1996A&A...309..800Z

We present near-infrared (NIR) broadband observations aimed at detecting flickering activity and long-term variation of MWC560. In addition, we have performed NIR spectroscopy around 1.084µm and at 2.16µm and have detected Brγ in emission. To improve the significance of any upper limit on variability, we adopted a differential measurement technique. The analysis of the broadband photometry shows that there are no hour-timescale fluctuations in the NIR of the sort detected at optical and ultraviolet wavelengths, while the internight variations, found in the K-band, are typical of late-type stars. All this clearly indicates that the JHK emission of MWC560 is dominated by its M-giant component, a result which allows us to decompose the optical emission of MWC560 into stellar and "hot" components and derive the intrinsic colors of the latter. Such a decomposition shows no evidence for an accretion disk, and reveals a clear separation between two states of activity: (i) discrete, and (ii) quasi-stationary mass ejection. Combining the NIR data with IRAS observations, an excess emission is found in the NIR fluxes of MWC560 and its most plausible explanation is emission from dust at temperatures T≃500-600K.