140 research outputs found
Observations of dusty torii and compact disks around evolved stars: the high spatial resolution IR view
International audienceThe recent high angular resolution observations have shown that the transition between a globally symmetrical giant and a source surrounded by a spatially complex environment occurs relatively early, as soon as the external layers of the stars are not tightly bound to the core of the star anymore. In this review, the emphasis will be put on the delineating the differences between the torus and disk classification through the presentation of many examples of near-IR and mid-IR high angular resolution observations. These examples cover the disks discovered in the core of some bipolar nebulae, post-AGB disks, the dusty environment around born-again stars and recent novae, and also the disks encountered around more massive evolved sources. We discuss the broad range of circumstances and time scales for which bipolar nebulae with disks are observed
High spatial resolution study of the inner environment around two young planetary nebulae
We present observations of the dusty emission from the young planetary
nebulae Hen2-113 and CPD-56 obtained with VLT/NACO, VLTI/MIDI. The central
stars of these two objects are Wolf-Rayet stars of the same spectral type
[WC10]. They share an impressive number of characteristics and are located at
similar distance, making the detection of any differences in their close
environment of great interest. Hen2-113 exhibits a clear ring-like structure of
about 0.4 arcsec in diameter, superimposed to a more diffuse environment
visible in L', M' and 8.7 micron bands. No clear core could be detected for
this object with MIDI through the N band. The dusty environment of CPD-568032
is much more compact, dominated by a bright, barely resolved, core whereas the
visible nebula exhibits an amazing complexity. From MIDI 8.7 micron acquisition
images (dominated by PAHs emission), the extension and geometry of the core
have been estimated and compared to the STIS/HST observations (De Marco et al.,
1997 and 2002). Moreover, high SNR fringes at low level have been detected with
projected baselines between 40 and 45 meters. This clear signal is interpreted
in terms of the bright inner rim of a dusty disk exposed to the flux from the
Wolf-Rayet star. The geometrical parameters of the N band flux distribution are
well constrained by means of simple geometrical models and a simple radiative
transfer model has been developed to extract the physical parameters of the
disk.Comment: Paper to be published in the procedings of the workshop: 'Stars with
the B[e] phenomenon', July 2005, Vlieland,Netherlan
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
Spectro-interferometric observations of interacting massive stars with VEGA/CHARA
We obtained spectro-interferometric observations in the visible of
Lyrae and Sgr using the instrument VEGA of the CHARA interferometric
array. For Lyrae, the dispersed fringe visibilities and differential
phases were obtained in spectral regions containing the H and HeI 6678
lines and the H and HeI 4921 lines. Whereas the source is unresolved in
the continuum, the source of the emission lines is resolved and the photocenter
of the bulk of the H emission exhibits offsets correlated with the
orbital phase. For Sgr, both the continuum and H sources are
resolved, but no clear binary signal is detected. The differential phase shift
across the line reveals that the bulk of the H emission is clearly
offset from the primary
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
Long Baseline Interferometry of Be Stars
We give an introduction to interferometrical concepts and their applicability
to Be stars. The first part of the paper concentrates on a short historic
overview and basic principles of two-beam interferometric observations. In the
second part, the VLTI/MIDI instrument is introduced and its first results on Be
stars, obtained on alpha Ara and delta Cen, are outlined.Comment: To appear in proceedings of the Astronomische Gesellshaft meeting,
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Interactions in massive binary stars as seen by interferometry
International audienceWith the advent of large-collecting-area instruments, the number of objects that can be reached by optical long-baseline interferometry is steadily increasing. We present here a few results on massive binary stars, showing the interest of using this technique for studying the insight of interactions in these systems. Indeed, many massive stars with extended environments host, or are suspected to host, companion stars. These companions could have an important role in shaping the circumstellar environment of the system. These examples provide a view in which binarity could be an ingredient, among many others, for the activity of these stars
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