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Astron. Astrophys. 348, L9-L12 (1999)

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Letter to the Editor

Optical observations of the black hole candidate XTE J1550-564 during the September/October 1998 outburst

C. Sánchez-Fernández 1, A.J. Castro-Tirado 1,2, H.W. Duerbeck 3, L. Mantegazza 4, V. Beckmann 5, V. Burwitz 6, L. Vanzi 7, A. Bianchini 8, M. Della Valle 8, A. Piemonte 9, B. Dirsch 10, I. Hook 11, L. Yan 12 and A. Giménez 1,2

1 Laboratorio de Astrofísica Espacial y Física Fundamental (LAEFF-INTA), P.O. Box 50727, E-28080 Madrid, Spain
2 Consejo Superior de Investigaciones Científicas, Instituto de Astrofísica de Andalucía (IAA), P.O. Box 3004, E-18080 Granada, Spain
3 Free University Brussels (VUB), Pleinlaan 2, B-1050 Brussels, Belgium
4 Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807 Merate, Italy
5 Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029 Hamburg, Germany
6 Max-Planck-Institut für Extraterrestische Physik, P.O. Box 1603 D-85740 Garching bei München, Germany
7 European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
8 Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, I-35122 Padova, Italy
9 Osservatorio Astrofisico di Asiago, Università di Padova, I-36012 Asiago, Italy
10 Universität Bonn, Sternwarte, Auf dem Hügel 71 D-53121 Bonn, Germany
11 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748, Garching bei München, Germany
12 Carnegie Observatories, 813 Santa Barbara St., Pasadena, CA, 91101, USA

Received 12 May 1999 / Accepted 28 June 1999

Abstract

We report here optical observations during the September/October 1998 outburst of the black hole candidate XTE J1550-564. CCD photometry was obtained for the optical counterpart with the 0.9m Dutch telescope at La Silla since the onset of this event. We analysed 211 U, V and i frames, from Sep 10 to Oct 23. Stochastic flaring activity was observed on Sep 11-16, but no evidence for a superhump period, as seen in other soft X-ray transients, was found. An optical flare nearly simultaneous to an X-ray flare that occurred on Sep 21 was observed in the V-band. A reddened optical spectrum showed the typical emission lines corresponding to X-ray transients in outburst. From the interstellar absorption lines, we derive E(B-V) = 0.70 [FORMULA] 0.10 and suggest D [FORMULA] 2.5 kpc. In such case, MB [FORMULA] +7 mag. for the progenitor, which is consistent with the spectral type of a low-mass [FORMULA] K0-K5 main-sequence companion.

Key words: X-rays: bursts – accretion, accretion disks – stars: binaries: general – stars: neutron

Send offprint requests to: A. J. Castro-Tirado (ajct@iaa.es)

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© European Southern Observatory (ESO) 1999

Online publication: July 16, 1999
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