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Optical identification of IGR J18308-1232 as a Cataclysmic Variable

ATEL # 1710; P. Parisi, N. Masetti (INAF/IASF, Bologna), E. Jimenez (UNAM, Mexico City), V. Chavushyan (INAOE, Puebla), L. Bassani (INAF/IASF, Bologna), A. Bazzano (INAF/IASF, Rome) and A.J. Bird (Univ. Southampton)
on 9 Sep 2008; 14:17 UT
Password Certification: Nicola Masetti (

Subjects: Optical, X-ray, Binaries, Cataclysmic Variables

We report on a spectroscopic analysis of optical sources inside the error circle of the XMM-Newton slew source XMMLS1 J183049.6-123218 (see Ibarra et al., ATel #1527), associated with the unidentified INTEGRAL source IGR J18308-1232 (Bird et al. 2007, ApJS, 170, 175).

The observations were performed on 2008 June 28, starting at 06:37 UT, with the Boller & Chivens spectrograph mounted on the 2.1m telescope of the Observatorio Astronomico Nacional (San Pedro Martir, Baja California, Mexico), for a total exposure time of 7200 s.
We found that the optical spectrum of source USNO-A2.0 0750-13371563 (with coordinates RA = 18 30 49.88, DEC = -12 32 18.7 and magnitude R ~ 17.0) shows a red continuum, possibly absorbed by the Galactic dust along the line of sight; superimposed on this continuum several Balmer, HeI and HeII narrow emission lines at a redshift consistent with zero are apparent. The Halpha emission is detected with an EW ~ 22 Angstrom.

This spectrum resembles that of a Cataclysmic Variable (similar to those reported in e.g. Masetti et al. 2006, A&A, 459, 21 and in Masetti et al. 2008, A&A, 482, 113), and the relative strength of the HeII 4686 Angstrom emission suggests the presence of a magnetic white dwarf in this system.
Thus we identify the object USNO-A2.0 0750-13371563 as the optical counterpart of the hard X-ray source IGR J18308-1232, and as a new, possibly magnetic, Cataclysmic Variable.

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