399 research outputs found
Observation of double star by long-baseline interferometry
This paper serves as a reference on how to estimate the parameters of binary
stars and how to combine multiple techniques, namely astrometry, interferometry
and radial velocities.Comment: F. Millour, A. Chiavassa, L. Bigot, O. Chesneau, A. Meilland \& P.
Stee. What can the highest angular resolution bring to stellar astrophysics?,
69-70, EDP sciences, 2015, EAS publication series, 978-2-7598-1833-4.
\<10.1051/eas/1569020\>.
\<http://www.eas-journal.org/articles/eas/abs/2014/04/contents/contents.html\&g
VLTI/MIDI observations of 7 classical Be stars
We measured the mid-infrared extension of the gaseous disk surrounding seven
Be stars in order to constrain the geometry of their circumstellar environments
and to try to infer physical parameters characterizing these disks. We used the
VLTI/MIDI instrument with baselines up to 130 m to obtain an angular resolution
of about 15 mas in the N band and compared our results with previous K band
measurements obtained with the VLTI/AMBER instrument and/or the CHARA
interferometer. We obtained one calibrated visibility measurement for each of
the four stars, p Car, zeta Tau, kappa CMa, and alpha Col, two for delta Cen
and beta CMi, and three for alpha Ara. Almost all targets remain unresolved
even with the largest VLTI baseline of 130m, evidence that their circumstellar
disk extension is less than 10 mas. The only exception is alpha Ara, which is
clearly resolved and well-fitted by an elliptical envelope with a major axis
a=5.8+-0.8mas and an axis ratio a/b=2.4+-1 at 8 microns. This extension is
similar to the size and flattening measured with the VLTI/AMBER instrument in
the K band at 2 microns. The size of the circumstellar envelopes for these
classical Be stars does not seem to vary strongly on the observed wavelength
between 8 and 12microns. Moreover, the size and shape of Alpha Ara's disk is
almost identical at 2, 8, and 12microns
Resolving the dusty circumstellar environment of the A[e] supergiant HD 62623 with the VLTI/MIDI
B[e] stars are hot stars surrounded by circumstellar gas and dust responsible
for the presence of emission lines and IR-excess in their spectra. How dust can
be formed in this highly illuminated and diluted environment remains an open
issue. HD 62623 is one of the very few A-type supergiants showing the B[e]
phenomenon. We obtained nine calibrated visibility measurements using the
VLTI/MIDI instrument in SCI-PHOT mode and PRISM spectral dispersion mode with
projected baselines ranging from 13 to 71 m and with various position angles.
We used geometrical models and physical modeling with a radiative transfer code
to analyze these data. The dusty circumstellar environment of HD 62623 is
partially resolved by the VLTI/MIDI even with the shortest baselines. The
environment is flattened and can be separated into two components: a compact
one whose extension grows from 17 mas at 8 microns to 30 mas at 9.6 microns and
stays almost constant up to 13 microns, and a more extended one that is
over-resolved even with the shortest baselines. Using the radiative transfer
code MC3D, we managed to model HD 62623's circumstellar environment as a dusty
disk with an inner radius of 3.85+-0.6 AU, an inclination angle of 60+-10 deg,
and a mass of 2x10^-7Mo. It is the first time that the dusty disk inner rim of
a supergiant star exhibiting the B[e] phenomenon is significantly constrained.
The inner gaseous envelope likely contributes up to 20% to the total N band
flux and acts like a reprocessing disk. Finally, the hypothesis of a stellar
wind deceleration by the companion's gravitational effects remains the most
probable case since the bi-stability mechanism does not seem to be efficient
for this star.Comment: 13 pages, 11 figures. A&A accepted pape
B[e] stars at the highest angular resolution: the case of HD87643
New results on the B[e] star HD87643 are presented here. They were obtained
with a wide range of different instruments, from wide-field imaging with the
WFI camera, high resolution spectroscopy with the FEROS instrument, high
angular resolution imaging with the adaptive optics camera NACO, to the highest
angular resolution available with AMBER on the VLTI. We report the detection of
a companion to HD87643 with AMBER, subsequently confirmed in the NACO data.
Implications of that discovery to some of the previously
difficult-to-understand data-sets are then presented.Comment: To be published in the proceedings of the 2009 SF2A conferenc
Optical interferometry and adaptive optics of bright transients
Bright optical transients (i.e. transients typically visible with the naked
eye) are populated mainly by novae eruptions plus a few supernovae (among which
the SN1987a event). One bright nova happen every two years, either in the North
ot in the South hemisphere. It occurs that current interferometers have
matching sensitivities, with typically visible or infrared limiting magnitude
in the range 5--7. The temporal development of the fireball, followed by a dust
formation phase or the appearance of many coronal lines can be sudied with the
Very Large Telescope Interferometer. The detailed geometry of the first phases
of novae in outburst remains virtually unexplored. This paper summarizes the
work which has been done to date using the VLTI.Comment: Hot-wiring the transien Universe 3, Santa Fe : United States (2013
Differential interferometry of QSO broad line regions I: improving the reverberation mapping model fits and black hole mass estimates
Reverberation mapping estimates the size and kinematics of broad line regions
(BLR) in Quasars and type I AGNs. It yields size-luminosity relation, to make
QSOs standard cosmological candles, and mass-luminosity relation to study the
evolution of black holes and galaxies. The accuracy of these relations is
limited by the unknown geometry of the BLR clouds distribution and velocities.
We analyze the independent BLR structure constraints given by super-resolving
differential interferometry. We developed a three-dimensional BLR model to
compute all differential interferometry and reverberation mapping signals. We
extrapolate realistic noises from our successful observations of the QSO 3C273
with AMBER on the VLTI. These signals and noises quantify the differential
interferometry capacity to discriminate and measure BLR parameters including
angular size, thickness, spatial distribution of clouds, local-to-global and
radial-to-rotation velocity ratios, and finally central black hole mass and BLR
distance. A Markov Chain Monte Carlo model-fit, of data simulated for various
VLTI instruments, gives mass accuracies between 0.06 and 0.13 dex, to be
compared to 0.44 dex for reverberation mapping mass-luminosity fits. We
evaluate the number of QSOs accessible to measures with current (AMBER),
upcoming (GRAVITY) and possible (OASIS with new generation fringe trackers)
VLTI instruments. With available technology, the VLTI could resolve more than
60 BLRs, with a luminosity range larger than four decades, sufficient for a
good calibration of RM mass-luminosity laws, from an analysis of the variation
of BLR parameters with luminosity.Comment: 19 pages, 14 figures, accepted by MNRAS on December 5, 201
The binary Be star Scorpii at high spectral and spatial resolution : II The circumstellar disk evolution after the periastron
Classical Be stars are hot non-supergiant stars surrounded by a gaseous
circumstellar disk that is responsible for the observed infrared (IR) excess
and emission lines. The influence of binarity on these phenomena remains
controversial. We followed the evolution of the environment surrounding the
binary Be star Scorpii one year before and one year after the 2011
periastron to check for any evidence of a strong interaction between its
companion and the primary circumstellar disk. We used the VLTI/AMBER
spectro-interferometric instrument operating in the K band in high (12000)
spectral resolution to obtain information on both the disk geometry and
kinematics. Observations were carried out in two emission lines: Br
(2.172\,m) and \ion{He}{i} (2.056\,m). We detected some important
changes in Scorpii's circumstellar disk geometry between the first
observation made in April 2010 and the new observation made in June 2012.
During the last two years the disk has grown at a mean velocity of
0.2\,km\,s. This is compatible with the expansion velocity previously
found during the 2001-2007 period. The disk was also found to be asymmetric at
both epochs, but with a different morphology in 2010 and 2012. Considering the
available spectroscopic data showing that the main changes in the emission-line
profiles occurred quickly during the periastron, it is probable that the
differences between the 2010 and 2012 disk geometry seen in our interferometric
data stem from a disk perturbation caused by the companion tidal effects.
However, taking into account that no significant changes have occurred in the
disk since the end of the 2011 observing season, it is difficult to understand
how this induced inhomogeneity has been "frozen" in the disk for such a long
period.Comment: Astronomy and Astrophysics (2013
Probing the properties of Be star discs with spectroastrometry and NLTE radiative transfer modelling: beta CMi
While the presence of discs around classical Be stars is well established,
their origin is still uncertain. To understand what processes result in the
creation of these discs and how angular momentum is transported within them,
their physical properties must be constrained. This requires comparing high
spatial and spectral resolution data with detailed radiative transfer
modelling. We present a high spectral resolution, R~80,000, sub milli-arcsecond
precision, spectroastrometric study of the circumstellar disc around the Be
star beta CMi. The data are confronted with three-dimensional, NLTE radiative
transfer calculations to directly constrain the properties of the disc.
Furthermore, we compare the data to disc models featuring two velocity laws;
Keperian, the prediction of the viscous disc model, and angular momentum
conserving rotation. It is shown that the observations of beta CMi can only be
reproduced using Keplerian rotation. The agreement between the model and the
observed SED, polarisation and spectroastrometric signature of beta CMi
confirms that the discs around Be stars are well modelled as viscous decretion
discs.Comment: Accepted for publication in MNRA
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