Molecular ions are known to be key reactive intermediates in interstellar environments, and H3 in particular is responsible for initiating a network of chemical reactions that ultimately results in the formation of the ∼170 molecules detected so far in space. Yet fundamental questions about the interstellar abundances of the two nuclear spin configurations of H3 (ortho-H + 3 , I = 3/2; and para...

This article synthesizes observational data from an extensive program aimed toward a comprehensive understanding of star formation in a low-mass star-forming molecular cloud. New observations and published data spanning from the centimeter wave band to the near infrared reveal the high and low density molecular gas, dust, and pre-main sequence stars in L1551. The total cloud mass of ∼ 160M cont...

We explore the gravitational influence of pressure supported stellar systems on the internal density distribution of a gaseous environment. We conclude that compact massive star clusters with masses & 10 M⊙ act as cloud condensation nuclei and are able to accrete gas recurrently from a warm interstellar medium which may cause further star formation events and account for multiple stellar popula...

I review the use of polarization data in the study of interstellar magnetic fields. On large scales in the interstellar medium, the polarization of background starlight is a good tracer of the projected plane-of-the-sky magnetic field structure in the neutral gas, and the field there appears to have roughly equal contributions from uniform and nonuniform components. In cases where a localized r...

Deuterated hydrogen cyanide (DCN) was detected in a comet, C/1995 O1 (Hale-Bopp), with the use of the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. The inferred deuterium/hydrogen (D/H) ratio in hydrogen cyanide (HCN) is (D/H)HCN = (2.3 +/- 0.4) x 10(-3). This ratio is higher than the D/H ratio found in cometary water and supports the interstellar origin of cometary ices. The observed val...

There is increasing observational evidence that hot, highly ionized interstellar and intergalactic gas plays a significant role in the evolution of galaxies in the local universe. The primary spectral diagnostics of the warm-hot interstellar/intergalactic medium are ultraviolet and X-ray absorption lines of Ovi and Ovii. In this paper, I summarize some of the recent highlights of spectroscopic ...

The reaction of ground-state carbon atoms with acetylene was studied under single-collision conditions in crossed beam experiments to investigate the chemical dynamics of forming cyclic and linear C3H isomers (c-C3H and l-C3H, respectively) in interstellar environments via an atom-neutral reaction. Combined state-of-the-art ab initio calculations and experimental identification of the carbon-hy...

Evidence for triggered star formation is difficult to establish because energy feedback from massive stars tend to erase the interstellar conditions that led to the star formation. Young stellar objects (YSOs) mark sites of current star formation whose ambient conditions have not been significantly altered. Spitzer observations of the Large Magellanic Cloud (LMC) effectively reveal massive YSOs...

The collision of a plane parallel shock wave with a plane parallel cloud of uniform density is analysed for the case in which magnetic fields and radiative losses are not considered. General analytic solutions are discussed for the case in which the density of the cloud is greater than that of the surrounding environment. This problem generalises one of the classical problems in gas dynamics: t...

The diffuse interstellar medium is dynamic, and its chemistry evolution determined by shock fronts as well photodissociation. Shocks are implied the supersonic motions velocity dispersion often statistically called "turbulence". We compare models of magnetohydrodynamic (MHD) shocks, with speeds typical cloud through ISM (3-25 km/s) densities cold neutral gas (~ 100 cm-3), to archival observatio...