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Querci, F.; Querci, M.

doi:10.1023/a:1001764130608

Cited by 21 publications

(23 citation statements)

References 2 publications

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“…We included the molecular species CN (an up-to-date compilation privately provided by B. Plez), C 2 (Querci et al 1971;U. Jørgensen, priv.…”

Section: Metallicitymentioning

confidence: 99%

Galactic chemical evolution of sulphur

Matrozis¹,

Ryde²,

Dupree³

2013

A&A

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Context. The Galactic chemical evolution of sulphur is still under debate. At low metallicities some studies find no correlation between [S/Fe] and [Fe/H], which is typical for α-elements, while others find [S/Fe] increasing towards lower metallicities, and still others find a combination of the two. Each scenario has different implications for the Galactic chemical evolution of sulphur. Aims. The aim of this study is to contribute to the discussion on the Galactic chemical evolution of sulphur by deriving sulphur abundances from non-local thermodynamic equilibrium (LTE) insensitive spectral diagnostics in disk and halo stars with homogeneously determined stellar parameters. Methods. We derived effective temperatures from photometric colours, surface gravities from stellar isochrones and Bayesian estimation, and metallicities and sulphur abundances from spectrum synthesis. We derived sulphur abundances from the [S ] λ1082 nm line in 39 mostly cool and metal-poor giants using 1D LTE MARCS model atmospheres to model our high-resolution near-infrared spectra obtained with the VLT, NOT, and Gemini South telescopes. Results. We derive homogeneous stellar parameters for 29 of the 39 stars. Our results argue for a chemical evolution of sulphur that is typical for α-elements, contrary to some previous studies that have found high sulphur abundances ([S/Fe] 0.6) for stars with −2.5 < [Fe/H] < −1. Our abundances are systematically higher by about 0.1 dex than those of other studies that arrived at similar conclusions using other sulphur diagnostics. Conclusions. We find the [S ] line to be a valuable diagnostic of sulphur abundances in cool giants down to [Fe/H] −2.3. We argue that a homogeneous determination of stellar parameters is necessary, since the derived abundances are sensitive to them. Our results ([S/Fe]) agree reasonably well with predictions of contemporary models of Galactic chemical evolution. In these models sulphur is predominantly created in massive stars by oxygen burning and is ejected into the interstellar medium during Type II supernovae explosions. Systematic differences with previous studies most likely fall within modelling uncertainties.

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“…We included the molecular species CN (an up-to-date compilation privately provided by B. Plez), C 2 (Querci et al 1971;U. Jørgensen, priv.…”

Section: Metallicitymentioning

confidence: 99%

Galactic chemical evolution of sulphur

Matrozis¹,

Ryde²,

Dupree³

2013

A&A

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“…It is therefore also important to estimate the abundance of Fe and Mg, as reliably as possible. Hence, the Fe, Mg, Si, and Ti abundances of our Arcturus modeling are based on the optically determined abundances derived by Fulbright et al (2007), but (Langhoff & Bauschlicher 1993), CH (Jørgensen et al 1996), CN (Jørgensen & Larsson 1990;and Plez 1998, private communications), OH (Goldman et al 1998), and C 2 (Querci et al 1971;and Jørgensen 2001, private communications). For the molecules, the linelists were adopted as they were, leading to the following C, N, and O abundances for Arcturus from the spectra in the Arcturus atlas (Hinkle et al 1995a): log ε C = 8.08 ± 0.11 (from CO lines), log ε N = 7.64 ± 0.09 (from CN lines), and log ε O = 8.70 ± 0.13 (from OH lines), which are in excellent agreement with the values derived by Ryde et al (2009) and by the optical work by Lecureur (2007), who derived log ε(C) = 7.96 ± 0.10, log ε(N) = 7.74 ± 0.10, and log ε(O) = 8.70 ± 0.05.…”

Section: Synthetic Spectramentioning

confidence: 99%

Chemical abundances of 11 bulge stars from high-resolution, near-IR spectra

Ryde

Gustafsson

Edvardsson

et al. 2010

A&A

114

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Context. It is debated whether the Milky Way bulge has characteristics more similar to those of a classical bulge than those of a pseudobulge. Detailed abundance studies of bulge stars are important when investigating the origin, history, and classification of the bulge. These studies provide constraints on the star-formation history, initial mass function, and differences between stellar populations. Not many similar studies have been completed because of the large distance and high variable visual extinction along the line-of-sight towards the bulge. Therefore, near-IR investigations can provide superior results. Aims. To investigate the origin of the bulge and study its chemical abundances determined from near-IR spectra for bulge giants that have already been investigated with optical spectra. The optical spectra also provide the stellar parameters that are very important to the present study. In particular, the important CNO elements are determined more accurately in the near-IR. Oxygen and other α elements are important for investigating the star-formation history. The C and N abundances are important for determining the evolutionary stage of the giants and the origin of C in the bulge. Methods. High-resolution, near-infrared spectra in the H band were recorded using the CRIRES spectrometer mounted on the Very Large Telescope. The CNO abundances are determined from the numerous molecular lines in the wavelength range observed. Abundances of the α elements Si, S, and Ti are also determined from the near-IR spectra. Results. The abundance ratios [O/Fe], [Si/Fe], and [S/Fe] are enhanced to metallicities of at least [Fe/H] = −0.3, after which they decline. This suggests that the Milky Way bulge experienced a rapid and early burst of star formation similar to that of a classical bulge. However, a similarity between the bulge trend and the trend of the local thick disk seems to be present. This similarity suggests that the bulge could have had a pseudobulge origin. The C and N abundances suggest that our giants are first-ascent red-giants or clump stars, and that the measured oxygen abundances are those with which the stars were born. Our [C/Fe] trend does not show any increase with [Fe/H], which is expected if W-R stars contributed substantially to the C abundances. No "cosmic scatter" can be traced around our observed abundance trends: the measured scatter is expected, given the observational uncertainties.

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“…The estimated accuracy should be slightly better than ±100 K, possibly ±80 K. These results are consistent with the mean direct effective temperatures as quoted in Table 3. We used older models from Querci et al (1974) and Querci & Querci (1976) for the hotter HC-stars. The value C/O 3.5 they adopted seems too high when compared to the results of Lambert et al (1986) for the CV stars (C/O ≤ 2.0).…”

Section: The Mean Seds Of the Photometric Groups And Model Atmospherementioning

confidence: 99%

The effective temperatures of carbon-rich stars

Bergeat

Knapik

Rutily

2001

A&A

151

207

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Abstract. We evaluate effective temperatures of 390 carbon-rich stars. The interstellar extinction on their lines of sights was determined and circumstellar contributions derived. The intrinsic (dereddened) spectral energy distributions (SEDs) are classified into 14 photometric groups (HCi, CVj and SCV with i = 0,5 and j = 1,7). The new scale of effective temperatures proposed here is calibrated on the 54 angular diameters (measured on 52 stars) available at present from lunar occultations and interferometry. The brightness distribution on stellar discs and its influence on diameter evaluations are discussed. The effective temperatures directly deduced from those diameters correlate with the classification into photometric groups, despite the large error bars on diameters. The main parameter of our photometric classification is thus effective temperature. Our photometric k 1/2 coefficients are shown to be angular diameters on a relative scale for a given photometric group, (more precisely for a given effective temperature). The angular diameters are consistent with the photometric data previously shown to be consistent with the true parallaxes from HIPPARCOS observations (Knapik, et al. 1998, Sect. 6). Provisional effective temperatures, as constrained by a successful comparison of dereddened SEDs from observations to model atmosphere predictions, are in good agreement with the values directly calculated from the observed angular diameters and with those deduced from five selected intrinsic color indices. These three approaches were used to calibrate a reference angular diameter Φ0 and the associated coefficient CT eff . The effective temperature proposed for each star is the arithmetic mean of two estimates, one ("bolometric") from a reference integrated flux F0, the other ("spectral") from calibrated color indices which are representative of SED shapes. Effective temperatures for about 390 carbon stars are provided on this new homogeneous scale, together with values for some stars classified with oxygen-type SEDs with a total of 438 SEDs (410 stars) studied. Apparent bolometric magnitudes are given. Objects with strong infrared excesses and optically thick circumstellar dust shells are discussed separately. The new effective temperature scale is shown to be compatible and (statistically) consistent with the sample of direct values from the observed angular diameters. The effective temperatures are confirmed to be higher than the mean color temperatures (from 140 to 440 K). They are in good agreement with the published estimates from the infrared flux method for T eff ≥ 3170 K, while an increasing discrepancy is observed toward lower temperatures. As an illustration of the efficiency of the photometric classification and effective temperature scale, the C/O ratios and the Merrill-Sanford (M-S) band intensities are investigated. It is shown that the maximum value, mean value and dispersion of C/O increase along the photometric CV-sequence, i.e. with decreasing effective temperature. The M-S bands of SiC2 are sho...

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Cited by 21 publications

References 2 publications

Galactic chemical evolution of sulphur

Galactic chemical evolution of sulphur

Chemical abundances of 11 bulge stars from high-resolution, near-IR spectra

The effective temperatures of carbon-rich stars

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