One of the major problems with 3D spectroscopy is the adequate and meaningful display and analysis of large image cubes. We use linear mixture modeling to analyze multispectral CCD images of M51 in the visible and near-IR. We find that M51 can be modeled within the noise limits of the data as a linear combination of six components taken three at a time.

The young emission-line star LkHα225 (V1318 Cyg) with a tiny cometary nebula is located in the small group of very young stars around the well-known Herbig Ae/Be star BD+40°4124. LkHα225 was discovered by Herbig (1960) and studied by several authors (see for references Ibragimov et al., 1988). The star undergoes strong variations of its light (nearly 3 magn.) in visible light as well as in infrared. Spectral type of LkHα225 is very uncertain, but its high luminosity (Lbol=460 L⊙) and mass (5.5 M⊙), as well as the presence of nebulosity suggests that it also belongs to the Herbig Ae/Be class of pre-main sequence (PMS) stars. This small and perhaps variable nebulous appendage on the NW-side of the star can be readily seen on the plates obtained with the 2.6-meter telescope of Byurakan Observatory.

Seen from Sirius through the eye of the telescope, our inner solar system would easily fit within one CCD-pixel. The purpose of the present paper is: i) to provide with a general overview of the use of imaging or 3D-spectroscopy for the study of the solid planetary surfaces, ii) to demonstrate that the analysis of 3D spectroscopic data on the basis of spectral mixture modelling permits to describe the subpixel spectral variability related to mineralogy of the planetary solid surfaces. In the following, a few cases are discussed concerning the remote sensing investigation in the UV-VIS-nIR domain of the lunar, terrestrial and martian surfaces, documented by means of multispectral or hyperspectral data, produced by telescopic, airborne or orbital imaging spectroscopic techniques.

High spectral and spatial resolution telescopic observations of the western hemisphere of Mars, using the integral field spectrograph TIGER at 0.8-1.1 µm, are described.

The PYTHEAS instrumental concept is an attempt to solve the problem of getting a complete tridimensional coverage of the observed field with a high spectral resolution across a wide spectral range. It is an integral field spectrometer derived from the TIGER spectrograph (field sampling with a microlens array) in which a scanning Fabry-Perot (FP) is introduced. The spectral resolution is given by the F P and the spectral range is that allowed by the grism of TIGER. The information is recorded on the CCD as a set of channeled spectra, for each microlens and each scanning step of the FP. The spectrum of each sampled field element is reconstructed from flux measurement of the Fabry spots defining the channeled spectra.

The application ranges of this instrument are reviewed with emphasis on the potential interest in globular cluster studies.

Development of 3D spectral methods on the 6-meter telescope prompted the necessity of creating specialized software for data reduction, adapted to personal computers IBM AT/386/486 class. We had to concentrate our efforts on preparing the software for bidimensional spectral data produced by Multi-Pupil Integral Field Spectrograph of the 6-meter telescope (MPFS) and analog of panoramic spectrophotometer with spectral channeling, using scanning Fabry-Perot interferometer (PYTHEAS-6).

MPFS - analog of spectrograph TIGER (Courtes et al., 1988), developed for the 6-meter telescope, provides bidimensional spectroscopy of extended sources, allowing the simultaneous detection of 99 individual spectra, produced by a lens raster from 9 by 11 microlenses. The main features of this instrument are described in (Afanasiev et al, 1994).

PYTHEAS is an imaging spectrophotometer giving high spectral and spatial resolutions in joining together several optical concepts (Le Coarer et al 1992, and Georgelin et al. in these Proceedings). It will be shown in this paper that, contrary to other spectrographs using somewhat complex methods of data reduction, the PYTHEAS imaging spectrometer requires simple photometric methods in order to reconstruct the spectra of astrophysical objects.

The CCD image of a continuous spectral energy distribution for a permanent gap between the layers of the Fabry-Perot consists in a series of channelled spectra: each elementary beam, spectrally filtered by the FP interferometer and sampled by a microlens in the frame, gives light to the whole surface of the grism which separates the various F-P orders by displaying them in a line on the detector. Each line or channelled spectrum consists of a series of Fabry pupils (spectral elements), each of them containing the luminous flux emitted on a certain wavelength by the object under investigation. After scanning the FP interferometer across its free spectral range, we obtain a series of shifted channelled spectra whose set provides us with a chart showing the photometric values of flux according to the wavelength. Consequently, some forms of calibration (continuum lamp, spectral lamp) allow the reconstruction of the spectra of the astrophysical object through simple photometric measures.

Crossing a low interference order Fabry-Perot etalon with an objective prism on a Schmidt telescope leads to a simple large field multiband spectrophotometric survey system well-adapted to the study of the spectral energy distribution of faint galaxies and redshift estimates.

With the advent of bidimensional array detectors the throughput advantage of a Fourier Transform Spectrometer (FTS) can be used to create a new type of 3-D spectrometer. The classical multiplex property in the spectral domain of a FTS is multiplied by the number of pixel of the array. The points of the entrance field are all observed in parallel. After discussing the properties of this instrument, the coupling of the FTS of the CFH Telescope to a camera equipped with a NICMOS 3 array is described. With this combination, spectro-imaging in any bandpass between 1 and 2.5 µm is possible within a circular 24” field of view, with a scale of 0.33”/pixel, at seeing-limited spatial resolution. Any spectral resolution is choosable up to 30,000. Illustrations are given by a study of the dark side of Venus at 1.27 µm and of planetary nebulae at 2 µm. Many other objects can benefit from this observing mode in the near infrared. Further developments of this 3-D technique are discussed.

We compare the relative merits of four different types of instrument for tridimensional spectrometry at visible and ultraviolet wavelengths: the echelle and long-slit spectrographs and two types of Fourier transform spectrometer (conventional scanning and fixed tilt spatially heterodyned). Each of these instruments requires different spatial and spectral scanning modes. It is shown that in certain limiting conditions all four are equally efficient, but that they differ in other important characteristics.

We report high spatial and spectral resolution near-infrared mapping results in the K’–Band obtained with BEAR towards the protoplanetary nebula AFGL 2688 and the planetary nebula NGC 7027.

This poster described a method under development that promises to be useful for 3-D spectroscopic studies of extremely faint, spatially extended astronomical sources. The method, which we call Spatial Heterodyne Spectroscopy (SHS), is a relative of the conventional scanning Fourier Transform Spectrometer (FTS), but is free of any scanning elements. We foresee ground-based and space applications for studies of the interstellar medium and the upper atmospheres of solar system objects. Basic configurations that have been tested in the laboratory were described. The SHS instrument we are currently emphasizing for development is intended for a rocket experiment to measure C IV λ1548,51 doublet emission at a resolving power of 20,000 from the hot ISM. Eventually we hope to provide velocity-resolved all-sky maps of selected FUV lines to complement maps obtained at other wavelengths.

We present the first results from a portable spectrometer for the visible and very near infrared based upon the principle of heterodyned holographic Fourier transform spectroscopy (HHS) (Dohi and Suzuki 1971, Dohlen 1994). The instrument uses a Michelson interferometer where one of the mirrors is replaced with a grating. This produces a spatially located, frequency-shifted interferogram which is read out by an all-reflective relay lens and a photo-diode array and processed on a portable PC. A battery pack ensures an autonomy of about 7 hours. Instrumental assets include high optical throughput, variable resolving power, and no moving parts.

We have successfully used the instrument in two different remote sensing applications: detection of vegetation reflectance and atmospheric absorption.

Stellar rotation maps the surface of a star into its line spectrum and gives a dimension to a point on the star - the Doppler dimension. This is of great importance for the detection of Zeeman polarization especially in certain cases. Typically a magnetic configuration will exhibit both polarities, thus the polarization signals of oposite signs may superpose and cancel. The Doppler coordinate will be in general different for parts of the stars having different polarities and therefore the polarization signals will also appear at different wavelengths and will not cancel. Moreover, the time variations plus the Doppler coordinate constitutes two variables that may allow the reconstruction of two dimensional map of the magnetic field over the star surface.

Attention will be given to the set-up that allows spectropolarimetry with high spectral resolution and high S/N ratio. The use of cross dispersion spectrographs allows one to observe several tens of spectral lines. The method of adding signals to increase S/N ratio will be indicated.

Several MSDP instruments are used in solar physics to observe simultaneously 2D-fields in a number of wavelengths.

We describe briefly the needs of 3D-data in solar physics, the different spectroscopic methods in use, and the principle of MSDP spectrographs. We discuss the relationships between spectral resolution, field of view and efficiency. We summarize the capabilities of the instruments, either presently working (Meudon, Pic du Midi, Tenerife and Wroclaw), or associated with the THEMIS project.

The solar results take into account the main performances of the MSDP, that is to say the very high spatial resolution and the high speed to cover a wide area on the sun within a short time (coordinated campaigns with space probes).

We conclude by a brief discussion of the capabilities which could be expected from the MSDP in night-time astronomy.

Differential Speckle Interferometry (DSI) combines high angular resolution techniques with medium to high resolution spectroscopy. For non resolved sources, it yields the displacement of the object photocenter with wavelength. Combined with the spectrum s (λ), can give information with spatial and/or spectral resolution well beyond the telescope or spectrograph limits. This complementarity is illustrated here with experimental results. For the binary system Capella, we measure the angular separation, separate the spectra of the components and derive the radial velocity difference and the rotation velocity of each component. For the slowly rotating star Aldebaran we obtain the position angle of the stellar rotation axis and a relation between the angular diameter and the rotation velocity which in this case gives the latest.

The GI2T is an optical long-baseline Michelson interferometer which analyses dispersed stellar fringes in the multi-speckle mode with a spectral resolution of one Angstrom while the spatial resolution is about one milliarcsecond. This makes the GI2T a powerful instrument able to perform MSI of extended sources like Be stars or shell stars. In order to interpret these data we have developed a latitude dependent radiative wind model for Be stars. This numerical code enables us to compare directly computed 2D maps in some Balmer lines (Hα and Hβ) with high angular resolution data of some Be stars.

Over the last four days, we have enjoyed a wide range of talks on developments in three dimensional spectroscopic techniques. The conference organizing committee are to be congratulated for the artful manner in which instrumental presentations were interleaved with talks on the scientific results from these instruments. The general thrust of most talks was to advance the versatility of traditional instruments either through the Jacquinot (throughput) advantage or through the multiplex advantage, or both. A number of groups have attempted to utilize the full aperture of scanning Fabry-Perot and Fourier Transform interferometers. Arguably, Fabry-Perot interferometers have a wider application at present, although imaging Fourier Transform devices appear to have finally arrived, at least in the near infrared.

It is a great pleasure for us, daily Fabry-Perot interferometer (hereafter referred to as FP) users, to pay homage to the genius inventors of the FP. Each day we are still bewildered by the power of this instrument which mainly consists of two pieces of half-silvered glass. Even if equations of physics are perfectly able to describe multiple-beam interferences (hereafter referred to as MBI), something magic remains in our mind.

We will tackle this paper from a historical point of view. As any discovery, the invention of the FP did not occur just by chance from nowhere. As pointed out by Connes (1986) the invention of the multiple-beam interferometer may be understood as having proceeded from the fortunate convergence of two independent developments: (i) During 2 centuries, MBI has been observed and even computed but its specific and pregnant feature, the fringe sharpening, was not understood before Fabry’s thesis, (ii) A long production of mirrors, leading to the semi-transparent silver film.