Multiwavelength Systematics of OB Spectra

Nolan R. Walborn

Space Telescope Science Institute

The systematics of OB spectra are reviewed in the optical domain,
dominated by photospheric lines, and in the far ultraviolet (both IUE
and FUSE ranges), in which the stellar-wind profiles dominate. First,
the two-dimensional (temperature, luminosity) trends in normal spectra
are surveyed. Then, the normal reference frame having been established,
various categories of peculiar objects can be distinguished relative to
it, which reveal several phenomena of structural and/or evolutionary
significance. Included are CNO anomalies at both early and late O
types, three varieties of rapid rotators, hot and cool Of/WN transition
objects, and the recently discovered second known magnetic O star.
The importance of both optical and UV observations to understand these
phenomena is emphasized; for instance, progress in understanding the
structure of the new O-type magnetic oblique rotator is hampered by the
current lack of a UV spectrograph. While progress in the physical
interpretation of these trends and anomalies has been and is
being made, increased attention to modeling the systematics would
accelerate future progress in this author's opinion. Finally,
preliminary results from a Chandra high-resolution survey of OB X-ray
spectra (PI W. Waldron) are presented. They provide evidence that, just
as emerged earlier in the UV, systematic morphological trends exist in
the X-ray domain that are correlated with the optical spectral types, and
hence the fundamental stellar parameters, contrary to prevailing opinion.

Reference: Proceedings, IAU XXVIth GA JD04 - THE ULTRAVIOLET UNIVERSE: STARS FROM BIRTH TO DEATH, ed. Ana I. Gomez de Castro & Martin A. Barstow (Universidad Complutense de Madrid)
Status: Conference proceedings