R. Gonzalez-Riestra, R.F. Viotti, T. Iijima, C. Rossi, F. Montagni, S. Bernabei, A. Frasca, A. Skopal
Image & caption:
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Image caption::
Comparison of the AAVSO light curve of AG Dra (dots) with the X-ray light curve (filled squares at the top). Solid symbols on the visual light curve mark the magnitude at times of the X-ray observations. The X-ray fluxes are in units of counts per sec. Anticorrelation between the optical and the X-ray brightness of AG Dra is clearly seen.
Description:
We revealed an anticorrelation between the supersoft X-ray fluxes and the optical fluxes, observed for the symbiotic star AG Draconis during its quiescent and active phases. This anticorrelation represents a general behaviour, which is independent from that how the outburst is strong and its type. During outbursts, the white dwarf luminosity increases, but the radiation is heavily absorbed by the circumstellar matter within the supersoft X-ray domain. In contrast, the brightness in the optical increases, as indicated by photometric observations and accurately calibrated low-resolution spectra. This is a consequence of the increased opacity at the vicinity of the white dwarf due to an increase of its stellar wind.
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