Spectral Classification

Morgan, W. W.; Keenan, Philip C.

doi:10.1146/annurev.aa.11.090173.000333

Cited by 269 publications

(180 citation statements)

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“…3). We will see that an effective temperature threshold Barnbaum et al (1996); 2: Bartkevicius (1996); 3: Eglitis et al (2003); 4: Keenan (1993); 5: Keenan & Morgan (1941); 6: Lee & Bartlett (1944);7: McClure (1970); 8: Morgan & Keenan (1973);9: Sanford (1944); 10: Schild (1973);11: Schmitt (1971);12: Shane (1928); 13: Stock & Welhau (1956);14: Upgren (1962);15: Vandervort (1958);16: Yamashita (1972);17: Yamashita (1975). The following stars show evidence of binarity: HIP 36 623 (Carquillat & Prieur 2008), HIP 109 158 (Makarov & Kaplan 2005), HIP 53 832 (Platais et al 2003) andHIP 85 750 (McClure 1997). of ∼3600 K seems to be a good criterion to distinguish between early-and late-R stars.…”

Section: Spectral Classificationmentioning

confidence: 93%

The chemical composition of carbon stars. The R-type stars

Zamora¹,

Abia²,

Plez

et al. 2009

A&A

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Aims. The aim of this work is to shed some light on the problem of the formation of carbon stars of R-type from a detailed study of their chemical composition.Methods. We use high-resolution and high signal-to-noise optical spectra of 23 R-type stars (both early-and late-types) selected from the Hipparcos catalogue. The chemical analysis is made using spectral synthesis in LTE and state-of-the-art carbon-rich spherical model atmospheres. We derive their CNO content (including the 12 C/ 13 C ratio), average metallicity, lithium, and light (Sr, Y, Zr) and heavy (Ba, La, Nd, Sm) s-element abundances. The observed properties of the stars (galactic distribution, kinematics, binarity, photometry and luminosity) are also discussed. Results. Our analysis shows that late-R stars are carbon stars with identical chemical and observational characteristics as the normal (N-type) AGB carbon stars. The s-element abundance pattern derived can be reproduced by low-mass AGB nucleosynthesis models where the 13 C(α, n) 16 O reaction is the main neutron donor. We confirm the results of the sole previous abundance analysis of early-R stars, namely that they are carbon stars with near solar metallicity showing enhanced nitrogen, low 12 C/ 13 C ratios and no s-element enhancements. In addition, we have found that early-R stars have Li abundances larger than expected for post RGB tip giants. We also find that a significant number (∼40%) of the early-R stars in our sample are wrongly classified, probably being classical CH stars and normal K giants. Conclusions. On the basis of the chemical analysis, we confirm the previous suggestion that late-R stars are just misclassified N-type carbon stars in the AGB phase of evolution. Their photometric, kinematic, variability and luminosity properties are also compatible with this. In consequence, we suggest that the number of true R stars is considerably lower than previously believed. This alleviates the problem of considering R stars as a frequent stage in the evolution of low-mass stars. We briefly discuss the different scenarios proposed for the formation of early-R stars. The mixing of carbon during an anomalous He-flash is favoured, although no physical mechanism able to trigger that mixing has been found yet. The origin of these stars still remains a mystery.

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Section: Spectral Classificationmentioning

confidence: 93%

The chemical composition of carbon stars. The R-type stars

Zamora¹,

Abia²,

Plez

et al. 2009

A&A

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“…Howard et al 2012;Petigura et al 2013), the observed atmospheric parameters (T eff , log g) were used to select solar-like dwarfs, to fit the historical Morgan-Keenan classification of stars (Morgan & Keenan 1973). Using these selection criteria, it is however difficult to make the distinction between main-sequence and sub-giant stars in the regime of early G-and F-type stars.…”

Section: The Stellar Reference Samplementioning

confidence: 99%

SOPHIE velocimetry ofKeplertransit candidates

Santerne

Moutou

Tsantaki

et al. 2016

A&A

268

263

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While giant extrasolar planets have been studied for more than two decades now, there are still some open questions as to their dominant formation and migration processes, as well as to their atmospheric evolution in different stellar environments. In this paper, we study a sample of giant transiting exoplanets detected by the Kepler telescope with orbital periods up to 400 days. We first defined a sample of 129 giant-planet candidates that we followed up with the SOPHIE spectrograph (OHP, France) in a 6-year radial velocity campaign. This allowed us to unveil the nature of these candidates and to measure a false-positive rate of 54.6 ± 6.5% for giant-planet candidates orbiting within 400 days of period. Based on a sample of confirmed or likely planets, we then derived the occurrence rates of giant planets in different ranges of orbital periods. The overall occurrence rate of giant planets within 400 days is 4.6 ± 0.6%. We recovered, for the first time in the Kepler data, the different populations of giant planets reported by radial velocity surveys. Comparing these rates with other yields, we find that the occurrence rate of giant planets is lower only for hot Jupiters but not for the longer-period planets. We also derive a first measurement of the occurrence rate of brown dwarfs in the brown-dwarf desert with a value of 0.29 ± 0.17%. Finally, we discuss the physical properties of the giant planets in our sample. We confirm that giant planets receiving moderate irradiation are not inflated, but we find that they are on average smaller than predicted by formation and evolution models. In this regime of low-irradiated giant planets, we find a possible correlation between their bulk density and the iron abundance of the host star, which needs more detections to be confirmed.

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“…The electronic bands of TiO are so prominent in late-type stars that the Morgan-Keenan spectroscopic classification is based in part on the relative strengths of these bands (Morgan & Keenan 1973). However, the electronic bands in these studies are photospheric absorption features, which do not provide any insight into the warm circumstellar chemistry.…”

Section: Introductionmentioning

confidence: 98%

Pure rotational spectra of TiO and TiO₂in VY Canis Majoris

Kamiński

Gottlieb

Menten

et al. 2013

A&A

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We report the first detection of pure rotational transitions of TiO and TiO 2 at (sub-)millimeter wavelengths towards the red supergiant VY CMa. A rotational temperature, T rot , of about 250 K was derived for TiO 2 . Although T rot was not well constrained for TiO, it is likely somewhat higher than that of TiO 2 . The detection of the Ti oxides confirms that they are formed in the circumstellar envelopes of cool oxygen-rich stars and may be the "seeds" of inorganic-dust formation, but alternative explanations for our observation of TiO and TiO 2 in the cooler regions of the envelope cannot be ruled out at this time. The observations suggest that a significant fraction of the oxides is not converted to dust, but instead remains in the gas phase throughout the outflow.

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Spectral Classification

Cited by 269 publications

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The chemical composition of carbon stars. The R-type stars

The chemical composition of carbon stars. The R-type stars

SOPHIE velocimetry ofKeplertransit candidates

Pure rotational spectra of TiO and TiO₂in VY Canis Majoris

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Spectral Classification

Cited by 269 publications

References 0 publications

The chemical composition of carbon stars. The R-type stars

The chemical composition of carbon stars. The R-type stars

SOPHIE velocimetry ofKeplertransit candidates

Pure rotational spectra of TiO and TiO2in VY Canis Majoris

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Pure rotational spectra of TiO and TiO₂in VY Canis Majoris