New Results for Two Optically Faint Low‐Mass X‐Ray Binary Systems

We present optical photometry of the low mass X-ray binary systems GX 349+2and Ser X-1. Extensive VRI photometry of the faint optical counterpart (V=18.4)to GX 349+2 reveals a period of 22.5 +/- 0.1 h and half-amplitude 0.2 mag. Thisresult confirms and extends our previously reported 22 h period. No colorchange is detected over the orbit, although the limits are modest. We alsoreport the discovery of two new variable stars in the field of GX 349+2,including a probable W UMa system. Ser X-1 is one of the most intensepersistent X-ray burst sources known. It is also one of only three burstsystems for which simultaneous optical and X-ray bursts have been observed. Thefaint blue optical counterpart MM Ser (B~19.2) has long been known to have acompanion 2.1" distant. Our images indicate that MM Ser is itself a furthersuperposition of two stars, separated by only 1". At the very least, the ratioof inferred burst to quiescent optical flux is affected by the discovery ofthis additional component. In the worst case, the wrong object may havepreviously been assumed as the optical counterpart.Comment: 16 pages including 10 figures and 3 tables; Uses AASTeX 4.0; Accepted for publication in The Astrophysical Journal, Volume 490, November 20, 199