Enrique Solano

Young stars and brown dwarfs surrounding Alnilam (

Aims: We look for new regions for the search of substellar objects. Methods: Two circular areas, 45 arcmin-radius each, centred on the young massive star systems Alnilam and Mintaka in the Orion Belt, have been explored. The regions are very young (less than 10 Ma), have low extinction, and are neighbours to sigma Orionis (~3 Ma), a young open cluster very rich in brown dwarfs and planetary-mass objects. We have used Virtual Observatory tools, the astro-photometric Tycho-2, DENIS and 2MASS catalogues, 10 control fields at similar galactic latitudes, and X-ray, mid-infrared and spectroscopic data from the literature. Results: We have compiled exhaustive lists of known young stars and new candidate members in the Ori OB1b association, and of fore- and background sources. A total of 136 stars display features of extreme youth, like early spectral types, lithium in absorption, or mid-infrared flux excess. Other two young brown dwarf and 289 star candidates have been identified from an optical/near-infrared colour-magnitude diagram. We list additional 74 known objects that might belong to the association. This catalogue can serve as an input for characterisation of the stellar and high-mass substellar populations in the Orion Belt. Finally, we have investigated the surface densities and radial distributions of young objects surrounding Alnilam and Mintaka, and compared them with those in the sigma Orionis cluster. We report a new open cluster centred on Mintaka. Conclusions: Both regions can be analogs to the sigma Orionis cluster, but more massive, more extended, slightly older, and less radially concentrated.

\epsilon

This is the first of two papers whose main goal is to update and improve the information available on the physical properties of the λ Bootis stars. The determination of the stellar parameters is of fundamental importance to shed light into the different theories proposed to explain the λ Bootis phenomenon. With this aim, projected rotational velocities, effective temperatures, surface gravities and chemical abundances of a sample of suspected λ Bootis stars have been calculated. Five objects showing composite spectra typical of binary systems were found in our analysis. The abundance distribution of the program stars does not resemble the chemical composition of the class prototype, λ Boo, which poses some concerns regarding the idea of a well-defined, chemically homogeneous group of stars. A possible relation between rotational velocities and the λ Bootis phenomenon has been found. This result would be in agreement with the accretion scenario proposed by Turcotte & Charbonneau ([CITE]).

Orionis) and Mintaka (

We have serendipitously discovered a previously unknown, bright source (BT = 11.75 ± 0.07 mag) with a very blue VT - Ks color, which we have named Albus 1. A photometric and astrometric study using Virtual Observatory tools has shown that it possesses an appreciable proper motion and magnitudes and colors very similar to those of the well-known white dwarf G191-B2B. We consider Albus 1 as a DA-type white dwarf located at about 40 pc. If its nature is confirmed, Albus 1 would be the sixth brightest isolated white dwarf in the sky, which would make it an excellent spectrophotometric standard.

\delta

We describe here the main capabilities of the COROT archive. The archive (http://sdc.laeff.inta.es/corotfa/jsp/searchform.jsp), managed at LAEFF in the framework of the Spanish Virtual Observatory (http://svo.laeff.inta.es), has been developed following the standards and requirements defined by IVOA (http://www.ivoa.net). The COROT archive at LAEFF will be publicly available by the end of 2008.

Orionis)

INTEGRAL, COROT and, in the near future, KEPLER and GAIA, are missions that are producing, or will produce, light curves as we have never seen before, because of their quantity or quality. The exploitation of the scientific potential hidden in these datasets is limited by size of the dataflows. For example, visual classification of the≈108 GAIA light curves is infeasible for any research team. Supervised classification of light curves has been one of the main research lines in the Spanish Virtual Observatory, and we are now co-leading the data analysis work group for the CoRoT mission. In this contribution we show the development of an automatic multistage classification system based on bayesian networks for the OMC (Optical Monitoring Camera) data. OMC is an optical camera on board ESA’s INTEGRAL, whose data archive is managed in the LAEFF Scientific Data Center (http://sdc.laeff.inta.es/omc).

Physical parameters of

In this paper we describe three lines of work that are being developed in the framework of the Spanish Virtual Observatory.

\mathsf{\lambda}

An analysis of the stars included in the catalogue of λ Bootis by Paunzen et al. (1997) and with IUE Low Resolution observations is presented here. Using line-ratios of carbon to heavier elements (Al and Ni) allows us to establish unambiguous membership criteria for the λ Bootis group. These criteria have been used to look for new λ Bootis candidates in the IUE Final Archive.