LITHIUM IN YOUNG SOLAR-TYPE STARS IN THE ORION NEBULA REGION

Lithium abundances have been determined for 24 late-type pre-main-sequ ence stars in the Orion Nebula region with V = 12-14 and B-V = 0.5-1.4 . All of the stars are within 20 arcmin of the Trapezium; they range f rom approximately 1.0 to 1.6 M(.) and from 10(6) to 10(7) years old. A pproximate chronological ordering of the stars is possible from their location in the color-magnitude diagram, but they show no obvious evol utionary sequence of lithium depletion. In particular, the trend seen in the Pleiades, that faster rotators tend to have more lithium, is no t seen here. There is no obvious correlation in the Orion stars betwee n Li and v sin i. On the average, stars in the present sample have gre ater Li abundances than similar stars in the older Pleiades cluster. O ne can infer that the process which depletes Li in these late-type sta rs requires more time to act than the age of this Orion sample. The st atus of Parenago 1799 as an ultrafast rotator (UFR) (Walker 1990, PASP , 102, 726) is qualitatively confirmed; it is shown that the star is r otating at an appreciable fraction of breakup velocity. This is the on ly UFR in the present sample, fewer than in a Pleiades sample of simil ar size. The two T Tauri stars in the binary system Parenago 1540 have similar lithium abundances, suggesting similar depletion histories, a nd consistent with the findings of Lee et al. (1994, AJ, 108, 1445). P arenago 1643 and 1929 are shown to have incorrect apparent colors via newly determined spectral types; their observed colors lead to very hi gh Li abundances, but their corrected colors suggest more typical lith ium abundances. Similarly, we have used spectral types and the spectra l type-color relation from Duncan (1993, ApJ, 406, 172) to refine the colors and thus improve our estimates of Li abundances for P1477 and P 1518.