Optical Candidates for X-Ray Sources

J. E. McClintock, Massachusetts Institute of Technology, reports that he has discovered at Cerro Tololo Interamerican Observatory a possible optical counterpart of 3U 1735-44, which has been identified with the burst source MXB1735-44 = KGX 345-6 (IAUC 3075) and is currently under scrutiny during a worldwide watch of x-ray bursters (IAUC 3078). The object, located (with an uncertainty of +/- 3") at R.A. = 17h35m19s.0, Decl. = -44o25'19" (equinox 1950.0), is near the center of the 2o-radius error circle given for 3U 1735-44 (2S 1735-444) by Jernigan et al. (to be submitted to Nature); it is designated as star No. 5 in their finding chart of the region. The object has a large ultraviolet excess, its photometric parameters (+/- 0.10 magnitude) being V = 17.5, U-B = -0.85, B-V = +0.20. J. van Paradijs, B. Hidajat and H. Hendricks, Bosscha Observatory, suggest for the optical counterpart of 3U 1626-67 (IAUC 3054) a variable star situated 20" northeast of a thirteenth-magnitude star at R.A. = 16h26m46s, Decl. = -67o21'.6 (equinox 1950.0). Kodak 103a-D exposures on June 11.76 and 14.68 UT show a brightness variation of at least one magnitude, between about magnitudes 17 and 18.