We report here the first evidence for planetesimal infall onto the very young
Herbig Be star LkHα​234. These results are based on observations
acquired over 31 days using spectroscopy of the sodium D lines, the He I
5876\AA, and hydrogen Hα​ lines. We find Redshifted Absorption
Components (RAC) with velocities up to 200 km/s and very mild Blueshifted
Absorption Components (BEC) up to 100 km/s in the Na I lines. No correlation is
observed between the appearance of the Na I RAC & BEC and the Hα​ and He
I line variability, which suggests that these (Na I RAC & BEC) are formed in a
process unrelated to the circumstellar gas accretion. We interpret the Na I RAC
as evidence for an infalling evaporating body, greater than 100 km in diameter,
which is able to survive at distances between 2.0 to 0.1 AU from the star. The
dramatic appearance of the sodium RAC and mild BEC is readily explained by the
dynamics of this infalling body making LkHα​234 the youngest (age ∼
0.1 Myr) system with evidence for the presence of planetesimals.Comment: Accepted for publications in ApJLetter