AAS 203rd Meeting, January 2004
Session 84 Binary Stars
Poster, Wednesday, January 7, 2004, 9:20am-6:30pm, Grand Hall

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[84.06] Discovery of the Orbital Period of the Ultracompact Low-Mass X-Ray Binary 4U 1543-624

Z. Wang, D. Chakrabarty (MIT)

The X-ray source 4U 1543-624 is one of several low-mass X-ray binaries suspected to be ultracompact systems (Porb < 80 minutes) with neon-rich degenerate donors. We present optical observations from the Magellan 6.5-m telescopes in Chile. Our time-resolved optical photometry of the system has revealed an 18 minute periodicity that is probably orbital in origin, verifying the ultracompact nature of the binary. Optical spectroscopy show evidence of composition anomalies consistent with an ultracompact scenario. Our results support the identification of several other systems with similar spectral features as ultracompact binaries and suggest that such binaries may be significantly more common than previously realized.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.