Direct constraint on the distance of γ2 Velorum from AMBER/VLTI observations
Beckmann, U.; Marconi, A.; Testi, L.; Weigelt, G.; Mathias, P.; Lopez, B.; Hofmann, K. -H.; Lagarde, S.; Millour, F.; Robbe-Dubois, S.; Schertl, D.; Lopez, M.; Monin, J. -L.; Domiciano de Souza, A.; Chesneau, O.; Mars, G.; Thiébaut, E.; Stee, P.; Driebe, T.; Petrov, R. G.; Vakili, F.; Forveille, T.; Acke, B.; Ohnaka, K.; Richichi, A.; Mouillet, D.; Schöller, M.; Le Contel, J. -M.; Perrier, C.; Perraut, K.; Duvert, G.; Bonneau, D.; Mourard, D.; Roussel, A.; Spang, A.; Tallon-Bosc, I.; Le Contel, D.; Valtier, J. -C.; Malbet, F.; Mège, P.; Dessart, L.; Tallon, M.; von der Lühe, O.; Blöcker, T.; Colin, J.; Feautrier, P.; Delboulbé, A.; Magnard, Y.; Puget, P.; Chelli, A.; Aristidi, E.; Baffa, C.; Gennari, S.; Kraus, S.; Fossat, E.; Zins, G.; Tatulli, E.; Antonelli, P.; Heininger, M.; Behrend, J.; Kern, P.; Ferruzzi, D.; Bechet, C.; Bresson, Y.; Dugué, M.; Glück, L.; Le Coarer, E.; Lisi, F.; Rantakyrö, F.; Accardo, M.; Agabi, K.; Altariba, E.; Arezki, B.; Bonhomme, S.; Busoni, S.; Cassaing, F.; Clausse, J. -M.; Connot, C.; Foy, R.; Fraix-Burnet, D.; Gallardo, A.; Giani, E.; Gil, C.; Glentzlin, A.; Heiden, M.; Hernandez Utrera, O.; Kamm, D.; Kiekebusch, M.; Lesourd, T.; Martinot-Lagarde, G.; Nussbaum, E.; Pacheco, J.; Rabbia, Y.; Rebattu, S.; Reynaud, F.; Robini, A.; Sacchettini, M.; Solscheid, W.; Stefanini, P.; Tasso, D.; Vannier, M.; Ventura, N.
France, United States, Germany, Italy, Chile, Belgium, Portugal
Abstract
Context: Interferometry can provide spatially resolved observations of massive star binary systems and their colliding winds, which thus far have been studied mostly with spatially unresolved observations.
Aims: We present the first AMBER/VLTI observations, taken at orbital phase 0.32, of the Wolf-Rayet and O (WR+O) star binary system
Methods: The AMBER/VLTI instrument was used with the telescopes UT2, UT3, and UT4 on baselines ranging from 46 m to 85 m. It delivered spectrally dispersed visibilities, as well as differential and closure phases, with a resolution R=1500 in the spectral band 1.95-2.17 μm. We interpret these data in the context of a binary system with unresolved components, neglecting in a first approximation the wind-wind collision zone flux contribution.
Results: Using WR- and O-star synthetic spectra, we show that the AMBER/VLTI observables result primarily from the contribution of the individual components of the WR+O binary system. We discuss several interpretations of the residuals, and speculate on the detection of an additional continuum component, originating from the free-free emission associated with the wind-wind collision zone (WWCZ), and contributing at most to the observed K-band flux at the 5% level. Based on the accurate spectroscopic orbit and the Hipparcos distance, the expected absolute separation and position angle at the time of observations were 5.1±0.9 mas and 66±15°, respectively. However, using theoretical estimates for the spatial extent of both continuum and line emission from each component, we infer a separation of 3.62+0.11-0.30 mas and a position angle of 73+9-11°, compatible with the expected one. Our analysis thus implies that the binary system lies at a distance of 368+38-13 pc, in agreement with recent spectrophotometric estimates, but significantly larger than the Hipparcos value of 258+41-31 pc.