L. E. B. Johansson

Long-term Evolution of the Outgassing of Comet Hale-Bopp From Radio Observations

C/1995 O1 (Hale-Bopp) has been observed on a regular basis since August 1995 at millimetre and submillimetre wavelengths using IRAM, JCMT, CSO and SEST radio telescopes. The production rates of eight molecular species (CO, HCN, CH3OH, H2CO,H2S, CS, CH3CN,HNC) have been monitored as a function of heliocentric distance(rh from 7 AU pre-perihelion to 4 AU post-perihelion. As comet Hale-Bopp approached and receded from the Sun, these species displayed different behaviours. Far from the Sun, the most volatile species were found in general relatively more abundant in the coma. In comparison to other species, HNC, H2CO and CS showed a much steeper increase of the production rate with decreasing rh. Less than 1.5 AU from the Sun, the relative abundances were fairly stable and approached those found in other comets near 1 AU.The kinetic temperature of the coma, estimated from the relative intensities of the CH3OH and CO lines, increased with decreasing rh, from about10 K at 7 AU to 110 K around perihelion. The expansion velocity of the gaseous species, derived from the line shapes, also increased with a law close torh3.

Low upper limits on the O2 abundance from the Odin satellite

For the first time, a search has been conducted in our Galaxy for the 119 GHz transition connecting to the ground state of O2, using the Odin satellite. Equipped with a sensitive 3 mm receiver (Tsy ...

N2H+(1–0) survey of massive molecular cloud cores

We present the results of N2H + (1-0) observations of 35 dense molecular cloud cores from the northern and southern hemispheres where massive stars and star clusters are formed. Line emission has been detected in 33 sources, for 28 sources detailed maps have been obtained. Peak N2H + column densities lie in the range: 3:6 10 12 1:5 10 14 cm 2 . Intensity ratios of (01-12) to (23-12) hyperfine components are slightly higher than the LTE value. The optical depth of (23-12) component toward peak intensity positions of 10 sources is0:2 1. In many cases the cores have elongated or more complex structures with several emission peaks. In total, 47 clumps have been revealed in 26 sources. Their sizes lie in the range 0.3-2.1 pc, the range of virial masses is30 3000 M. Mean N2H + abundance for 36 clumps is 5 10 10 . Integrated intensity maps with axial ratios<2 have been fitted with a power-law radial distribution r p convolved with the telescope beam. Mean power-law index for 25 clumps is close to 1.3. For reduced maps where positions of low intensity are rejected mean power-law index is close to unity corresponding to ther 2 density profile provided N 2H + excitation conditions do not vary inside these regions. In those cases where we have relatively extensive and high quality maps, line widths of the cores either decrease or stay constant with distance from the center, implying an enhanced dynamical activity in the center. There is a correlation between total velocity gradient direction and elongation angle of the cores. However, the ratio of rotational to gravitational energy is too low (4 10 4 - 7:1 10 2 ) for rotation to play a significant role in the dynamics of the cores. A correlation between mean line widths and sizes

The 1995-2002 Long-Term Monitoring of Comet C/1995 O1 (HALE-BOPP) at Radio Wavelength

The bright comet Hale-Bopp provided the first opportunity to follow the outgassing rates of a number of molecular species over a large range of heliocentric distances. We present the results of our observing campaign at radio wavelengths which began in August 1995 and ended in January 2002. The observations were carried out with the telescopes of Nancay, IRAM, JCMT, CSO and, since September 1997, SEST. The lines of nine molecules (OH, CO, HCN, CH3OH, H2CO, H2S, CS, CH3CN and HNC) were monitored. CS, H2S, H2CO, CH3CN were detected up to r h = 3–4 AU from the Sun, while HCN and CH3OH were detected up to 6 AU. CO, which is the main driver of cometary activity at heliocentric distances larger than 3–4 AU, was last detected in August 2001, at r h = 14 AU.

Results of the ESO-SEST Key Programme on CO in the Magellanic Clouds X. CO emission from star formation regions in LMC and SMC

We present J = 1 0a ndJ = 2 1 12 CO maps of several star-forming regions in both the Large and the Small Magellanic Cloud, and briefly discuss their structure. Many of the detected molecular clouds are relatively isolated and quite small with dimensions of typically 20 pc. Some larger complexes have been detected, but in all cases the extent of the molecular clouds sampled by CO emission is significantly less than the extent of the ionized gas of the star-formation region. Very little diuse extended CO emission was seen; diuse CO in between or surrounding the detected discrete clouds is either very weak or absent. The majority of all LMC lines of sight detected in 13 CO has an isotopic emission ratio I( 12 CO)=I( 13 CO) of about 10, i.e. twice higher than found in Galactic star-forming complexes. At the lowest 12 CO intensities, the spread of isotopic emission ratios rapidly increases, low ratios representing relatively dense and cold molecular gas and high ratios marking CO photo- dissociation at cloud edges.

Search for Class I methanol masers in low-mass star formation regions

A survey of young bipolar outflows in regions of low-to-intermediate-mass star formation has been carried out in two Class I methanol maser transitions: 7(0) - 6(1)A+ at 44 GHz and 4(-1) - 3(0)E at 36 GHz. We detected narrow features towards NGC 1333I2A, NGC 1333I4A, HH25MMS and L1157 at 44 GHz, and towards NGC 2023 at 36 GHz. Flux densities of the lines detected at 44 GHz are no higher than 11 Jy and the relevant source luminosities are about 1022 erg s-1, which is much lower than those of strong masers in high-mass star formation regions. No emission was found towards 39 outflows. All masers detected at 44 GHz are located in clouds with methanol column densities of the order of or larger than a few x1014 cm-2. The upper limits for the non-detections are typically of the order of 3-5 Jy. Observations in 2004, 2006 and 2008 did not reveal any significant variability of the 44 GHz masers in NGC 1333I4A, HH25MMS and L1157.

Molecular gas conditions in NGC 4945 and the Circinus galaxy

We present results of a multi-transition study of the dense molecular gas in the central part of the hybrid star-burst/Seyfert galaxies NGC 4945 and the Circinus galaxy. From the results of radiative transfer calculations, we estimate in NGC 4945

APEX: the Atacama Pathfinder EXperiment

n_{{\rm H}_2}=3 10^3{-}10^4

First detection of NH3 (10 -g 00) from a low mass cloud core. On the low ammonia abundance of the rho Oph A core

cm -3 and

A 4-6 GHz SPECTRAL SCAN AND 8-10 GHz OBSERVATIONS OF THE DARK CLOUD TMC-1

T_{\rm kin}\approx100