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Optical Observations of EXO 0748-676 in Quiescence

ATEL # 1816; Robert Hynes, Erica Jones (Louisiana State University)
on 28 Oct 2008; 19:02 UT
Password Certification: Robert Hynes (

Subjects: Infra-Red, Optical, Binaries, Neutron Stars, Transients
Referred to by ATEL #: 1817

EXO 0748-676 has been reported to be in X-ray quiescence by Wolff et al. (ATEL #1812). We performed optical (R band) and near-IR (J band) observations of the optical counterpart, UY Vol, on 2008 October 28.33 using Andicam on the SMARTS 1.3m telescope. We obtained a total of 1350 sec exposure in R and 1000 sec in J. The observations corresponds to binary orbital phases 0.38-0.49.

The counterpart is detected in R but clearly considerably fainter than previously observed. From our preliminary photometry, we estimate R=21.9+/-0.1. No counterpart is visible in the J band images.

The quiescent position measured relative to nearby stars agrees with that previously measured in the bright state using the same instrument to better than 0.2 pixels (0.1 arcsec) so we believe this is indeed the X-ray binary rather than a previously undetected interloper.

We will continue to monitor the source.

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