No abstract

This paper presents, for the Ðrst time, a complete 2.4È25 km spectrum of the dust-embedded young stellar object W33A. The spectrum was obtained with the Short Wavelength Spectrometer of the Infrared Space Observatory at a mean resolving power of D750. The spectrum displays deep ice and silicate 1 Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries : France, Germany, the Netherlands, and the United Kingdom) and with the participation of ISAS and NASA.

We present new observations with the Infrared Spectrograph on board the Spitzer Space Telescope of the solid-CO 2 absorption feature near 15 m in the spectra of eight field stars behind the Taurus complex of dark clouds. Solid CO 2 is detected in six lines of sight. New results are combined with previous data to investigate the correlation of CO 2 column density with those of other major ice constituents (H 2 O and CO) and with extinction. CO 2 is shown to display a ''threshold extinction'' effect, i.e., a minimum extinction (A 0 ¼ 4:3 AE 1:0 mag) required for detection, behavior similar to that previously reported for H 2 O and CO. We find a particularly tight correlation through the origin between N(CO 2 ) and N(H 2 O), confirming that these species form in tandem and coexist in the same (polar) ice layer on the grains. The observed composition of the mantles is broadly consistent with the predictions of photochemical models with diffusive surface chemistry proposed by Ruffle & Herbst. Comparison of our results for Taurus with published data for Serpens indicates significant differences in ice composition consistent with enhanced CO 2 production in the latter cloud. Our results also place constraints on the distribution of elemental oxygen between ices and other potential reservoirs. Assuming a constant N(H) to extinction ratio, we show that~65% of the solar O abundance is accounted for by summing the contributions of ices (~26%), refractory dust (~30%) and gas-phase CO (~9%). If the Sun is an appropriate standard for the interstellar medium, the ''missing'' oxygen may reside in atomic O i gas and/or (undetected) O 2 within the ices.

We present gas-phase abundances of species found in the organic-rich hot core G327.3-0.6. The data were taken with the Swedish-ESO Submillimetre Telescope (SEST). The 1-3 mm spectrum of this source is dominated by emission features of nitrile species and saturated organics, with abundances greater than those found in many other hot cores, including Sgr B2 and OMC-1. Population diagram analysis indicates that many species (CH3CN, C2H3CN, C2H5CN, CH3OH, etc.) have hot components that originate in a compact (~2") region. Gas-phase chemical models cannot reproduce the high abundances of these molecules found in hot cores, and we suggest that they originate from processing and evaporation of icy grain mantle material. In addition, we report the first detection of vibrationally excited ethyl cyanide and the first detection of methyl mercaptan (CH3SH) outside the Galactic center.

We discuss 2.8-3.9 lm spectra from the United Kingdom Infrared Telescope of seven sight lines toward IR sources near Sagittarius A* in the Galactic center (GC). In all lines of sight, the 3.0 lm H 2 O ice feature is present with optical depths in the range 0.33-1.52. By constructing a simple ice model, we show that the ice profile is not fully accounted for by pure H 2 O ice mantles. Residual absorption is present at 2.95 and 3.2-3.6 lm. Aliphatic hydrocarbon absorption at 3.4 lm is shown to vary by a factor of 1.7, indicating significant changes in the foreground extinction across the small field. By determining the true ice profile for the GC line of sight, we reveal an additional broad absorption component around $3.3 lm, which partially underlies the 3.4 lm aliphatic hydrocarbon feature. Its carrier resides in the diffuse interstellar medium. The width of this absorption is deduced to be at least $100 cm À1 , much broader than individual polycyclic aromatic hydrocarbon molecules produced in the laboratory or unidentified infrared emission features observed in the interstellar medium. The 4.62 lm '' XCN '' feature is detected in the molecular clouds along the line of sight toward IRS 19. In the solar neighborhood, this feature is seen only toward some deeply embedded protostars. Toward the GC, it may indicate the serendipitous presence of such an object in the line of sight to IRS 19, or it might conceivably arise from the processing of ices in the circumnuclear ring of the GC itself.

On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics.

Organic volatiles and water in Oort Cloud comets were investigated at infrared wavelengths. The detected species include H20, CO, CH30H, Cl& C2H2, C&, OCS, HCN, NH3, and HzCO. Several daughter fragments (CN, OH, NH*, etc.) are also measured, and OH prompt emission provides a proxy for water. Long-slit spectra are taken at high spectral dispersion and high spatial resolution, eliminating several sources of systematic error. The resulting parent volatile production rates are highly robust, permitting a sensitive search for compositional diversity among comets. Here, seven OC comets are compared. Six (including Halley) exhibit similar compositions (excepting CO and CI$). Their low formation temperatures (-30 K) suggest this group probably formed beyond 30 AU from the young sun. However, C/1999 S4 is severely depleted in hypervolatiles and also in methanol, and it likely formed near 5 -10 AU. C/2001 A2 is discussed briefly to illustrate future prospects.

We quantified eight parent volatiles (H 2 O, C 2 H 6 , HCN, CO, CH 3 OH, H 2 CO, C 2 H 2 , and CH 4 ) in the Jupiter-family comet Tempel 1 using high-dispersion infrared spectroscopy in the wavelength range 2.8 to 5.0 micrometers. The abundance ratio for ethane was significantly higher after impact, whereas those for methanol and hydrogen cyanide were unchanged. The abundance ratios in the ejecta are similar to those for most Oort cloud comets, but methanol and acetylene are lower in Tempel 1 by a factor of about 2. These results suggest that the volatile ices in Tempel 1 and in most Oort cloud comets originated in a common region of the protoplanetary disk.