41 research outputs found
Near-Infrared Band Strengths of Molecules Diluted in N2 and H2O Ice Mixtures Relevant to Interstellar and Planetary Ices
The relative abundances of ices in astrophysical environments rely on accurate laboratory measurements of physical parameters, such as band strengths (or absorption intensities), determined for the molecules of interest in relevant mixtures. In an extension of our previous study on pure-ice samples, here we focus on the near-infrared absorption features of molecules in mixtures with the dominant components of interstellar and planetary ices, H2O and N2. We present experimentally measured near-infrared spectral information (peak positions, widths, and band strengths) for both H2O- and N2-dominated mixtures of CO (carbon monoxide), CO2 (carbon dioxide), CH4 (methane), and NH3 (ammonia). Band strengths were determined during sample deposition by correlating the growth of near-infrared features (10,000-4000 per centimeter, 1-2.5 micrometers) with better-known mid-infrared features (4000-400 per centimeter, 2.5-25 micrometers) at longer wavelengths
Recent results from the Leiden Observatory Laboratory: (a) band strengths in mixed ices; (b) UV photolysis of solid methanol
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
ISO Spectroscopy of Young Stellar Objects
Observations of gas-phase and solid-state species toward
young stellar objects (YSOs) with the spectrometers
on board the Infrared Space Observatory
are reviewed. The excitation and abundances of
the atoms and molecules are sensitive to the changing
physical conditions during star-formation. In
the cold outer envelopes around YSOs, interstellar
ices contain a significant fraction of the heavy element
abundances, in particular oxygen. Different ice
phases can be distinguished, and evidence is found for
heating and segregation of the ices in more evolved
objects. The inner warm envelopes around YSOs are
probed through absorption and emission of gas-phase
molecules, including CO, CO_2, CH_4 and H_2O. An
overview of the wealth of observations on gas-phase
H_2O in star-forming regions is presented. Gas/solid
ratios are determined, which provide information on
the importance of gas-grain chemistry and high temperature
gas-phase reactions. The line ratios of molecules
such as H_2, CO and H_2O are powerful probes
to constrain the physical parameters of the gas. Together
with atomic and ionic lines such as [0 I]
63 µm, [S I] 25 µm and (Si II] 35 µm, they can also
be used to distinguish between photon- and shock-heated
gas. Finally, spectroscopic data on circumstellar
disks around young stars are mentioned. The
results are discussed in the context of the physical
and chemical evolution of YSOs
A new method for simulating photoprocesses in astrochemical models
Interstellar matter and star formatio