tokens: of 1.5. Convection sets in close to the point where the cold branch of the S-curve ends which leaves this point sensitive to α ml . This effect is even stronger on the critical point where the hot branch starts, as this is where convection is the strongest. Higher values of α ml shift both critical points at which the S-curve bends closer together, leading to a smaller Q Σ crit . This alters the global behaviour of the disc and the outburst properties: the decay from the outburst in a disc with $α ml $ = 6 starts at higher Σ and higher T eff , and less mass is accreted and accumulated in the disc during the outburst cycle. Therefore, more efficient convection produces outbursts that are more frequent and of lower amplitude, and even lack quiescent phases. While it is important to note that this lack of quiescence may be related to uncertainties in the end of the lower branch, there are other ways out. In the discussion below, we examine a few options to restore or modify quiescence. The comparison of DIMRI with $α ml $ = 1.5 and DIMa (Figs 10 and 9 c) highlights the importance of changing the dissipation profile, as this is the only difference between these two models. The main difference is that the outbursts in DIMRI with $α ml $ = 1.5 are wider and the quiescence is longer than in the DIMa light curve. Changing the mixing length parameter is not the only way to increase the outburst amplitude and restore quiescent phases to the DIMRI models. Increasing the mass transfer rate, while all other parameters are fixed, makes the disc hotter and denser. This means that the surface density everywhere in the quiescent disc is closer to the critical value and the disc luminosity is higher. The result is more frequent lower amplitude outbursts for higher mass transfer rate regardless of model, as illustrated by comparing the two mass transfer rates shown in Fig. 9 for each of our three models. Hence, merely reducing the mass transfer rate in the DIMRI model can increase the outburst amplitude and restore quiescent phases. If one sets as low as g s −1 in the DIMRI (with α ml = 6), the elapsed time between two consecutive outbursts starts to be longer and also the outburst amplitude rises (see Table 1 and Fig. 11 ). Note that for such a low , the discs in DIM and DIMa become cold and stable. There is yet another alternative way to restore quiescence in the DIMRI light curves. Observed X-ray fluxes in quiescent dwarf novae are far too large compared to what models predict. A solution to this problem is a truncation of the inner disc. Numerical calculations by Hameury, Lasota Warner ( 2000 ) and Schreiber, Hameury Lasota ( 2003 ) confirm that truncating the inner disc has substantial influence on the dwarf nova light curves and may solve the discrepancy between observations and theory. This truncation may be caused by the magnetic field of the primary white dwarf. A white dwarf magnetic field in the range 10 4 –10 7 G (which translates to a magnetic
ner_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model O B-Formula I-Formula I-Formula I-Formula I-Formula O B-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model O B-Formula I-Formula I-Formula I-Formula I-Formula O O O O O O O O O O B-Model O O O O O O O O O O O O O O O O O O O O O O O B-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model I-Model O O O O O O O O O O O O O O O O O O O O B-Model O B-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model O B-Model O O O O O O O O O O O O O O O B-Model O O O B-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O