Mohr-Smith, M.; Drew, J. E.; Napiwotzki, R.; Simón-Díaz, S.; Wright, N. J.; Barentsen, G.; Eislöffel, J.; Farnhill, H. J.; Greimel, R.; Monguió, M.; Kalari, V.; Parker, Q. A.; Vink, J. S.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 465, Issue 2, p.1807-1830
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2
2017
Citations
31
Refereed citations
29
Description
Massive OB stars are critical to the ecology of galaxies and yet our
knowledge of OB stars in the Milky Way, fainter than V ˜ 12,
remains patchy. Data from the VST Photometric Hα Survey (VPHAS+)
permit the construction of the first deep catalogues of blue
excess-selected OB stars, without neglecting the stellar field. A total
of 14 900 candidates with 2MASS cross-matches are blue-selected from a
42 deg2 region in the Galactic plane, capturing the Carina
Arm over the Galactic longitude range 282° ≲ ℓ ≲
293°. Spectral energy distribution fitting is performed on these
candidates' combined VPHAS+ u, g, r, i and 2MASS J, H, K magnitudes.
This delivers effective temperature constraints, statistically
separating O from early-B stars and high-quality extinction parameters,
A0 and RV (random errors typically ˜0.1).
The high-confidence O-B2 candidates number 5915 and a further 5170 fit
to later B spectral type. Spectroscopy of 276 of the former confirms 97
per cent of them. The fraction of emission-line stars among all
candidate B stars is 7-8 per cent. Greyer (RV > 3.5)
extinction laws are ubiquitous in the region, over the distance range
2.5-3 to ˜10 kpc. Near prominent massive clusters, RV
tends to rise, with particularly large and chaotic excursions to
RV ˜ 5 seen in the Carina Nebula. The data reveal a
hitherto unnoticed association of 108 O-B2 stars around the O5If+ star
LSS 2063 (ℓ = 289.77°, b = -1.22°). Treating the OB star
scaleheight as a constant within the thin disc, we find an orderly mean
relation between extinction (A0) and distance in the Galactic
longitude range, 287.6° <ℓ < 293.5°, and infer the
subtle onset of thin-disc warping. A halo around NGC 3603, roughly a
degree in diameter, of ˜500 O-B2 stars with 4 <
A0(mag) < 7 is noted.
Related projects
The IACOB project: A new Era in the Study of Galactic OB Stars
IACOB is an ambitious long-term project whose main scientific goal is to provide an unprecedented empirical overview of the main physical properties of Galactic massive O- and B-type stars which can be used as definitive anchor point for our theories of stellar atmospheres, winds, interiors and evolution of massive stars
Sergio
Simón Díaz