Investigating the properties of the near contact binary system TW CrB
  TW Coronae Borealis (TW CrB) is a binary system likely to be active showing
evidence of starspots and a hotspot. We calculated a new ephemeris based on all
available timings from 1946 and find the period to be 0.58887492(2) days. We
have revised the average rate of change of period down from 1.54(16) x 10-7
days yr-1 to 6.66(14) x10-8 days yr-1. Based on light curve simulation analysis
we conclude that the two stars are close to filling their Roche lobes, or
possibly that one of the stars' Roche lobe has been filled. The modelling also
led to a hotspot and two starspots being identified. Conservative mass transfer
is one of a number of possible mechanisms considered that could explain the
change in period, but the mass transfer rate would be significantly lower than
previous estimates. We found evidence that suggests the period was changing in
a cyclical manner, but we do not have sufficient data to make a judgement on
the mechanism causing this variation. The existence of a hotspot suggests mass
transfer with a corresponding increase in the amplitude in the B band as
compared with the R and V bands. The chromospheric activity implied by the
starspots make this binary a very likely X-ray source.
