Evidence of Planetesimal Infall onto the Very Young Herbig Be Star LkH 234

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Abstract
We report here the first evidence of 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 Å line, and hydrogen Hα lines. We find redshifted absorption components (RACs) with velocities up to 200 km s-1 and very mild blueshifted emission components (BECs) up to 100 km s-1 in the Na I lines. No correlation is observed between the appearance of the Na I RACs and BECs and the Hα and He I line variability, which suggests that these (Na I RACs and BECs) are formed in a process unrelated to the circumstellar gas accretion. We interpret the Na I RACs as evidence for an infalling evaporating body, greater than 100 km in diameter, which is able to survive at distances between 2.0 and 0.1 AU from the star. The dramatic appearance of the sodium RACs and mild BECs 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.
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