5. PG 0824+289
This star is a spectroscopic binary (hot DA plus dwarf carbon star) accompanied by a visually separated M3-4 dwarf (Heber et al. 1993, Green & Margon 1994). The DA white dwarf belongs to the sample recently analysed by Wolff et al. (1995) on the basis of ROSAT spectral data. A model atmosphere analysis of available spectral observations yielded 36 000 K at the assumed , with the estimated error of several thousands K. The model atmosphere analysis was performed with pure hydrogen LTE models (Koester et al. 1979). Following a brief discussion Wolff et al. (1995) concluded, that the pure H atmosphere of the DA white dwarf satisfactorily represents the X-ray flux of PG 0824+289, and that both the dC and the dM dwarfs do not contribute to the X-ray luminosity of the whole system.
Model atmosphere computations with Compton scattering did not produce any significant rise at the outer boundary, and significant effects of noncoherent scattering appear in the X-ray spectrum alone. Fig. 4. displays X-ray branch of the theoretical Comptonized spectrum of PG 0824+289 (solid line). The continuum flux exhibits a cutoff at (0.3 keV), and a deficiency of flux at as compared to the Thomson scattering model (long-dashed line). The effect of flux depression and cutoff in X-ray domain is very similar to that in HZ 43 A.
The value of equals to -0.10 at the cutoff . This value is also similar to that in HZ 43 at the corresponding cutoff.
© European Southern Observatory (ESO) 1998
Online publication: November 9, 1998