Technetium and the third dredge up in AGB stars

Lebzelter, T.; Hron, J.

doi:10.1051/0004-6361:20065463

Cited by 48 publications

(76 citation statements)

References 50 publications

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“…Uttenthaler et al (2007) find evidence of the third dredge-up in four out of 27 bulge AGB stars based on the presence of radioactive technetium. The third dredge-up is not expected to operate in 1 M stars and requires a younger population.…”

Section: The Age Of the Bulgementioning

confidence: 84%

Accelerated post-AGB evolution, initial-final mass relations, and the star-formation history of the Galactic bulge

Gęsicki

Zijlstra

Hajduk

et al. 2014

A&A

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Aims. We study the star-formation history of the Galactic bulge, as derived from the age distribution of the central stars of planetary nebulae that belong to this stellar population. Methods. The high resolution imaging and spectroscopic observations of 31 compact planetary nebulae are used to derive their central star masses. We use the Blöcker post asymptotic giant branch (post-AGB) evolutionary models, which are accelerated by a factor of three in this case to better fit the white dwarf mass distribution and asteroseismological masses. Initial-final mass relations (IFMR) are derived using white dwarfs in clusters. These are applied to determine original stellar masses and ages. The age distribution is corrected for observational bias as a function of stellar mass. We predict that there are about 2000 planetary nebulae in the bulge. Results. The planetary nebula population points at a young bulge population with an extended star-formation history. The Blöcker tracks with the cluster IFMR result in ages, which are unexpectedly young. We find that the Blöcker post-AGB tracks need to be accelerated by a factor of three to fit the local white dwarf masses. This acceleration extends the age distribution. We adjust the IFMR as a free parameter to map the central star ages on the full age range of bulge stellar populations. This fit requires a steeper IFMR than the cluster relation. We find a star-formation rate in the Galactic bulge, which is approximately constant between 3 and 10 Gyr ago. The result indicates that planetary nebulae are mainly associated with the younger and more metal-rich bulge populations. Conclusions. The constant rate of star-formation between 3 and 10 Gyr agrees with suggestions that the metal-rich component of the bulge is formed during an extended process, such as a bar interaction.

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Section: The Age Of the Bulgementioning

confidence: 84%

Accelerated post-AGB evolution, initial-final mass relations, and the star-formation history of the Galactic bulge

Gęsicki

Zijlstra

Hajduk

et al. 2014

A&A

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“…There is another, even stronger piece of evidence coming from the RV distributions of AGB stars and planetary nebulae (PNe) in the PG3 field that supports this explanation. RVs of Mira and semi-regular variables (SRVs) in the PG3 have been presented by Schultheis (1998) and Uttenthaler et al (2007). The 27 AGB stars studied by Uttenthaler et al (2007) by means of high-resolution UVES/VLT spectra have a velocity dispersion of 90.9 ± 12.6 km s −1 .…”

Section: Comparison With the Fux Modelmentioning

confidence: 99%

Constraining the structure and formation of the Galactic bulge from a field in its outskirts

Uttenthaler¹,

Schultheis²,

Nataf³

et al. 2012

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Context. The presence of two stellar populations in the Milky Way bulge has been reported recently, based on observations of giant and dwarf stars in the inner and intermediate bulge.Aims. We aim at studying the abundances and kinematics of stars in the outer Galactic bulge, thereby providing additional constraints on formation models of the bulge. Methods. Spectra of 401 red giant stars in a field at (l, b) = (0 • , −10 • ) were obtained with the FLAMES-GIRAFFE spectrograph at the VLT. Stars of luminosities down to below the two bulge red clumps are included in the data set. From these spectra we measured general metallicities, abundances of iron and the α-elements, and radial velocities of the stars. The abundances were derived from an interpolation and fitting procedure within a grid of COMARCS model atmospheres and spectra. These measurements as well as photometric data were compared to simulations with the Besançon and TRILEGAL models of the Galaxy. Results. We confirm the presence of two populations among our sample stars: i) a metal-rich one at [M/H] ∼ +0.3, comprising about 30% of the sample, with low velocity dispersion and low α-abundance, and ii) a metal-poor population at [M/H] ∼ −0.6 with high velocity dispersion and high α-abundance. The metallicity difference between the two populations, a systematically and statistically robust figure, is Δ[M/H] = 0.87 ± 0.03. The metal-rich population could be connected to the Galactic bar. We identify this population as the carrier of the double red clump feature. We do not find a significant difference in metallicity or radial velocity between the two red clumps, a small difference in metallicity being probably due to a selection effect and contamination by the metal-poor population. The velocity dispersion agrees well with predictions of the Besançon Galaxy model, but the metallicity of the "thick bulge" model component should be shifted to lower metallicity by 0.2 to 0.3 dex to well reproduce the observations. We present evidence that the metallicity distribution function depends on the evolutionary state of the sample stars, suggesting that enhanced mass loss preferentially removes metal-rich stars. We also confirm the decrease of α-element over-abundance with increasing metallicity. Conclusions. Our sample is consistent with the existence of two populations, one being a metal-rich bar, the second one being more like a metal-poor classical bulge with larger velocity dispersion.

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“…The resolution of these spectra is R = λ/Δλ 50 000, and the wavelength coverage is approximately 380 − 490 nm in the "blue arm", and 667−1000 nm in the "red arm" of UVES. These observations are described in Uttenthaler et al (2007a), and the spectra are 1 http://webviz.u-strasbg.fr/viz-bin/VizieR analysed for Tc in Lebzelter & Hron (2003). We thus refer to these papers for more details.…”

Section: Sample and Observationsmentioning

confidence: 99%

“…The signal-to-noise ratio (SNR) of the spectra is estimated to be in the range 6−10 at the wavelength of the Tc lines, and > ∼ 100 at the wavelength of the 670.8 nm Li line 2 . As shown by Uttenthaler et al (2007a), an SNR of 6−10 is sufficient to decide on the presence of Tc based on a flux-ratio method (see next section), as long as the spectral resolution is high enough.…”

Section: Sample and Observationsmentioning

confidence: 99%

“…The differences to literature values are usually small (a few km s −1 ), and can be fully explained by rv variations caused by the stellar pulsation. We corrected the observed spectra by the measured rv shift to check them for the Tc lines using the flux-ratio method introduced by Uttenthaler et al (2007a). In this method, the mean flux in a small wavelength interval around a quasi-continuum point close to the Tc line is divided by the mean flux in a small wavelength interval centred on the Tc line itself.…”

Section: Analysis With Respect To Tcmentioning

confidence: 99%

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Correlation between technetium and lithium in a sample of oxygen-rich AGB variables

Uttenthaler¹,

Lebzelter²

2010

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Context. The elements technetium and lithium are two important indicators of internal nucleosynthesis and mixing in late-type stars. Studying their occurrence and abundance can give deep insight into the structure and evolution in the late phases of the stellar life cycle. Aims. The aims of this paper are: 1) to revisit the Tc content of a sample of oxygen-rich (M-type) asymptotic giant branch (AGB) variables and 2) to increase the number of such stars for which the Li abundance has been measured to provide constraints on the theoretical models of extra-mixing processes. Methods. To this end, we analysed high-resolution spectra of 18 sample stars for the presence of absorption lines of Tc and Li. The abundance of the latter was determined by comparing the observed spectra to hydrostatic MARCS model spectra. Bolometric magnitudes were established from near-IR photometry and pulsation periods. Results. We correct the classification with respect to the presence of Tc for a number of stars. We reclassify the star V441 Cyg as Tc-rich, and the unusual Mira star R Hya, as well as W Eri, as Tc-poor. The abundance of Li, or an upper limit to it, was determined for all of the sample stars. In all stars with Tc we also detected Li. Most of them have a Li content slightly below the solar photospheric value, except for V441 Cyg, which is super-Li rich with ∼1000 times the solar abundance. We also found that, similar to Tc, a lower luminosity limit seems to exist for the presence of Li. Conclusions. We conclude that the higher Li abundance found in the cooler and higher luminosity objects could stem from a Li production mechanism operating on the thermally pulsing AGB. The stellar mass might have a crucial influence on this (extra mixing) production mechanism. Our findings for R Hya and V441 Cyg have some important consequences for these intriguing objects. It was speculated that the declining pulsation period of R Hya is caused by a recent thermal pulse (TP). While not detecting Tc does not rule out a TP, it indicates that the TPs are not strong enough to drive 3DUP in R Hya. The pieces of evidence concerning the mass of V441 Cyg are not entirely conclusive. It could either be a low-mass, intrinsic S-star that produced its large amount of Li by extra-mixing processes, or an intermediate-mass star (M > ∼ 4 M ) undergoing Li production via hot bottom burning.

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Technetium and the third dredge up in AGB stars

Cited by 48 publications

References 50 publications

Accelerated post-AGB evolution, initial-final mass relations, and the star-formation history of the Galactic bulge

Accelerated post-AGB evolution, initial-final mass relations, and the star-formation history of the Galactic bulge

Constraining the structure and formation of the Galactic bulge from a field in its outskirts

Correlation between technetium and lithium in a sample of oxygen-rich AGB variables

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