The orbital period of CI Cam (XTE J0421+560)
ATel #416; E. A. Barsukova, N. V. Borisov, A. N. Burenkov, V. G. Klochkova (Special Astrophysical Observatory, Russia), V. P. Goranskij, N. V. Metlova (Sternberg Astronomical Institute, Moscow University)
on 20 Feb 2005; 20:40 UT
Credential Certification: Barsukova E.A. (bars@sao.ru)
Subjects: Optical, Binary, Transient, Variables
CI Cam is a known B[e] star and X-ray transient. We perform
photometric and medium-resolution spectroscopic monitoring
of CI Cam in the quiet state during 7 years since April 1998
outburst. We have detected orbital light variations with the
period of 19.41+/-0.02 day. The modulation has an amplitude
of 0.032 mag in V band. The epoch of maximum is at
JD 2452200.75. We find large regular variations of the
radial velocity in HeII 4686A emission line with this
photometric period.
The velocity curve has a sawtooth shape and a semi-amplitude
of about 230 km/s with gamma-velocity at -51 km/s. Modelling
of the velocity curve results in the orbital eccentricity of
about 0.62, and a*sin(i) ~42 million km. The inferior
conjunction epoch is at JD 2452199.6+/-0.2, and periastron
passage occurs near the moment of inferior conjunction.
Maximum brightness occurs 0.06P later by phase. Mass function
of HeII emission source is equal to 12 solar masses. This
is a lower limit on the primary star mass, the spectrum of which
we define as B4 III-V. We have not found any detectable
motion in a HeI line that may belong to the primary B type star.
So, the fast moving HeII emitting object should have at least
25 times smaller mass than the primary star. More likely this
object is a white dwarf surrounded by an accretion disk.
CI Cam: details, light curve, radial velocity curve, tables
