1994A&A...289..419C

The error circles of ten X-ray sources are investigated at optical and infrared wavelengths using Palomar sky survey plates, and deep photographic survey plates obtained with the UK Schmidt telescope at the Anglo-Australian observatory. The objects were cross-identified with the catalogs of variable stars, IRAS point sources and Einstein of X-ray sources in the same sky region. As expected, very strong interstellar dust absorption is typical for all the X-ray source fields. Variable star No 2547 from the list by Terzan & Gosset (1992) was found to be located near the southern boundary of the KS 1731-260 error circle. The star is identified with the source IRAS 17311-2604, and varies from 16mag to fainter than 20mag on our r-band plates. IRAS 17342-2908 and another infrared source 358.83+1.39 discovered by Kawara et al. (1983) at 2.21 µm are located near the error box of GRS 1734-292. We have found an optical counterpart for these infrared sources, the star is very red and bright in the near infrared with no signs of high amplitude light variations. It may be a highly reddened OB-star. As in the previous case, the positions of IRAS 17342-2908 and infrared source 358.83+139, were found to coincide with a red star also bright in the near infrared and all these objects are covered by the error circle of GRS 1736-297. The error circle of KS 1741-293 is covered by both error boxes of IRAS 17417-2919 and of FIR 5, a far infrared source discovered earlier by Odenwald & Fazio (1984) at 40-250 m wavelength band. The latter object is known to be extended with the diameter of 2.7'±0.6' and coincides with the radio source G 359.54-068 also known to be extended with the diameter of 2.90'. No trace of an optical counterpart to this object is seen on optical and near infrared plates, and there are no highly reddened star in the error box. The center of highly reddened globular cluster Terzan 6 is located on the south-western boundary of the 95 arcsecond diameter error circle of GRS 1747-312. On the deep infrared UKST plates the cluster is seen to extend inside the error circle. So this may be another association of a globular cluster with an X-ray source. Optical photographic reproductions of error circles and their neighborhood are presented, some stars with outstanding blue or red colors are marked.