Volume 446, Number 3, February II 2006
|Page(s)||L17 - L20|
|Published online||20 January 2006|
Letter to the Editor
Two new candidate ultra-compact X-ray binaries
Astronomical Institute, Utrecht University, PO Box 80 000, 3508 TA Utrecht, The Netherlands e-mail: firstname.lastname@example.org
2 SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS83, Cambridge, Massachusetts, USA
Accepted: 21 December 2005
We present the identification of the optical counterparts to the low-mass X-ray binaries 1A 1246-588 and 4U 1812-12. We determine the X-ray position of 1A 1246-588 from ROSAT/PSPC observations and find within the error circle a blue star with , and which we identify as the counterpart. Within the Chandra error circle of 4U 1812-12, a single star is present which appears blue with respect to the stars in the vicinity. It has , . Distance estimates for both systems indicate that the optical counterparts are intrinsically faint, suggesting that they are ultra-compact X-ray binaries. These identifications would increase the number of candidate ultra-compact X-ray binaries from 2 to 4, whereas orbital periods are measured for only 7 systems in the Galactic disk.
Key words: X-rays: binaries / X-rays: individual: 1A 1246-588, 4U 1812-12
© ESO, 2006
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