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K-band Spectroscopy of IGR J16493-4348

ATel #1396; Elisa Nespoli, Juan Fabregat (University of Valencia, Spain) and Ronald E. Mennickent (University of Concepcion, Chile)
on 25 Feb 2008; 10:35 UT
Credential Certification: Juan Fabregat (juan.fabregat@uv.es)

Subjects: Infra-Red, X-ray, Binary, Neutron Star

We report results from Ks band spectroscopy of the INTEGRAL source IGR J16493-4348. The corresponding proposed infrared counterpart (2MASS J16492695-4349090, Kuiper et al. 2005, ATEL #654) was observed in service mode on 2007 April 5th with the ISAAC spectrograph on UT1 in Paranal (ESO proposal 079.D-0668-B). The sky was clear during the observation, the seeing was ≤1.4''and the target was observed at airmass 1.08. Data were taken in the Short Wavelength - Low Resolution mode, with a pixel scale of 0.147'' and a resolution of ~ 500. The retrieved snr averaged 150.

The spectrum shows no metal lines (no N III or C IV); He I 20581 Å is detected in strong emission (EW = -4.02 Å), He I 21126 is in absorption (EW = 1.90 Å) and Brγ 21661 Å is in relatively strong absorption (EW = 2.68 Å). The atomic transitions detected are the typical ones of OB stars spectra. In particular, the 20581 Å is a prominent feature in supergiant stars and it is observed in emission in B type supergiants. The He I 21126 Å line is present in late O - early B spectra. By comparing the relative strength of the identified lines with those from the atlas of Hanson et al. (1996), we estimated the spectral type to B0.5 Ib, with an uncertainty of one subtype. Together with information provided by X-ray data (see Hill et al. 2007), our result thus permits to classify the system as a neutron star SGXRB.