Volume 547, November 2012
|Number of page(s)||6|
|Section||Stellar structure and evolution|
|Published online||23 October 2012|
The near-IR counterpart of IGR J17480-2446 in Terzan 5⋆
1 INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Italy
2 Dipartimento di Fisica, Università di Palermo, via Archirafi 36, 90123 Palermo, Italy
3 Università di Cagliari, Dipartimento di Fisica, SP Monserrato-Sesto km 0.7, 09042 Monserrato (CA), Italy
4 Institut de Cìencies de l’Espai (IEEC-CSIC), Campus UAB, Fac. de Cìencies, Torre C5, parell, 2a planta, 08193 Barcelona, Spain
Received: 27 June 2012
Accepted: 25 September 2012
Context. Some globular clusters in our Galaxy are noticeably rich in low-mass X-ray binaries. Terzan 5 has the richest population among globular clusters of X- and radio-pulsars and low-mass X-ray binaries.
Aims. The detection and study of optical/IR counterparts of low-mass X-ray binaries is fundamental to characterizing both the low-mass donor in the binary system and investigating the mechanisms of the formation and evolution of this class of objects. We aim at identifying the near-IR counterpart of the 11 Hz pulsar IGR J17480-2446 discovered in Terzan 5.
Methods. Adaptive optics (AO) systems represent the only possibility for studying the very dense environment of GC cores from the ground. We carried out observations of the core of Terzan 5 in the near-IR bands with the ESO-VLT NAOS-CONICA instrument.
Results. We present the discovery of the likely counterpart in the KS band and discuss its properties both in outburst and in quiescence. Archival HST observations are used to extend our discussion to the optical bands.
Conclusions. The source is located at the blue edge of the turn-off area in the color–magnitude diagram of the cluster. Its luminosity increase from quiescence to outburst, by a factor 2.5, allows us to discuss the nature of the donor star in the context of the double stellar generation population of Terzan 5 by using recent stellar evolution models.
Key words: pulsars: general / pulsars: individual: IGR J17480-2446 / binaries: close / globular clusters: individual: Terzan 5
Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, DDT proposal 286.D-5012. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.
© ESO, 2012
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