We present VLTI-MIDI (the Mid-Infrared Interferometric Instrument at ESO's Very Large Telescope Interferometer)
observations of MWC349 A, which are a prime example of the power of combined spatial and spectral
resolution for addressing complex astrophysical phenomena.
Previous observations of the peculiar emission line star MWC349A suggest that it is a young massive star in
the short-lived phase of already having dissipated its parent cloud, but still being surrounded by the accretion
disk, which is seen nearly edge-on. It is believed that the unique hydrogen recombination line maser / laser
activity of MWC349A from mm to infrared wavelengths is also a consequence of this viewing geometry.
We have taken 13 measurements with MIDI at the VLTI (Very Large Telescope Interferometer) in the GRISM
mode covering the N band (8 to 13 microns) at a spectral resolution R ≈ 230. The wavelength dependence of
the continuum visibility agrees with model calculations for circumstellar dust disks. In addition, the signatures
of at least a dozen emission lines have been identified in the interferometric data.
We present a first analysis of visibility amplitudes and differential phase data. In particular we show that a
simple model can represent the SED and visibility amplitude of the continuum flux. Also the visibilities for the
hydrogen and forbidden lines are discussed.
Gamma ray bursts (GRBs) are the most energetic eruptions known in the Universe. Instruments such as Compton-GRO/BATSE and the GRB monitor on BeppoSAX have detected more than 2700 GRBs and, although observational confirmation is still required, it is now generally accepted that many of these bursts are associated with the collapse of rapidly spinning massive stars to form black holes. Consequently, since first generation stars are expected to be very massive, GRBs are likely to have occurred in significant numbers at early epochs. <i>X-red</i> is a space mission concept designed to detect these extremely high redshifted GRBs, in order to probe the nature of the first generation of stars and hence the time of reionisation of the early Universe. We demonstrate that the gamma and x-ray luminosities of typical GRBs render them detectable up to extremely high redshifts (<i>z</i> ~ 10to30), but that current missions such as HETES and SWIFT operate outside the observational range for detection of high redshift GRB afterglows. Therefore, to redress this, we present a complete mission design from teh science case to the mission architecture and payload, the latter comprising three instruments, namely wide field x-ray cameras to detect high redshift gamma-rays, an x-ray focussing telescope to determine accurate coordinates and extract spectra, and an infrared spectrograph to observe the high redshift optical afterglow. The mission is expected to detect and identify for the first time GRBs with <i>z</i> > 10, thereby providing constraints on properties of the first generation of stars and the history of the early Universe.
The PRIMA facility will implement dual-star astrometry at the VLTI. We have formed a consortium that will build the PRIMA differential delay lines, develop an astrometric operation and calibration plan, and deliver astrometric data reduction software. This will enable astrometric planet surveys with a target precision of 10μas. Our scientific goals include determining orbital inclinations and masses for planets already known from radial-velocity surveys, searches for planets around stars that are not amenable to high-precision radial-velocity observations, and a search for large rocky planets around
nearby low-mass stars.
Knowledge of the dispersion due to (humid) air in the light path of the Very Large Telescope Interferometer (VLTI) is crucial to obtaining good science data from MIDI, PRIMA and GENIE. To calculate the refraction due to air at infra red wavelengths in the ducts and delay line tunnel, the temperature and humidity has to be monitored during observations. To accomplish these measurements an easy to use and reliable system was assembled, based on commercially available components. In-house calibration of four humidity and temperature sensors of the system was done in Leiden. A test and calibration program was carried out to make sure that they work reliably and accurately and to determine the sensor characteristics. For this purpose a calibration box was designed which isolates the sensors from the environment so that there is no exchange of air with the outside environment. Using constant humidity salt solutions, the humidity in the box can be controlled. This allows the calibrations to be carried out for typical values of relative humidity and temperature at Cerro Paranal. Calibration of the sensors includes: 1. Reducing the systematic relative humidity differences between the sensors to less than 0.1 % and 2. Reducing the systematic temperature differences between the sensors to less than 0.01 K. In this paper we will present the outcome of the calibrations and the future of the sensors at Paranal.
This investigation focuses on observational measurements of the differential interferometric phase between spectral channels in the VLTI/MIDI instrument. Measurements of target stars are compared with theoretical predictions in order to investigate the effects of dispersion in humid air on differential phase measurements at N band (~10 micron wavelength). An accuracy of 1 degree RMS phase error is achieved after calibration during stable environmental conditions, but this accuracy is degraded if there are fluctuations in humidity between observations. Stabilisation and/or monitoring of the environmental conditions in the VLTI ducts and tunnels will be required in order to achieve the best differential phase performance with MIDI. The measured differential phases are found to be consistent with a model for the refractive index of air based on the HITRAN database.