Title:A double plateau and unprecendented circumstellar variable sodium in the transient SN 2011A.

Abstract:
We present optical spectroscopic/photometric study of a low luminosity SNe IIn 2011A. Our data covers 
epochs between 4-140 days and 7- 150 days for spectroscopy and photometry respectively. Thanks to our 
optical spectra we think that the CSM may compose by two mass-loss rate phase, because spectra shown 
sequence of P-Cygni profile/Not profile. Moreover we see that the sodium doublet absorption becomes 
stronger with time. Indeed equivalent width is equal to more o less 3A and increases to a value bigger than 
7A after the first 50 days. This evolution is also accompanied by a change of line profile. When the 
absorption becomes stronger, a P-Cygni profil appears. The last specrtum does not show absorption o 
P-Cygni profile but an emission.
In 2011A light curve we can see cleary in V -;R- band two plateau, an initial plateau which lasts 15 days with 
a slope a 0.0042 mag/days in V . After this first plateau, the light curve decline with a slope more or less 
equal to 0.034 mag/days in V . Then there is a second plateau phase with a slope of 0.0028 mag/days, 
which is flatter and longer lasting at longer wavelenghts.
We find an absolute magnitude about -16.4 in V - band. In literature we find that this is relatively low for the 
SN IIn class type IIn (-16< MV <-20) but it is significately higher than the most luminous impostors (-16< MV 
) (Van Dyk et al 2000).