2013A&A...554A.143K

The B[e] phenomenon can be present in stars of different types and at different evolutionary stages. Very extended circumstellar matter prohibits the study of the atmosphere of these stars, since no photospheric lines are usually observed. Standard stellar atmosphere models are thus not applicable when determining stellar parameters. One of a few possibilities for comprehending the nature of these objects is to study their time variations. Unfortunately, almost no set of spectra with an adequate time description is available for these objects. We obtained an extensive set of MWC 342 spectra (102) during the years 2004-2010 in the wavelength interval around the Hα line (6265-6765Å) to focus on the time variability of the spectral lines in this region. We chose MWC 342 from the known stars showing the B[e] phenomenon since, although this star is very bright, its evolutionary status and the role of binarity in the appearance of the B[e] phenomenon are unknown. The time dependence of radial velocities and equivalent widths of emission lines was measured for the Hα line, HeI 6678Å, [OI] 6300, 6364Å, FeII 6318, 6384, 6344 and 6456Å, and SiII 6347, 6371Å. We detected variability in the spectral lines on both short and long time scales. HeI 6678Å shows day-to-day changes in its line profile. We observed pure absorption, pure emission, the P Cygni profile, and the inverse P Cygni profile in this line. There are time intervals where this line disappeared. The Hα line also shows considerable changes in its line profile, radial velocities, and equivalent widths. A cycle of about 1560 days was detected in its radial velocities. The detailed description of the variations in MWC 342 spectra reveals its important properties. The inner atmosphere is affected by changes of days, while existing long-term waves are propagated into the outer regions. It is highly probable that the continuum radiation in the visual region is also variable. The inverse P Cygni profile was probably observed when the continuum radiation reached its maximum. These properties indicate the complicated nature of this object. We discuss here a possible explanation of the observations by a stellar wind supported by pulsations.