000002085 001__ 2085
000002085 005__ 20160706150659.0
000002085 0247_ $$2DOI$$a10.1051/0004-6361/201526871
000002085 037__ $$aASTROimport-242
000002085 100__ $$aRauw, G.
000002085 245__ $$aTesting the theory of colliding winds: the periastron passage of 9 Sagittarii. I. X-ray and optical spectroscopy
000002085 260__ $$c2016
000002085 520__ $$aContext. The long-period, highly eccentric O-star binary 9 Sgr, known for its non-thermal radio emission and its relatively bright X-ray emission, went through its periastron in 2013.  Aims: Such an event can be used to observationally test the predictions of the theory of colliding stellar winds over a broad range of wavelengths.  Methods: We conducted a multi-wavelength monitoring campaign of 9 Sgr around the 2013 periastron. In this paper, we focus on X-ray observations and optical spectroscopy.  Results: The optical spectra allow us to revisit the orbital solution of 9 Sgr and to refine its orbital period to 9.1 years. The X-ray flux is maximum at periastron over all energy bands, but with clear differences as a function of energy. The largest variations are observed at energies above 2 keV, whilst the spectrum in the soft band (0.5-1.0 keV) remains mostly unchanged, indicating that it arises far from the collision region, in the inner winds of the individual components. The level of the hard emission at periastron clearly deviates from the 1 /r relation expected for an adiabatic wind-interaction zone, whilst this relation seems to hold at the other phases that are covered by our observations. The spectra taken at phase 0.946 reveal a clear Fe xxv line at 6.7 keV, but no such line is detected at periastron (
000002085 700__ $$aBlomme, R.
000002085 700__ $$aNazé, Y.
000002085 700__ $$aSpano, M.
000002085 700__ $$aMahy, L.
000002085 700__ $$aGosset, E.
000002085 700__ $$aVolpi, D.
000002085 700__ $$avan Winckel, H.
000002085 700__ $$aRaskin, G.
000002085 700__ $$aWaelkens, C.
000002085 773__ $$cA121$$pAstronomy and Astrophysics$$v589$$y2016
000002085 85642 $$ahttp://esoads.eso.org/abs/2016A%26A...589A.121R
000002085 905__ $$apublished in
000002085 980__ $$aREFERD