Consistent Evolution of F Stars: Diffusion, Radiative Accelerations, and Abundance Anomalies

AbstractThe observations of AmFm, λ Booti, HgMn and He rich stars that are explained without any arbitrary parameter by diffusion are briefly reviewed, followed by those observations that are not explained by this simple model. Mass loss is then shown to explain a large fraction of the observations that are not explained in the parameter free model. It seems to play a role in the λ Booti, AmFm, He rich and the hot horizontal branch stars. It is only of about 10−15 to 10−13 Mo/yr. Abundance anomalies then help to determine stellar hydrodynamics. It is finally suggested that recent observations of Li underabundances in F stars of the Hyades represent an extension of the AmFm star phenomenon.

Main Sequence Abundances, Mass Loss and Meridional Circulation

International Astronomical Union Colloquium ◽

10.1017/s0252921100093325 ◽

1988 ◽

Vol 108 ◽

pp. 3-12

Author(s):

Georges Michaud

Keyword(s):

Mass Loss ◽

Loss Rate ◽

Main Sequence ◽

Meridional Circulation ◽

Mass Loss Rate ◽

Rotational Velocity ◽

Open Clusters ◽

Halo Stars ◽

Abundance Anomalies ◽

F Stars

AbstractConstraints that abundance anomalies observed on main sequence stars put on turbulence, meridional circulation and mass loss are reviewed. The emphasis is on recent observations of Li abundances.Upper limits to turbulence are obtained from the Be abundance in the Sun and from underabundances of Ca and Sc in FmAm stars. The Li abundance in G type stars suggests the presence of turbulence below convection zones.The abundance anomalies, both over and underabundances, observed in FmAm and λ Booti stars can be explained by diffusion in the presence of mass loss. A mass loss rate of 10−15 Mo yr−1 is required to explain the FmAm stars while a mass loss rate of 10−13 Mo yr−1 is required by the λ Booti stars.The position and width of the Li abundance gap observed in Hyades and other open clusters is explained by diffusion. A detailed reproduction of the Li(Teff) curve seems to require a mass loss rate of slightly more than 10−15 Mo yr−1, of the same order as the mass loss rate required by the FmAm stars. In the presence of such a mass loss only small overabundances of heavy elements are expected. The observed variations in the Li abundance as a function of the age of clusters suggests that the Li abundance observed in old halo stars does not represent the cosmological abundance.Detailed two dimensional calculations of diffusion in presence of meridional circulation for HgMn and FmAm stars lead to a cut-off of about 100 km s−1 for the maximum equatorial rotational velocity at which abundance anomalies are expected in these objects. This agrees with observations. A similar calculation for the F stars of the Hyades where Li underabundances are observed leads to a contradiction, unless meridional circulation patterns are modified by the presence of convection zones once they become as large as in late F stars. There remains a possibility that meridional circulation would be responsible for some of the reduction of the Li abundance as observed in the Hyades and UMa. Further observations are suggested to distinguish the effects of settling and nuclear destruction.

Constraints on Stellar Hydrodynamics from Abundance Anomalies of LiBeB and Metals

Symposium - International Astronomical Union ◽

10.1017/s0074180900167051 ◽

2000 ◽

Vol 198 ◽

pp. 460-469

Author(s):

Georges Michaud ◽

Jacques Richer ◽

Olivier Richard

Keyword(s):

Stellar Evolution ◽

Convection Zone ◽

Turbulence Models ◽

Open Clusters ◽

Atomic Diffusion ◽

Atomic Data ◽

Additional Information ◽

Metal Abundances ◽

Abundance Anomalies ◽

F Stars

The availability of large atomic data bases has made it possible to calculate stellar evolution models taking into detailed account the atomic diffusion of all important contributors to opacity. The radiative accelerations and the opacity are continuously calculated during evolution taking the abundance changes of 28 species into account. This leads to the first self-consistent stellar evolution models for A and F stars. In A and F stars an iron-peak convection zone appears.The calculated abundance anomalies are very similar to those observed in AmFm stars in open clusters except that they are larger by a factor of about 3. To reduce the calculated anomalies to the observed ones, an additional source of turbulence (or some other hydrodynamical process) must be introduced. The mixed zone must extend about 5 times deeper than the iron convection zone. Detailed comparisons to a few AmFm stars have been carried out.The LiBeB abundances observed in clusters give additional information. The abundances of the 28 species offer considerable constraints on the models. Various potential turbulence models have been introduced in a stellar evolution code and results of evolutionary calculations for Li gap stars are discussed in the light of the constraints offered by the abundances of LiBeB and metals. The radiative accelerations of LiBeB have also been recalculated taking the effect of changing metal abundances into account. This modifies the expected Li gap in the absence of turbulence.

Elemental Abundances of Sharp-Lined Metallic-Lined and Comparable Normal Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100020546 ◽

1993 ◽

Vol 138 ◽

pp. 213-217

Author(s):

Dursun Koçer ◽

Saul J. Adelman ◽

Çetin Bolcal ◽

Graham Hill

Keyword(s):

Elemental Abundances ◽

Abundance Anomalies ◽

F Stars

AbstractWe are performing elemental abundances of sharp-lined metallic-lined stars and normal late A through middle F stars using 2.4 Å mm−1 photographic region spectrograms taken with the coudé spectrograph of the 1.4-m telescope of the Dominion Astrophysical Observatory. Our initial studies of the Am stars 15 Vul and 32 Aqr and the normal stars θ Cyg (F4 V) and ɩ Psc (F7 V) showed that the elemental abundances of the normal stars were close to solar while 15 Vul shows smaller abundance anomalies than does 32 Aqr. These analyses are being done consistently with SJA’s studies of the HgMn and hotter normal stars.

Mechanisms of Separation of Elements

International Astronomical Union Colloquium ◽

10.1017/s0252921100020881 ◽

1993 ◽

Vol 138 ◽

pp. 439-449 ◽

Cited By ~ 5

Author(s):

Georges Michaud ◽

C. R. Proffitt

Keyword(s):

High Signal ◽

The Sun ◽

Signal To Noise ◽

Continuous Development ◽

Gravitational Settling ◽

Halo Stars ◽

Solar Type ◽

Abundance Anomalies ◽

F Stars ◽

Ap Stars

Since the last IAU Colloquium devoted to Ap stars, die continuous development of high signal to noise observations and of computerized analysis tools have greatly increased the effectiveness of abundance anomalies as a probe of hydrodynamical processes in stars. Until the 1980s, they seemed limited to ApBp and AmFm stars where the effects are largest. More recently the abundances of Li and He have been suggested to play important diagnostic roles for hydrodynamics in both the Sun (Proffitt and Michaud 1991b, Pinsonneault et al. 1989) and Halo stars (Proffitt and Michaud 1991a, Pinsonneault et al. 1992, Vauclair 1988, Charbonnel et al. 1992, Deliyannis and Demarque 1991). The observation of a Li abundance gap in F stars of clusters has raised the question of the link between these objects and the AmFm stars (Michaud 1986, Charbonneau and Michaud 1988, 1991) or alternately with solar type stars. The observed Li abundance on die subgiant branch sheds some light on this problem (Charbonneau et al. 1989; Charbonnel and Vauclair 1992). In solar type stars, the observed Li abundance constrains the superficial turbulence that may inhibit surface He gravitational settling (Proffitt and Michaud 1991b) whose effects can be detected using solar seismology (Guzik and Cox 1992, Dziembowski et al. 1992).

Photo-electric Hβ and uvby photometry

Symposium - International Astronomical Union ◽

10.1017/s0074180900053407 ◽

1966 ◽

Vol 24 ◽

pp. 170-180

Author(s):

D. L. Crawford

Keyword(s):

Narrow Band ◽

Line Strength ◽

Interference Filter ◽

B Stars ◽

Relative Line ◽

The Mean ◽

F Stars ◽

Two Parameters ◽

Filter Photometry ◽

The Continuum

Early in the 1950's Strömgren (1, 2, 3, 4, 5) introduced medium to narrow-band interference filter photometry at the McDonald Observatory. He used six interference filters to obtain two parameters of astrophysical interest. These parameters he calledlandc, for line and continuum hydrogen absorption. The first measured empirically the absorption line strength of Hβby means of a filter of half width 35Å centered on Hβand compared to the mean of two filters situated in the continuum near Hβ. The second index measured empirically the Balmer discontinuity by means of a filter situated below the Balmer discontinuity and two above it. He showed that these two indices could accurately predict the spectral type and luminosity of both B stars and A and F stars. He later derived (6) an indexmfrom the same filters. This index was a measure of the relative line blanketing near 4100Å compared to two filters above 4500Å. These three indices confirmed earlier work by many people, including Lindblad and Becker. References to this earlier work and to the systems discussed today can be found in Strömgren's article inBasic Astronomical Data(7).

Spectrum synthesis of sharp-line B, A and F stars

EAS Publications Series ◽

10.1051/eas:2005138 ◽

2005 ◽

Vol 17 ◽

pp. 345-348 ◽

Cited By ~ 2

Author(s):

J. Silaj ◽

A. Townshend ◽

F. Kupka ◽

J. Landstreet ◽

A. Sigut

Keyword(s):

Sharp Line ◽

Spectrum Synthesis ◽

F Stars

Abundance Anomalies in the X‐Ray Spectra of Planetary Nebulae NGC 7027 and BD +30o3639

The Astrophysical Journal ◽

10.1086/374414 ◽

2003 ◽

Vol 589 (1) ◽

pp. 439-443 ◽

Cited By ~ 18

Author(s):

Holly L. Maness ◽

Saeqa D. Vrtilek ◽

Joel H. Kastner ◽

Noam Soker

Keyword(s):

Planetary Nebulae ◽

X Ray ◽

Ngc 7027 ◽

Abundance Anomalies

When nature tries to trick us

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833693 ◽

2018 ◽

Vol 619 ◽

pp. A84 ◽

Cited By ~ 6

Author(s):

Henri M. J. Boffin ◽

David Jones ◽

Roger Wesson ◽

Yuri Beletsky ◽

Brent Miszalski ◽

...

Keyword(s):

Planetary Nebula ◽

Binary Star ◽

Central Star ◽

Equal Mass ◽

Type I ◽

Eclipsing Binary ◽

Common Envelope ◽

Bright Object ◽

F Stars ◽

Central Stars

Bipolar planetary nebulae (PNe) are thought to result from binary star interactions and, indeed, tens of binary central stars of PNe have been found, in particular using photometric time-series that allow for the detection of post-common envelope systems. Using photometry at the NTT in La Silla we have studied the bright object close to the centre of PN M 3-2 and found it to be an eclipsing binary with an orbital period of 1.88 days. However, the components of the binary appear to be two A or F stars, of almost equal mass, and are therefore too cold to be the source of ionisation of the nebula. Using deep images of the central star obtained in good seeing conditions, we confirm a previous result that the central star is more likely much fainter, located 2″ away from the bright star. The eclipsing binary is thus a chance alignment on top of the planetary nebula. We also studied the nebular abundance and confirm it to be a Type I PN.

Accreting pre-main-sequence models and abundance anomalies in globular clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stv2254 ◽

2015 ◽

Vol 454 (4) ◽

pp. 4037-4053 ◽

Cited By ~ 8

Author(s):

E. Tognelli ◽

P. G. Prada Moroni ◽

S. Degl'Innocenti

Keyword(s):

Globular Clusters ◽

Main Sequence ◽

Abundance Anomalies