4U 1543-45

R. J. Blissett and the EXOSAT Observatory Team report that a 3-hr EXOSAT observation on Aug. 28 located the transient x-ray source 4U 1543-45 (IAUC 3854) at a position preliminarily determined as R.A. = 15h43m34s, Decl. = -47deg31'1 (equinox 1950.0; maximum error radius 30"). This is 3' northwest of the 50" region of uncertainty previously quoted. The 2-10-keV spectrum is unusually soft with a characteristic temperature of ~ 1.7 keV, similar to that previously reported from A0620-00 (V616 Mon) after maximum. With the help of the above report, H. Pedersen, M. Veron, P. Veron and H.-E. Schuster, European Southern Observatory, communicate that comparison of a red plate taken with the 1.0-m Schmidt telescope on Aug. 31.0 UT with the red ESO Sky Survey shows a star at R.A. = 15h43m33s9, Decl. = -47deg30'54" (equinox 1950.0) that has increased in brightness by ~ 1 mag. The position is 8" northwest of the mag 12 star that appears 13 mm northwest of the northwest corner of the error box shown by Matilsky et al. (1972, Ap.J. 174, L53). CCD observations on Sept. 2.0 with the 1.54-m Danish telescope give V = 14.9, B-V = +0.7. Low-dispersion spectra obtained on Sept. 2.0 and 3.0 with the 3.6-m telescope show emission lines from N III 463.4 and 464.2 nm, He II 469 nm and He I 668 nm; H-alpha emission, if present, is weak; absorption lines include Na D (equivalent width 0.25 nm) and 628.4 nm (interstellar).