ROSAT OPTICAL OBSERVATIONS OF 2S 0114+65 - A STUDY OF THE 2.8 HOUR PERIODIC OUTBURSTS

Observations of the massive X-ray binary 2S 0114 + 65 acquired in 1992 July with the ROSAT PSPC in the 0.1-2.4 keV X-ray band and in 1992 September with the 0.9 m telescope at KPNO in the optical V band are reported. The X-ray data confirm the presence of persistent 2.78 hr outbursts as previously deduced from archival data. The X-ray source displays apparent orbital effects consistent with noncircularity. Variable intrinsic absorption and intrinsic spectral variations are excluded as the cause of the observed X-ray modulation. The optical V-band photometric data do not reveal any periodic modulation. The possibility that the 2.78 hr period is the rotation of the neutron star component is entertained.