541 research outputs found
HD 152246 - a new high-mass triple system and its basic properties
Analyses of multi-epoch, high-resolution (R ~ 50.000) optical spectra of the
O-type star HD 152246 (O9 IV according to the most recent classification),
complemented by a limited number of earlier published radial velocities, led to
the finding that the object is a hierarchical triple system, where a close
inner pair (Ba-Bb) with a slightly eccentric orbit (e = 0.11) and a period of
6.0049 days revolves in a 470-day highly eccentric orbit (e = 0.865) with
another massive and brighter component A. The mass ratio of the inner system
must be low since we were unable to find any traces of the secondary spectrum.
The mass ratio A/(Ba+Bb) is 0.89. The outer system has recently been resolved
using long-baseline interferometry on three occasions. The interferometry
confirms the spectroscopic results and specifies elements of the system. Our
orbital solutions, including the combined radial-velocity and interferometric
solution indicate an orbital inclination of the outer orbit of 112{\deg} and
stellar masses of 20.4 and 22.8 solar masses. We also disentangled the spectra
of components A and Ba and compare them to synthetic spectra from two
independent programmes, TLUSTY and FASTWIND. In either case, the fit was not
satisfactory and we postpone a better determination of the system properties
for a future study, after obtaining observations during the periastron passage
of the outer orbit (the nearest chance being March 2015). For the moment, we
can only conclude that component A is an O9 IV star with v*sin(i) = 210 +\- 10
km/s and effective temperature of 33000 +\- 500 K, while component Ba is an O9
V object with v*sin(i) = 65 +/- 3 km/s and T_eff = 33600 +\- 600 K.Comment: 9 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
A List of Bright Interferometric Calibrators measured at the ESO VLTI
In a previous publication (Richichi & Percheron 2005) we described a program
of observations of candidate calibrator stars at the ESO Very Large Telescope
Interferometer (VLTI), and presented the main results from a statistical point
of view. In the present paper, we concentrate on establishing a new homogeneous
group of bright interferometric calibrators, based entirely on publicly
available K-band VLTI observations carried out with the VINCI instrument up to
July 2004. For this, we have defined a number of selection criteria for the
quality and volume of the observations, and we have accordingly selected a list
of 17 primary and 47 secondary calibrators. We have developed an approach to a
robust global fit for the angular diameters using the whole volume of
quality-controlled data, largely independent of a priori assumptions. Our
results have been compared with direct measurements, and indirect estimates
based on spectrophotometric methods, and general agreement is found within the
combined uncertainties. The stars in our list cover the range K=-2.9 to +3.0
mag in brightness, and 1.3 to 20.5 milliarcseconds in uniform-disk diameter.
The relative accuracy of the angular diameter values is on average 0.4% and 2%
for the primary and secondary calibrators respectively. Our calibrators are
well suited for interferometric observations in the near-infrared on baselines
between ~20m and ~200m, and their accuracy is superior, at least for the
primary calibrators, to other similar catalogues. Therefore, the present list
of calibrators has the potential to lead to significantly improved
interferometric scientific results
Multiplicity of Galactic Cepheids from long-baseline interferometry. II. The Companion of AX Circini revealed with VLTI/PIONIER
Aims: We aim at detecting and characterizing the main-sequence companion of
the Cepheid AX Cir ( 18 yrs). The long-term objective is
to estimate the mass of both components and the distance to the system.
Methods: We used the PIONIER combiner at the VLT Interferometer to obtain the
first interferometric measurements of the short-period Cepheid AX Cir and its
orbiting component. Results: The companion is resolved by PIONIER at a
projected separation mas and projection angle . We measured -band flux ratios between the companion and
the Cepheid of % and %, respectively at a
pulsation phase for the Cepheid and 0.48. The lower contrast at
is due to increased brightness of the Cepheid compared to the
. This gives an average apparent magnitude mag. The limb-darkened angular diameter of the Cepheid at the
two pulsation phases was measured to be
mas and mas, respectively at and 0.48. A lower limit on the total mass of the system was also derived
based on our measured separation, we found .Comment: Accepted for publication in Astronomy and Astrophysic
Inner disk clearing around the Herbig Ae star HD\,139614: Evidence for a planet-induced gap ?
Spatially resolving the inner dust cavity of the transitional disks is a key
to understanding the connection between planetary formation and disk dispersal.
The disk around the Herbig star HD 139614 is of particular interest since it
presents a pretransitional nature with an au-sized gap, in the dust, that was
spatially resolved by mid-IR interferometry. Using new NIR interferometric
observations, we aim to characterize the 0.1-10~au region of the HD~139614 disk
further and identify viable mechanisms for the inner disk clearing. We report
the first multiwavelength radiative transfer modeling of the interferometric
data acquired on HD~139614 with PIONIER, AMBER, and MIDI, complemented by
Herschel/PACS photometries. We confirm a gap structure in the um-sized dust,
extending from about 2.5 au to 6 au, and constrained the properties of the
inner dust component: e.g., a radially increasing surface density profile, and
a depletion of 10^3 relative to the outer disk. Since self-shadowing and
photoevaporation appears unlikely to be responsible for the au-sized gap of
HD~139614, we thus tested if dynamical clearing could be a viable mechanism
using hydrodynamical simulations to predict the gaseous disk structure. Indeed,
a narrow au-sized gap is expected when a single giant planet interacts with the
disk. Assuming that small dust grains are well coupled to the gas, we found
that a ~ 3~Mjup planet located at 4.5 au from the star could, in less than 1
Myr, reproduce most of the aspects of the dust surface density profile, while
no significant depletion in gas occurred in the inner disk, in contrast to the
dust. However, the dust-depleted inner disk could be explained by the expected
dust filtration by the gap and the efficient dust growth/fragmentation in the
inner disk regions. Our results support the hypothesis of a giant planet
opening a gap and shaping the inner region of the HD~139614 disk.Comment: Version accepted in A&A, with typos corrections in the tex
Roche-lobe filling factor of mass-transferring red giants - the PIONIER view
Using the PIONIER visitor instrument that combines the light of the four
Auxiliary Telescopes of ESO's Very Large Telescope Interferometer, we measure
precisely the diameters of several symbiotic and related stars: HD 352, HD
190658, V1261 Ori, ER Del, FG Ser, and AG Peg. These diameters - in the range
of 0.6 to 2.3 milli-arcseconds - are used to assess the filling factor of the
Roche lobe of the mass-losing giants and provide indications on the nature of
the ongoing mass transfer. We also provide the first spectroscopic orbit of ER
Del, based on CORAVEL and HERMES/Mercator observations. The system is found to
have an eccentric orbit with a period of 5.7 years. In the case of the
symbiotic star FG Ser, we find that the diameter is changing by 13% over the
course of 41 days, while the observations of HD 352 are indicative of an
elongation. Both these stars are found to have a Roche filling factor close to
1, as is most likely the case for HD 190658 as well, while the three other
stars have factors below 0.5-0.6. Our observations reveal the power of
interferometry for the study of interacting binary stars - the main limitation
in our conclusions being the poorly known distances of the objects.Comment: A&A, in pres
The BinaMIcS project: understanding the origin of magnetic fields in massive stars through close binary systems
It is now well established that a fraction of the massive (M>8 Msun) star
population hosts strong, organised magnetic fields, most likely of fossil
origin. The details of the generation and evolution of these fields are still
poorly understood. The BinaMIcS project takes an important step towards the
understanding of the interplay between binarity and magnetism during the
stellar formation and evolution, and in particular the genesis of fossil
fields, by studying the magnetic properties of close binary systems. The
components of such systems are most likely formed together, at the same time
and in the same environment, and can therefore help us to disentangle the role
of initial conditions on the magnetic properties of the massive stars from
other competing effects such as age or rotation. We present here the main
scientific objectives of the BinaMIcS project, as well as preliminary results
from the first year of observations from the associated ESPaDOnS and Narval
spectropolarimetric surveys.Comment: To appear in New Windows on Massive Stars, proceedings of the IAU
Symposium 30
GG Tau: the fifth element
We aim at unveiling the observational imprint of physical mechanisms that
govern planetary formation in young, multiple systems. In particular, we
investigate the impact of tidal truncation on the inner circumstellar disks. We
observed the emblematic system GG Tau at high-angular resolution: a
hierarchical quadruple system composed of low-mass T Tauri binary stars
surrounded by a well-studied, massive circumbinary disk in Keplerian rotation.
We used the near-IR 4-telescope combiner PIONIER on the VLTI and
sparse-aperture-masking techniques on VLT/NaCo to probe this proto-planetary
system at sub-AU scales. We report the discovery of a significant closure-phase
signal in H and Ks bands that can be reproduced with an additional low-mass
companion orbiting GG Tau Ab, at a (projected) separation rho = 31.7 +/- 0.2mas
(4.4 au) and PA = 219.6 +/- 0.3deg. This finding offers a simple explanation
for several key questions in this system, including the missing-stellar-mass
problem and the asymmetry of continuum emission from the inner dust disks
observed at millimeter wavelengths. Composed of now five co-eval stars with
0.02 <= Mstar <= 0.7 Msun, the quintuple system GG Tau has become an ideal test
case to constrain stellar evolution models at young ages (few 10^6yr).Comment: 5pages, 3 figures, 1 appendix (online material
Multiplicity of massive O stars and evolutionary implications
Nearby companions alter the evolution of massive stars in binary systems.
Using a sample of Galactic massive stars in nearby young clusters, we
simultaneously measure all intrinsic binary characteristics relevant to
quantify the frequency and nature of binary interactions. We find a large
intrinsic binary fraction, a strong preference for short orbital periods and a
flat distribution for the mass-ratios. Our results do not support the presence
of a significant peak of equal-mass `twin' binaries. As a result of the
measured distributions, we find that over seventy per cent of all massive stars
exchange mass with a companion. Such a rate greatly exceeds previous estimates
and implies that the majority of massive stars have their evolution strongly
affected by interaction with a nearby companion.Comment: 4 pages, 2 figures. Conference proceedings to appear in "370 years of
astronomy in Utrecht
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