91̽»¨

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.

Abstract:

We report 1″ imaging spectroscopy of the 1.95-2.4 μm wavelength region in the z = 2.284 galaxy IRAS FSC 10214+4724. We find that the rest-frame Hα and [N II] emission have different spatial extents. We also detect broad (ΔνFWZP ≈ 3500 km s^-1) Hα emission. FSC 10214 is a very luminous gravitationally lensed galaxy, which intrinsically contains both a type 1 active galactic nucleus and a more extended star-forming disk. The AGN and circumnuclear star formation both contribute significantly to the total luminosity of ∼ 10¹³ L⊙. © 1996. The American Astronomical Society. All rights reserved.

Abstract:

L1551-IRS5 is a classic example of a low-mass young stellar object. We present near-infrared images with a FWHM of 0.3 arcsec obtained using the 'Shift and Add' technique. These observations are combined with existing multiwaveband data to constrain Monte Carlo models of the system in scattered light. The models demonstrate that the observed flux distribution arises not from a disc but from a circumstellar envelope with an evacuated bipolar cavity. The envelope has a mass of 0.1-0.3 M⊙ within a radius of 670 au, and shows no evidence of a significant population of large dust grains.