Abundance anomalies in pre-main-sequence stars

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

doi:10.1051/0004-6361/201015533

Cited by 31 publications

(36 citation statements)

References 33 publications

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“…These weak winds may also show multicomponent structure with the difference between the heavier elements and hydrogen and helium becoming comparable with the thermal speed. Moderate winds trigger some abundance peculiarities, while strong winds wash out any peculiarities (Vauclair 1975;Landstreet et al 1998;Unglaub 2008;Vick et al 2011). Consequently, winds in subluminous stars may be also important for the explanation of surface abundances.…”

Section: Discussionmentioning

confidence: 99%

Stellar wind models of subluminous hot stars

Krtička

Kubát

Krtičková

2016

A&A

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1Ú stav teoretické fyziky a astrofyziky, Masarykova univerzita, Kotlářská 2, CZ-611 37 Brno, Czech Republic 2 Astronomickýústav, Akademie vědČeské republiky, Fričova 298, CZ-251 65 Ondřejov, Czech Republic Received ABSTRACTContext. Mass-loss rate is one of the most important stellar parameters. Mass loss via stellar winds may influence stellar evolution and modifies stellar spectrum. Stellar winds of subluminous hot stars, especially subdwarfs, have not been studied thoroughly. Aims. We aim to provide mass-loss rates as a function of subdwarf parameters and to apply the formula for individual subdwarfs, to predict the wind terminal velocities, to estimate the influence of the magnetic field and X-ray ionization on the stellar wind, and to study the interaction of subdwarf wind with mass loss from Be and cool companions. Methods. We used our kinetic equilibrium (NLTE) wind models with the radiative force determined from the radiative transfer equation in the comoving frame (CMF) to predict the wind structure of subluminous hot stars. Our models solve stationary hydrodynamical equations, that is the equation of continuity, equation of motion, and energy equation and predict basic wind parameters. Results. We predicted the wind mass-loss rate as a function of stellar parameters, namely the stellar luminosity, effective temperature, and metallicity. The derived wind parameters (mass-loss rates and terminal velocities) agree with the values derived from the observations. The radiative force is not able to accelerate the homogeneous wind for stars with low effective temperatures and high surface gravities. We discussed the properties of winds of individual subdwarfs. The X-ray irradiation may inhibit the flow in binaries with compact components. In binaries with Be components, the winds interact with the disk of the Be star. Conclusions. Stellar winds exist in subluminous stars with low gravities or high effective temperatures. Despite their low mass-loss rates, they are detectable in the ultraviolet spectrum and cause X-ray emission. Subdwarf stars may lose a significant part of their mass during the evolution. The angular momentum loss in magnetic subdwarfs with wind may explain their low rotational velocities. Stellar winds are especially important in binaries, where they may be accreted on a compact or cool companion.

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Section: Discussionmentioning

confidence: 99%

Stellar wind models of subluminous hot stars

Krtička

Kubát

Krtičková

2016

A&A

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“…All of these hypotheses are related to dust-gas separation and the accretion of dust-depleted material, with two notable exceptions: (i) the refuted composite-spectrum hypothesis, which was covered in Sect. 1, and has been more comprehensively reviewed by Murphy et al (2015); and (ii) the diffusion and mass-loss mechanism (Michaud & Charland 1986), which tends to produce overabundances of Fe-peak elements typical of Am stars (Vick et al 2010(Vick et al , 2011, rather than the underabundances observed in λ Boo stars. We suggest that it is not a single mechanism that is responsible, but that several channels can form λ Boo spectra under certain conditions.…”

Section: Influence On Pulsationmentioning

confidence: 99%

Gaia's view of the λ Boo star puzzle

Murphy

Paunzen

2016

Mon. Not. R. Astron. Soc.

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The evolutionary status of the chemically peculiar class of λ Boo stars has been intensely debated. It is now agreed that the λ Boo phenomenon affects A stars of all ages, from star formation to the terminal age main sequence, but the cause of the chemical peculiarity is still a puzzle. We revisit the debate of their ages and temperatures in order to shed light on the phenomenon, using the new parallaxes in Gaia Data Release 1 with existing Hipparcos parallaxes and multicolour photometry. We find that no single formation mechanism is able to explain all the observations, and suggest that there are multiple channels producing λ Boo spectra. The relative importance of these channels varies with age, temperature and environment.

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“…It is not clear whether it is turbulence or mass loss which competes with diffusion to lower the abundance anomalies. For example, Vick et al (2011) find that diffusion in the presence of weak mass loss can explain the observed abundance anomalies of pre‐main‐sequence stars. This is in contrast to turbulence models which do not allow for abundance anomalies to develop on the pre‐main‐sequence.…”

Section: Introductionmentioning

confidence: 99%

Abundances in HD 27411 and the helium problem in Am stars

Catanzaro

Balona

2012

Monthly Notices of the Royal Astronomical Society

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We analyse a high‐resolution spectrum of the A3m star HD 27411. We compare abundances derived from atlas9 model atmospheres with those using the more computationally intensive atlas12 code. We found very little differences in the abundances, suggesting that atlas9 can be used for moderate chemical peculiarity. Our abundances agree well with the predictions of diffusion theory, though for some elements it was necessary to calculate line profiles in non‐thermodynamic equilibrium to obtain agreement. We investigate the effective temperatures and luminosities of Am/Fm stars using synthetic Strömgren indices derived from calculated spectra with the atmospheric abundances of HD 27411. We find that the effective temperatures of Am/Fm stars derived from Strömgren photometry are reliable, but the luminosities are probably too low. Caution is required when deriving the reddening of these stars owing to line blanketing effects. A comparison of the relative proportions of pulsating and non‐pulsating Am stars with δ Scuti stars shows quite clearly that there is no significant decrease of helium in the driving zone, contrary to current models of diffusion.

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Abundance anomalies in pre-main-sequence stars

Cited by 31 publications

References 33 publications

Stellar wind models of subluminous hot stars

Stellar wind models of subluminous hot stars

Gaia's view of the λ Boo star puzzle

Abundances in HD 27411 and the helium problem in Am stars

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