Molecules in the Sun and Stars

Russell, Henry Norris

doi:10.1086/143539

Cited by 112 publications

(37 citation statements)

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“…The stability of CO is so strong that, whatever the value of the C/O ratio, the majority of the atoms of the least abundant element is locked up in the CO molecule, whereas the excess of the other one can take part to the formation of other molecular species. This feature, pointed out long ago by Russell (1934), is responsible for the abrupt change in the atomic and molecular equilibria (involving C and O atoms) as soon as the gas mixture passes from oxygen-rich to carbon-rich (and vice versa).…”

Section: Molecular Concentrationsmentioning

confidence: 95%

“…For instance, oxygen-rich stars exhibit strong bands of TiO, VO, H 2 O, whereas carbonrich stars show large absorption features of C 2 , CN, SiC. These striking spectral differences between oxygen-rich and carbon-rich stars were first quantitatively explained by Russell (1934), on the basis of molecular equilibria calculations. The key-point is that the binding energy of the CO molecule is so high that almost all atoms of the least abundant element -C or O -are locked to form CO, while the excess atoms of the most abundant element are involved in the formation of the characteristic molecular bands.…”

Section: Introductionmentioning

confidence: 99%

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Asymptotic Giant Branch evolution at varying surface C/O ratio: effects of changes in molecular opacities

Marigo

2002

A&A

210

278

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Abstract.We investigate the effects of molecular opacities on the evolution of TP-AGB stars that experience the third dredge-up, i.e. with surface abundances of carbon and oxygen varying with time. To this aim, a routine is constructed to derive the molecular concentrations through dissociation equilibrium calculations, and estimate the opacities due to H2, H2O, OH, C2, CN, and CO for any given density, temperature and chemical composition of the gas. Then, synthetic TP-AGB models with dredge-up are calculated by either adopting the newly developed routine, or interpolating between fixed opacity tables for solar chemical composition. The comparison between the two cases shows that the change in the dominant opacity sources, as the C/O ratio grows from below to above unity, crucially affects the evolution of the effective temperature, i.e. causing a notable cooling of the carbonrich models (with C/O> 1). From the comparison with observational data, it turns out that TP-AGB models with variable molecular opacities are able to reproduce the observed range of effective temperatures, mass-loss rates, and wind expansion velocities of C-type giants in the solar neighbourhood, otherwise failed if assuming fixed molecular opacities for solar-scaled mixtures. Finally, we mention other possibly important evolutionary and observational effects that result from the adoption of the variable opacities, such as: i) significant shortening of the C-star phase due to the earlier onset of the super-wind; ii) consequent reduction of the carbon yields; iii) reproduction of the observed range of near-infrared colours of C-stars.

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Section: Molecular Concentrationsmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Asymptotic Giant Branch evolution at varying surface C/O ratio: effects of changes in molecular opacities

Marigo

2002

A&A

210

278

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“…While the most relevant molecules were identified several decades ago (e.g. Russell 1934;de Jager & Neven 1957) molecular data is still one of the limiting factors when working with cool dwarfs. Dominating molecules are TiO and H 2 O, but also other oxides (e.g.…”

Section: Methodsmentioning

confidence: 99%

Metallicity determination of M dwarfs

Lindgren

Heiter

Seifahrt

2016

A&A

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Context. Several new techniques to determine the metallicity of M dwarfs with better precision have been developed over the last decades. However, most of these studies were based on empirical methods. In order to enable detailed abundance analysis, standard methods established for warmer solar-like stars, i.e. model-dependent methods using fitting of synthetic spectra, still need to be used. Aims. In this work we continue the reliability confirmation and development of metallicity determinations of M dwarfs using highresolution infrared spectra. The reliability was confirmed through analysis of M dwarfs in four binary systems with FGK dwarf companions and by comparison with previous optical studies of the FGK dwarfs. Methods. The metallicity determination was based on spectra taken in the J band (1.1-1.4 µm) with the CRIRES spectrograph. In this part of the infrared, the density of stellar molecular lines is limited, reducing the amount of blends with atomic lines enabling an accurate continuum placement. Lines of several atomic species were used to determine the stellar metallicity. Results. All binaries show excellent agreement between the derived metallicity of the M dwarf and its binary companion. Our results are also in good agreement with values found in the literature. Furthermore, we propose an alternative way to determine the effective temperature of M dwarfs of spectral types later than M2 through synthetic spectral fitting of the FeH lines in our observed spectra. Conclusions. We have confirmed that a reliable metallicity determination of M dwarfs can be achieved using high-resolution infrared spectroscopy. We also note that metallicites obtained with photometric metallicity calibrations available for M dwarfs only partly agree with the results we obtain from high-resolution spectroscopy.

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“…The dependence of CN line strength on T eff and log g is due to a combination of the well-documented impact of temperature and pressure on molecular dissociation equlibrium (e.g., Russell 1934;Tsuji 1973) and the ratio between continuum and molecular line opacity (e.g., Bell & Tripicco 1991). The abundances of C and O affect CN lines due to their impact on the concentration of the CN molecule in the stellar atmosphere, via molecular dissociation equilibrium (e.g., Russell 1934;Tsuji 1973). To simplify matters, we control for these parameters, by choosing two stars with nearly identical T eff , log g, [C/Fe], and [O/Fe], but vastly different [N/Fe], for our comparison.…”

Section: Spectra and Spectral Fitsmentioning

confidence: 99%

Chemical tagging with APOGEE: discovery of a large population of N-rich stars in the inner Galaxy

Schiavon

Zamora

Carrera

et al. 2016

Mon. Not. R. Astron. Soc.

187

157

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Formation of globular clusters (GCs), the Galactic bulge, or galaxy bulges in general, are important unsolved problems in Galactic astronomy. Homogeneous infrared observations of large samples of stars belonging to GCs and the Galactic bulge field are one of the best ways to study these problems. We report the discovery by APOGEE of a population of field stars in the inner Galaxy with abundances of N, C, and Al that are typically found in GC stars. The newly discovered stars have high [N/Fe], which is correlated with [Al/Fe] and anti-correlated with [C/Fe]. They are homogeneously distributed across, and kinematically indistinguishable from, other field stars in the same volume. Their metallicity distribution is seemingly unimodal, peaking at [Fe/H]∼-1, thus being in disagreement with that of the Galactic GC system. Our results can be understood in terms of different scenarios. N-rich stars could be former members of dissolved GCs, in which case the mass in destroyed GCs exceeds that of the surviving GC system by a factor of ∼8. In that scenario, the total mass contained in so-called "first-generation" stars cannot be larger than that in "second-generation" stars by more than a factor of ∼9 and was certainly smaller. Conversely, our results may imply the absence of a mandatory genetic link between "second generation" stars and GCs. Last, but not least, N-rich stars could be the oldest stars in the Galaxy, the by-products of chemical enrichment by the first stellar generations formed in the heart of the Galaxy.

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Molecules in the Sun and Stars

Cited by 112 publications

References 0 publications

Asymptotic Giant Branch evolution at varying surface C/O ratio: effects of changes in molecular opacities

Asymptotic Giant Branch evolution at varying surface C/O ratio: effects of changes in molecular opacities

Metallicity determination of M dwarfs

Chemical tagging with APOGEE: discovery of a large population of N-rich stars in the inner Galaxy

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