Identification of the Optical Counterpart of LMC X-1
Session 102 -- X-Ray Variables, Binaries and Transients
Display presentation, Thursday, 12, 1995, 9:20am - 6:30pm

## [102.06] Identification of the Optical Counterpart of LMC X-1

A.L. Anderson, A.P. Cowley, P.C. Schmidtke, T.K. McGrath (ASU)

LMC X-1 is one of the most luminous and highly variable X-ray sources in the LMC. However, there has been a long standing uncertainty about its optical identification. The Einstein --HRI position lay between the early-type supergiant R148 and a peculiar O7 III star, known as Star \#32 (Cowley et al. 1978), which has a resolved He II nebula surrounding it (Pakull \& Angebualt 1986). The system is of particular interest since it appears to contain a black hole. A new X-ray position for LMC X-1 has been derived using 23 ROSAT --HRI observations. Corrections for a small field rotation (Kuerster 1993) and an optical$-$X-ray offset (Schmidtke et al. 1994) have been applied. The resulting position is $\sim1^{\prime\prime}$ from Star \#32, confirming its identification with LMC X-1. In addition, quasi-periodic oscillations (QPO) have been found in some of the data. They show a centroid frequency of 0.0718 Hz, slightly lower than the frequency detected by Ebisawa {\it et al.} (1989) using Ginga data.