19,313 research outputs found
Spectroscopic study of early-type multiple stellar systems II. New binary subsystems
Context. This work is part of a long-term spectroscopic study of a sample of
30 multiple stars with early-type components. In this second paper we present
the results of six multiple systems in which new stellar components have been
detected.
Aims. The main aim is to increase the knowledge of stellar properties and
dynamical structure of early-type multiple stellar systems.
Methods. Using spectroscopic observations taken over a time baseline of more
than 5 years we measured RVs by cross-correlations and applied a spectral
disentangling method to double-lined systems. Besides the discovery of objects
with double-lined spectra, the existence of new spectroscopic subsystems have
been inferred from the radial velocity variations of single-lined components
and through the variation of the barycentric velocity of double-lined
subsystems. Orbital elements have been calculated when possible.
Results. Seven new stellar components and two members that we expect to
confirm with new observations have been discovered in the six studied
multiples. We present orbital parameters for two double-lined binaries and
preliminary orbits for three single-lined spectroscopic binaries. Five of the
six analysed systems are quadruples, while the remaining has five components
distributed in four hierarchical levels. These multiplicity orders are in fact
lower limits, since these systems lack high-resolution visual observations and
additional hierarchical level might exist in that separation range.
Conclusions. The six analysed systems have greater multiplicity degree and a
more complex hierarchical structure than previously known, which suggests that
high-order multiple systems are significantly more frequent that it is
currently estimated. The long term spectroscopic monitoring of multiple systems
has shown to be useful for the detection of companions in intermediate
hierarchical levels.Comment: 13 pages, 9 figures. Accepted by Astronomy and Astrophysic
Obliquities of Kepler Stars: Comparison of Single- and Multiple-Transit Systems
The stellar obliquity of a transiting planetary system can be constrained by
combining measurements of the star's rotation period, radius, and projected
rotational velocity. Here we present a hierarchical Bayesian technique for
recovering the obliquity distribution of a population of transiting planetary
systems, and apply it to a sample of 70 Kepler Objects of Interest. With ~95%
confidence we find that the obliquities of stars with only a single detected
transiting planet are systematically larger than those with multiple detected
transiting planets. This suggests that a substantial fraction of Kepler's
single-transiting systems represent dynamically hotter, less orderly systems
than the "pancake-flat" multiple-transiting systems.Comment: 8 pages, 7 figures, accepted to Ap
New triple systems in the RasTyc sample of stellar X-ray sources
During the study of a large set of late-type stellar X-ray sources, we
discovered a large fraction of multiple systems. In this paper we investigate
the orbital elements and kinematic properties of three new spectroscopic triple
systems as well as spectral types and astrophysical parameters (T_eff, log g,
vsin i, log N(Li)) of their components. We conducted follow-up optical
observations, both photometric and spectroscopic at high resolution, of these
systems. We used a synthetic approach and the cross-correlation method to
derive most of the stellar parameters. We estimated reliable radial velocities
and deduced the orbital elements of the inner binaries. The comparison of the
observed spectra with synthetic composite ones, obtained as the weighted sum of
three spectra of non-active reference stars, allowed us to determine the
stellar parameters for each component of these systems. We found all are only
composed of main sequence stars. These three systems are certainly stable
hierarchical triples composed of short-period inner binaries plus a tertiary
component in a long-period orbit. From their kinematics and/or Lithium content,
these systems result to be fairly young.Comment: Accepted for publication in A&A (on July 22, 2008
Observations of Hierarchical Solar-Type Multiple Star Systems
Twenty multiple stellar systems with solar-type primaries were observed at
high angular resolution using the PALM-3000 adaptive optics system at the 5 m
Hale telescope. The goal was to complement the knowledge of hierarchical
multiplicity in the solar neighborhood by confirming recent discoveries by the
visible Robo-AO system with new near-infrared observations with PALM-3000. The
physical status of most, but not all, of the new pairs is confirmed by
photometry in the Ks band and new positional measurements. In addition, we
resolved for the first time five close sub-systems: the known astrometric
binary in HIP 17129AB, companions to the primaries of HIP 33555, and HIP
118213, and the companions to the secondaries in HIP 25300 and HIP 101430. We
place the components on a color-magnitude diagram and discuss each multiple
system individually.Comment: Accepted to Astronomical Journa
Limits on the primordial stellar multiplicity
Most stars - especially young stars - are observed to be in multiple systems.
Dynamical evolution is unable to pair stars efficiently, which leads to the
conclusion that star-forming cores must usually fragment into \geq 2 stars.
However, the dynamical decay of systems with \geq 3 or 4 stars would result in
a large single-star population that is not seen in the young stellar
population. Additionally, ejections would produce a significant population of
hard binaries that are not observed. This leads to a strong constraint on star
formation theories that cores must typically produce only 2 or 3 stars. This
conclusion is in sharp disagreement with the results of currently available
numerical simulations that follow the fragmentation of molecular cores and
typically predict the formation of 5--10 seeds per core. In addition, open
cluster remnants may account for the majority of observed highly hierarchical
higher-order multiple systems in the field.Comment: A&A in press, 5 pages (no figures
Multiple Stellar Evolution: a population synthesis algorithm to model the stellar, binary, and dynamical evolution of multiple-star systems
In recent years, observations have shown that multiple-star systems such as
hierarchical triple and quadruple-star systems are common, especially among
massive stars. They are potential sources of interesting astrophysical
phenomena such as compact object mergers, leading to supernovae, and
gravitational wave events. However, many uncertainties remain in their often
complex evolution. Here, we present the population synthesis code Multiple
Stellar Evolution (MSE), designed to rapidly model the stellar, binary, and
dynamical evolution of multiple-star systems. MSE includes a number of new
features not present in previous population synthesis codes: (1) an arbitrary
number of stars, as long as the initial system is hierarchical, (2) dynamic
switching between secular and direct N-body integration for efficient
computation of the gravitational dynamics, (3) treatment of mass transfer in
eccentric orbits, which occurs commonly in multiple-star systems, (4) a simple
treatment of tidal, common-envelope, and mass transfer evolution in which the
accretor is a binary instead of a single star, (5) taking into account planets
within the stellar system, and (6) including gravitational perturbations from
passing field stars. MSE, written primarily in the C++ language, will be made
publicly available and has few prerequisites; a convenient Python interface is
provided. We give a detailed description of MSE and illustrate how to use the
code in practice. We demonstrate its operation in a number of examples.Comment: Accepted for publication in MNRAS (fixed typos and updated
references). 35 pages, 8 figures. Code can be found at
https://github.com/hamers/ms
Proto-Brown Dwarf Disks as Products of Protostellar Disk Encounters
The formation of brown dwarfs via encounters between proto-stars has been
confirmed with high-resolution numerical simulations with a restricted
treatment of the thermal conditions. The new results indicate that young brown
dwarfs (BDs) formed this way are disk-like and often reside in multiple
systems. The newly-formed proto-BDs disks are up to 18 AU in size and spin
rapidly making small-scale bipolar outflows, fragmentation and the possible
formation of planetary companions likely as have recently been observed for
BDs. The object masses range from 2 to 73 Jupiter masses, distributed in a
manner consistent with the observed sub-stellar initial mass function. The
simulations usually form multiple BDs on eccentric orbits about a star. One
such system was hierarchical, a BD binary in orbit around a star, which may
explain recently observed hierarchical systems. One third of the BDs were
unbound after a few thousand years and interactions among orbiting BDs may
eject more or add to the number of binaries. Improvements over prior work
include resolution down to a Jupiter mass, self-consistent models of the
vertical structure of the initial disks and careful attention to avoid
artificial fragmentation.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
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