On the Size of the Non-Thermal Component in the Radio Emission from Cyg OB2 #5

Luis F. Rodriguez$^1$, Yolanda Gomez$^1$, Laurent Loinard$^1$, and Amy J. Mioduszewski$^2$

1 - Centro de Radioastronomia y Astrofisica, Universidad
Nacional Auonoma de Mexico, Campus Morelia, 2 - National Radio Astronomy Observatory, USA

Cyg OB2 #5 is a contact binary system with variable
radio continuum emission. This emission has a low-flux state where
it is dominated by thermal emission from the ionized stellar
wind and a high-flux state where an additional non-thermal component appears.
The variations are now known to have
a period of 6.7+-0.2 yr. The non-thermal component has been attributed to
different agents: an expanding envelope ejected periodically from the
binary, emission from a wind-collision region,
or a star with non-thermal emission in an eccentric orbit around the
binary. The determination of the angular size of the non-thermal component
is crucial to discriminate between these alternatives.
We present the analysis of VLA archive observations made at 8.46 GHz in 1994 (low state)
and 1996 (high state), that allow us to subtract the effect of the persistent
thermal emission and to estimate an angular size of <=0.02''
for the non-thermal component. This compact size favors the explanation
in terms of a star with non-thermal emission or of a
wind-collision region.

Reference: Revista Mexicana de Astronomia y Astrofisica
Status: Manuscript has been accepted

Weblink: arXiv:1005.2342


Email: l.rodriguez@crya.unam.mx