In the last few years , we had devoted our time to the study of a sample of southern unclB [ e ] stars .
For most of them , there are few works in the literature , and their physical parameters are still very uncertain .
Our research was concentrated on the analysis of the optical and IR data , making use of high ( FEROS ) and low ( B & C ) resolution spectra , obtained by us at ESO ( La Silla , Chile ) and LNA ( Brazópolis , Brazil ) and using public ISO and IRAS spectra .
In this work we will present the results for a curious star : CD-42 ^ { \circ } 11721 .
This object has a doubtful evolutionary stage , being either a pre-main sequence star ( HAeB [ e ] ) or an evolved star ( supergiant B [ e ] or sgB [ e ] ) .
This confusion concerning its nature is caused by the complete absence of reliable physical paramenters for this object , especially its distance .
Our optical investigation could be splitted in two parts , a qualitative study based on the identification of the numerous emission lines present in the spectra and the classification of their line profiles , which indicate a non-spherically symmetric circumstellar environment , and a quantitative analysis of numerous forbidden lines , e.g .
[ O i ] , [ O ii ] , [ N ii ] and [ S ii ] .
Assuming a typical circumstellar scenario for a sgB [ e ] , i.e .
a fast , low-density polar wind and a slow , high-density disc forming equatorial wind , we can reproduce very well the line luminosities of the forbidden lines .
From this analysis , we can determine the mass loss rate of the star lying in the range from \dot { M } \simeq ( 4.4 \pm 0.8 ) \times 10 ^ { -6 } { M } _ { \odot } { yr } ^ { -1 } to \dot { M } \simeq ( 2.2 \pm 0.4 ) \times 10 ^ { -5 } { M } _ { \odot } { yr } ^ { -1 } , depending on the considered redenning .
In addition , our IR study could also be splitted in two parts : the identification of several features in the SWS ISO spectrum , and the modeling of the SED of CD-42 ^ { \circ } 11721 .
The first part shows the presence of many unindentified features and specially the presence of a mixed chemistry , i.e .
C- and O-rich dust in the same circumstellar medium .
The presence of specially C-rich dust could in principle favour a young nature , however this is not so clear , since also other evolved stars like e.g .
LBVs , show this kind of dust .
We have tried to model the SED , by using a numerical code written by us which considers a spherical circumstellar scenario .
Although the answer concerning the evolutionary stage of CD-42 ^ { \circ } 11721 is still not very clear , we believe that our analysis will improve the discussion about the nature of this curious star .