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
Credential Certification: Nicola Masetti (firstname.lastname@example.org)
Subjects: Optical, X-ray, Binary, Cataclysmic Variable
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.