Southworth, J. (John) and Clausen, J. V.. (2007) Absolute dimensions of eclipsing binaries. XXIV, The Be star system DW Carinae, a member of the open cluster Collinder 228. Astronomy & Astrophysics, Vol.461 (No.3). pp. 1077-1093. ISSN 0004-6361

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Abstract

Context. The study of detached eclipsing binaries which are members of stellar clusters is is a powerful way of determining the properties of the cluster and of constraining the physical ingredients of theoretical stellar evolutionary models. Aims. DWCarinae is a close but detached early B-type eclipsing binary in the young open cluster Collinder 228. We have measured accurate physical properties of the components of DWCar (masses and radii to 1%, effective temperatures to 0.02 dex) and used these to derive the age, metallicity and distance of Collinder 228. Methods. The rotational velocities of both components of DWCar are high, so we have investigated the performance of double-Gaussian fitting, one- and two-dimensional cross-correlation and spectral disentangling for deriving spectroscopic radial velocites in the presence of strong line blending. Gaussian and cross-correlation analyses require substantial corrections for the effects of line blending, which are only partially successful for cross-correlation. Spectral disentangling is to be preferred because it does not assume anything about the shapes of spectral lines, and is not significantly affected by blending. However, it suffers from a proliferation of local minima in the least-squares fit. We show that the most reliable radial velocities are obtained using spectral disentangling constrained by the results of Gaussian fitting. Complete Strömgren uvby light curves have been obtained and accurate radii have been measured from them by modelling the light curves using the Wilson-Devinney program. This procedure also suffers from the presence of many local minima in parameter space, so we have constrained the solution using an accurate spectroscopic light ratio. The effective temperatures and reddening of the system have been found from Strömgren photometric calibrations. Results. The mass and radius of DWCarA are MA = 11.34 ± 0.12 M and RA = 4.558 ± 0.045 R. The values for DWCar B are MB =10.63 ± 0.14 M and RB = 4.297 ± 0.055 R. Strömgren photometric calibrations give effective temperatures of TeffA = 27 900 ±1000 K and TeffB = 26 500 ± 1000 K, and a reddening of Eb−y = 0.18 ± 0.02, where the quoted uncertainties include a contribution from the intrinsic uncertainty of the calibrations. The membership of DWCar in Cr 228 allows us to measure the distance, age and chemical composition of the cluster. We have used empirical bolometric corrections to calculate a distance modulus of 12.24 ±0.12 mag for DWCar, which is in agreement with, and more accurate than, literature values. A comparison between the properties of DWCar and the predictions of recent theoretical evolutionary models is undertaken in the mass-radius and mass-Teff diagrams. The model predictions match the measured properties of DWCar for an age of about 6 Myr and a fractional metal abundance of Z ≈ 0.01.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	Eclipsing binaries, Be stars, Stars -- Clusters, Stars -- Evolution
Journal or Publication Title:	Astronomy & Astrophysics
Publisher:	EDP Sciences
ISSN:	0004-6361
Date:	January 2007
Volume:	Vol.461
Number:	No.3
Page Range:	pp. 1077-1093
Identification Number:	10.1051/0004-6361:20065614
Status:	Peer Reviewed
Access rights to Published version:	Open Access
Funder:	Instrumentcenter for Dansk Astrofysik [Instrument Centre for Danish Astrophsics] (IDA), Danmarks Grundforskningsfond [Danish National Research Foundation], Denmark. Astronomisk udvalg [Board for Astronomical Research], United States. National Aeronautics and Space Administration (NASA), National Science Foundation (U.S.) (NSF)
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