We present absolute astrometry of four radio sources in the Becklin-Neugebauer/Kleinman-Low (BN/KL) region, derived from archival data (taken in 1991, 1995, and 2000) as well as from new observations (taken in 2006). All data consist of 3.6 cm continuum emission and were taken with the Very Large Array in its highest angular resolution A configuration. We confirm the large proper motions of the BN object, the radio source I (GMR I) and the radio counterpart of the infrared source n (Orion-n), with values from 15 to 26 km s −1 . The three sources are receding from a point between them from where they seem to have been ejected about 500 years ago, probably via the disintegration of a multiple stellar system. We present simulations of very compact stellar groups that provide a plausible dynamical scenario for the observations. The radio source Orion-n appeared as a double in the first three epochs, but as single in 2006. We discuss this morphological change. The fourth source in the region, GMR D, shows no statistically significant proper motions. We also present new, accurate relative astrometry between BN and radio source I that restrict possible dynamical scenarios for the region. During the 2006 observations, the radio source GMR A, located about 1 ′ to the NW of the BN/KL region, exhibited an increase in its flux density of a factor of ∼3.5 over a timescale of one hour. This rapid variability at cm wavelengths is similar to that previously found during a flare at millimeter wavelengths that took place in 2003.

We present absolute astrometry of 35 radio sources in the Orion Trapezium and Becklin-Neugebauer/Kleinman-Low regions, obtained from Very Large Array archival observations collected over a period of 15 years. By averaging the results for all the sources, we estimate the mean absolute proper motion of Orion to be -in Galactic coordinatesµ ℓ cos b = +2.1 ± 0.2 mas yr −1 ; µ b = −0.1 ± 0.2 mas yr −1 . These values agree remarkably well with those expected from the differential rotation of the Milky Way. Subtraction of this mean motion from the individual measurements allows us to register all proper motions to the rest frame of the Orion nebula, and identify radio sources with large residual velocities. In the KL region, we find three sources in this situation: the BN object, the radio source I, and the radio counterpart of the infrared source n. All three objects appear to be moving away from a common point where they must all have been located about 500 years ago. This suggests that all three sources were originally part of a multiple massive stellar system that recently disintegrated as a result of a close dynamical interaction.

We present absolute astrometry of the core of the Orion molecular cloud, made with Very Large Array archive data taken over the last two decades. Our analysis reveals that both the BN object and the radio source I have proper motions: the BN object has a proper motion of mas yr Ϫ1 (corresponding to a velocity of 12.6 ‫ע‬ 0.6 km s Ϫ1 at an adopted distance of 450 pc) to the northwest, while the radio source I has a proper motion 27 ‫ע‬ 1 of mas yr Ϫ1 (corresponding to a velocity of km s Ϫ1 ) to the southeast. The motion of the two 5.6 ‫ע‬ 0.7 12 ‫ע‬ 2 sources is nearly antiparallel, diverging from a point in between them, where they were located about 500 years ago. These results suggest that the BN object and the radio source I were part of a multiple young stellar system that disintegrated in the recent past.

No modern catalogue of wide binary and multiple systems (WBMS) exists for the region of the solar vicinity (stars nearer than ~22 pc), that include updated information on their membership to moving clusters and an age classification. With the aim of filling this gap, and also because of its importance for investigating the dynamical evolution of double and multiple systems, we have compiled a WBMS list extracted from the catalogues of nearby stars of Gliese (1969, also Gliese & Jahreiss 1979), as well as Luyten’s NLTT (Luyten 1979–1980, Luyten & Hughes 1980, see also Warren et al. 1989), the Bright Star Catalogue (Hoffleit 1982), the catalogue of Woolley et al. (1970) and other sources.By comparing the transverse velocities of WBM systems with those expected for members of the Hyades and Sirius Superclusters, membership of some WBMS to them has been established. We have classified as probably young systems (PYS) those with one component satisfying at least one of various criteria of youth. A system that is not a PYS is classified as probably old (POS).The catalogue contains 385 binaries and 85 systems of higher multiplicity. Out of these, 129 binaries are PYS and 256 are POS, while 32 multiples are PYS and 53 are POS.

We present a 4-planet Keplerian fit for the radial velocity curve of the F8V star υ Andromeda, indicating the presence of a fourth planet in the system. We detect an additional fifth coherent signal in the radial velocity curve which we attribute to stellar activity. The discovery of a new planet around υ Andromedae makes this system the fifth to contain, at least, four planets. These four planets have minimum masses of 0.69, 1.98, 4.13 and 1.06 M Jup and orbital periods of 4.62, 241.26, 1276.46 and 3848.9 days, respectively. We have numerically integrated the orbital solution for these four planets and find that the system is stable for at least 10 Myr. The orbit of the fourth planet coincides with an island of stability reported by Rivera & Haghighipour (2007, MNRAS, 374, 599). We find that the characteristics of the new fourth planet are very similar to those of Jupiter and that the planets in this system have very strong interactions with each other. As previously found, υ And−b and υ And−c are in apsidal alignment, while the orbit of the new planet (υ And−e) is close to an external 3:1 resonance with υ And−c.