22 research outputs found
The Frequency Distribution of Semi-major Axis of Wide Binaries. Cosmogony and Dynamical Evolution
The frequency distribution f(a) of semi-major axis of double and multiple
systems, as well as their eccentricities and mass ratios, contain valuable
fossil information about the process of star formation and the dynamical
history of the systems. In order to advance in the understanding of these
questions, we have made an extensive analysis of the frequency distribution f
(a) for wide binaries (a>25 AU) in the various published catalogues, as well as
in our own (Poveda et al., 1994; Allen et al., 2000; Poveda & Hernandez, 2003).
Based upon all these studies we have established that the frequency f(a) is
function of the age of the system and follows Oepik's distribution f(a) ~ 1/a
in the range of 100 AU < a < a[c](t), where a[c](t) is a critical semi-major
axis beyond which binaries have dissociated by encounters with massive objects.
We argue that the physics behind the distribution f(a) ~ 1/a is a process of
energy relaxation, analogous to that present in stellar clusters (secular
relaxation) or in spherical galaxies (violent relaxation). The frequency
distribution of mass ratios in triple systems as well as the existence of
runaway stars, indicate that both types of relaxation are important in the
process of binary and multiple star formation.Comment: International Astronomical Union. Symposium no. 240, held 22-25
August, 2006 in Prague, Czech Republi
Dynamical decay of a massive multiple system in Orion KL?
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 coordinates-- = +2.1 0.2 mas
yr; = 0.1 0.2 mas yr. 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 dynamicalComment: Accepted for publication in the Ap
Monitoring the Large Proper Motions of Radio Sources in the Orion BN/KL Region
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. 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.Comment: Accepted for publication in Ap
The exo-planetary system of 55 Cancri and the TitiusâBode law, arXiv: 0803.2240 [astro-ph
The exo-planetary system of 55 cancri and the titius-bode law Revista Mexicana de AstronomĂa y AstrofĂsica, vol. 44, nĂșm. 1, abril, 2008, pp. 243-246 Instituto de AstronomĂa Distrito Federal, MĂ©xico ABSTRACT The recent discovery of a fifth planet bound to 55 Cancr