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

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.

16 pages, 12 figures, accepted for publication in ApJ

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• A Multiwavelength Look at Galactic Massive Star Forming Regions
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• Age spreads and the temperature dependence of age estimates in Upper Sco
• Gaia-DR2 distance to the W3 Complex in the Perseus Arm
• Interaction between the Supernova Remnant HB 3 and the Nearby Star-Forming Region W3
• A Faraday Rotation Study of the Stellar Bubble and HII Region Associated with the W4 Complex
• A constraint on the formation timescale of the young open cluster NGC 2264: Lithium abundance of pre-main sequence stars
• Candidate X-ray-Emitting OB Stars in the MYStIX Massive Star-Forming Regions
• Interaction Between HII Region and AFGL333-Ridge: Implications to the Star Formation Scenario
• Open clusters in AurOB2
• The Initial Mass Function of Low-mass Stars and Brown Dwarfs in the W3 Complex
• tonalli: an asexual genetic code to characterise APOGEE-2 stellar spectra. I. Validation with synthetic and solar spectra