The influence of shocks on star formation in the OMC1 Ridge

Observations are presented of the OMC1 Ridge (a narrow band of molecular gas containing high-mass embedded sources), in the transitions CN N = 2 - 1, 13CO J = 2 - 1 and 13S J = 5 - 4. Variations in velocities and line widths indicate that three distinct regions are present in the area mapped, and that at least one of these is rotating. The resulting shocks when these fragments collided will have compressed the gas to a density nH2~107-8cm-3, sufficient to trigger collapse and to explain the presence of high-mass stars at the edges of the cloud fragments, rather than in their cores. These observational results support theoretical predictions of the importance of collisions in star formation

X-ray variability of the quasar 3C273

Observations of the quasar 3C273 made during 1975-77 have shown that the X-ray flux varied on a time scale of several months. No similar variation was present in radio and optical data taken at similar times. If this variation results from luminosity variations of a central compact object, then an upper limit of ≤4 x 1017cm can be set on its dimensions

Molecular line maps of the Galactic Centre Circumnuclear Disk

Prelimary results are discussed for a long-term programme carried out with the James Clerk Maxwell 15m Telescope, to map the structure and dynamics of the Circumnuclear Disc at the Galactic Centre in a wide range of millimetre and submilletre wavelength molecular line transitions

CO and CI observations of shock excited gas in IC443C

The blast-wave at the edge of the supernova remnant IC443 is colliding with nearby quiescent gas. In this paper a multi-transition study of CO J = 1 - 0 → J = 4 - 3 is presented of one of these clouds, IC443C, and the detection of atomic carbon, CI, reported. The CO is optically thin with Tex ~ 45K, a measured isotopic ratio CO/13CO = 80, and N(CO) ~ 2 - 4 1017. Atomic carbon emission was detected for the first time in shocked gas only towards the IC443C C-shocked region, with an abundance ratio CI/CO ~ 1.3 - 2.9. CI is overabundant by one order of magnitude compared with quiescent molecular cloud cores, suggesting that shock(s), or an enhanced cosmic ray flux density, has increased the CI/CO ratio. A narrow CO absorption line towards the shocked region IC443G has Tex ~ 13-18K, and nH2 ~ 2-3 103 cm-3, which may be typical of conditions in the pre-shock gas

LYNDS 379 - a new source of bipolar molecular flow

A study has been made incorporating molecular line CO J = 2-1 and optical star counting techniques of the sharp-edged Lynds dark cloud 379. It is found to lie at a distance of 200 pc, and to have an average extinction, AB, of <2 mag. Molecular mapping has revealed the presence of a new bipolar molecular flow source coincident with a strong IRAS far infrared peak. This indicates the presence of active star formation at the edge of the cloud - possibly as a consequence of the mechanism (such as an interstellar shock) which has led to compression of the edge of L379

Towards a Molecular Inventory of Protostellar Discs

The chemical environment in circumstellar discs is a unique diagnostic of the thermal, physical and chemical environment. In this paper we examine the structure of star formation regions giving rise to low mass stars, and the chemical environment inside them, and the circumstellar discs around the developing stars.Comment: 9 page PDF, 550 kbyte

A high resolution millimetre and submillimetre study of W3

The continuum bolometer receiver on the James Clerk Maxwell telescope has been used to map the dense core of the star formation region W3 with a spatial resolution of 15-20 arcsec. At 350 and 800 μm, the region appears as two principal peaks around the known IR sources IRS4 and IRS5, while at 1100 μm, a further peak is noted which is interpreted as being due to free-free emission around IRS2. Taking into account the free-free contribution to the intensity, the continuum dust emission from the region is found to be consistent with optically thin emission at all of the three wavelengths considered. Values for the dust optical depth, hydrogen column density, mass, and central density have been obtained for each of the main peaks

CI, CO and 790 μm continuum observations of the Orion molecular cloud and ionisation bar

The spatial distributions of the 3P1-3P0 atomic fine structure of carbon (CI), the CO J=4-3,the CO J=2→1 transitions of CO, 13CO, C18O and C17O and the 790 μm continuum emission have been mapped towards the central region of the Orion molecular cloud (OMC1 cloud), and the Bright Bar ionisation front. The CO data are analysed in a consistent way, allowing the inter isotopomeric abundance ratios to be studied over a wide range of extinction values. The 13CO lines are optically thick; the 13CO abundance being enhanced because of strong isotopic fractionation near the Bright Bar, but less convincingly in the OMC1 cloud. The fractionation occurs mostly in the less opaque regions where the 13CO column density N(13CO) may be enhanced by up to one order of magnitude, relative to the more shielded parts. No isotope selective enhancement of the other CO isotopomers was seen; C18O may in fact show a slight depletion in more exposed material. The C18O and C17O lines are optically thin, and correlated with the 790 μm dust continuum emission. The CI emission comes from hot optically thin gas; the abundance ratios of CI/CO are typically 0.05-0.3, with the larger ratios towards the northern section of the Orion ridge. The CI abundance ratios remain high along the edge of the Bright Bar which is adjacent to the HII region (and the Trapezium cluster which excites it), but decrease in the dense shielded material behind the Bar