The deep OB-star population in Carina from the VST Photometric H-alpha Survey (VPHAS+)
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◦ 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 ( = 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 << 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.
Item Type | Article |
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Uncontrolled Keywords | surveys - stars: early type-dust; extinction - Galaxy: disc-open clusters and associations: general |
Subjects | Physics and Astronomy(all) |
Date Deposited | 26 Jul 2024 18:04 |
Last Modified | 26 Jul 2024 18:04 |
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Read more research from the creator(s):
- Mohr-Smith, M.
- Drew, Janet
- Napiwotzki, Ralf
- Simon-Diaz, S.
- Wright, N. J.
- Barentsen, Geert
- Eisloeffel, J.
- Farnhill, Hywel
- Greimel, R.
- Monguio, Maria
- Kalari, V.
- Parker, Q. A.
- Vink, Jorick S.
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- http://www.vphasplus.org/carina-database.csv [error in script]