Abstract. We continue our search, based on Hipparcos data, for stars which have encountered or will encounter the solar system (García-Sánchez et al. 1999). Hipparcos parallax and proper motion data are combined with ground-based radial velocity measurements to obtain the trajectories of stars relative to the solar system. We have integrated all trajectories using three different models of the galactic potential: a local potential model, a global potential model, and a perturbative potential model. The agreement between the models is generally very good. The time period over which our search for close passages is valid is about ±10 Myr. Based on the Hipparcos data, we find a frequency of stellar encounters within one parsec of the Sun of 2.3 ± 0.2 per Myr. However, we also find that the Hipparcos data is observationally incomplete. By comparing the Hipparcos observations with the stellar luminosity function for star systems within 50 pc of the Sun, we estimate that only about one-fifth of the stars or star systems were detected by Hipparcos. Correcting for this incompleteness, we obtain a value of 11.7 ± 1.3 stellar encounters per Myr within one pc of the Sun. We examine the ability of two future missions, FAME and GAIA, to extend the search for past and future stellar encounters with the Sun.

Abstract.We have compiled optical and radio astrometric data of the microquasar LS 5039 and derived its proper motion. This, together with the distance and radial velocity of the system, allows us to state that this source is escaping from its own regional standard of rest, with a total systemic velocity of about 150 km s −1 and a component perpendicular to the galactic plane larger than 100 km s −1 . This is probably the result of an acceleration obtained during the supernova event that created the compact object in this binary system. We have computed the trajectory of LS 5039 in the past, and searched for OB associations and supernova remnants in its path. In particular, we have studied the possible association between LS 5039 and the supernova remnant G016.8−01.1, which, despite our efforts, remains dubious. We have also discovered and studied an H i cavity in the ISM, which could have been created by the stellar wind of LS 5039 or by the progenitor of the compact object in the system. Finally, in the symmetric supernova explosion scenario, we estimate that at least 17 M were lost in order to produce the high eccentricity observed. Such a mass loss could also explain the observed runaway velocity of the microquasar.

We have combined Hipparcos proper motion and parallax data for nearby stars with ground-based radial velocity measurements to find stars which may have passed (or will pass) close enough to the Sun to perturb the Oort cloud.Close stellar encounters could deflect large numbers of comets into the inner solar system, which would increase the impact hazard at the Earth. We find that the rate of close approaches by star systems (single or multiple stars) within a distance D (in parsecs) from the Sun is given by N = 4.2 D2-O2 Myr-I, less than the numbers predicted by simple stellar dynamics models. However, we consider this a lower limit because of observational incompleteness in the Hipparcos data set. One star, Gliese 710, is estimated to have a closest approach of less than 0.4 parsec, and several stars come within about 1 parsec during about a f 1 0 Myr interval. We have performed dynamical simulations which show that none of the passing stars will perturb the Oort cloud sufficiently to create a substantial increase in the long-period comet flux at the Earth's orbit. We have begun a program to obtain radial velocities for stars in our sample with no previously published values.

[1] We use artificial neural networks (ANNs) to predict sea surface temperatures (SSTs) in the western Mediterranean Sea. The ANNs are trained with meteorological variables as input and concurrent satellite-derived SSTs as target. The trained ANNs predict well both the seasonal and the interannual variability of SST in that region. We also reproduce the impact of the heat wave that occurred during the summer of 2003 on the SSTs of the western Mediterranean Sea. The ANN technique allows us to predict SST maps in the western Alboran Sea for time coordinates before SST satellite availability. The presence and later partial collapse of the western Alboran gyre throughout 1980 is detected with good agreement by both the ANN predictions and the concurrent results from a 3-D circulation model. The same methodology is used to reconstruct incomplete SST satellite images. Citation: GarciaGorriz, E., and J. Garcia-Sanchez (2007), Prediction of sea surface temperatures in the western Mediterranean Sea by neural networks using satellite observations, Geophys.