Prof. Niranjan Thatte

Abstract:

One of the most important techniques for astrophysics with adaptive optics is the ability to do spectroscopy at diffraction limited scales. The extreme difficulty of positioning a faint target accurately on a very narrow slit can be avoided by using an integral field unit, which provides the added benefit of full spatial coverage. During 1998, working with ALFA and the 3D integral field spectrometer, we demonstrated the validity of this technique by extracting and distinguishing spectra from binary stars separated by only 0.26 ". The combination of ALFA&3D is also ideally suited to imaging distant galaxies or the nuclei of nearby ones, as its field of view can be changed between 1.2 " x1.2 " and 4 " x4 ", depending on the pixel scale chosen. Ln this contribution we present new results both on galactic targets, namely young stellar objects, as well as extra-galactic objects including a Seyfert and a starburst nucleus.

Abstract:

Conducting resolved spectroscopy on large samples of very faint objects is a strong requirement for the Next Generation Space Telescope (NGST). We are presenting the IFMOS concept, a 1 to 5 microns integral field spectrograph developed under contract with ESA. Image slicers are feeding compact spectrograph modules with very few moving parts. The wide field survey mode has low spatial - low spectral resolution over a field similar to 46 x 40 arcsec(2) (0.19 arcsec per resolved element). The high spatial -high spectral resolution mode covers a field 3.8 x 2.6 arcsec(2) sampled at 0.05 arcsec, a pointed object mode at the diffraction limit of the telescope. A detailed opto-mechanical design has been produced, meeting the environmental requirements for the NGST payload.

Abstract:

The results from the IFMOS ESA 1-5 microns integral field multiobject spectrograph study are presented. A review of the science requirements indicates that integral field 2D spectroscopy is a powerful concept of great value for the NGST. We present the opto-mechanical design of the instrument, based on image slicers. A low resolution and a high resolution channels are working in parallel, with only one mechanical motion. The low resolution channel covers a field 40 x 46 arcsec(2) at R similar to 150, while the high resolution channel covers 2.6 x 3.8 arcsec at R = 3000. We show that the performances on single sources is equal or better than classical dispersive spectrographs, and yet very efficient on large galaxy surveys, and conclude that IFMOS is both scientifically attractive and technically feasible.

Abstract:

We present SPIFFI, the integral field spectrometer for the VLT. This instrument allows simultaneous observation of infrared spectra in more than 1000 image points of a two dimensional field. With its set of four gratings and a pixel scale that can be varied by a factor of ten, SPIFFI provides high flexibility, and at the same time offers the unique possibility of diffraction limited imaging spectroscopy at an 8m-class telescope, when fed by the adaptive optics system MACAO. We outline the scientific drivers for building such an instrument, the concept of image slicing, the optical design, and the implementation of SPIFFI.

Abstract:

We present multi-wavelength imaging observations of three nearby and famous active galaxies obtained with of NICMOS, ISOCAM and the MPE near-In integral held spectrometer. The data reveal a variety of features and properties that are missed in optical studies and in traditional IR monodimensional spectroscopy.