We report on a search for the parental molecular clouds of the TW Hya association (TWA), using CO emission and Na I absorption lines. TWA is the nearest young (∼ 50 pc; ∼ 10 Myr) stellar association, yet in spite of its youth, there are no detection of any associated natal molecular gas, as is the case for other typical young clusters. Using infrared maps as a guide, we conducted a CO cloud sur...

Context. The ∆-variance analysis is an efficient tool for measuring the structural scaling behaviour of interstellar turbulence in astronomical maps. It has been applied both to simulations of interstellar turbulence and to observed molecular cloud maps. In paper I we proposed essential improvements to the ∆-variance analysis and tested them on artificial structures with known characteristics. ...

We have observed the 492 GHz ground-state line of atomic carbon in the edge-on ionization fronts in M17 and .s1~0. y.te find that, contrary to expectation, the C I emission peaks farther into the molecular cloud from t~e Iomza~IO~ fro~t than does the CO. In fact the peak C I abundance in M17 occurs more than 60 mag of visual extmctton mto the cloud from the ionization front. Calculations of the...

Infrared spectra have been obtained for laboratory residues of photoprocessed low-temperature ices which have been exposed to long-term solar ultraviolet radiation on the EURECA satellite. This is an analog to the ultraviolet processing of interstellar dust mantles in diffuse clouds after leaving molecular clouds. The 3.4 mm absorption features of these organic materials match those of the diff...

We have observed emission from the 492 GHz lines of C I toward six positions in the Ophiuchus molecular cloud complex for which accurate visual extinctions are available. We find that the column density of C I increases with Av to greater than 2 x 1017 em 2 at 100 mag, the column-averaged fractional abundance reaches a peak of about 2.2 x 10-s for Av in the range 4-11 mag and the column-average...

Recent high resolution numerical simulations have suggested that the interstellar atomic hydrogen clouds have a complex two-phase structure. Since molecular clouds form through the contraction of HI gas, the question arises as to whether this structure is maintained in the molecular phase or not. Here we investigate whether the warm neutral atomic hydrogen (WNM) can exist in molecular clouds. W...

We study the formation and evolution of several molecules in a collapsing interstellar cloud using a reasonably large reaction network containing more then four hundred atomic and molecular species. We employ a time dependent, spherically symmetric, hydrodynamics code to follow the hydrodynamic and chemical evolution of the collapsing cloud. The flow is assumed to be self-gravitating. We use tw...

The interstellar cloud surrounding the solar system regulates the galactic environment of the Sun, and determines the boundary conditions of the heliosphere. Both the Sun and interstellar clouds move through space, so these boundary conditions change with time. Data and theoretical models now support densities in the cloud surrounding the solar system of n(H)=0.22±0.06 cm, and n(e)∼0.1 cm, with...

We present results from a deep optical (VRI) and near infrared (JHK) survey of the central part of the Serpens molecular cloud. A total of 138 sources were detected in the 19 arcmin2 surveyed area down to a limiting magnitude of 16.3 in K. We find that the form of the observed K Luminosity Function (KLF) of stars belonging to the Serpens Molecular cloud is consistent with that predicted from a ...

We present a two-component gasdynamic model of an interstellar cloud embedded in a hot plasma. It is assumed that the cloud consists of atomic hydrogen gas, interstellar plasma is quasineutral. Hydrogen atoms and plasma protons interact through a charge exchange process. Magnetic fields and radiative processes are ignored in the model. The influence of heat conduction within plasma on the inter...