J/MNRAS/455/1275 Radial velocities of WR21a (Tramper+, 2016) ================================================================================ The mass of the very massive binary WR21a. Tramper F., Sana H., Fitzsimons N.E., de Koter A., Kaper L., Mahy L., Moffat A. =2016MNRAS.455.1275T (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Binaries, spectroscopic ; Stars, Wolf-Rayet ; Radial velocities Keywords: binaries: close - binaries: spectroscopic - stars: early-type - stars: fundamental parameters - stars: individual: WR21a - stars: Wolf-Rayet Abstract: We present multi-epoch spectroscopic observations of the massive binary system WR21a, which include the 2011 January periastron passage. Our spectra reveal multiple SB2 lines and facilitate an accurate determination of the orbit and the spectral types of the components. We obtain minimum masses of 64.4+/-4.8M_{sun} and 36.3+/-1.7M_{sun} for the two components of WR21a. Using disentangled spectra of the individual components, we derive spectral types of O3/WN5ha and O3Vz ((f*)) for the primary and secondary, respectively. Using the spectral type of the secondary as an indication for its mass, we estimate an orbital inclination of i=58.8+/-2.5{deg} and absolute masses of 103.6+/-10.2M_{sun} and 58.3+/-3.7M_{sun}_, in agreement with the luminosity of the system. The spectral types of the WR21a components indicate that the stars are very young (1-2Myr), similar to the age of the nearby Westerlund 2 cluster. We use evolutionary tracks to determine the mass-luminosity relation for the total system mass. We find that for a distance of 8kpc and an age of 1.5Myr, the derived absolute masses are in good agreement with those from evolutionary predictions. Description: All observations of WR21a have been obtained with the X-Shooter spectrograph mounted on the European Southern Observatory's VLT. The observational campaign has been designed to intensively cover the 2011 January periastron passage, as well as to provide coverage of the orbit on longer time-scales. Objects: ------------------------------------------------------- RA (2000) DE Designation(s) ------------------------------------------------------- 10 25 56.50 -57 48 43.5 WR21a = AX J1025.9-5749 ------------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 52 26 Observational log and RV measurements -------------------------------------------------------------------------------- Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 2 I2 --- Epoch Epoch of observation 4- 12 F9.4 d HJD Heliocentric Julian date at mid-exposure (HJD-2450000) 14 I1 --- Nexp Number of 90s exposures 16- 19 F4.2 --- Airmass Average airmass during observation 21- 22 I2 --- SNR Signal-to-noise ratio per wavelength bin of 0.2 nm 24- 28 F5.3 --- Phase Orbital phase 30- 35 F6.1 km/s RVwr Radial velocity (RV) of the WR-star component 37- 40 F4.1 km/s e_RVwr 1 sigma error on the RV of the WR-star component 42- 47 F6.1 km/s RVo RV of the O-star component 49- 52 F4.1 km/s e_RVo 1 sigma error on the RV of the O-star component -------------------------------------------------------------------------------- Acknowledgements: Frank Tramper, F.Tramper(at)uva.nl ================================================================================ (End) Frank Tramper [UvA, Netherlands], Patricia Vannier [CDS] 09-Feb-2015