Variations in the HCN/HNC abundance ratio in the Orion molecular cloud

We have used observations of the rare isotopes of HCN and HNC to determine the relative abundance of these two chemical isomers along the central ridge of the Orion molecular cloud. The abundance ratio [HCN]/[HNC] decreases by more than an order of magnitude from the relatively warm plateau and hot core sources toward the KL nebula to the colder, more quiescent clouds to the north and south. Even in the cooler regions, however, the ratio is an order of magnitude larger than that found in previous investigations of cold dark clouds. We determine the kinetic temperature in the regions we have studied from new observations of methylacetylene (CH3CCH), together with other recent estimates of the gas temperature near KL. The results suggest that the warmer portions of the cloud are dominated by different chemical pathways than those in the general interstellar cloud material.     

1300 micron continuum and C18O line mapping of the giant molecular cloud cores in Orion, W49, and W51

We present observations of the 1300 micron continuum emission and the C18O spectral-line emission from three well-studied giant molecular cloud cores: Orion, W49, and W51. The observations were obtained at the Five College Radio Astronomy Observatory, and they provide a means to examine the consistency of these two methods to trace the column density structure of molecular clouds. We find a good general correlation between the 1300 micron continuum, which traces the column density of dust, and the C18O J = 2 --> 1 line emission, which traces the column density of molecular gas, when the effects of source temperature are taken into consideration. Moreover, nominal values for the gas and dust abundances and the dust properties reproduce the observed continuum-to-line ratios. Thus, no strong C18O abundance gradients within sources has been found, and it appears that either the C18O emission lines or the submillimeter dust emission may be used to derive the mass column density within molecular clouds accurately.     

An upper limit to the acetylene abundance toward BN in the Orion molecular cloud

We report a search for the acetylene (C2H2) nu 3 infrared vibration-rotation absorption near 3 micrometers toward the Becklin-Neugebauer source in the Orion molecular cloud. The relative abundance of C2H2/CO in the quiescent gas (9 km s-1 component) is less than 3 x 10(-3) (5 sigma).     

Observations of molecular jets in Orion A

We report on the results of a wide field near infrared survey for protostellar jets identified via their emission in the 2.12μm line of shock heated molecular hydrogen, done over a 1.2 square degree area in Orion A. We derive an evolutionary sequence for protostellar jets, based on the observed lenghts and H₂ luminosities as well as the evolutionary stage and bolometric luminosity of their driving sources. Protostellar jets start from zero length, evolve quickly to parsec scale extents during the Class 0 phase, and shrink during the Class I and Class II phase. They are first very bright in H₂ emission, and fade later on. This is indicative of strongly time-variably mass accretion onto the driving protostar, with a peak early on, and a subsequent continous decay of accretion activity. Finally, we present evidence for a molecular CO jet from a Class 0 object, supporting the idea that a very efficient outflow phase at very early evolutionary stages should produce very dense, molecular jets.     

The star-forming content of the W3 giant molecular cloud

We have surveyed a ∼0.9 square degree area of the W3 giant molecular cloud (GMC) and star-forming region in the 850-μm continuum, using the Submillimetre Common-User Bolometer Array on the James Clerk Maxwell Telescope. A complete sample of 316 dense clumps were detected with a mass range from around 13 to  2500 M_⊙  . Part of the W3 GMC is subject to an interaction with the H  ii region and fast stellar winds generated by the nearby W4 OB association. We find that the fraction of total gas mass in dense, 850-μm traced structures is significantly altered by this interaction, being around 5–13 per cent in the undisturbed cloud but ∼25–37 per cent in the feedback-affected region. The mass distribution in the detected clump sample depends somewhat on assumptions of dust temperature and is not a simple, single power law but contains significant structure at intermediate masses. This structure is likely to be due to crowding of sources near or below the spatial resolution of the observations. There is little evidence of any difference between the index of the high-mass end of the clump mass function in the compressed region and in the unaffected cloud. The consequences of these results are discussed in terms of current models of triggered star formation.     

On the possible equation of state of a giant molecular cloud

We intend to probe into the nature of the thermodynamical equilibrium of an idealized isothermal, spherical, self-gravitating, giant molecular cloud. The necessity of invoking a frozen in magnetic field has been pointed out for clouds with uniform mass distribution. An equation of state corresponding to the macroscopic statistical equilibrium of the cloud, steeped into a weak homogeneous magnetic field, has also been derived.     

A search for 22-GHz water masers within the giant molecular cloud associated with RCW 106

We report the results of a blind search for 22-GHz water masers in two regions, covering approximately half a square degree, within the giant molecular cloud associated with RCW 106. The complete search of the two regions was carried out with the 26-m Mount Pleasant radio telescope and resulted in the detection of nine water masers, five of which are new detections. Australia Telescope Compact Array (ATCA) observations of these detections have allowed us to obtain positions with arcsecond accuracy, allowing meaningful comparison with infrared and molecular data for the region. We find that for the regions surveyed there are more water masers than either 6.7-GHz methanol, or main-line OH masers. The water masers are concentrated towards the central axis of the star formation region, in contrast to the 6.7-GHz methanol masers which tend to be located near the periphery. The colours of the GLIMPSE point sources associated with the water masers are similar to those of 6.7-GHz methanol masers, but slightly less red. We have made a statistical investigation of the properties of the ¹³CO and 1.2-mm dust clumps with and without associated water masers. We find that the water masers are associated with the more massive, denser and brighter ¹³CO and 1.2-mm dust clumps. We present statistical models that are able to predict those ¹³CO and 1.2-mm dust clumps that are likely to have associated water masers, with a low misclassification rate.     

A comparison of the rotational properties of T Tauri stars in Orion and Taurus

We analyse the distribution of projected equatorial velocities ( v  sin  i ) for a magnitude-limited sample of stars in Taurus, in order to assess whether this sample can contain a population of fast rotators (missed in previous photometric monitoring campaigns) similar to those recently discovered in Orion by Stassun et al. We find strong evidence, in line with the results of photometric monitoring campaigns in Taurus, that there is no such population of stars in Taurus that rotate at a large fraction of breakup velocity. We thus demonstrate that the stellar rotation distributions in the two star-forming regions are intrinsically different (with a statistical significance of this discrepancy in excess of 3 σ ), and discuss possible origins for this difference.     

Detection of new filamentary nebulosity near the giant non-thermal radio loop II

IIIaJ survey plates from the 1.2m SRC Schmidt have been high contrast copied in search for nebulosity at high galactic latitudes in the vicinity of the giant radio loop II. Some filamentary nebulosity, possibly reflection, has been certainly detected.     

Evolution of filamentary molecular clouds in the presence of magnetic fields

The purpose of this paper is to explore the effect of magnetic fields on the dynamics of magnetized filamentary molecular clouds.We suppose there is a filament with cylindrical symmetry and two components of axial and toroidal magnetic fields.In comparison to previous works,the novelty in the present work involves a similarity solution that does not define a function of the magnetic fields or density.We consider the effect of the magnetic field on the collapse of the filament in both axial and toroidal directions and show that the magnetic field has a braking effect,which means that the increasing intensity of the magnetic field reduces the velocity of collapse.This is consistent with other studies.We find that the magnetic field in the central region tends to be aligned with the filament axis.Also,the magnitude and the direction of the magnetic field depend on the magnitude and direction of the initial magnetic field in the outer region.Moreover,we show that more energy dissipation from the filament causes a rise in the infall velocity.     

The expansion of the giant filamentary shell, DEM 171, in the Magellanic Bridge

The giant filamentary shell, DEM 171, is found to be expanding at approximately 37 km s⁻¹. A supernova and stellar wind origin are both explored as possible causes for the expanding shell. A stellar wind origin would imply a mass-loss rate of the order of 10⁻⁵ M_⊙ yr⁻¹, indicating that it could be caused by a Wolf–Rayet star. A number of blue stars are found to lie within the shell and one is identified as a Wolf–Rayet candidate.     

A giant Hii ring and energetic stellar winds in the large magellanic cloud

A large ring, 50 pc diameter, of H+[Nii] emission in the LMC has been investigated using several instruments. It is suggested that stellar winds from O and B stars could play a vital role in the formation of the structures revealed.     

Optical surface features and morphologic properties of the Orion Nebula

In the field partsH, K, L andM of the Orion Nebula, indicated in Figure 2, no obvious differences do appear in the monochromatic photographs obtained in H+[Nii], [Oii], the visual continuum and the range of the Balmer continuum. A different situation we meet in the rest of the field, where one observes two types of featuresA andB, distinguished in Figure 1 by solid and dashed bordering lines respectively. Relative to the conditions in the H+[Nii] pictures, the typeA areas gain in intensity in the photographs taken in the visual continuum. the emission in the forbidden [Oii] lines at 3727 Å is correlated with H+[Nii], the emission in the range of the Balmer continuum with the visual continuum. According to these properties theA-areas must have a particularly high percentage of scattered star light.Most of the areas with identical monochromatic features show a high deficiency of cluster stars correlated with a low surface brightnesss and a reduced gas density. This is explained by an opaqueness of the emission strata in the direction in the line of sight and a position of the same nearer to the observer than the extension of the cluster. There appear surface structures at large distances from the Trapezium which show a correlation between the intensity of scattered star light and the intensity of the emission of the higher ions ([Oiii], [Neiii]). This observation is considered as a proof that canals through the nebular cloud complex allow in some directions the exciting radiation to reach large distances from the star without having suffered an appreciable absorption or scattering.     

Atmospheric and cloud structures of the Jovian planets

Wet adiabatic atmospheric models are computed for the four Jovian planets. Possible cloud-forming condensates considered are H₂O ice, aqueous NH₃ solution, NH₄SH, and solid NH₃, CH₄, and Ar. Some techniques for computer calculation of condensation in a multiphase system of variable composition are discussed. Nominal models are computed for all four-planets, and the effects of variations in composition and different pressure-temperature regimes are investigated in detail for Jupiter. The meaning of the calculated cloud densities and their relation to the actual densities are discussed. The computed atmospheric profiles represent average conditions, subject to considerable local variations.