STRINGENT LIMITS ON THE IONIZED MASS-LOSS FROM A-DWARF AND F-DWARF

Following the suggestion of Willson, Bowen, and Struck-Marcell that A- and F-type main-sequence stars might undergo significant mass loss due to pulsationally driven winds, we have obtained upper limits to the ionized mass loss from A and F dwarfs using VLA observations. These stringent upper limits show that the level of ionized mass loss would have at most only a small effect on stellar evolution. Radiative equilibrium atmospheric and wind models for early A dwarfs indicate that it is highly likely that a wind flowing from such stars would be significantly ionized. In addition, late A and early F dwarfs exhibit chromospheric emission indicative of significant nonradiative heating. Our mass-loss limits are thus representative of the total mass-loss rates for these stars. Therefore, we conclude that A and F dwarfs are not losing sufficient mass to cause A dwarfs to evolve into G dwarfs as has been proposed.