Astronomical instrumentation

Abstract:

The proposed 15m NNTT offers a gain in collecting area over a 4m telescope of 14 and a gain in speed of up to 200. In this paper the types of problem where the gain in limiting flux is inversely proportional to area (D2-problems) and those in which the gain goes only as the diameter (D-problems) are identified. The performance of the NNTT is compared to a 4m telescope and to the Space Telescope in three configurations. The NNTT isshown to have a small advantage over the Space Telescope for spectroscopy of point sources even at low resolutions. For work on sources of diameter one arcsecond or greater the gains are (formula omitted) a factor of 15. Even for the direct imaging of point sources the NNTT is only a little slower than the Space Telescope when there is no confusion. Three areas of astronomical investigation, studies of star formation, the Galactic halo and high redshift galaxies, are used to illustrate the impact a 15m telescope would make scientifically. These astronomical problems make substantial demands on the telescope performance and instrumentation. If these can be met the NNTT will lead to considerable advancement in the understanding of current problems and, given the order of magnitude improvement in infrared performance and spectroscopic capability, is likely to lead to the discovery of new phenomena. © 1983 SPIE.

Abstract:

Spectrophotometry at 8 - 13 μm of Mkn 231 confirms that the 10 μm minimum is due to large columns of silicate dust in the line-of-sight to the nucleus. Fits to the detailed spectral shape demonstrate that the cool absorbing grains are at the emission (z = 0.042) rather than the absorption (z \equiv 0.025) redshift and are located within the nuclear region.

Abstract:

Parsamian 13 is found to be a cometary nebula, with a deeply embedded star suffering strong absorption by silicate grains. A feature near 2.7 microns, attributed to absorption by terminal OH groups, may represent the first detection in an astrophysical environment of water ice grains diluted by another molecule, for example by CO. The bolometric luminosity suggests that this star is either an extremely young T Tauri star or an evolved low-mass star, now a red giant, high on its convective track. Most unusual is the presence of cold (50 K) TiO gas in sufficient abundance to show in absorption in the optical and very near-infrared regions; this material probably represents very recently expelled photospheric layers.

Abstract:

8-13-micron spectra of eight moderately extended planetary nebulae have been obtained at a resolution of 0.24 micron using a 20-arcsec circular aperture. More compact planetaries which have been studied in this way generally show a strong continuum due to emission from dust, together with fine structure line emission. In contrast, these more extended objects have very weak continuum emission, and are dominated by fine structure line emission, especially by S IV forbidden lines which in several cases accounts for most of the broad-band 10-micron flux. There appears to be very little warm (equal to or greater than 150 K) dust in some of these objects.

Abstract:

The authors present infrared spectrophotometry of 20 symbiotic stars, mostly of the dust-rich variety. HDE330036 is unique in showing an emission feature at 11.3 μm. The remainder combine a hot grey component and/or optically thin silicate emission. A model in which the grey component is due to optically thick silicate dust is not consistent with the spectra. The authors propose instead that iron-based grains, expected to form in the ejecta of cool stars, are heated by the ultraviolet radiation field of the hot companion.