Astronomical instrumentation

Abstract:

Infrared spectroscopic observations have been made with sufficient spatial resolution to separate some of the members of the BNKL infrared complex in the Orion Nebula; 8-13 micron spectra of BN, IRc2 and IRc4 together with 3-4 micron spectra of BN and IRc2 are presented. These spectra show significantly more extinction attributed to water ice to IRc2 than to BN, and the extinction attributed to silicate grains also increase in the sequence BN, IRc2 and IRc4. The silicate absorption feature observed in the case of IRc4 has a significantly different shape from that observed in most heavily obscured infrared sources, but this is shown to be a natural consequence of a large amount of absorbing material being close to the source of luminosity. These observations are interpreted in terms of independent sources of comparable luminosity situated progressively deeper within the Orion molecular cloud.

Abstract:

Spectrophotometry in the range 2.1-4.0 microns is presented for the Seyfert galaxies NGC 1068, NGC 4151 and Mrk 231 and the quasar 3C 273, together with broadband and narrowband observations of the Seyfert galaxies in the range 8-13 microns. The spectra of NGC 1068 and NGC 4151 are found to contain a significant component due to starlight, especially at shorter wavelengths. The nonstellar component in NGC 1068 is observed to fall off rapidly at wavelengths shorter than 4 microns, consistent with the interpretation of the excess beyond 5 microns as thermal reradiation by dust. Observations confirm the variability of NGC 4151, and indicate the presence of two components of the flux other than starlight: a nonthermal variable component predominant at shorter wavelengths and a constant, probably thermal component at wavelengths greater than 3 microns. Mrk 231 and 3C 273 exhibit no discernable stellar component and were not observed to vary by more than 10%. Evidence is obtained for a broad minimum in the 8 to 13 micron spectrum of Mrk 231, as well as possible structure between rest wavelengths of 2.8 and 2.9 microns, and the spectrum is not a power law. The spectrum of 3C 273 is consistent with a power law from 1.2 to 10 microns, with small but significant deviations.

Abstract:

8-13 micron spectrophotometry of V1016 Cyg shows a broad emission feature attributed to radiation from silicate grains. This emission feature more closely resembles that of the circumstellar shells of oxygen-rich supergiants than the more dilute feature, typical of the interstellar medium, which is observed from the Trapezium source in the Orion nebula. It appears to be possible to distinguish the evolutionary status of an object from the form of its silicate excess.