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XTE J1752-223: Optical spectroscopy and infrared counterpart detection

ATel #2268; M. A. P. Torres (CfA), D. Steeghs (Warwick/CfA), P. G. Jonker (SRON/CfA),, I. Thompson (Carnegie), A. M. Soderberg (CfA)
on 27 Oct 2009; 13:19 UT
Credential Certification: Manuel Torres (mtorres@cfa.harvard.edu)

Subjects: Infra-Red, Optical, Binary, Black Hole, Transient

Referred to by ATel #: 2269, 2278, 2280, 2775

Prompted by the discovery of its bright optical counterpart and the announcement of increased X-ray activity (ATels #2258, #2259, #2261, #2265, #2263), we have acquired additional observations of XTE J1752-223 at optical and near-infrared wavelengths.

OPTICAL SPECTROSCOPY: An optical spectrum covering 3330-9165 Angstrom was obtained with the MIKE echelle spectrograph on the Magellan Clay telescope starting on 2009 Oct 26 UT 23:52. The hour long exposure revealed the presence of broad H-alpha in emission (EW~4 AA, FWHM~750 km/s), as expected for an accreting binary. Several strong and resolved diffuse interstellar bands are also detected reflecting the reddening towards the source. No additional emission features of either Hydrogen or Helium appear to be present at this stage.

NEAR-INFRARED (NIR) PHOTOMETRY: In order to search for the NIR counterpart, observations were performed in the J, H and Ks bands starting on 2009 Oct 26 23:48 UT using the PANIC camera on the 6.5-m Magellan Baade telescope. The frames (totaling 45s on source in each band) were acquired with a seeing of ~0.6". Astrometric and photometric solutions were defined using 2MASS sources in the field of view, achieving a positional rms of 0.1" and a zero-point error < 0.1 mag.

A NIR source, not present in 2MASS or UKIDSS, is detected in the three bandpasses with a position consistent with the location of the optical counterpart (ATel #2263). Using relative (PSF-fitting) photometry we determine magnitudes of J = 14.84 +/- 0.01, H = 14.22 +/- 0.01 and Ks = 13.98 +/- 0.01 for the NIR counterpart.