arXiv subjects

A. Boogert

Publications and source records attributed to A. Boogert.

21 records · Page 2Linked to original sources

arXiv2010

Detection of interstellar oxidaniumyl: abundant H2O+ towards the star-forming regions DR21, Sgr B2, and NGC6334

We identify a prominent absorption feature at 1115 GHz, detected in first HIFI spectra towards high-mass star-forming regions, and interpret its astrophysical origin. The characteristic hyperfine pattern of the H2O+ ground-state rotational transition, and the lack of other known low-energy transitions in this frequency range, identifies the feature as H2O+ absorption against the dust continuum background and allows us to derive the velocity profile of the absorbing gas. By comparing this velocity profile with velocity profiles of other tracers in the DR21 star-forming region, we constrain the frequency of the transition and the conditions for its formation. In DR21, the velocity distribution of H2O+ matches that of the [CII] line at 158μ\m and of OH cm-wave absorption, both stemming from the hot and dense clump surfaces facing the HII-region and dynamically affected by the blister outflow. Diffuse foreground gas dominates the absorption towards Sgr B2. The integrated intensity of the absorption line allows us to derive lower limits to the H2O+ column density of 7.2e12 cm^-2 in NGC 6334, 2.3e13 cm^-2 in DR21, and 1.1e15 cm^-2 in Sgr B2.

astro-ph.GA↗

arXiv2008

The c2d Spitzer Spectroscopic Survey of Ices Around Low-Mass Young Stellar Objects: I. H2O and the 5-8 um Bands

With the goal to study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low luminosity YSOs using 3-38 um Spitzer and ground-based spectra. The long-known 6.0 and 6.85 um bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. In almost all sources the 6.0 um band is deeper than expected from the bending mode of pure solid H2O. The depth and shape variations of the remaining 5-7 um absorption indicate that it consists of 5 independent components, which, by comparison to laboratory studies, must be from at least 8 different carriers. Simple species are responsible for much of the absorption in the 5-7 um region, at abundances of 1-30% for CH3OH, 3-8% for NH3, 1-5% for HCOOH, ~6% for H2CO, and ~0.3% for HCOO- with respect to solid H2O. The 6.85 um band likely consists of one or two carriers, of which one is less volatile than H2O because its abundance relative to H2O is enhanced at lower H2O/tau_9.7 ratios. It does not survive in the diffuse interstellar medium (ISM), however. The similarity of the 6.85 um bands for YSOs and background stars indicates that its carrier(s) must be formed early in the molecular cloud evolution. If an NH4+ salt is the carrier its abundance with respect to solid H2O is typically 7%, and low temperature acid-base chemistry or cosmic ray induced reactions must have been involved in its formation. Possible origins are discussed for the carrier of an enigmatic, very broad absorption between 5 and 8 um. Finally, all the phenomena observed for ices toward massive YSOs are also observed toward low mass YSOs, indicating that processing of the ices by internal ultraviolet radiation fields is a minor factor in the early chemical evolution of the ices. [abridged]

astro-ph↗

arXiv2004

Spitzer Space Telescope Spectroscopy of Ices toward Low Mass Embedded Protostars

Sensitive 5-38 um Spitzer Space Telescope (SST) and ground based 3-5 um spectra of the embedded low mass protostars B5 IRS1 and HH46 IRS show deep ice absorption bands superposed on steeply rising mid-infrared continua. The ices likely originate in the circumstellar envelopes. The CO2 bending mode at 15 um is a particularly powerful tracer of the ice composition and processing history. Toward these protostars, this band shows little evidence for thermal processing at temperatures above 50 K. Signatures of lower temperature processing are present in the CO and OCN- bands, however. The observed CO2 profile indicates an intimate mixture with H2O, but not necessarily with CH3OH, in contrast to some high mass protostars. This is consistent with the low CH3OH abundance derived from the ground based L band spectra. The CO2/H2O column density ratios are high in both B5 IRS1 and HH46 IRS (~35%). Clearly, the SST spectra are essential to study ice evolution in low mass protostellar environments, and to eventually determine the relation between interstellar and solar system ices.

astro-ph↗