Tarja Liljestrom

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 ...

Submilliarcsecond Linear Polarization Observations of Water Masers in W51 M

We present the first 22 GHz polarimetric VLBI images of low-velocity water masers in the star-forming region W51 M. The compact maser concentration found near the reference position of W51 M is identified as a protostellar cocoon with both rotational and radial motions. The inner and outer radii of this water maser cocoon are 5 and 66 AU, respectively. Adjacent to this protostellar cocoon we see a 1200 AU long linear maser structure at a position angle of 200° (the streamer), which is roughly aligned with the Galactic magnetic field projection on the sky and the polarization position angle of these masers. The streamer masers move longitudinally along this direction with a median space velocity of 25 (±8.4) km s-1 relative to the centroid of the cocoon. In contrast to the cocoon masers, which show a mean linear polarization of only 3% (maximum 13%), the masers in the streamer exhibit higher degrees of linear polarization (mean 12%; maximum 35%). The level of distortion in the polarization directions of the streamer masers from the magnetic field direction together with the observationally estimated nonthermal velocity dispersion of the streamer spots with respect to the mean velocity of the streamer yield a preshock magnetic field strength, perpendicular to the shock velocity, of 0.9-1.2 (±0.25) mG. Inside the streamer masers we estimate the typical magnetic field strength to be 38 (±15) mG. We present statistics of the cocoon and streamer masers and discuss the origin of the maser stream, which is difficult to explain as an outflow from W51 M. Most likely the streamer is produced by shocks caused by the nearby expanding H II region, which interacts with the dense molecular core of W51 M on its western side. The proximity to the protostar suggests that these shocks have affected, or even triggered, the star formation in W51 M.

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

Odin has successfully observed the molecular core rho Oph A in the 572.5 GHz rotational ground state line of ammonia, NH3 (JK = 10 -> 00). The interpretation of this result makes use of compleme ...

Water and ammonia abundances in S140 with the Odin satellite

We investigate the effect of the physical environment on water and ammonia abundances across the S140 photodissociation region (PDR) with an embedded outflow. We used the Odin satellite to obtain strip maps of the ground-state rotational transitions of ortho-water and ortho-ammonia, as well as CO(5-4) and 13co(5-4) across the PDR, and H_2^18O in the central position. A physi-chemical inhomogeneous PDR model was used to compute the temperature and abundance distributions for water, ammonia, and CO. A multi-zone escape probability method then calculated the level populations and intensity distributions. These results are compared to a homogeneous model computed with an enhanced version of the RADEX code. H_2O, NH_3, and ^13CO show emission from an extended PDR with a narrow line width of ~3 km/s. Like CO, the water line profile is dominated by outflow emission, but mainly in the red wing. Even though CO shows strong self-absorption, no signs of self-absorption are seen in the water line. The H_2^18O molecule is not detected. The PDR model suggests that the water emission arises mainly from the surfaces of optically thick, high-density clumps with n(H_2)>10^6 cm^-3 and a clump water abundance, with respect to H_2, of 5*10^-8. The mean water abundance in the PDR is 5*10^-9 and between ~4*10^-8 - 4*10^-7 in the outflow derived from a simple two-level approximation. The RADEX model points to a somewhat higher average PDR water abundance of 1*10^-8. At low temperatures deep in the cloud, the water emission is weaker, likely due to adsorption onto dust grains, while ammonia is still abundant. Ammonia is also observed in the extended clumpy PDR, likely from the same high density and warm clumps as water. The average ammonia abundance is about the same as for water: 4*10^-9 and 8*10^-9 given by the PDR model and RADEX, respectively. The differences between the models most likely arise from uncertainties in density,beam-filling, and volume-filling of clumps. The similarity of water and ammonia PDR emission is also seen in the almost identical line profiles observed close to the bright rim. Around the central position, ammonia also shows some outflow emission, although weaker than water in the red wing. Predictions of the H_2O 1(1,0)-1(0,1) and 1(1,1)-0(0,0) antenna temperatures across the PDR are estimated with our PDR model for the forthcoming observations with the Herschel Space Observatory.