24 research outputs found
The High Angular Resolution Multiplicity of Massive Stars
We present the results of a speckle interferometric survey of Galactic
massive stars that complements and expands upon a similar survey made over a
decade ago. The speckle observations were made with the KPNO and CTIO 4 m
telescopes and USNO speckle camera, and they are sensitive to the detection of
binaries in the angular separation regime between 0.03" and 5" with relatively
bright companions (Delta V < 3). We report on the discovery of companions to 14
OB stars. In total we resolved companions of 41 of 385 O-stars (11%), 4 of 37
Wolf-Rayet stars (11%), and 89 of 139 B-stars (64%; an enriched visual binary
sample that we selected for future orbital determinations). We made a
statistical analysis of the binary frequency among the subsample that are
listed in the Galactic O Star Catalog by compiling published data on other
visual companions detected through adaptive optics studies and/or noted in the
Washington Double Star Catalog and by collecting published information on
radial velocities and spectroscopic binaries. We find that the binary frequency
is much higher among O-stars in clusters and associations compared to the
numbers for field and runaway O-stars, consistent with predictions for the
ejection processes for runaway stars. We present a first orbit for the O-star
Delta Orionis, a linear solution of the close, apparently optical, companion of
the O-star Iota Orionis, and an improved orbit of the Be star Delta Scorpii.
Finally, we list astrometric data for another 249 resolved and 221 unresolved
targets that are lower mass stars that we observed for various other science
programs.Comment: 76 pages, 6 figures, 11 table
The relevance of prior inclination determination for direct imaging of Earth-like planets
Direct imaging and characterization of extrasolar Earth-like planets is
strongly impacted by the orbital inclination of the planet to be studied, as a
combination of pure geometrical effects and the impact of exozodiacal dust.
Here, we perform simulations to quantify the impact of a priori knowledge of
inclination for the efficiency of a typical coronagraphic or occulter-based
mission. The relative impact and complementarity with prior knowledge of
exozodiacal brightness down to achievable levels is examined and discussed. It
is found that inclination has an even greater impact than the exozodiacal
brightness, though the two have excellent complementarity. We also discuss
different methods for inclination determination, and their respective
applicability to the context of precursor science to an imaging mission. It is
found that if technologically achievable, a combined effort to determine
inclinations and exozodiacal brightnesses with ground-based facilities would
substantially increase the efficiency of a space-based dedicated mission to
image and characterize Earth-like planets.Comment: 9 pages, 5 figures, accepted for publication in MNRA
An exact solution to determination of an open orbit
We present an exact solution of the equations for orbit determination of a
two body system in a hyperbolic or parabolic motion. In solving this problem,
we extend the method employed by Asada, Akasaka and Kasai (AAK) for a binary
system in an elliptic orbit. The solutions applicable to each of elliptic,
hyperbolic and parabolic orbits are obtained by the new approach, and they are
all expressed in an explicit form, remarkably, only in terms of elementary
functions. We show also that the solutions for an open orbit are recovered by
making a suitable transformation of the AAK solution for an elliptic case.Comment: 28 pages, text improved, references added; version accepted by
Celestial Mec
Multiplicity of late-type B stars with HgMn peculiarity
Observations at various wavelengths of late B-type stars exhibiting strong
overabundances of the chemical elements Hg and Mn in their atmospheres indicate
that these stars are frequently found in binary and multiple systems.
We intend to study the multiplicity of this type of chemically peculiar
stars, looking for visual companions in the range of angular separation between
0.05" and 8".
We carried out a survey of 56 stars using diffraction-limited near-infrared
imaging with NAOS-CONICA at the VLT.
Thirty-three companion candidates in 24 binaries, three triples, and one
quadruple system were detected. Nine companion candidates were found for the
first time in this study. Five objects are likely chance projections. The
detected companion candidates have K magnitudes between 5.95m and 18.07m and
angular separations ranging from <0.05" to 7.8", corresponding to linear
projected separations of 13.5-1700 AU.
Our study clearly confirms that HgMn stars are frequently members of binary
and multiple systems. Taking into account companions found by other techniques,
the multiplicity fraction in our sample may be as high as 91%. The membership
in binary and multiple systems seems to be a key point to understanding the
abundance patterns in these stars.Comment: 12 pages, 5 figures, 3 tables, accepted for publication in A&
Magnetic field measurements and wind-line variability of OB-type stars
Context. The first magnetic fields in O- and B-type stars that do not belong
to the Bp-star class, have been discovered. The cyclic UV wind-line
variability, which has been observed in a significant fraction of early-type
stars, is likely to be related to such magnetic fields. Aims. We attempt to
improve our understanding of massive-star magnetic fields, and observe
twenty-five carefully-selected, OB-type stars. Methods. Of these stars we
obtain 136 magnetic field strength measurements. We present the UV wind-line
variability of all selected targets and summarise spectropolarimetric
observations acquired using the MUSICOS spectropolarimeter, mounted at the TBL,
Pic du Midi, between December 1998 and November 2004. From the average Stokes I
and V line profiles, derived using the LSD method, we measure the magnetic
field strengths, radial velocities, and first moment of the line profiles.
Results. No significant magnetic field is detected in any OB-type star that we
observed. Typical 1{\sigma} errors are between 15 and 200 G. A possible
magnetic-field detection for the O9V star 10 Lac remains uncertain, because the
field measurements depend critically on the fringe- effect correction in the
Stokes V spectra. We find excess emission in UV-wind lines, centred about the
rest wavelength, to be a new indirect indicator of the presence of a magnetic
field in early B-type stars. The most promising candidates to host magnetic
fields are the B-type stars {\delta} Cet and 6 Cep, and a number of O stars.
Conclusions. Although some O and B stars have strong dipolar field, which cause
periodic variability in the UV wind-lines, such strong fields are not
widespread. If the variability observed in the UV wind-lines of OB stars is
generally caused by surface magnetic fields, these fields are either weak
(<~few hundred G) or localised.Comment: A&A publishe