157 research outputs found
Formation of wide binary stars from adjacent cores
Wide gravitationally bound pairs of stars can be formed from adjacent
prestellar cores that happen to move slowly enough relative to each other.
These binaries are remnants of the primordial clustering. It is shown that the
expected fraction of wide bound pairs in low-density star formation regions can
be larger than the fraction of wide pairs in the field. On the other hand, wide
binaries do not form or survive in dense clusters. Recent works on the
separation distribution of young binaries, summarized here, confirm these
expectations. Alternative formation mechanisms of wide binaries such as cluster
dissolution or unfolding of triple stars cannot explain the large observed
fraction of young wide pairs and therefore are not dominant. The fact that more
than a half of wide pairs contain subsystems matches the general multiplicity
statistics and does not imply that hierarchical multiplicity and wide binaries
are genetically related.Comment: Accepted by MNRAS. 7 pages, 4 figures, 1 tabl
Spectroscopic subsystems in nearby wide binaries
Radial velocity (RV) monitoring of solar-type visual binaries has been
conducted at the CTIO/SMARTS 1.5-m telescope to study short-period systems.
Data reduction is described, mean and individual RVs of 163 observed objects
are given. New spectroscopic binaries are discovered or suspected in 17
objects, for some of them orbital periods could be determined. Subsystems are
efficiently detected even in a single observation by double lines and/or by the
RV difference between the components of visual binaries. The potential of this
detection technique is quantified by simulation and used for statistical
assessment of 96 wide binaries within 67pc. It is found that 43 binaries
contain at least one subsystem and the occurrence of subsystems is equally
probable in either primary or secondary components. The frequency of subsystems
and their periods match the simple prescription proposed by the author (2014,
AJ, 147, 87). The remaining 53 simple wide binaries with a median projected
separation of 1300AU have the distribution of the RV difference between their
components that is not compatible with the thermal eccentricity distribution
f(e)=2e but rather matches the uniform eccentricity distribution.Comment: Accepted by Astronomical Journal. 10 pages, 7 figures, 1 electronic
tabl
Imaging survey of subsystems in secondary components to nearby southern dwarfs
To improve the statistics of hierarchical multiplicity, secondary components
of wide nearby binaries with solar-type primaries were surveyed at the SOAR
telescope for evaluating the frequency of subsystems. Images of 17 faint
secondaries were obtained with the SOAR Adaptive Module that improved the
seeing; one new 0.2" binary was detected. For all targets, photometry in the
g', i', z' bands is given. Another 46 secondaries were observed by speckle
interferometry, resolving 7 close subsystems. Adding literature data, the
binarity of 95 secondary components is evaluated. We found that the
detection-corrected frequency of secondary subsystems with periods in the
well-surveyed range from 10^3 to 10^5 days is 0.21+-0.06, same as the normal
frequency of such binaries among solar-type stars, 0.18. This indicates that
wide binaries are unlikely to be produced by dynamical evolution of N-body
systems, but are rather formed by fragmentation.Comment: Accepted by the Astronomical Journal; 7 pages, 7 figure
From binaries to multiples I: Data on F and G dwarfs within 67 pc of the Sun
Data on the multiplicity of F- and G-type dwarf stars within 67pc of the Sun
are presented. This distance-limited sample based on the Hipparcos catalog
contains 4847 primary stars (targets) with 0.590% complete.
There are 2196 known stellar pairs, some of them belong to 361 hierarchical
systems from triples to quintuples. Models of companion detection by radial
velocity, astrometric acceleration, direct resolution, and common proper motion
are developed. They serve to compute completeness for each target, using the
information on its coverage collected here. About 80% of companions to the
primary stars are detected, but the census of sub-systems in the secondary
components is only about 30%. Masses of binary components are estimated from
their absolute magnitudes or by other methods, the periods of wide pairs are
evaluated from their projected separations. A third of binaries with periods
shorter than ~100yr are spectroscopic and/or astrometric pairs with yet unknown
periods and mass ratios. These data are used in the accompanying Paper II to
derive unbiased statistics of hierarchical multiple systems.Comment: Accepted by AJ. 14 pages, 12 figures. Full tables are available at
http://www.ctio.noao.edu/~atokovin/papers/multiples-tables.tar.g
Spectroscopic orbits of subsystems in multiple stars. III
Spectroscopic orbits are computed for inner pairs in six nearby hierarchical
multiple systems (HIP 35733, 95106/95110, 105441, 105585/105569, 105947, and
109951). Radial velocities and resolved measurements, when available, are used
to derive combined sets of outer orbital elements for three systems. Each
multiple system is discussed individually. Additionally, HIP 115087 is a simple
7.9 day single-lined binary. Although the minimum companion mass is sub-stellar
(in the brown dwarf desert regime), it appears to be a 0.2 solar-mass star in a
low-inclination orbit.Comment: Accepted by AJ. 7 pages, 5 figures. Electronic tables are available
from the author upon reques
Orbits of four young triple-lined multiple systems
Each of the nearby triple systems HIP 7601, 13498, 23824, and 113597 (HD
10800, 18198, 35877, 217389) consists of solar-type dwarfs with comparable
masses, where all three components are resolved spectrally, while the outer
pairs are resolved both visually and spectrally. These stars are relatively
young (between 100 and 600 Myr) and chromospherically active (X-ray sources),
although they rotate slowly. Spectroscopic orbits of the inner subsystems
(periods 19.4, 14.1, 5.6, 20.3 days) and orbits of the outer systems (periods
1.75, 51, 27, 500 yrs, respectively) are determined. For HIP 7601 and 13498,
the combined spectro-interferometric outer orbits produce direct measurement of
masses of all components, allowing comparison with stellar models. The 6708A
lithium line is present and its strength is measured in each component
individually by subtracting the contributions of other components. The inner
and outer orbits of HIP 7601 are nearly circular, likely co-planar, and have a
modest period ratio of 1:33. This study contributes to the characterization of
hierarchical multiplicity in the solar neighborhood and provides data for
testing stellar evolutionary models and chronology.Comment: Accepted by the Astronomical Journal. 16 pages, 14 figures, 10 tabl
Kappa Fornaci, a triple radio-star
Bright and nearby (22pc) solar-type dwarf Kappa Fornaci (HIP 11072) is a
triple system. The close pair of M-type dwarfs Ba,Bb with a tentative period of
3.7 days moves around the main component A on a 26-year orbit. The mass of the
"dark companion" Ba+Bb is comparable to the mass of A, causing large motion of
the photo-center. The combined spectro-interferometric orbit of AB is derived
and the relative photometry of the components A and B is given. A weak
signature of Ba and Bb is detected in the high-resolution spectra by
cross-correlation and by variable emission in the Bahlmer hydrogen lines. The
activity of the M-dwarfs, manifested by a previously detected radio-flare, is
likely maintained by synchronization with their tight orbit. We discuss the
frequency of similar hidden triple systems, methods of their detection, and the
implications for multiple-star statistics.Comment: Accepted by AJ. 7 pages, 5 figures, 5 table
Dancing twins: stellar hierarchies that formed sequentially?
This paper attracts attention to the class of resolved triple stars with
moderate ratios of inner and outer periods (possibly in a mean motion
resonance) and nearly circular, mutually aligned orbits. Moreover, stars in the
inner pair are twins with almost identical masses, while the mass sum of the
inner pair is comparable to the mass of the outer component. Such systems could
be formed either sequentially (inside-out) by disk fragmentation with
subsequent accretion and migration or by a cascade hierarchical fragmentation
of a rotating cloud. Orbits of the outer and inner subsystems are computed or
updated in four such hierarchies: LHS 1070 (GJ 2005, periods 77.6 and 17.25
years), HIP 9497 (80 and 14.4 years), HIP 25240 (1200 and 47.0 years), and HIP
78842 (131 and 10.5 years).Comment: 8 pages, 7 figures, 4 tables. Accepted by Astronomical Journa
Ten years of speckle interferometry at SOAR
Since 2007, close binary and multiple stars are observed by speckle
interferometry at the 4.1 m Southern Astrophysical Research (SOAR) telescope.
The HRCam instrument, observing strategy and planning, data processing and
calibration methods, developed and improved during ten years, are presented
here in a concise way. Thousands of binary stars were measured with
diffraction-limited resolution (29mas at 540nm wavelength) and a high accuracy
reaching 1mas; two hundred new pairs or subsystems were discovered. To date,
HRCam has performed over 11000 observations with a high efficiency (up to 300
stars per night). An overview of the main results delivered by this instrument
is given.Comment: Accepted by PASP. 12 pages, 11 figure
Orbits of subsystems in four hierarchical multiple stars
Seven spectroscopic orbits in nearby solar-type multiple stars are presented.
The primary of the chromospherically active star HIP 9642 is a 4.8-day
double-lined pair; the outer 420-yr visual orbit is updated, but remains poorly
constrained. HIP 12780 is a quadruple system consisting of the resolved 6.7-yr
pair FIN 379 Aa,Ab, for which the combined orbit, masses, and orbital parallax
are determined here, and the single-lined binary Ba,Bb with a period of 27.8
days. HIP 28790 is a young quintuple system composed of two close binaries
Aa,Ab and Ba,Bb with periods of 221 and 13 days, respectively, and a single
distant component C. Its subsystem Ba,Bb is peculiar, having the spectroscopic
mass ratio of 0.89 but a magnitude difference of ~2.2 mag. HIP 64478 also
contains five stars: the A-component is a 29-year visual pair with a previously
known 4-day twin subsystem, while the B-component is a contact binary with a
period of 5.8 hours, seen nearly pole-on.Comment: Accepted by Astronomical Journal. 12 pages, 10 figures, 6 table
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