Optically Observable Zero-Age Main-Sequence O Stars

Nolan R. Walborn

Space Telescope Science Institute

A list of fifty optically observable O stars that are likely on or very
near the ZAMS is presented. They have been selected on the basis of five
distinct criteria, although some of them exhibit more than one. Three of
the criteria are spectroscopic (He II 4686 absorption stronger
than in normal luminosity class V spectra, abnormally broad or strong
Balmer lines, weak UV wind profiles for their spectral types), one is
environmental (association with dense, dusty nebular knots), and one is
photometric (derived absolute magnitudes fainter than class V). Very few
of these stars have been physically analyzed, and they have not been
considered in the current framework of early massive stellar evolution.
In particular, they may indicate that the earliest, embedded phases are
not as large a fraction of the main-sequence lifetimes as is currently
believed. Detailed analyses of these objects will likely prove essential
to a complete understanding of the early evolution of massive stars.

Reference: STScI 2006 May Symposium, Massive Stars:
Pop III and GRBs to the Milky Way, ed. M. Livio & E. Villaver,
(Cambridge University Press)
Status: Conference proceedings

Weblink: http://arxiv.org/abs/astro-ph/0701573


Email: walborn@stsci.edu