Astron. Astrophys. 356, 50-62 (2000)

Photometric observations of the radio bright B[e]/X-ray binary CI Cam

J.S. Clark ¹, A.S. Miroshnichenko ^2,3, V.M. Larionov ⁴, V.M. Lyuty ⁵, R.I. Hynes ^6,7, G.G. Pooley ⁸, M.J. Coe ⁶, M. McCollough ⁹, S. Dieters ⁹, Yu.S. Efimov ^10,11, J. Fabregat ¹², V.P. Goranskii ⁵, C.A. Haswell ⁷, N.V. Metlova ⁵, E.L. Robinson ¹³, P. Roche ¹⁴, V.I. Shenavrin ⁵ and W.F. Welsh <sup>13

1</sup> University of Sussex, Astronomy Centre, Falmer, Brighton, BN1 9QH, UK
² Pulkovo Observatory, 196140 Saint-Petersburg, Russia
³ University of Toledo, Dept. of Physics & Astronomy, Toledo, OH 43606, USA
⁴ Astronomical Institute of St. Petersburg University, 198904 St. Petersburg, Russia
⁵ Crimean Laboratory of Sternberg Astronomical Institute of Moscow University, Russia
⁶ University of Southampton,Department of Physics & Astronomy, Highfield, Southampton SO17 1BJ, UK
⁷ The Open University, Department of Physics, Walton Hall, Milton Keynes MK7 6AA, UK
⁸ Mullard Radio Astronomy Observatory, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, UK
⁹ NASA/Marshall Space Flight Center, Huntsville, Alabama, AL 35812, USA
¹⁰ Crimean Astrophysical Observatory, Nauchny, Crimea, 334413, Ukraine
¹¹ Isaac Newton Institute of Chile, Crimean Branch
¹² Departmento de Astronomia, Universidad de Valencia, 46100 Burjassot, Valencia, Spain
¹³ Dept. of Astronomy, University of Texas, Austin, TX 78712, USA
¹⁴ NSSC, Mansion House, 41 Guildhall Lane, Leicester, LE1 5FQ, UK

Received 22 December 1999 / Accepted 27 January 2000

Abstract

We present multiwavelength (optical, IR, radio) observations of CI Cam, the optical counterpart to the transient X-ray source XTE J0421+560. Pre-outburst quiescent observations reveal the presence of a dusty envelope around the system. Pronounced short term variability is observed at all wavebands from U-K, but no indication of prior flaring of a similar magnitude to the 1998 April outburst is found in these data.

Data obtained during the 1998 April X-ray flare reveal pronounced optical-radio flaring. The optical flux was observed to quickly return to quiescent levels, while the radio flare was of much longer duration. The optical component is likely to result from a combination of free-free/free-bound emission, emission line and thermal dust emission, caused by re-radiation of the X-ray flux, while the behaviour of the multiwavelength radio data is consistent with emission from expanding ejecta emitting via the synchrotron mechanism.

Post-outburst (1998 August-1999 March) U-M broadband photometric observations reveal that while the optical (UBV) flux remains at pre-outburst quiescent levels, near IR (JHKLM) fluxes exceed the pre-outburst fluxes by 0.5 magnitudes. Modelling the pre- and post-outburst spectral energy distribution of CI Cam reveals that the structure and/or composition of the dusty component of the circumstellar envelope appears to have changed. Due to a lack of information on the precise chemical composition of the dust within the system several explanations for this behaviour are possible, such as the production of new dust at the inner edge of the envelope, or modification of the composition of the dust due to X-ray irradiation.

Key words: stars: binaries: general stars: circumstellar matter stars: individual: CI Cam stars: winds, outflows X-rays: stars

Send offprint requests to: J.S. Clark

Correspondence to: (jsc@star.cpes.susx.ac.uk)

© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000

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