Astronomical instrumentation

Abstract:

We present linear spectropolarimetry in the wavelength range 4.5-4.8 μm of the embedded infrared source W33A. Our observations show for the first time the presence of polarization associated with the CO and XCN ice features, demonstrating that the absorbers reside in or on aligned grains. Both narrow and broad components of the solid CO feature near 4.67 μm are polarized. The detection of polarization associated with the narrow CO component is particularly significant, as the ices responsible are thought to exist only in dense, cold regions of molecular clouds, where gas and grain temperatures are expected to be closely coupled and traditional grain alignment mechanisms should become ineffective. We discuss the significance of this result with regard to current grain alignment theories. Mechanisms in which grain rotational energy is enhanced by interaction with cosmic rays merit further investigation. © 1996. The American Astronomical Society. All rights reserved.

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.