We are using the Very Long Baseline Array and the Japanese VLBI Exploration of Radio Astronomy project to measure trigonometric parallaxes and proper motions of masers found in high-mass star-forming regions across the Milky Way. Early results from 18 sources locate several spiral arms. The Perseus spiral arm has a pitch angle of 16 • ± 3 • , which favors four rather than two spiral arms for the Galaxy. Combining positions, distances, proper motions, and radial velocities yields complete 3-dimensional kinematic information. We find that star forming regions on average are orbiting the Galaxy ≈ 15 km s −1 slower than expected for circular orbits. By fitting the measurements to a model of the Galaxy, we estimate the distance to the Galactic center R 0 = 8.4 ± 0.6 kpc and a circular rotation speed Θ 0 = 254 ± 16 km s −1 . The ratio Θ 0 /R 0 can be determined to higher accuracy than either parameter individually, and we find it -2to be 30.3 ± 0.9 km s −1 kpc −1 , in good agreement with the angular rotation rate determined from the proper motion of Sgr A*. The data favor a rotation curve for the Galaxy that is nearly flat or slightly rising with Galactocentric distance. Kinematic distances are generally too large, sometimes by factors greater than two; they can be brought into better agreement with the trigonometric parallaxes by increasing Θ 0 /R 0 from the IAU recommended value of 25.9 km s −1 kpc −1 to a value near 30 km s −1 kpc −1 . We offer a "revised" prescription for calculating kinematic distances and their uncertainties, as well as a new approach for defining Galactic coordinates. Finally, our estimates of Θ 0 and Θ 0 /R 0 , when coupled with direct estimates of R 0 , provide evidence that the rotation curve of the Milky Way is similar to that of the Andromeda galaxy, suggesting that the dark matter halos of these two dominant Local Group galaxy are comparably massive.

IRAS 04368+2557 is a solar-type (low-mass) protostar embedded in a protostellar core (L1527) in the Taurus molecular cloud, which is only 140 parsecs away from Earth, making it the closest large star-forming region. The protostellar envelope has a flattened shape with a diameter of a thousand astronomical units (1 AU is the distance from Earth to the Sun), and is infalling and rotating. It also has a protostellar disk with a radius of 90 AU (ref. 6), from which a planetary system is expected to form. The interstellar gas, mainly consisting of hydrogen molecules, undergoes a change in density of about three orders of magnitude as it collapses from the envelope into the disk, while being heated from 10 kelvin to over 100 kelvin in the mid-plane, but it has hitherto not been possible to explore changes in chemical composition associated with this collapse. Here we report that the unsaturated hydrocarbon molecule cyclic-C3H2 resides in the infalling rotating envelope, whereas sulphur monoxide (SO) is enhanced in the transition zone at the radius of the centrifugal barrier (100 ± 20 AU), which is the radius at which the kinetic energy of the infalling gas is converted to rotational energy. Such a drastic change in chemistry at the centrifugal barrier was not anticipated, but is probably caused by the discontinuous infalling motion at the centrifugal barrier and local heating processes there.

We have detected the high-excitation lines of carbon-chain molecules such as C 4 H 2 (J ¼ 10 0;10

We have determined the abundances of HCN and HNC toward 19 nearby dark cloud cores by observations of optically thin H13CN (J \ 1È0) and HN13C (J \ 1È0) lines. The column density of HCN is found to be correlated with that of HNC. The abundance ratio of [HNC]/[HCN] is determined to be 0.54È4.5 in the observed dark cloud cores. These results are consistent with the idea that HCN and HNC are produced mainly by a recombination reaction of HCNH`with electrons in dark cloud cores. Furthermore, the [HNC]/[HCN] ratio does not show any signiÐcant di †erences between star-forming cores and starless cores. The HCN and HNC abundances are compared with those for the OMC-1 cores previously reported. Although the abundances of HCN in the OMC-1 cores are comparable to those in the dark cloud cores, the abundances of HNC in OMC-1 are 1È2 orders of magnitude less than those in dark cloud cores. It is suggested that HNC is destroyed by neutral-neutral reactions in high kinetic temperature regions.

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We have surveyed the N 2 H + J=1-0, HC 3 N J=5-4, CCS J N =4 3 -3 2 , NH 3 (J, K) = (1, 1), (2, 2), (3, 3), and CH 3 OH J=7-6 lines toward the 55 massive clumps associated with infrared dark clouds by using the Nobeyama Radio Observatory 45 m telescope and the Atacama Submillimeter Telescope Experiment 10 m telescope. The N 2 H + , HC 3 N, and NH 3 lines are detected toward most of the objects. On the other hand, the CCS emission is detected toward none of the objects. The [CCS]/[N 2 H + ] ratios are found to be mostly lower than unity even in the Spitzer 24 µm dark objects. This suggests that most of the massive clumps are chemically more evolved than the low-mass starless cores. The CH 3 OH emission is detected toward 18 out of 55 objects. All the CH 3 OH-detected objects are associated with the Spitzer 24 µm sources, suggesting that star formation has already started in all the CH 3 OH-detected objects. The velocity widths of the CH 3 OH J K =7 0 -6 0 A + and 7 −1 -6 −1 E lines are broader than those of N 2 H + J=1-0. The CH 3 OH J K =7 0 -6 0 A + and 7 −1 -6 −1 E lines tend to have broader linewidth in the MSX dark objects than in the others, the former being younger or less luminous than the latter. The origin of the broad emission is discussed in terms of the interaction between an outflow and an ambient cloud.

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Sub-arcsecond (0. 5) images of H 2 CO and CCH line emission have been obtained in the 0.8 mm band toward the low-mass protostar IRAS 15398-3359 in the Lupus 1 cloud as one of the Cycle 0 projects of the Atacama Large Millimeter/Submillimeter Array. We have detected a compact component concentrated in the vicinity of the protostar and a well-collimated outflow cavity extending along the northeast-southwest axis. The inclination angle of the outflow is found to be about 20 • , or almost edge-on, based on the kinematic structure of the outflow cavity. This is in contrast to previous suggestions of a more pole-on geometry. The centrally concentrated component is interpreted by use of a model of the infalling rotating envelope with the estimated inclination angle, and the mass of the protostar is estimated to be less than 0.09 M . Higher spatial resolution data are needed to infer the presence of a rotationally supported disk for this source, hinted at by a weak high-velocity H 2 CO emission associated with the protostar.