The O- and B-Type Stellar Population in W3: Beyond the High-Density Layer

TL;DR

This study characterizes the high-mass stellar population in the W3 star-forming complex, revealing a broader distribution of B-type stars and suggesting earlier spontaneous star formation, supported by new spectral classifications and improved observational methods.

Contribution

It provides the first extensive spectral classification of W3's high-mass stars and introduces a method for optimizing sky subtraction in nebular regions.

Findings

High-mass slope of the mass function aligns with Salpeter IMF.

B-type stars are more dispersed than previously thought.

Star formation in W3 began spontaneously 8-10 million years ago.

Abstract

We present the first results from our survey of the star-forming complex W3, combining VRI photometry with multiobject spectroscopy to identify and characterize the high-mass stellar population across the region. With 79 new spectral classifications, we bring the total number of spectroscopically-confirmed O- and B-type stars in W3 to 105. We find that the high-mass slope of the mass function in W3 is consistent with a Salpeter IMF, and that the extinction toward the region is best characterized by an Rv of approximately 3.6. B-type stars are found to be more widely dispersed across the W3 giant molecular cloud (GMC) than previously realized: they are not confined to the high-density layer (HDL) created by the expansion of the neighboring W4 HII region into the GMC. This broader B-type population suggests that star formation in W3 began spontaneously up to 8--10 Myr ago, although at a lower level than the more recent star formation episodes in the HDL. In addition, we describe a method of optimizing sky subtraction for fiber spectra in regions of strong and spatially-variable nebular emission.