Astronomical instrumentation

Abstract:

3D, the new MPE NIR imaging spectrometer, provides us with a unique opportunity to probe in detail the structure of the stars, ionized gas, and hot molecular gas in the very centers of AGN. The instrument delivers data cubes with 16×160.5″ pixels which are 256 spectral channels deep. Thus, in a single observation we are able to obtain data on the entire K-Band over an 8″×8″ field of view, with a spectral resolution of R = λ/Δλ = 1000. In this paper we detail the working principles behind the instrument, and show first results from observations of the inner regions of the Seyfert 1 galaxy NGC 7469 made at the Calar Alto observatory. Copyright ©1996 Elsevier Science Ltd.

Abstract:

The new MPE near infrared imaging spectrometer 3D represents a new generation of astronomical instrumentation. It is based on a 2562 NICMOS-3 Rockwell array and can simultaneously obtain 256 H- or K-band spectra at R= 1100 or 2100 from a square 16×16 pixel field on the sky. Typical pixel scales are 0.3″/pixel or 0.5″/pixel. 3D is a combination of a novel image slicer and a liquid nitrogen cooled long slit spectrometer. It includes high definition on-axis lens optics, a high efficiency directly ruled KRS-5 grism as well as a cold closed-loop piezo-driven tilt mirror allowing full spectral sampling. The instrument efficiency including detector is 15%. Combining the advantages of imaging and spectroscopy increases the observing efficiency on key astronomical objects (e.g. galactic nuclei) by such a large factor over existing grating or Fabry-Perot spectrometers that subarcsecond near-IR spectroscopy of faint Seyferts, starbursts, quasars, or distant galaxy clusters becomes feasible for the first time with 4m-class telescopes. As a portable instrument 3D has already been successfully deployed on several 2 and 4m-class telescopes.

Abstract:

Spectra are presented of 21 planetary nebulae spanning the well-known, but still unidentified, narrow emission features at 3.2-3.6 μm. The equivalent width of the 3.29-μm emission band is strongly correlated with the gas-phase carbon-to-oxygen ratio, as expected for a band origin in carbon-rich grains or molecules. It displays an approximately linear dependence upon the C/O ratio, with a threshold near C/O ∼0.6. The emission band is present in 18 of the 21 nebulae, being absent in three of the six oxygen-rich objects and only weakly present in a fourth. The profile of the , 3.29-μm band is closely similar in all of the nebulae and distinct from the band profile seen in some stellar envelopes. Weaker emission features in the 3.4-3.5 μm region are detected in nine objects, and are prominent only in nitrogen-rich type I nebulae. The intensity of the 3.4-μm feature in these objects is correlated with that of the 3.29-μm band, while the ratio of the two bands is strongly correlated with the nitrogen abundance. Possible explanations for this behaviour are discussed.

Abstract:

Near-infrared imaging spectroscopy at spatial resolutions of 0.5 arc sec can already be achieved by combining the spatial and spectral resolution of an IR-imaging spectrometer with a first-oreder adaptive-optics system and accurate autoguider. This development makes high-resolution near-IR imaging spectroscopy possible for astronomy.

Abstract:

We present observations of solid-state absorption features due to water ice, CO ice, and silicate dust in the spectrum of the bright infrared source (1RS 1) associated with the Herbig-Haro nebula HH 100 in the R Coronae Australis dark cloud. These absorptions are shown to arise predominantly in the molecular cloud rather than in circumstellar matter associated with the infrared source itself, which we deduce to be a premain-sequence star obscured by ∼25 mag of visual extinction. In common with other lines of sight, the spectra indicate the presence of distinct hydrogen-rich (polar) and hydrogen-poor (nonpolar) phases in the ice toward HH 100-IR. The nonpolar phase is dominated by CO. The strength of the solid CO feature at 4.67 μm suggests that as much as ∼40% of all CO in the line of sight may be in the solid phase. Our data show a lack of significant absorption at 4.62 μm that might arise in CN-bearing molecules formed by energetic processing of the mantles. A previous report of structure in the profile of the 3 μm water-ice feature in HH 100-IR that might be attributed to the N-H resonance in condensed ammonia at ∼2.96 μm is not confirmed. The abundance ratio NH3:H2O in the ices is found to be no more than ∼8%, which is probably insufficient to account for the 3.3-3.6 μm "ice-band wing" in terms of ammonium hydrate. However, we propose that the wing might be explained by hydrates containing other bases in addition to ammonia. Further progress is likely to require new laboratory data for appropriate ice mixtures. © 1996. The American Astronomical Sodely. All rights reserved.