EDP Sciences
Free Access
Volume 412, Number 1, December II 2003
Page(s) 185 - 198
Section Formation, structure and evolution of stars
DOI https://doi.org/10.1051/0004-6361:20031372

A&A 412, 185-198 (2003)
DOI: 10.1051/0004-6361:20031372

Dusty ring nebulae around new candidate Luminous Blue Variables

J. S. Clark1, M. P. Egan2, P. A. Crowther1, 3, D. R. Mizuno4, V. M. Larionov5, 6 and A. Arkharov7

1  Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
2  US Air Force Research Laboratory: MDA/AS, 7100 Defence Pentagon, Washington, DC 20301-7100, USA
3  Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield, S3 7RH, UK
4  Institute for Scientific Research, Boston College, 140 Commonwealth Avenue, Chestnut Hill, MA 02467-2862, USA
5  Astronomical Institute of St. Petersburg University, St. Petersburg, Petrodvorets, Universitetsky pr. 28, 198504 St. Petersburg, Russia
6  Isaac Newton Institute of Chile, St. Petersburg Branch, Russia
7  Central Astronomical Observatory, 196140 St. Petersburg, Russia

(Received 2 June 2003 / Accepted 2 September 2003)

We report on the discovery of a further two ring nebulae in the Midcourse Space Experiment (MSX) Galactic Plane Survey; G24.73+0.69 and G26.47+0.02 . Morphologically, both appear similar to the nebulae found around the Luminous Blue Variable (LBV) candidates G79.29+0.46 and Wra 17-96 . A central, unresolved point source was identified in both cases - positional coincidence with the star StRS 237 was found for G26.47+0.02 , while no optical counterpart could be identified for G24.73+0.69 . However, subsequent near IR broadband imaging of the G24.73+0.69 field identified a very red - $(J-K) \sim$ 2 mag - stellar counterpart to the central object. Near-IR spectroscopy of both objects reveal rich emission line spectra dominated by H I, He I and low excitation metals, suggesting classification as luminous B supergiants and revealing a striking superficial similarity to the other MSX ring sources and known LBVs. We utilised a NLTE model atomsphere code to model the  K band spectra and near-IR spectral energy distributions of the central stars in order to determine their physical parameters. Adopting a distance, d= 5.2 kpc to G24.73+0.69 yields a temperature, T= 12 kK, luminosity, log ( L/ $L_{\odot}$)  = 5.6 and mass loss rate, $\dot{M}=1\times 10^{-5}~M_{\odot}$ yr -1. G26.47+0.02 appears to be a more extreme object; adopting d= 6.5 kpc results in T= 17 kK, log ( L/ $L_{\odot}$)  = 6.0 and $\dot{M}=9\times 10^{-5}$  $M_{\odot}$ yr -1, placing it at the Humphreys-Davidson limit for massive stellar objects. Analysis of the spatially resolved mid-IR fluxes of both objects reveal extended periods of enhanced mass loss, resulting in comparatively low mass nebulae, with chemistries dominated by O-rich dust (with a population of small Fe grains existing co-spatially with the silicate dust). Comparison to the other MSX ring nebulae sources reveals a homogeneous group of objects, with both stellar and nebular properties consistent with known LBVs. With both spectroscopic and/or photometric variability observed for those sources with multiepoch observations, we propose a close affinity between both classes of object and suggest that long term monitoring of the MSX sources will reveal them to be bona fide LBVs.

Key words: stars: emission line, Be -- stars: circumstellar matter -- stars: winds, outflows

Offprint request: J. S. Clark, jsc@star.ucl.ac.uk

SIMBAD Objects

© ESO 2003

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.