO-mosphere (Wiedemann et al, 1994). This interpretation has met with criticism (Kalkofen et al, 1999;Kalkofen, 2001), but Ayres (2002) argues that much of what was classically considered the chromosphere is indeed quite cool, and Rutten (2007b) goes so far as to suggest that the chromosphere comprises merely the H mottles and fibrils -which leads us full circle to the beautiful pink annulus of Figure 1, though with a far different conceptual basis.…”

Section: The High Resolution Chromospherementioning

confidence: 96%

Stellar Chromospheric Activity

Hall

2008

Living Rev. Solar Phys.

167

131

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The Sun, stars similar to it, and many rather dissimilar to it, have chromospheres, regions classically viewed as lying above the brilliant photosphere and characterized by a positive temperature gradient and a marked departure from radiative equilibrium. Stellar chromospheres exhibit a wide range of phenomena collectively called activity, stemming largely from the time evolution of their magnetic fields and the mass flux and transfer of radiation through the complex magnetic topology and the increasingly optically thin plasma of the outer stellar atmosphere. In this review, I will (1) outline the development of our understanding of chromospheric structure from 1960 to the present, (2) discuss the major observational programs and theoretical lines of inquiry, (3) review the origin and nature of both solar and stellar chromospheric activity and its relationship to, and effect on, stellar parameters including total energy output, and (4) summarize the outstanding problems today.

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Section: The High Resolution Chromospherementioning

confidence: 96%

Stellar Chromospheric Activity

Hall

2008

Living Rev. Solar Phys.

167

131

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“…Mauas et al (1990) and Wedemeyer-Böhm & Steffen (2007). Wiedemann et al (1994) concluded that the observed infrared CO Δv = 1 spectrum at 4.6 μm of one group of stars, containing α Boo, α Tau and γ Dra, is well described by homogeneous radiative equilibrium models. The near-IR CO spectra for this group of so-called "quiet" stars indicate that the cool regions dominate the stellar surface for heights between ∼10 −1/2 and 10 −2 g/cm 2 in mass column density, and have large filling factors.…”

Section: Influence Of a Chromosphere At Nir Wavelengthsmentioning

confidence: 96%

“…They are selected for their brightness in the micrometer and submillimetre wavelength ranges and for their low chromospheric and coronal activity (see, e.g., Wiedemann et al 1994;Obrien & Lambert 1986, and further in Sects. 6.2 and 6.1).…”

Section: Sample Selectionmentioning

confidence: 99%

“…In particular, the strongest CO Δv = 1 lines occur at or above the temperature minimum in chromospheric solar and stellar models. Wiedemann et al (1994) interpreted the CO observations in terms of a "thermal bifurcation" model for the atmospheres of their sample stars. It consists of two distinct physical phases that co-exist at chromospheric altitudes.…”

Section: Influence Of a Chromosphere At Nir Wavelengthsmentioning

confidence: 99%

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Structure of the outer layers of cool standard stars

Dehaes

Bauwens

Decin

et al. 2011

A&A

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Context. Among late-type red giants, an interesting change occurs in the structure of the outer atmospheric layers as one moves to later spectral types in the Hertzsprung-Russell diagram: a chromosphere is always present, but the coronal emission diminishes and a cool massive wind steps in. Aims. Where most studies have focussed on short-wavelength observations, this article explores the influence of the chromosphere and the wind on long-wavelength photometric measurements. The goal of this study is to assess wether a set of standard near-infrared calibration sources are fiducial calibrators in the far-infrared, beyond 50 μm. Methods. The observational spectral energy distributions were compared with the theoretical model predictions for a sample of nine K-and M-giants. The discrepancies found are explained using basic models for flux emission originating in a chromosphere or an ionised wind. Results. For seven out of nine sample stars, a clear flux excess is detected at (sub)millimetre and/or centimetre wavelengths, while only observational upper limits are obtained for the other two. The precise start of the excess depends upon the star under consideration. For six sources the flux excess starts beyond 210 μm and they can be considered as fiducial calibrators for Herschel/PACS (60-210 μm). Out of this sample, four sources show no flux excess in the Herschel/SPIRE wavelength range (200-670 μm) and are good calibration sources for this instrument as well. The flux at wavelengths shorter than ∼1 mm is most likely dominated by an optically thick chromosphere, where an optically thick ionised wind is the main flux contributor at longer wavelengths. Conclusions. Although the optical to mid-infrared spectrum of the studied K-and M-type infrared standard stars is represented well by a radiative equilibrium atmospheric model, a chromosphere and/or ionised stellar wind at higher altitudes dominates the spectrum in the (sub)millimetre and centimetre wavelength ranges. The presence of a flux excess has implications on the role of the stars as fiducial spectrophotometric calibrators in these wavelength ranges.

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“…spectra of late K and M giants and supergiants, had already been reported by Tsuji et al (1997);Tsuji (2000Tsuji ( , 2001; Matsuura et al (1999Matsuura et al ( , 2002. In order to explain the line depths of the strongest CO fundamental band lines of a number of cool stars, Wiedemann et al (1994) discarded the chromospheric temperature rise and required the boundary temperature to fall to 2400 K in the highest layers contributing the CO line cores. Ayres (2002) also inferred cool CO gas above the classical temperature minimum in the case of the Sun.…”

Section: Shortcomings Attributed To Modellingmentioning

confidence: 98%

On the analysis of band 3 of the ISO–SWS calibration sources

Malderen

Decin

Kester

et al. 2004

A&A

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Abstract. We analyse ISO-SWS 01 (R ∼ 1500) 12−27.5 µm (band 3) spectra of the 10 standard calibration stars with the highest flux using synthetic spectra generated from () atmosphere models. The comparison between the observed and synthetic spectra reveals the quality of (1) the atmospheric model construction and subsequent synthetic spectra computation and of (2) the (OLP 10.1) calibration and data reduction of the spectrometer at these wavelengths. The models represent the general features of the observations, but the synthetic spectrum computation is hampered by the lack of comprehensive molecular and atomic line lists. We also suspect some problems with the temperature distribution in the outer layers of the model and inaccuracies in the extrapolation of the collision-induced absorption coefficients of H 2 pairs. We detect baseline ripples and fringes in the observed spectra, that survive the calibration and detailed reduction process. Photometric calibration uncertainties are estimated by means of the scaling factors between the synthetic and observed spectra.

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Carbon Monoxide Fundamental Bands in Late-Type Stars. III. Chromosphere or CO-mosphere?

Cited by 54 publications

References 0 publications

Stellar Chromospheric Activity

Stellar Chromospheric Activity

Structure of the outer layers of cool standard stars

On the analysis of band 3 of the ISO–SWS calibration sources

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