The near-infrared counterpart of 4U 1636-53: (Research Note)

D. M. Russell, K. O'Brien, T. Muñoz-Darias, P. Casella, P. Gandhi, M. G. Revnivtsev

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Context. The optical counterpart of the neutron star X-ray binary and well known X-ray burster, 4U 1636-53 (=4U 1636-536 = V801 Ara) has been studied for three decades. However, no infrared studies have been reported to date. Aims. Our aims are to identify and investigate the near-infrared (NIR) counterpart of 4U 1636-53. Methods. We present deep, K S-band (2.2 μm) imaging of the region of 4U 1636-53 taken with the Infrared Spectrometer And Array Camera (ISAAC) on the Very Large Telescope. Archival optical and UV data were used to infer the 0.2-2.2 μm spectral energy distribution (SED). Results. One star is located at coordinates α = 16:40:55.57, δ =-53:45:05.2 (J2000; 1σ positional uncertainty of ∼0.3 arcsec), which is consistent with the known optical position of 4U 1636-53; its magnitude is K S = 16.14 ± 0.12. This star is also detected in the 2MASS survey in the J-band and has a magnitude of J = 16.65 ±0.22. Assuming that the persistent emission is quite steady, the 0.4-2.2 μm de-reddened SED can be described by a power law F νν 1.5 ± 0.3, with some possible curvature (F νν 1.5) at 0.2-0.4 μm. The SED can be approximated by a blackbody of temperature ∼27000 K. This is typical for an active low-mass X-ray binary, and the emission can be explained by the outer regions of a (likely irradiated) accretion disc. We therefore interpret this K S-band star as the NIR counterpart.

Original languageEnglish (US)
Article numberA53
JournalAstronomy and Astrophysics
StatePublished - 2012


  • Infrared: stars
  • Stars: neutron
  • X-rays: binaries

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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