Astron. Astrophys. 326, 780-792 (1997)

The age-mass relation for chromospherically active binaries

II. Lithium depletion in dwarf components ^{* **}

D. Barrado y Navascués ^{1, 2}, M.J. Fernández-Figueroa ³, R.J. Garca López ⁴, E. De Castro ³ and M. Cornide <sup>3

1</sup> MEC/Fulbright Fellow at the Smithsonian Astrophysical Observatory, 60 Garden St, Cambridge, MA 02138, USA
² Real Colegio Complutense at Harvard University, Trowbridge St, Cambridge, MA 02138, USA
³ Dpto. Astrofsica, Facultad de Fsicas, Universidad Complutense, E-28040 Madrid, Spain
⁴ Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain

Received 18 November 1996 / Accepted 2 April 1997

Abstract

We present an extensive study of lithium abundances in dwarf components of chromospherically active binary stars (CABS). Since most of these binaries have known radii, masses and ages, this kind of data is especially useful for comparisons with theoretical models which try to explain the Li depletion phenomenon. We show that a significant part of these stars have clear Li overabundances with respect to the typical values for stars of the same mass and evolutionary stage. These excesses are evident when comparing our sample of CABS with binary and single stars belonging to open clusters of different ages, namely Pleiades, Hyades, NGC752, M67 and NGC188, which have ages ranging from 7 10⁷ to 10¹⁰ yr. The Li excesses are more conspicuous for masses in the range 0.75-0.95 M, indicating that the rate of Li depletion has been less pronounced in CABS than in single stars. This phenomenon is interpreted in the context of transport of angular momentum from the orbit to the stellar rotation due to tidal effects. This angular momentum transfer would avoid the radial differential rotation and the associated turbulent mixing of material in the stellar interior. Other explanations, however, can not be ruled out. This is the case of transport of material induced by internal gravity waves, which could be inhibited due to the presence of strong magnetic fields associated with the effective dynamo in CABS. The confirmed existence of a relation between Li abundances and the fluxes in Ca II H&K lines can also be accommodated within both scenarios.

Key words: stars: activity - stars: binaries: close - stars: abundances - stars: late type

* Tables 1 and 2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
** Based on observations collected with the 2.2m telescope of the German-Spanish Observatorio de Calar Alto (Almería, Spain), and with the 2.56m Nordic Optical Telescope in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias (La Palma, Spain)

Send offprint requests to: D. Barrado y Navascués (dbarrado@cfa.harvard.edu)

SIMBAD Objects

Contents

• 1. Introduction
• 2. Dwarf components of CABS
  • 2.1. The evolutionary status
  • 2.2. Program stars
• 3. Observations and data reduction
• 4. Lithium abundances
  • 4.1. Equivalent widths
  • 4.2. Effective temperatures
  • 4.3. Lithium abundances and errors
  • 4.4. Li abundance vs. effective temperature
• 5. Comparison with open clusters
• 6. Li abundance, stellar activity and rotation
• 7. Summary and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997
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