Call for data on Cyg OB2 #9

To the massive star community :

As announced in two recent papers (Van Loo et al., Naze et al., A&A, in press, see and, the non-thermal radio emitter Cyg OB2 #9 is a very eccentric binary with a long period (~2.4yrs). In order to derive a full orbital solution, more data are clearly needed, especially close to the periastron passages. If you have any archival optical data of this star (spectroscopy, photometry), we would like to invite you to contact us.

Best regards,
Yael Naze, Michael De Becker & Gregor Rauw