R. G. Smith

On the Formation of Interstellar Water Ice: Constraints from a Search for Hydrogen Peroxide Ice in Molecular Clouds

Recent surface chemistry experiments have shown that the hydrogenation of molecular oxygen on interstellar dust grains is a plausible formation mechanism, via hydrogen peroxide (H2O2), for the production of water (H2O) ice mantles in the dense interstellar medium. Theoretical chemistry models also predict the formation of a significant abundance of H2O2 ice in grain mantles by this route. At their upper limits, the predicted and experimental abundances are sufficiently high that H2O2 should be detectable in molecular cloud ice spectra. To investigate this further, laboratory spectra have been obtained for H2O2/H2O ice films between 2.5 and 200 μm, from 10 to 180 K, containing 3%, 30%, and 97% H2O2 ice. Integrated absorbances for all the absorption features in low-temperature H2O2 ice have been derived from these spectra. For identifying H2O2 ice, the key results are the presence of unique features near 3.5, 7.0, and 11.3 μm. Comparing the laboratory spectra with the spectra of a group of 24 protostars and field stars, all of which have strong H2O ice absorption bands, no absorption features are found that can definitely be identified with H2O2 ice. In the absence of definite H2O2 features, the H2O2 abundance is constrained by its possible contribution to the weak absorption feature near 3.47 μm found on the long-wavelength wing of the 3 μ mH 2O ice band. This gives an average upper limit for H2O2, as a percentage of H2O, of 9% ± 4%. This is a strong constraint on parameters for surface chemistry experiments and dense cloud chemistry models.

H2O Ice in the Envelopes of OH/IR Stars

In an attempt to better understand the conditions under which molecules condense onto grains in the envelopes of evolved stars, we have searched for the presence of H2O ice in the circumstellar envelopes of several evolved (OH/IR) stars. The sample of stars observed was selected on the basis of mass-loss rates, luminosities, and outflow velocities in order to cover a range of physical conditions that might affect the amount of ice present in stellar envelopes. Despite the clear presence of H2O ice around other, previously observed, evolved stars, our search in six OH/IR stars has resulted in only one clear detection, in OH 26.5 + 0.6, and the tentative detection in one other, OH 26.4-1.9. We provide column densities or upper limits for the amount of ice that is present on the grains around these stars and explore the possibility that there could be a relationship between M* or M*/L* and the H2O ice column density to explain the observations.

On the Nature of the Enigmatic Object IRAS 19312+1950: A Rare Phase of Massive Star Formation?

IRAS 19312+1950 is a peculiar object that has eluded firm characterization since its discovery, with combined maser properties similar to an evolved star and a young stellar object (YSO). To help determine its true nature, we obtained infrared spectra of IRAS 19312+1950 in the range 5-550

Chemical chronology of the Southern Coalsack

mu

Interstellar dust absorption features in the infrared spectrum of HH 100-IR: Searching for the nitrogen component of the ices

m using the Herschel and Spitzer space observatories. The Herschel PACS maps exhibit a compact, slightly asymmetric continuum source at 170

Molecular ices as temperature indicators for interstellar dust: the 44- and 62-μm lattice features of H2O ice

mu

Crystalline water ice in OH32.8–0.3

m, indicative of a large, dusty circumstellar envelope. The far-IR CO emission line spectrum reveals two gas temperature components:

Al2O3 dust in OH/IR stars

approx0.22M_{odot}

The librational band of water ice in AFGL 961: revisited

of material at

The phase of H2O ice and the librational band in OH231.8+4.2: new interpretations

280pm18