Search

We present the spectroscopic analysis of a large sample of late-M, L, and T dwarfs from the United Kingdom Deep Infrared Sky Survey. Using the YJHK photometry from the Large Area Survey and the red-optical photometry from the Sloan Digital Sky Survey we selected a sample of 262 brown dwarf candidates and we have followed-up 196 of them using the echelle spectrograph X-shooter on the Very Large Telescope. The large wavelength coverage (0.30-2.48 μm) and moderate resolution (R ~ 5000-9000) of X-shooter allowed us to identify peculiar objects including 22 blue L dwarfs, 2 blue T dwarfs, and 2 low-gravity M dwarfs. Using a spectral indices-based technique, we identified 27 unresolved binary candidates, for which we have determined the spectral type of the potential components via spectral deconvolution. The spectra allowed us to measure the equivalent width of the prominent absorption features and to compare them to atmospheric models. Cross-correlating the spectra with a radial velocity standard, we measured the radial velocity of our targets, and we determined the distribution of the sample, which is centred at -1.7 ± 1.2 km s-1 with a dispersion of 31.5 km s-1. Using our results, we estimated the space density of field brown dwarfs and compared it with the results of numerical simulations. Depending on the binary fraction, we found that there are (0.85 ± 0.55) × 10-3 to (1.00 ± 0.64) × 10-3 objects per cubic parsec in the L4-L6.5 range, (0.73 ± 0.47) × 10-3 to (0.85 ± 0.55) × 10-3 objects per cubic parsec in the L7-T0.5 range, and (0.74 ± 0.48) × 10-3 to (0.88 ± 0.56) × 10-3 objects per cubic parsec in the T1-T4.5 range. We notice that there seems to be an excess of objects in the L-T transition with respect to the late-T dwarfs, a discrepancy that could be explained assuming a higher binary fraction than expected for the L-T transition, or that objects in the high-mass end and low-mass end of this regime form in different environments, i.e. following different initial mass functions. [ABSTRACT FROM AUTHOR]

We have used the Two-Micron All-Sky Survey and the Wide-field Infrared Survey Explorer to look for ultracool dwarfs that are part of multiple systems containing main-sequence stars. We cross-matched L dwarf candidates from the surveys with Hipparcos and Gliese stars, finding two new systems. The first system, G255-34AB, is an L2 dwarf companion to a K8 star, at a distance of 36 pc. We estimate its bolometric luminosity as log L/L⊙ = −3.78 ± 0.045 and Teff = 2080 ± 260 K. The second system, GJ499ABC, is a triple, with an L5 dwarf as a companion to a binary with an M4 and K5 star. These two new systems bring the number of L dwarf plus main-sequence star multiple systems to 24, which we discuss. We consider the binary fraction for L dwarfs and main-sequence stars, and further assess possible unresolved multiplicity within the full companion sample. This analysis shows that some of the L dwarfs in this sample might actually be unresolved binaries themselves, since their MJ appears to be brighter than the expected for their spectral types. [ABSTRACT FROM AUTHOR]

Dyeing fibers at low temperatures has many advantages such as savings in energy and avoiding alterations to the physical properties of the fibers being dyed or other fibers also present in blends. The problem of low temperature dyeing in synthetic fibers is that it difficults the dye diffusion into the fiber. In the case of polyamide 6.6 microfibers, by using benzyl alcohol as an auxiliary dyeing, it was shown that good diffusion was obtained for the dye exhaustion with metal complex dyes at temperatures more than 30°C below the normal dyeing temperature for the dye exhaustion with metal complex dyes. Using thermal analysis methods these results were shown to be caused by the lowering of the Tg of the fiber when in the presence of benzyl alcohol. [ABSTRACT FROM AUTHOR]

The objective of our work has been the microencapsulation of dyes with lecithin from soybean, with the formation of liposomes, as a substitute for synthetic auxiliaries so as to improve the quality of the effluent. Current scenarios promote the disintegration and leakage of the liposomes, such as, changes in temperature, pH and the use of surfactants. Since dyeing process is a mix of all these parameters, we pretended to study each one separately. Rhodamine 6G fluorescence is known to be concentration quenched through the formation of non-fluorescent dimmers and, additionally, through the energy transfer from rhodamine monomer to these dimmers (Baptista ALF, Coutinho PJG, Real Oliveira MECD, Gomes JINR. Proceedings of 13th International Symposium of Surfactants, SIS 2000, Gainesville, USA, 2000). The temperature, the surfactant and pH induce a release of the encapsulated dye resulting in rhodamine dilution and consequently alterations in the dimerization/binding equilibrium. The experimental spectra indicate that rhodamine binds almost completely to liposomes. The decomposition of the rhodamine fluorescence spectra allowed us to determine the percentage of released dye during a simulated dyeing process, and allowed us to conclude that the dimerization process occurs mainly at the inner interfaces. The amount of dye released induced by temperature changes was greater in the presence of surfactant. [ABSTRACT FROM AUTHOR]

The objective of our work has been the microencapsulation of dyes with lecithin from soybean, with the formation of liposomes, as a substitute for synthetic auxiliaries so as to improve the quality of the effluent. Current scenarios promote the disintegration and leakage of the liposomes, such as, changes in temperature, pH, and the use of surfactants. Since dyeing process is a mix of all these parameters, we pretended to study each one separately. Changes in pH at constant temperature induce a release of dye similar with changes in temperature. In acid conditions, we found a very fast initial dye release which doesn't occur in basic conditions. Using carboxyfluorescein, as a pH fluorescence probe, we concluded that the liposome membrane doesn't protect the liposome interior from changes on the external pH. [ABSTRACT FROM AUTHOR]