Blue Lines as Chromospheric Diagnostics: The Si<scp>i</scp>Lines at 3906 and 4103 A

Cincunegui, C.; Mauas, P. J. D.

doi:10.1086/320566

Cited by 11 publications

(8 citation statements)

References 36 publications

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“…Figure 5 also shows the NLTE departure coefficients for Si i and in this case the agreement between SRPM and PANDORA is much better. Again, SRPM used the Seaton formula for the collisional strengths and PANDORA used the values given by Cincunegui & Mauas (2001). These collisional strength values are not very reliable because they do not derive from detailed quantummechanics calculations.…”

Section: Departures From Ltementioning

confidence: 99%

Semiempirical Models of the Solar Atmosphere. Iii. Set of Non-Lte Models for Far-Ultraviolet/Extreme-Ultraviolet Irradiance Computation

Fontenla

Curdt

Haberreiter

et al. 2009

ApJ

173

243

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Semiempirical atmospheric models of solar surface features as observed at moderate resolution are useful tools for understanding the observed solar spectral irradiance variations. Paper I described a set of models constructed to reproduce the observed radiance spectrum for solar surface features at ∼2 arcsec resolution that constitute an average over small-scale features such as granulation. Paper II showed that a revision of previous models of low-chromospheric inter-network regions explains the observed infrared CO lines in addition to the UV and radio continuum from submillimeter to centimetric wavelengths. The present paper (1) shows that the Ca ii H and K line wing observations are also explained by the new quiet-Sun-composite model, (2) introduces new low-chromospheric models of magnetic features that follow the ideas in Paper II, (3) introduces new upper chromospheric structures for all quiet-Sun and active-region models, and (4) shows how the new set of models explains EUV/FUV observations of spectral radiance and irradiance. This paper also discusses the chromospheric radiative-loss estimates in each of the magnetic features. The new set of models provides a basis for the spectral irradiance synthesis at EUV/FUV wavelengths based on the features observed on the solar surface.

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Section: Departures From Ltementioning

confidence: 99%

Semiempirical Models of the Solar Atmosphere. Iii. Set of Non-Lte Models for Far-Ultraviolet/Extreme-Ultraviolet Irradiance Computation

Fontenla

Curdt

Haberreiter

et al. 2009

ApJ

173

243

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“…Maintaining the same T versus (vs.) log(m) distribution, we self-consistently recomputed the non-LTE radiative transfer and the statistical and hydrostatic equilibrium equations, assuming different values of the He abundance. Using the program Pandora (Avrett & Loeser 1984), in each case we computed non-LTE populations for 10 levels of H, 9 of C i (see Mauas et al 1990), 15 of Fe i, 8 of Si i (see Cincunegui & Mauas 2001), 8 of Ca i and Na i, 6 of Al i (see Mauas et al 2002), and 7 of Mg i (see Mauas et al 1988). In addition, we computed 6 levels of He ii and Mg ii, and 5 of Ca ii.…”

Section: He Abundance Differencementioning

confidence: 99%

Measuring helium abundance difference in giants of NGC 2808

Pasquini

Mauas

Käufl

et al. 2011

A&A

106

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Context. Multiple populations have been detected in several globular clusters (GC) that do not display a spread in metallicity. Unusual features of their observed colour-magnitude diagrams (CMD) can be interpreted in terms of differences in the helium content of the stars belonging to the sub-populations. Aims. Even if evidence gathered so far is compelling, differences in He abundance have never been directly observed. We attempt to measure these differences in two giant stars of NGC 2808 with very similar astrophysical parameters but different Na and O abundances, hence that presumably belong to different sub-populations, by directly comparing their He I 10 830 Å lines. Methods. The He 10 830 Å line forms in the upper chromosphere. Our detailed models derive the chromospheric structure using the Ca II and Hα chromospheric lines, and simulate the corresponding He I 10 830 line profiles as a function of the helium abundance. We show that, at a given value of He abundance, the He I 10 830 equivalent width cannot significantly change without a corresponding much larger change in the Ca II chromospheric lines. We have used the VLT-CRIRES to obtain high-resolution spectra in the 10 830 Å region, and the VLT-UVES to obtain spectra of the Ca II and Hα lines of our target stars. Results. The two target stars have very similar Ca II and Hα chromospheric lines, but different appearances in the He region. One line, blueshifted by 17 km s −1 with respect to the He 10 830 rest wavelength, is detected in the spectrum of the Na-rich star, whereas the Na-poor star spectrum is consistent with a non-detection. From a detailed chromospheric modeling, we show that the difference in the spectra is consistent and most closely explained by an He abundance difference between the two stars of ΔY ≥ 0.17. Our optical observations bracket the infrared ones over a range of about 50 days and we do not observe any substantial variability in the Ca II and Hα lines. Conclusions. We provide direct evidence of a significant He line strength difference in giant stars of NGC 2808 belonging to different sub-populations, which had been previously detected by other photometric and spectroscopic means. The use of appropriate model chromospheres allows us for the first time to provide an approximate quantitative estimate of this difference, which is clearly consistent with the expected difference in abundance required by the stellar evolution theory to account for the observed peculiarities of this cluster's cmD.

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“…For these calculations we use the Si atomic model studied in Cincunegui & Mauas (2001), which is much more detailed than the one used in previous papers (Vernazza et al 1976), and we found a much larger contribution to the cooling in the temperature-minimum region.…”

Section: Energy Requirementsmentioning

confidence: 99%

Chromospheric models of solar analogues with different activity levels

Vieytes

Mauas

Cincunegui

2005

A&A

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Abstract.We computed chromospheric models of the Sun as a star and of nine solar analogues. The atmospheric models were constructed to obtain the best possible match with the Ca II K and Hβ lines, including the asymmetry of the lines due to macroscopic velocity fields. The stars were chosen with 0.62 < B − V < 0.68 (the solar B − V = 0.65) and have a wide variety of magnetic activity levels, which allows us to study the differences in atmospheric structures induced by activity. For the less active stars we found that the changes with activity are in the region of the temperature minimum, while the most active stars show changes all along their atmospheric structures, mainly in the upper chromosphere. Regarding the macroscopic velocity fields, we can distinguish between the two groups. The most active group has a velocity field in the temperature-minimum region, and the other group in the chromospheric plateau. We also computed the net radiative losses for each model, and found that they depend linearly on the usual index of chromospheric activity, S CaII .

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Blue Lines as Chromospheric Diagnostics: The SiiLines at 3906 and 4103 A

Cited by 11 publications

References 36 publications

Semiempirical Models of the Solar Atmosphere. Iii. Set of Non-Lte Models for Far-Ultraviolet/Extreme-Ultraviolet Irradiance Computation

Semiempirical Models of the Solar Atmosphere. Iii. Set of Non-Lte Models for Far-Ultraviolet/Extreme-Ultraviolet Irradiance Computation

Measuring helium abundance difference in giants of NGC 2808

Chromospheric models of solar analogues with different activity levels

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