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Papers by Bruno Castilho
Symposium - International Astronomical Union, 2000
Five giants and 11 subgiants of the metal-poor globular cluster NGC 6397 are analysed. In this Po... more Five giants and 11 subgiants of the metal-poor globular cluster NGC 6397 are analysed. In this Poster we present the lithium abundances derived. The present Li abundances and those of turnoff stars by Pasquini…
Astronomy & Astrophysics, 2002
We have investigated a group of stars known to have low chromospheric ages, but high kinematical ... more We have investigated a group of stars known to have low chromospheric ages, but high kinematical ages. Isochrone, chemical and lithium ages are estimated for them. The majority of stars in this group show lithium abundances much smaller than expected for their chromospheric ages, which is interpreted as an indication of their old age. Radial velocity measurements in the literature also show that they are not close binaries. The results suggest that they can be formed from the coalescence of short-period binaries. Coalescence rates, calculated taking into account several observational data and a maximum theoretical time scale for contact, in a short-period pair, predict a number of coalesced stars similar to what we have found in the solar neighbourhood.
Monthly Notices of the Royal Astronomical Society, 2005
Along with the spectral attenuation properties, the focal ratio degradation (FRD) properties of o... more Along with the spectral attenuation properties, the focal ratio degradation (FRD) properties of optical fibres are the most important for instrumental applications in astronomy. We present a special study about the FRD of optical fibres with a core size of 50 µm to evaluate the effects of stress when mounting the fibre. Optical fibres like this were used to construct the Eucalyptus integral field unit. This fibre is very susceptible to the FRD effects, especially after the removal of the acrylate buffer. This operation is sometimes necessary to allow close packing of the fibres at the input to the spectrograph. Without the acrylate buffer, the protection of the cladding and core of the fibre may be easily damaged. In the near future, fibres of this size will be used to build the Southern Observatory for Astronomical Research (SOAR) integral field unit spectrograph (SIFS) and other instruments. It is important to understand the correct procedure which minimizes any increase in FRD during the construction of the instrument.
Symposium - International Astronomical Union, 2000
Five giants and 11 subgiants of the metal-poor globular cluster NGC 6397 are analysed. In this Po... more Five giants and 11 subgiants of the metal-poor globular cluster NGC 6397 are analysed. In this Poster we present the lithium abundances derived. The present Li abundances and those of turnoff stars by Pasquini…
Astronomy & Astrophysics, 2002
We have investigated a group of stars known to have low chromospheric ages, but high kinematical ... more We have investigated a group of stars known to have low chromospheric ages, but high kinematical ages. Isochrone, chemical and lithium ages are estimated for them. The majority of stars in this group show lithium abundances much smaller than expected for their chromospheric ages, which is interpreted as an indication of their old age. Radial velocity measurements in the literature also show that they are not close binaries. The results suggest that they can be formed from the coalescence of short-period binaries. Coalescence rates, calculated taking into account several observational data and a maximum theoretical time scale for contact, in a short-period pair, predict a number of coalesced stars similar to what we have found in the solar neighbourhood.
Monthly Notices of the Royal Astronomical Society, 2005
Along with the spectral attenuation properties, the focal ratio degradation (FRD) properties of o... more Along with the spectral attenuation properties, the focal ratio degradation (FRD) properties of optical fibres are the most important for instrumental applications in astronomy. We present a special study about the FRD of optical fibres with a core size of 50 µm to evaluate the effects of stress when mounting the fibre. Optical fibres like this were used to construct the Eucalyptus integral field unit. This fibre is very susceptible to the FRD effects, especially after the removal of the acrylate buffer. This operation is sometimes necessary to allow close packing of the fibres at the input to the spectrograph. Without the acrylate buffer, the protection of the cladding and core of the fibre may be easily damaged. In the near future, fibres of this size will be used to build the Southern Observatory for Astronomical Research (SOAR) integral field unit spectrograph (SIFS) and other instruments. It is important to understand the correct procedure which minimizes any increase in FRD during the construction of the instrument.