Lithium Abundances in F5-G8 Dwarfs.

Abstract

view Abstract Citations (223) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Lithium Abundances in F5-G8 Dwarfs. Herbig, G. H. Abstract A survey of some 100 nearby F5-G8 dwarfs at 4 and 16 A/mm with the coude' spectrograph, 120-inch telescope, has shown that there is a major variation in their lithium abundances, from values of 1 (Li/Ca) */(Li/Ca)O as large as 35 down to the limit of detection near 1 1. The fundamental hypothesis under test is whether these results can be explained by convective destruction of Li on a long time scale, following the arrival of each star on the main sequence with a Li content comparable with that found in the pre-main-sequence T Tauri stars. If there is no subsequent replacement of the Li, its abundance should decay exponentially with a time constant t , which is expected to be sharply mass-dependent Comparison of the present solar Li abundance with that of chondritic meteorites yields a value of = 1 32 X 10 years. This time dependence can in principle be checked against the Li abundances of F-G dwarfs in galactic clusters of known age. Observations are available for seven stars in the Hyades, one in the Pleiades, and three in Coma. The abundances show a trend that conforms to expectation, but the scatter is not negligible, and the test cannot be considered a critical one. Less direct checks are possible through correlations of Li abundances with other convection- and age- dependent properties. The frequency function of 1 varies with main-sequence spectral type (i.e., with mass) in the sense that in the F's, stars of all 1 values are present in roughly comparable numbers; while toward the later C's, large 1 values become rare, and after G8, no Li has been detected at all in K, M, or Me dwarfs. There is also a rather good correlation between low 1 values and high space velocities, and conversely. The correlation between (photometric) metal abundance and 1 is in qualitative accord with expectation in the C dwarfs, namely, that the Li-rich stars tend to have the higher metal abundances, but no such relationship is apparent in the later F stars. This difference may result from the shallower convection zones in the F stars, or a lack of a tight dependence of metal content upon age. There is also a statistical correlation between 1 and the strength of Ca ii emission cores for GS and earlier, as expected from evolutionary considerations based on the T Tauri stars, but individual objects show a considerable scatter. In general, both components of spectroscopic and visual binary pairs show consistent Li abundances so long as they do not span the Li "cutoff" near K0, but UMa constitutes an exception, which may however be explained by rotation-induced shortening of t in the fainter component. The relative rates of formation of F-G dwarfs in the past should be inferable from the 1 statistics, provided that the proper values of I are known If the solar t is used, the results definitely do not show the expected excess of very old F-G dwarfs. Any of several explanations are possible, including that of replenishment of surface Li But in general the fundamental hypothesis is supported by the material studied here, although there are some points that still require explanation. Publication: The Astrophysical Journal Pub Date: February 1965 DOI: 10.1086/148147 Bibcode: 1965ApJ...141..588H full text sources ADS | data products SIMBAD (98) Related Materials (1) Erratum: 1965ApJ...141.1592H