AmFm and lithium gap stars

Vick, M.; Michaud, G.; Richer, Jacques; Richard, Olivier

doi:10.1051/0004-6361/201014307

Cited by 74 publications

(112 citation statements)

References 86 publications

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“…Given the range of abundances observed for any given species, the agreement seemed satisfactory. In Vick et al (2010), similar results were obtained through a similar approach but with mass loss as the competing process. Because the observational error bars were too large, these authors were unable to delineate which of mass loss or turbulence was responsible for its abundance anomalies.…”

Section: Astrophysical Contextsupporting

confidence: 74%

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Sirius A: turbulence or mass loss?

Michaud

Richer

Vick

2011

A&A

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Context. Abundance anomalies observed in a fraction of A and B stars of both Pop I and II are apparently related to internal particle transport. Aims. Using available constraints from Sirius A, we wish to determine how well evolutionary models including atomic diffusion can explain observed abundance anomalies when either turbulence or mass loss is used as the main competitor to atomic diffusion. Methods. Complete stellar evolution models, including the effects of atomic diffusion and radiative accelerations, have been computed from the zero age main-sequence of 2.1 M stars for metallicities of Z 0 = 0.01 ± 0.001, and shown to closely reproduce the observed parameters of Sirius A. Surface abundances were predicted for three values of the mass loss rate and four values of the mixed surface zone. Results. A mixed mass of ∼10 −6 M or a mass loss rate of 10 −13 M /yr were determined through comparison with observations. There are 17 abundances that were determined observationally and that are included in our calculations. Up to 15 of them can be predicted to within 2σ; three of the four determined upper limits are compatible. Conclusions. While the abundance anomalies can be reproduced slightly better using turbulence as the process competing with atomic diffusion, mass loss probably ought to be preferred since the mass loss rate required to fit abundance anomalies is compatible with the observationally determined rate. A mass loss rate within a factor of 2 of 10 −13 M /yr is preferred. This restricts the range of the directly observed mass loss rate.

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Section: Astrophysical Contextsupporting

confidence: 74%

“…In this paper, stellar evolution models with atomic diffusion as described in Richer et al (2000) and in Vick et al (2010) are used to determine the original metallicity of Sirius A using the age, radius and mass as constraints (Sect. 2).…”

Section: Astrophysical Contextmentioning

confidence: 99%

Sirius A: turbulence or mass loss?

Michaud

Richer

Vick

2011

A&A

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“…Przybilla & Butler 2001). This has the potential to solve one of the most prominent discrepancies between observation and predictions from diffusion models for Am stars (Richer et al 2000;Vick et al 2010, and references therein). Discrepancies in the ionisation equilibria of some elements that can be currently analysed in LTE only hint on the presence of (substantial) non-LTE effects for these as well.…”

Section: Discussionmentioning

confidence: 99%

Candidate exoplanet host HD 131399A: a nascent Am star

Przybilla

Aschenbrenner

Buder

2017

A&A

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Direct imaging suggests that there is a Jovian exoplanet around the primary A-star in the triple-star system HD 131399. We investigate a high-quality spectrum of the primary component HD 131399A obtained with FEROS on the ESO/MPG 2.2 m telescope, aiming to characterise the star's atmospheric and fundamental parameters, and to determine elemental abundances at high precision and accuracy. The aim is to constrain the chemical composition of the birth cloud of the system and therefore the bulk composition of the putative planet. A hybrid non-local thermal equilibrium (non-LTE) model atmosphere technique is adopted for the quantitative spectral analysis. Comparison with the most recent stellar evolution models yields the fundamental parameters. The atmospheric and fundamental stellar parameters of HD 131399A are constrained to T eff = 9200 ± 100 K, log g = 4.37 ± 0.10, M = 1.95 +0.08 −0.06 M , R = 1.51 +0.13 −0.10 R , and log L/L = 1.17 ± 0.07, locating the star on the zero-age main sequence. Non-LTE effects on the derived metal abundances are often smaller than 0.1 dex, but can reach up to ∼0.8 dex for individual lines. The observed lighter elements up to calcium are overall consistent with present-day cosmic abundances, with a C/O ratio of 0.45 ± 0.07 by number, while the heavier elements show mild overabundances. We conclude that the birth cloud of the system had a standard chemical composition, but we witness the onset of the Am phenomenon in the slowly rotating star. We furthermore show that non-LTE analyses have the potential to solve the remaining discrepancies between observed abundances and predictions by diffusion models for Am stars. Moreover, the present case allows mass loss, not turbulent mixing, to be identified as the main transport process competing with diffusion in very young Am stars.

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“…There are other physical processes that could work in addition to the diffusion modifying the abundances, such as mass loss (e.g. Vick et al 2008Vick et al , 2010 or turbulence mixing (e.g. Richer et al 2000;Richard et al 2001).…”

Section: Abundances Of Sn Stars Vs Cp Starsmentioning

confidence: 99%

On the nature of sn stars

Saffe

Levato

2014

A&A

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The sn stars were first discoved by Abt & Levato when studying the spectral types in different open clusters. These stars present sharp Balmer lines, sharp metallic lines (C II, Si II, Ca II, Ti II, Fe II), and broad coreless He I lines. Some of the sn stars seem to be related to CP stars. Initially Abt & Levato proposed a shell-like nature to explain the sn stars, although this scenario was subsequently questioned. There is no general agreement about their origin. We aim to derive abundances for a sample of 9 stars, including sn and non-sn stars, to determine the possible relation between sn and CP stars and compare their chemical abundances. That most sn stars belong to open clusters allows us to search for a possible relation with fundamental parameters, including the age and rotation. We also study the possible contribution of different effects to the broad He I lines observed in these stars, such as Stark broadening and the possible He-stratification. Effective temperature and gravity were estimated by Strömgren photometry and then refined by requiring ionization and excitation equilibrium of Fe lines. We derived the abundances by fitting the observed spectra with synthetic spectra using an iterative procedure with the SYNTHE and ATLAS9 codes. We derived metallic abundances of 23 different chemical elements for 9 stars and obtained low projected rotational velocities for the sn stars in our sample (v sin i up to 69 km s −1 ). We also compared 5 stars that belong to the same cluster (NGC 6475) and show that the sn characteristics appear in the 3 stars with the lower rotational velocity. However, the apparent preference of sn stars for objects with the lower v sin i values should be taken with caution due to the small number of objects studied here. We analysed the photospheric chemical composition of sn stars and show that approximately ∼40% of them display chemical peculiarities (such as He-weak and HgMn stars) within a range of temperature of 10 300 K−14 500 K. However, there are also sn stars with solar or nearly-solar (i.e. non-CP) chemical composition. We have studied the possible contribution of different processes to the broad He I lines present in the sn stars. Although NLTE effects could not be completely ruled out, it seems that NLTE is not directly related to the broad He I profiles observed in the sn stars. The broad-line He I 4026 Å is the clearest example of the sn characteristics in our sample. We succesfully fit this line in 4 out of 7 sn stars by using the appropriate Stark broadening tables, while small differences appear in the other 3 stars. Studying the plots of abundance vs. depth for the He I lines resulted in some sn stars probably being stratified in He. However, a further study of variability in the He I lines would help for determining whether a possible non-uniform He superficial distribution could also play a role in these sn stars. We conclude that the broad He I lines that characterize the sn class could be modelled (at least in some of these stars) by the usual radiati...

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AmFm and lithium gap stars

Cited by 74 publications

References 86 publications

Sirius A: turbulence or mass loss?

Sirius A: turbulence or mass loss?

Candidate exoplanet host HD 131399A: a nascent Am star

On the nature of sn stars

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