The close O-type eclipsing binary TU Muscae.
Abstract
Summary. New spectroscopic and photometric observations of TU Mus are presented and discussed. From t4 double-lined spectra we derive circular orbital elements of V0=+t.8kms K1=25t.3kms and K2= 370.5 km s- . The spectral type of the primary component is estimated to be 07-08, the secondary appearing somewhat fainter and of slightly later spectral type. The uvby light curves (703 observations in each filter) are analysed with the programme of Wood (t97t, t972), approximating the stars by triaxial ellipsoids, and are found to be fairly well reproduced with the elements r1 =0.45, r2=0.37, i= 760, T1 = 33600 0K, T2= 29600 0K. However, with these radii the stars exceed their Roche lobes, and we conclude that with realistic geometry the stars must be (nearly) in contact. A tentative model of TU Mus is proposed with the following physical properties: masses 23.5 and t5.8 M0, radii 8.0 and 6.6R0, Mboi= 7m.4 and -6 4, and components, respectively. A distance of 2.2 kpc is found for an assumed visual absorption of t .2, placing TU Mus in the Carina arm. Uncertainties in the masses and radii are estimated to be of the order of tO %. The spectroscopic values of light ratio and rotation are adequately reproduced. The stars appear essentially unevolved, with a probable age of a few million years. It is concluded that our preliminary model needs considerable refinement, and suggestions for further work are given. Measurement of the Balmer lines result in masses too small by about 30 % because of pair blending, even with a value of K1+K2> . This is taken to imply that use of the Balmer lines leads to erroneous mass determinations in all early-type double-lined binaries. Key words: eclipsing binary spectroscopic orbit photometric elements absolute dimensions Mv = - 4rn.2 and - 3 5 for the primary and secondary
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 1975
- Bibcode:
- 1975A&A....45..107A