355 research outputs found
The PHASES Differential Astrometry Data Archive. I. Measurements and Description
The Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES)
monitored 51 sub-arcsecond binary systems to determine precision binary orbits,
study the geometries of triple and quadruple star systems, and discover
previously unknown faint astrometric companions as small as giant planets.
PHASES measurements made with the Palomar Testbed Interferometer (PTI) from
2002 until PTI ceased normal operations in late 2008 are presented. Infrared
differential photometry of several PHASES targets were measured with Keck
Adaptive Optics and are presented.Comment: 33 pages emulateapj, Accepted to A
Masses, luminosities, and orbital coplanarities of the ” Orionis quadruple-star system from phases differential astrometry
ÎŒ Orionis was identified by spectroscopic studies as a quadruple-star system. Seventeen high-precision differential astrometry measurements of ÎŒ Ori have been collected by the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES). These show both the motion of the long-period binary orbit and short-period perturbations superimposed on that caused by each of the components in the long-period system being themselves binaries. The new measurements enable the orientations of the long-period binary and short-period subsystems to be determined. Recent theoretical work predicts the distribution of relative inclinations between inner and outer orbits of hierarchical systems to peak near 40 and 140 degrees. The degree of coplanarity of this complex system is determined, and the angle between the planes of the AâB and AaâAb orbits is found to be 136.7 ± 8.3 degrees, near the predicted distribution peak at 140 degrees; this result is discussed in the context of the handful of systems with established mutual inclinations. The system distance and masses for each component are obtained from a combined fit of the PHASES astrometry and archival radial velocity observations. The component masses have relative precisions of 5% (component Aa), 15% (Ab), and 1.4% (each of Ba and Bb). The median size of the minor axes of the uncertainty ellipses for the new measurements is 20 micro-arcseconds (ÎŒas). Updated orbits for ÎŽ Equulei, Îș Pegasi, and V819 Herculis are also presented
The VAST Survey - III. The multiplicity of A-type stars within 75 pc
With a combination of adaptive optics imaging and a multi-epoch common proper
motion search, we have conducted a large volume-limited (D 75 pc)
multiplicity survey of A-type stars, sensitive to companions beyond 30 au. The
sample for the Volume-limited A-STar (VAST) survey consists of 435 A-type
stars: 363 stars were observed with adaptive optics, 228 stars were searched
for wide common proper motion companions and 156 stars were measured with both
techniques. The projected separation coverage of the VAST survey extends from
30 to 45,000 au. A total of 137 stellar companions were resolved, including 64
new detections from the VAST survey, and the companion star fraction, projected
separation distribution and mass ratio distribution were measured. The
separation distribution forms a log-normal distribution similar to the
solar-type binary distribution, but with a peak shifted to a significantly
wider value of 387 (+132,-98) au. Integrating the fit to the distribution over
the 30 to 10,000 au observed range, the companion star fraction for A-type
stars is estimated as 33.8%+-2.6%. The mass ratio distribution of closer (<125
au) binaries is distinct from that of wider systems, with a flat distribution
for close systems and a distribution that tends towards smaller mass ratios for
wider binaries. Combining this result with previous spectroscopic surveys of
A-type stars gives an estimate of the total companion star fraction of
68.9%+-7.0%. The most complete assessment of higher order multiples was
estimated from the 156-star subset of the VAST sample with both adaptive optics
and common proper motion measurements, combined with a literature search for
companions, yielding a lower limit on the frequency of single, binary, triple,
quadruple and quintuple A-type star systems of 56.4 (-4.0,+3.8), 32.1
(-3.5,+3.9), 9.0 (-1.8,+2.8), 1.9 (-0.6,+1.8) and 0.6 (-0.2,+1.4) per cent,
respectively.Comment: 46 pages, 24 figures. Accepted for publication in the Monthly Notices
of the Royal Astronomical Society, 7th October 201
Noninteracting Black Hole Binaries with Gaia and LAMOST
Until recently, black holes (BHs) could be discovered only through accretion
from other stars in X-ray binaries, or in merging double compact objects.
Improvements in astrometric and spectroscopic measurements have made it
possible to detect BHs also in non-interacting BH binaries (nBHB) through a
precise analysis of the companion's motion. In this study, using an updated
version of the Startrack binary-star population modelling code and a detailed
model of the Milky Way (MW) galaxy we calculate the expected number of
detections for Gaia and LAMOST surveys. We develop a formalism to convolve the
binary population synthesis output with a realistic stellar density
distribution, star-formation history (SFH), and chemical evolution for the MW,
which produces a probability distribution function of the predicted
compact-binary population over the MW. This avoids the additional statistical
uncertainty which is introduced by methods which Monte Carlo sample from binary
population synthesis output to produce one potential specific realisation of
the MW compact-binary distribution, and our method is also comparatively fast
to such Monte Carlo realisations. Specifically, we predict - nBHBs
to be observed by Gaia, although the numbers may drop to - if the
recent ( Myr) star formation is low (/yr ). For
LAMOST we predict detectable nBHBs, which is lower partially
because its field-of-view covers just of the Galaxy.Comment: 23 pages, 15 figures, 8 table
Masses, Luminosities, and Orbital Coplanarities of the mu Orionis Quadruple Star System from PHASES Differential Astrometry
mu Orionis was identified by spectroscopic studies as a quadruple star
system. Seventeen high precision differential astrometry measurements of mu Ori
have been collected by the Palomar High-precision Astrometric Search for
Exoplanet Systems (PHASES). These show both the motion of the long period
binary orbit and short period perturbations superimposed on that caused by each
of the components in the long period system being themselves binaries. The new
measurements enable the orientations of the long period binary and short period
subsystems to be determined. Recent theoretical work predicts the distribution
of relative inclinations between inner and outer orbits of hierarchical systems
to peak near 40 and 140 degrees. The degree of coplanarity of this complex
system is determined, and the angle between the planes of the A-B and Aa-Ab
orbits is found to be 136.7 +/- 8.3 degrees, near the predicted distribution
peak at 140 degrees; this result is discussed in the context of the handful of
systems with established mutual inclinations. The system distance and masses
for each component are obtained from a combined fit of the PHASES astrometry
and archival radial velocity observations. The component masses have relative
precisions of 5% (component Aa), 15% (Ab), and 1.4% (each of Ba and Bb). The
median size of the minor axes of the uncertainty ellipses for the new
measurements is 20 micro-arcseconds. Updated orbits for delta Equulei, kappa
Pegasi, and V819 Herculis are also presented.Comment: 12 Pages, Accepted for publication in A
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