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Paper: The Optical and IR Properties of Southern Galactic Unclassified B[e] Stars: The Case of CD-42°11721
Volume: 355, Stars With the B[e] Phenomenon
Page: 327
Authors: Borges Fernandes, M.; Lorenz Martins, S.; Kraus, M.; de Araujo F.X.
Abstract: 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 (Brazopolis, Brazil) and using public ISO and IRAS spectra. In this work we present the results for a curious star: CD−42°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. [OI], [OII], [NII] and [SII]. 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 dM/dt ≅ (4.4 ± 0.8) × 10−6MSolaryr−1 to dM/dt ≅ (2.2 ± 0.4) × 10−5MSolaryr−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°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°11721 is still not very clear, we believe that our analysis will improve the discussion about the nature of this curious star.
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