SIMBAD references

We present results from ∼2 years of optical monitoring of an unusual interacting compact binary MS 1603+2600 together with the results of ROSAT observations. Our CCD-photometry confirms the erratic behaviour of the optical light curve shape reported by Morris et al. (1990ApJ...365..686M). The ROSAT-PSPC observations suggest that MS 1603 might be a short period soft X-ray transient (SXT) never seen in outburst. This would probably require, that the compact object in MS 1603 is a black hole rather than a neutron star. In addition to optical photometry and ROSAT data, we present first circular polarimetric observations of the source and discuss the nature and origin of MS 1603+2600.