New OB star candidates in the Carina Arm aroundWesterlund 2 from VPHAS+

M. Mohr-Smith; J. E. Drew; G. Barentsen; N. J. Wright; R. Napiwotzki; R. L M Corradi; J. Eislöffel; P. Groot; V. Kalari; Q. A. Parker; R. Raddi; S. E. Sale; Y. C. Unruh; J. S. Vink; R. Wesson

doi:10.1093/mnras/stv843

New OB star candidates in the Carina Arm aroundWesterlund 2 from VPHAS+

M. Mohr-Smith, J. E. Drew, G. Barentsen, N. J. Wright, R. Napiwotzki, R. L M Corradi, J. Eislöffel, P. Groot, V. Kalari, Q. A. Parker, R. Raddi, S. E. Sale, Y. C. Unruh, J. S. Vink, R. Wesson

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Abstract

O and early B stars are at the apex of galactic ecology, but in the Milky Way, only a minority of them may yet have been identified. We present the results of a pilot study to select and parametrize OB star candidates in the Southern Galactic plane, down to a limiting magnitude of g = 20. A 2 deg² field capturing the Carina Arm around the young massive star cluster, Westerlund 2, is examined. The confirmed OB stars in this cluster are used to validate our identification method, based on selection from the (u - g, g - r) diagram for the region. Our Markov Chain Monte Carlo fitting method combines VPHAS+ u, g, r, i with published J, H, K photometry in order to derive posterior probability distributions of the stellar parameters log (T_eff) and distance modulus, together with the reddening parameters A₀ and R_V. The stellar parameters are sufficient to confirm OB status while the reddening parameters are determined to a precision of Σ(A0) ~ 0.09 and Σ(RV) ~ 0.08. There are 489 objects that fit well as new OB candidates, earlier than ~B2. This total includes 74 probable massive O stars, 5 likely blue supergiants and 32 reddened subdwarfs. This increases the number of previously known and candidate OB stars in the region by nearly a factor of 10. Most of the new objects are likely to be at distances between 3 and 6 kpc. We have confirmed the results of previous studies that, at these longer distances, these sight lines require non-standard reddening laws with 3.5 < RV < 4.

Original language	English
Pages (from-to)	3855-3873
Number of pages	19
Journal	Monthly Notices of the Royal Astronomical Society
Volume	450
Issue number	4
DOIs	https://doi.org/10.1093/mnras/stv843
Publication status	Published - 11 Jul 2015

Bibliographical note

Copyright 2015 The Authors. First published in Monthly Notices of the Royal Astronomical Society, 450(4), 3855-3873. The original publication is available at http://doi.org/10.1093/mnras/stv843, published by Oxford University Press on behalf of the Royal Astronomical Society. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

Keywords

Dust, extinction
Galaxy: structure
Open clusters and associations: individual: Westerlund 2
Stars: early-type
Stars: massive
Surveys

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10.1093/mnras/stv843

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Mohr-Smith, M., Drew, J. E., Barentsen, G., Wright, N. J., Napiwotzki, R., Corradi, R. L. M., Eislöffel, J., Groot, P., Kalari, V., Parker, Q. A., Raddi, R., Sale, S. E., Unruh, Y. C., Vink, J. S., & Wesson, R. (2015). New OB star candidates in the Carina Arm aroundWesterlund 2 from VPHAS+. Monthly Notices of the Royal Astronomical Society, 450(4), 3855-3873. https://doi.org/10.1093/mnras/stv843

@article{1c4cad1b3130494d9bfd18996af0cf99,

title = "New OB star candidates in the Carina Arm aroundWesterlund 2 from VPHAS+",

abstract = "O and early B stars are at the apex of galactic ecology, but in the Milky Way, only a minority of them may yet have been identified. We present the results of a pilot study to select and parametrize OB star candidates in the Southern Galactic plane, down to a limiting magnitude of g = 20. A 2 deg2 field capturing the Carina Arm around the young massive star cluster, Westerlund 2, is examined. The confirmed OB stars in this cluster are used to validate our identification method, based on selection from the (u - g, g - r) diagram for the region. Our Markov Chain Monte Carlo fitting method combines VPHAS+ u, g, r, i with published J, H, K photometry in order to derive posterior probability distributions of the stellar parameters log (Teff) and distance modulus, together with the reddening parameters A0 and RV. The stellar parameters are sufficient to confirm OB status while the reddening parameters are determined to a precision of Σ(A0) ~ 0.09 and Σ(RV) ~ 0.08. There are 489 objects that fit well as new OB candidates, earlier than ~B2. This total includes 74 probable massive O stars, 5 likely blue supergiants and 32 reddened subdwarfs. This increases the number of previously known and candidate OB stars in the region by nearly a factor of 10. Most of the new objects are likely to be at distances between 3 and 6 kpc. We have confirmed the results of previous studies that, at these longer distances, these sight lines require non-standard reddening laws with 3.5 < RV < 4.",

keywords = "Dust, extinction, Galaxy: structure, Open clusters and associations: individual: Westerlund 2, Stars: early-type, Stars: massive, Surveys",

author = "M. Mohr-Smith and Drew, {J. E.} and G. Barentsen and Wright, {N. J.} and R. Napiwotzki and Corradi, {R. L M} and J. Eisl{\"o}ffel and P. Groot and V. Kalari and Parker, {Q. A.} and R. Raddi and Sale, {S. E.} and Unruh, {Y. C.} and Vink, {J. S.} and R. Wesson",

note = "Copyright 2015 The Authors. First published in Monthly Notices of the Royal Astronomical Society, 450(4), 3855-3873. The original publication is available at http://doi.org/10.1093/mnras/stv843, published by Oxford University Press on behalf of the Royal Astronomical Society. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.",

year = "2015",

month = jul,

day = "11",

doi = "10.1093/mnras/stv843",

language = "English",

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pages = "3855--3873",

journal = "Monthly Notices of the Royal Astronomical Society",

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Mohr-Smith, M, Drew, JE, Barentsen, G, Wright, NJ, Napiwotzki, R, Corradi, RLM, Eislöffel, J, Groot, P, Kalari, V, Parker, QA, Raddi, R, Sale, SE, Unruh, YC, Vink, JS & Wesson, R 2015, 'New OB star candidates in the Carina Arm aroundWesterlund 2 from VPHAS+', Monthly Notices of the Royal Astronomical Society, vol. 450, no. 4, pp. 3855-3873. https://doi.org/10.1093/mnras/stv843

TY - JOUR

T1 - New OB star candidates in the Carina Arm aroundWesterlund 2 from VPHAS+

AU - Mohr-Smith, M.

AU - Drew, J. E.

AU - Barentsen, G.

AU - Wright, N. J.

AU - Napiwotzki, R.

AU - Corradi, R. L M

AU - Eislöffel, J.

AU - Groot, P.

AU - Kalari, V.

AU - Parker, Q. A.

AU - Raddi, R.

AU - Sale, S. E.

AU - Unruh, Y. C.

AU - Vink, J. S.

AU - Wesson, R.

N1 - Copyright 2015 The Authors. First published in Monthly Notices of the Royal Astronomical Society, 450(4), 3855-3873. The original publication is available at http://doi.org/10.1093/mnras/stv843, published by Oxford University Press on behalf of the Royal Astronomical Society. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

PY - 2015/7/11

Y1 - 2015/7/11

N2 - O and early B stars are at the apex of galactic ecology, but in the Milky Way, only a minority of them may yet have been identified. We present the results of a pilot study to select and parametrize OB star candidates in the Southern Galactic plane, down to a limiting magnitude of g = 20. A 2 deg2 field capturing the Carina Arm around the young massive star cluster, Westerlund 2, is examined. The confirmed OB stars in this cluster are used to validate our identification method, based on selection from the (u - g, g - r) diagram for the region. Our Markov Chain Monte Carlo fitting method combines VPHAS+ u, g, r, i with published J, H, K photometry in order to derive posterior probability distributions of the stellar parameters log (Teff) and distance modulus, together with the reddening parameters A0 and RV. The stellar parameters are sufficient to confirm OB status while the reddening parameters are determined to a precision of Σ(A0) ~ 0.09 and Σ(RV) ~ 0.08. There are 489 objects that fit well as new OB candidates, earlier than ~B2. This total includes 74 probable massive O stars, 5 likely blue supergiants and 32 reddened subdwarfs. This increases the number of previously known and candidate OB stars in the region by nearly a factor of 10. Most of the new objects are likely to be at distances between 3 and 6 kpc. We have confirmed the results of previous studies that, at these longer distances, these sight lines require non-standard reddening laws with 3.5 < RV < 4.

AB - O and early B stars are at the apex of galactic ecology, but in the Milky Way, only a minority of them may yet have been identified. We present the results of a pilot study to select and parametrize OB star candidates in the Southern Galactic plane, down to a limiting magnitude of g = 20. A 2 deg2 field capturing the Carina Arm around the young massive star cluster, Westerlund 2, is examined. The confirmed OB stars in this cluster are used to validate our identification method, based on selection from the (u - g, g - r) diagram for the region. Our Markov Chain Monte Carlo fitting method combines VPHAS+ u, g, r, i with published J, H, K photometry in order to derive posterior probability distributions of the stellar parameters log (Teff) and distance modulus, together with the reddening parameters A0 and RV. The stellar parameters are sufficient to confirm OB status while the reddening parameters are determined to a precision of Σ(A0) ~ 0.09 and Σ(RV) ~ 0.08. There are 489 objects that fit well as new OB candidates, earlier than ~B2. This total includes 74 probable massive O stars, 5 likely blue supergiants and 32 reddened subdwarfs. This increases the number of previously known and candidate OB stars in the region by nearly a factor of 10. Most of the new objects are likely to be at distances between 3 and 6 kpc. We have confirmed the results of previous studies that, at these longer distances, these sight lines require non-standard reddening laws with 3.5 < RV < 4.

KW - Dust, extinction

KW - Galaxy: structure

KW - Open clusters and associations: individual: Westerlund 2

KW - Stars: early-type

KW - Stars: massive

KW - Surveys

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JF - Monthly Notices of the Royal Astronomical Society

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New OB star candidates in the Carina Arm aroundWesterlund 2 from VPHAS+

Abstract

Bibliographical note

Keywords

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