Challenging the Disk Instability Model. I. The Case of YZ LMi

Abstract Observations of YZ LMi show enhanced emission along the stream trajectory beyond impact at disk rim during outbursts as well when quiescent is large. We investigated whether these features can be explained in terms either gas overflow or penetration within frameworks instability model (DIM) and mass-transfer (MTIM) outbursting disks. Gas not possible because vertical scale height significantly lower than that outer there no combination parameters which enables on a larger while preventing it smaller disk. Stream requires to denser regions. This requirement cannot met by low-viscosity DIM its density over whole range rates where thermal-viscous occurs. On other hand, high-viscosity MTIM has much densities decrease with increasing radius, easily allowing for (when rate increase) large The observed are consistent DIM, but plausibly MTIM. These results suggest response bursts rate. In this case, outburst decline timescale (2–3) days implies viscosity parameter α = 3–4.