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Our objective is to develop of the mid-infrared imaging for the VLTI. Several areas of astrophysics will benefit of this new capability. APreS-MIDI comprises a beam combiner which interfaces with the current MIDI instrument. It thus constitutes an extension to the two-beam interferometric instrument MIDI by increasing the number of recombined beams up to four. This extension provides better uv-coverage (6 visibility points measured in one set) and moreover will allow measurement of 4 closure phase relations thus providing for the first time aperture synthesis images in the mid-infrared spectral regime. The mid-infrared spectral domain is very relevant for the study of the environments of various astrophysical sources. The science cases are broad. There are illustrated in the first part of this article by the perspective of imaging the circumstellar discs of young stellar objects. The APreS-MIDI instrument is described in a second part of this article. [ABSTRACT FROM AUTHOR]

We report on interferometry of the high-mass young stellar object M8E-IR performed with MIDI at the ESO-VLTI. The observations were carried out using the UT1-UT3 and UT2-UT3 baselines. The visibilities in the 8...13 micron range derived from the spectrally dispersed fringes indicate the presence of circumstellar emission presumably originating from warm dust. We resolve the MIR emission of M8E-IR and derive an extension between 15 and 30mas which correspond to linear sizes of 30-50AU at the distance of the source. These are the scales at which circumstellar disks around massive stars are expected. We discuss the properties of the dust envelope based on the results of our preliminary model and in the context of supplementary NACO observations. [ABSTRACT FROM AUTHOR]

The young stellar object MWC297 is a B1.5Ve star exhibiting strong hydrogen emission lines. This object has been observed by the AMBER/VLTI instrument in 2-telescope mode in a sub-region of the K spectral band centered around the Brγ line at 2.1656μm. The object has not only been resolved in the continuum with a visibility of 0.50±0.10, but also in the Brγ line, where the flux is about twice larger, with a visibility about twice smaller (0.33±0.06). The continuum emission is consistent with the expectation of an optically thick thermal emission from dust in a circumstellar disk. The hydrogen emission can be understood by the emission of a halo above the disk surface. It can be modelled as a latitudinal-dependant wind model and it explains the width, the strength and the visibibility through the emission lines. The AMBER data associated with a high resolution ISAAC spectrum constrains the apparent size of the wind but also its kinematics [ABSTRACT FROM AUTHOR]

The mechanism driving dust production in massive stars remains somewhat mysterious. However, recent aperture-masking and interferometric observations of late-type WC Wolf-Rayet (WR) stars strongly support the theory that dust formation in these objects is a result of colliding winds in binaries. Consistent with this theory, there is also evidence that suggests the prototypical Luminous Blue Variable (LBV) star, Eta Carinae, is a binary. To explore and quantify this possible explanation, we have conducted a high resolution interferometric survey of late-type massive stars utilizing the VLTI, Keck, and IOTA interferometers. We present here the motivation for this study as well as the first results from the MIDI instrument on the VLTI. (Details of the Keck Interferometer and IOTA interferometer observations are discussed in this workshop by Rajagopal et al.). Our VLTI study is aimed primarily at resolving and characterizing the dust around the WC9 star WR 85a and the LBV WR 122, both dust-producing but at different phases of massive star evolution. The pectrally-dispersed visibilities obtained with the MIDI observations will provide the first steps towards answering many outstanding issues in our understanding of this critical phase of massive star evolution [ABSTRACT FROM AUTHOR]

We present interferometric observations of the Be star 51 Ophiuchi. These observations were obtained during the science demonstration phase of the MIDI instrument at the VLTI in June 2003. The baseline UT1-UT3 was used, corresponding to 102 m. It is currently known that this object presents a circumstellar dust and gas disk that shows a very different composition from other Herbig Ae disks. The nature of the 51 Oph system is still a mystery to be solved. Observations with MIDI at the VLTI allowed us to reach high-angular resolution (20 mas). We have several uv points that allowed us to constrain the disk model. We have modeled 51 Oph visibilities and were able to constrain the size and geometry of the 51 Oph circumstellar disk. [ABSTRACT FROM AUTHOR]

AMBER is the first near infrared focal instrument of the VLTI. It combines three telescopes and produces spectrally resolved interferometric measures. This paper discusses some preliminary results of the first scientific observations of AMBER with three Unit Telescopes at medium (1500) and high (12000) spectral resolution. We derive a first set of constraints on the structure of the circumstellar material around the Wolf Rayet γ2 Velorum and the LBV η Carinae. [ABSTRACT FROM AUTHOR]

The core of the nebula surrounding Eta Carinae has recently been observed with VLT/NACO, VLTI/VINCI, VLTI/MIDI and VLTI/AMBER in order to spatially and spectrally constrain the warm dusty environment and the central object. Narrow-band images at 3.74 μm and 4.05 μm reveal the structured butterfly-shaped dusty environment close to the central star with an unprecedented spatial resolution of about 60 mas. VINCI has resolved the present-day stellar wind of Eta Carinae on a scale of several stellar radii owing to the spatial resolution of the order of 5 mas (~ 11 AU). The VINCI observations show that the object is elongated with a de-projected axis ratio of approximately 1.5. Moreover the major axis is aligned with that of the large bipolar nebula that was ejected in the 19th century. Fringes have also been obtained in the Mid-IR with MIDI using baselines of 75m. A peak of correlated flux of 100 Jy is detected 0.3" south-east from the photocenter of the nebula at 8.7 μm is detected. This correlated flux is partly attributed to the central object but it is worth noting that at these wavelengths, virtually all the 0.5" x 0.5" central area can generate detectable fringes witnessing the large clumping of the dusty ejecta. These observations provide an upper limit for the SED of the central source from 3.8 μm to 13.5 μm and constrain some parameters of the stellar wind which can be compared to Hillier's model. Lastly, we present the great potential of the AMBER instrument to study the numerous near-IR emissive lines from the star and its close vicinity. In particular, we discuss its ability to detect and follow the faint companion. [ABSTRACT FROM AUTHOR]

A new version of ASPRO "Virtual observatory" companion tool looking for possible calibrators in the vicinity of a science object has been released. This user dedicated software creates an evolutive catalog of stars giving the useful information for the selection of calibrators with respect to the requirements of the astrophysical program and of the instrumental configuration. SearchCal (for Search Calibrators) includes an K-Band (for AMBER) and an N-Band (for MIDI) calibrator search. It can be found on the JMMC Web site: http://mariotti.fr/aspro_page.htm [ABSTRACT FROM AUTHOR]

Until now, most interpretations have been limited to spherical geometry (or axisymmetric one when a dust torus is seen for instance). However, many measurements (polarisation, high resolution imagery...) have already showed that dust shells may deviate from spherical symmetry. We present here some scientific cases concerning evolved stars. The APreS-MIDI beam combiner presented elsewhere in these proceedings: Lopez et al.) will allow image reconstruction of these circumstellar environments of different families of evolved stars. [ABSTRACT FROM AUTHOR]

We present observations of the dusty emission from the planetary nebulae CPD-568032 by VLTI/MIDI. The dusty environment of CPD-568032 exhibits a bright unresolved core and a more diffuse environment. From MIDI acquisition images at 8.7 micron (dominated by PAHs emission), the extension and geometry of the core have been estimated and compared to the geometry of the nebula and the equatorial disk observed by the HST (De Marco et al., 1997 and 2002). The UT2 and UT3 telescopes were used providing projected baselines between 40 and 45 meters. The bright infrared core is almost fully resolved with these baselines although high SNR fringes at low level have been detected. This clear signal reveals a ring structure interpreted as the bright inner rim of the equatorial disk exposed to the flux from the Wolf-Rayet star at the center of the system. These observations bring a new insight of the mechanism at the origin of the dust observed at the center of some asymmetric planetary nebulae. [ABSTRACT FROM AUTHOR]