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In this paper we present a study of chemical abundances in six star-forming regions. Stellar parameters and metallicities are derived using high-resolution, high S/N spectra of weak-line T-Tauri stars in each region. The results show that nearby star-forming regions have a very small abundance dispersion (only 0.033 dex in [Fe/H]). The average metallicity found is slightly below that of the Sun, although compatible with solar once the errors are taken into account. The derived abundances for Si and Ni show that the observed stars have the abundances typical of Galactic thin disk stars of the same metallicity. The impact of these observations is briefly discussed in the context of the Galactic chemical evolution, local inter-stellar medium abundances, and in the origin of metal-rich stars in the solar neighbourhood (namely, stars more likely to harbour planets). The implication for future planet-search programmes around very young, nearby stars is also discussed.

The effect of C12E8 (polyoxyethylene 8 lauryl ether) and sodium laurate on the structural properties of soybean lecithin vesicles was studied in different concentrations of surfactants, using the fluorescent probes NBD-PE (N-7-nitro-2,1,3-benzodiazoyl phosphatidylethanolamine) and N-Rh-PE (N-lissamine rhodamine B sulfonyl phosphatidylethanolamine). Direct energy transfer studies were carried out in labelled vesicles with addition of surfactants. Rhodamine emission with maximum at β585 nm was detected by excitation of NBD at λ = 473 nm. This fact is caused by direct energy transfer process from NBD to rhodamine. The yield of this process decreases with increasing amounts of surfactants, indicating that the average spatial separation of the lipid probes increases, as a result of the enlargement of the vesicle size and due to alteration of its structure to mixed micelles.

Exhaustion of a reactive dye for wool is studied in the presence of liposome-forming compounds (lecithin). Both analytical and commercial products are used as a source for the lecithin. Liposome formation is tested with different preparation procedures (ultrasound and mechanical agitation), and the stability is evaluated under different conditions of time, temperature, and the presence pf a tensoactive product. The effect of these different conditions and the variation of liposome concentration on exhaustion and levelness is presented. A practical method for dyeing wool with reactive dyes using liposome-forming compounds is proposed based on the results.

Context. The Vela Molecular Ridge hosts a number of young embedded star clusters at the same evolutionary stage.Aims. We test whether the fraction of members with a circumstellar disk in a sample of clusters in the cloud D of the Vela Molecular Ridge, is consistent with relations derived for larger samples of star clusters with an age spread. In addition, we constrain the age of the young embedded star clusters associated with cloud D.Methods. We carried out L(3.78 μm) photometry using images of six young embedded star clusters associated with cloud D of the Vela Molecular Ridge, taken with ISAAC at the VLT. These data are complemented with the available HKsphotometry. The 6 clusters are of roughly the same size and appear to be at the same evolutionary stage. The fraction of stars with a circumstellar disk was measured in each cluster by counting the fraction of sources found to have a NIR excess in colour-colour (HKsL) diagrams.Results. The Lphotometry allowed us to identify the NIR counterparts of the IRAS sources associated with the clusters. The fraction of stars with a circumstellar disk appears to be constant within the errors for the 6 clusters. There is a hint that this is lower for the most massive stars. The age of the clusters is constrained to be $\sim $1–2 Myr.Conclusions. The fraction of stars with a circumstellar disk in the observed sample is consistent with the relations derived from larger samples of star clusters and with other age estimates for cloud D. The fraction may be lower for the most massive stars. Our results agree with a scenario where all intermediate and low-mass stars form with a disk, whose lifetime is shorter for higher mass stars.

Context. The Vela Molecular Ridge hosts a number of young embedded star clusters at the same evolutionary stage.