363 research outputs found
The long period eccentric orbit of the particle accelerator HD167971 revealed by long baseline interferometry
Using optical long baseline interferometry, we resolved for the first time
the two wide components of HD167971, a candidate hierarchical triple system
known to efficiently accelerate particles. Our multi-epoch VLTI observations
provide direct evidence for a gravitational link between the O8 supergiant and
the close eclipsing O + O binary. The separation varies from 8 to 15 mas over
the three-year baseline of our observations, suggesting that the components
evolve on a wide and very eccentric orbit (most probably e>0.5). These results
provide evidence that the wide orbit revealed by our study is not coplanar with
the orbit of the inner eclipsing binary. From our measurements of the
near-infrared luminosity ratio, we constrain the spectral classification of the
components in the close binary to be O6-O7, and confirm that these stars are
likely main-sequence objects. Our results are discussed in the context of the
bright non-thermal radio emission already reported for this system, and we
provide arguments in favour of a maximum radio emission coincident with
periastron passage. HD167971 turns out to be an efficient O-type particle
accelerator that constitutes a valuable target for future high angular
resolution radio imaging using VLBI facilities.Comment: 8 pages, including 4 figures, accepted by Monthly Notices of the
Royal Astronomical Societ
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
Imaging the dust sublimation front of a circumbinary disk
We present the first near-IR milli-arcsecond-scale image of a post-AGB binary
that is surrounded by hot circumbinary dust. A very rich interferometric data
set in six spectral channels was acquired of IRAS08544-4431 with the new RAPID
camera on the PIONIER beam combiner at the Very Large Telescope Interferometer
(VLTI). A broadband image in the \textit{H} band was reconstructed by combining
the data of all spectral channels using the SPARCO method. We spatially
separate all the building blocks of the IRAS08544-4431 system in our
milliarcsecond-resolution image. Our dissection reveals a dust sublimation
front that is strikingly similar to that expected in early-stage protoplanetary
disks, as well as an unexpected flux signal of 4\% from the secondary
star. The energy output from this companion indicates the presence of a compact
circum-companion accretion disk, which is likely the origin of the fast outflow
detected in H. Our image provides the most detailed view into the heart
of a dusty circumstellar disk to date. Our results demonstrate that binary
evolution processes and circumstellar disk evolution can be studied in detail
in space and over time.Comment: PR @ http://www.eso.org/public/news/eso1608
Ellipsoidal primary of the RS CVn binary zeta And: Investigation using high-resolution spectroscopy and optical interferometry
We have obtained high-resolution spectroscopy, optical interferometry, and
long-term broad band photometry of the ellipsoidal primary of the RS CVn-type
binary system zeta And. Based on the optical interferometry the apparent limb
darkened diameter of zeta And is 2.55 +/- 0.09 mas using a uniform disk fit.
The Hipparcos distance and the limb-darkened diameter obtained with a uniform
disk fit give stellar radius of 15.9 +/- 0.8 Rsolar, and combined with
bolometric luminosity, it implies an effective temperature of 4665 +/- 140 K.
The temperature maps obtained from high resolution spectra using Doppler
imaging show a strong belt of equatorial spots and hints of a cool polar cap.
The equatorial spots show a concentration around the phase 0.75. This spot
configuration is reminiscent of the one seen in the earlier published
temperature maps of zeta And. Investigation of the Halpha line reveals both
prominences and cool clouds in the chromosphere. Long-term photometry spanning
12 years shows hints of a spot activity cycle, which is also implied by the
Doppler images, but the cycle length cannot be reliably determined from the
current data.Comment: 9 pages, 9 figures, accepted for A&
The Three body system delta Circini
Delta Cir is known as an O7.5 III eclipsing and spectroscopic binary with an
eccentric orbit. Penny et al. discovered the presence of a third component in
the IUE spectra. The eclipsing binary and the third body revolve around a
common centre of gravity with a period of 1644 days in an eccentric orbit with
the semimajor axis of 10 AU. We demonstrate the presence of the apsidal-line
rotation with a period of about 141 years, which is considerably longer than
its theoretically predicted value, based on the published radii of the binary
components derived from the Hipparchos Hp light curve. However, our new
solution of the same light curve resulted in smaller radii and a better
agreement between the observed and predicted period of the apsidal- line
advance. There are indications that the third body is a binary. The object was
resolved by VLTI with the PIONIER combiner; in June 2012 the separation was
3.78 mas, magnitude difference in the H region 1.75 mag. This result means that
(assuming the distance 770 pc) the inclination of the long orbit is 87.7
degrees.Comment: Accepted for publication in the Astronomical Journa
Southern Massive Stars at High Angular Resolution: Observational Campaign and Companion Detection
Multiplicity is one of the most fundamental observable properties of massive
O-type stars and offers a promising way to discriminate between massive star
formation theories. Nevertheless, companions at separations between 1 and 100
mas remain mostly unknown due to intrinsic observational limitations. [...] The
Southern MAssive Stars at High angular resolution survey (SMASH+) was designed
to fill this gap by providing the first systematic interferometric survey of
Galactic massive stars. We observed 117 O-type stars with VLTI/PIONIER and 162
O-type stars with NACO/SAM, respectively probing the separation ranges 1-45 and
30-250mas and brightness contrasts of Delta H < 4 and Delta H < 5. Taking
advantage of NACO's field-of-view, we further uniformly searched for visual
companions in an 8''-radius down to Delta H = 8. This paper describes the
observations and data analysis, reports the discovery of almost 200 new
companions in the separation range from 1mas to 8'' and presents the catalog of
detections, including the first resolved measurements of over a dozen known
long-period spectroscopic binaries.
Excluding known runaway stars for which no companions are detected, 96
objects in our main sample (DEC < 0 deg; H<7.5) were observed both with PIONIER
and NACO/SAM. The fraction of these stars with at least one resolved companion
within 200mas is 0.53. Accounting for known but unresolved spectroscopic or
eclipsing companions, the multiplicity fraction at separation < 8'' increases
to f_m = 0.91 +/- 0.03. The fraction of luminosity class V stars that have a
bound companion reaches 100% at 30mas while their average number of physically
connected companions within 8'' is f_c = 2.2 +/- 0.3. This demonstrates that
massive stars form nearly exclusively in multiple systems. Additionally, the
nine non-thermal (NT) radio emitters observed by SMASH+ are all resolved [...]Comment: 57 pages, 20 figures, 7 tables; accepted for publication in ApJ
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
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