122 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 Phases Differential Astrometry Data Archive. IV. The Triple Star Systems 63 Gem A and HR 2896
Differential astrometry measurements from the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES) are used to constrain the astrometric orbit of the previously known ≾2 day subsystem in the triple system 63 Gem A and have detected a previously unknown two-year Keplerian wobble superimposed on the visual orbit of the much longer period (213 years) binary system HR 2896. 63 Gem A was already known to be triple from spectroscopic work, and absorption lines from all three stars can be identified and their individual Doppler shifts measured; new velocities for all three components are presented to aid in constraining the orbit and measuring the stellar masses. In fact, 63 Gem itself is a sextuple system: the hierarchical triple (Aa1-Aa2)-Ab (in which Aa1 and Aa2 orbit each other with a rapid period just under 2 days, and Ab orbits these every two years), plus three distant common proper motion companions. The very small astrometric perturbation caused by the inner pair in 63 Gem A stretches the limits of current astrometric capabilities, but PHASES observations are able to constrain the orientation of the orbit. The two bright stars comprising the HR 2896 long-period (213 year) system have a combined spectral type of K0III and the newly detected object's mass estimate places it in the regime of being an M dwarf. The motion of the stars are slow enough that their spectral features are always blended, preventing Doppler studies. The PHASES measurements and radial velocities (when available) have been combined with lower precision single-aperture measurements covering a much longer time frame (from eyepiece measurements, speckle interferometry, and adaptive optics) to improve the characterization of the long-period orbits in both binaries. The visual orbits of the short- and long-period systems are presented for both systems and used to calculate two possible values of the mutual inclinations between inner and outer orbits of 152° ± 12° or a less likely value of 31° ± 11° for 63 Gem A and 10.°2 ± 2.°4 or 171.°2 ± 2.°8 for HR 2896. The first is not coplanar, whereas the second is either nearly coplanar or anti-coplanar
SB9: The Ninth Catalogue of Spectroscopic Binary Orbits
The Ninth Catalogue of Spectroscopic Binary Orbits
(http://sb9.astro.ulb.ac.be) continues the series of compilations of
spectroscopic orbits carried out over the past 35 years by Batten and
collaborators. As of 2004 May 1st, the new Catalogue holds orbits for 2,386
systems. Some essential differences between this catalogue and its predecessors
are outlined and three straightforward applications are presented: (1)
Completeness assessment: period distribution of SB1s and SB2s; (2) Shortest
periods across the H-R diagram; (3) Period-eccentricity relation.Comment: Accepte for publication in A&A, 6 pages, 6 figure
The PHASES Differential Astrometry Data Archive. V. Candidate Substellar Companions to Binary Systems
The Palomar High-precision Astrometric Search for Exoplanet Systems monitored
51 subarcsecond binary systems to evaluate whether tertiary companions as small
as Jovian planets orbited either the primary or secondary stars, perturbing
their otherwise smooth Keplerian motions. Six binaries are presented that show
evidence of substellar companions orbiting either the primary or secondary
star. Of these six systems, the likelihoods of two of the detected
perturbations to represent real objects are considered to be "high confidence",
while the remaining four systems are less certain and will require continued
observations for confirmation.Comment: 16 Pages, Accepted to A
SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits (http://sb9.astro.ulb.ac.be) continues the series of compilations of spectroscopic orbits carried out over the past 35 years by Batten and collaborators. As of 2004 May 1st, the new Catalogue holds orbits for 2386 systems. Some essential differences between this catalogue and its predecessors are out-lined and three straightforward applications are presented: (1) completeness assessment: period distribution of SB1s and SB2s; (2) shortest periods across the H-R diagram; (3) period-eccentricity relation.Facultad de Ciencias Astronómicas y Geofísica
First Results from the CHARA Array. II. A Description of the Instrument
The CHARA Array is a six 1-m telescope optical/IR interferometric array
located on Mount Wilson California, designed and built by the Center for High
Angular Resolution Astronomy of Georgia State University. In this paper we
describe the main elements of the Array hardware and software control systems
as well as the data reduction methods currently being used. Our plans for
upgrades in the near future are also described
The Multiplicity of Massive Stars: A High Angular Resolution Survey with the HST Fine Guidance Sensor
We present the results of an all-sky survey made with the Fine Guidance
Sensor on Hubble Space Telescope to search for angularly resolved binary
systems among the massive stars. The sample of 224 stars is comprised mainly of
Galactic O- and B-type stars and Luminous Blue Variables, plus a few luminous
stars in the Large Magellanic Cloud. The FGS TRANS mode observations are
sensitive to detection of companions with an angular separation between 0."01
and 1."0 and brighter than . The FGS observations resolved 52
binary and 6 triple star systems and detected partially resolved binaries in 7
additional targets (43 of these are new detections). These numbers yield a
companion detection frequency of 29% for the FGS survey. We also gathered
literature results on the numbers of close spectroscopic binaries and wider
astrometric binaries among the sample, and we present estimates of the
frequency of multiple systems and the companion frequency for subsets of stars
residing in clusters and associations, field stars, and runaway stars. These
results confirm the high multiplicity fraction, especially among massive stars
in clusters and associations. We show that the period distribution is
approximately flat in increments of log P. We identify a number of systems of
potential interest for long term orbital determinations, and we note the
importance of some of these companions for the interpretation of the radial
velocities and light curves of close binaries that have third companions.Comment: 37 pages, 4 figures, 5 tables; AJ, in press; Full version with
extended tables and large figure set can be found:
http://www.astro.umontreal.ca/~emily/fgs.pd
Abundances of metal-weak thick-disc candidates
High resolution spectra of 5 candidate metal-weak thick-disc stars suggested
by Beers & Sommer-Larsen (1995) are analyzed to determine their chemical
abundances. The low abundance of all the objects has been confirmed with
metallicity reaching [Fe/H]=-2.9. However, for three objects, the astrometric
data from the Hipparcos catalogue suggests they are true halo members. The
remaining two, for which proper-motion data are not available, may have
disc-like kinematics. It is therefore clear that it is useful to address
properties of putative metal-weak thick-disc stars only if they possess full
kinematic data. For CS 22894-19 the abundance pattern similar to those of
typical halo stars is found, suggesting that chemical composition is not a
useful discriminant between thick-disc and halo stars. CS 29529-12 is found to
be C enhanced with [C/Fe]=+1.0; other chemical peculiarities involve the s
process elements: [Sr/Fe]=-0.65 and [Ba/Fe]=+0.62, leading to a high [Ba/Sr]
considerably larger than what is found in more metal-rich carbon-rich stars,
but similar to LP 706-7 and LP 625-44 discussed by Norris et al (1997a).
Hipparcos data have been used to calculate the space velocities of 25 candidate
metal-weak thick-disc stars, thus allowing us to identify 3 bona fide members,
which support the existence of a metal-poor tail of the thick-disc, at variance
with a claim to the contrary by Ryan & Lambert (1995).Comment: to be published in MNRA
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