SIMBAD references

1998A&AS..127..277K - Astron. Astrophys., Suppl. Ser., 127, 277-294 (1998/January-2)

Are metallic A-F giants evolved Am stars? Rotation and rate of binaries among giant F stars.


Abstract (from CDS):

We test the hypothesis of Berthet (1991A&A...251..171B) which foresees that Am stars become giant metallic A and F stars (defined by an enhanced value of the blanketing parameter {DELTA}m2 of the Geneva photometry) when they evolve. If this hypothesis is right, Am and metallic A-FIII stars need to have the same rate of binaries and a similar distribution of vsini. From our new spectroscopic data and from vsin i and radial velocities in the literature, we show that it is not the case. The metallic giant stars are often fast rotators with vsin i larger than 100km/s, while the maximum rotational velocity for Am stars is about 100km/s. The rate of tight binaries with periods less than 1000 days is less than 30% among metallic giants, which is incompatible with the value of 75% for Am stars (Abt & Levy 1985ApJS...59..229A). Therefore, the simplest way to explain the existence of giant metallic F stars is to suggest that all normal A and early F stars might go through a short ``metallic" phase when they are finishing their life on the main sequence. Besides, it is shown that only giant stars with spectral type comprised between F0 and F6 may have a really enhanced {DELTA}m2 value, while all A-type giants seem to be normal.

Abstract Copyright:

Journal keyword(s): stars: binaries: spectroscopic - stars: chemically peculiar - stars: evolution - stars: rotation - stars: δ Scuti

VizieR on-line data: <Available at CDS (J/A+AS/127/277): table2 table3 table6 tables.tex>

Simbad objects: 88

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