ASTRONOMY: Disappearing Proplyds

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Science  14 Jan 2000:
Vol. 287, Issue 5451, pp. 193g
DOI: 10.1126/science.287.5451.193g

Proplyds are low-mass young stars that are surrounded by disks of circumstellar material, which is photoionized by hydrogen gas from nearby stars into a teardrop shape. Proplyds reveal details about the early life of young stars; planet formation can occur within the circumstellar disks if they survive long enough. The Orion nebula is a rich region for star formation and contains many bright proplyds. Henney and O'Dell obtained high-resolution spectra of four proplyds in the Orion nebula with the HIRES spectrograph on the Keck I telescope in Hawaii. From these data, they were able to model several increasingly dense ionized layers on the head of the proplyd (the side exposed to bombardment by ionizing stellar radiation) and a narrow tail on the shielded side. From this model they extracted a mass loss rate from a typical proplyd disk of 0.4 × 106 solar masses per year, which is extremely rapid and inconsistent with the predicted lifetimes of the proplyds, suggesting that either the masses of the circumstellar disks have been underestimated or another process maintains these fragile disks.—LR

Astronomical J. 118, 2350 (1999).

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