Search

Using the OVRO, Nobeyama, and IRAM mm-arrays, we searched for ``disk''-outflow systems in three high-mass (proto)star forming regions: G16.59-0.05, G23.01-0.41, and G28.87+0.07. These were selected from a sample of NH3 cores associated with OH and H2O maser emission and with no or very faint continuum emission. Our imaging of molecular line (including rotational transitions of CH3CN and 3mm dust continuum emission revealed that these are compact, massive, and hot molecular cores (HMCs), that is likely sites of high-mass star formation prior to the appearance of UCHII regions. All three sources turn out to be associated with molecular outflows from CO and/or HCO+ J=1--0 line imaging. In addition, velocity gradients of 10 -- 100 km/s per pc in the innermost densest regions of the G23.01 and G28.87 HMCs are identified along directions roughly perpendicular to the axes of the corresponding outflows. All the results suggest that these cores might be rotating about the outflow axis, although the contribution of rotation to gravitational equilibrium of the HMCs appears to be negligible. Our analysis indicates that the 3 HMCs are close to virial equilibrium due to turbulent pressure support. Comparison with other similar objects where rotating toroids have been identified so far shows that in our case rotation appears to be much less prominent; this can be explained by the combined effect of unfavorable projection, large distance, and limited angular resolution with the current interferometers., Comment: Accepted by ApJ main journal, the paper with the original quality figures are available from http://subarutelescope.org/staff/rsf/publication.html

This article reports first results of a long-term observational program aimed to study the earliest evolution of jet/disk systems in low-mass YSOs by means of VLBI observations of the 22.2 GHz water masers. We report here data for the cluster of low-mass YSOs in the Serpens molecular core and for the single object RNO~15-FIR. Towards Serpens SMM1, the most luminous sub-mm source of the Serpens cluster, the water maser emission comes from two small (< 5 AU in size) clusters of features separated by ~25 AU, having line of sight velocities strongly red-shifted (by more than 10 km/s) with respect to the LSR velocity of the molecular cloud. The two maser clusters are oriented on the sky along a direction that is approximately perpendicular to the axis of the radio continuum jet observed with the VLA towards SMM1. The spatial and velocity distribution of the maser features lead us to favor the interpretation that the maser emission is excited by interaction of the receding lobe of the jet with dense gas in the accretion disk surrounding the YSO in SMM1. Towards RNO~15-FIR, the few detected maser features have both positions and (absolute) velocities aligned along a direction that is parallel to the axis of the molecular outflow observed on much larger angular scales. In this case the maser emission likely emerges from dense, shocked molecular clumps displaced along the axis of the jet emerging from the YSO. The protostar in Serpens SMM1 is more massive than the one in RNO~15-FIR. We discuss the case where a high mass ejection rate can generate jets sufficiently powerful to sweep away from their course the densest portions of circumstellar gas. In this case, the excitation conditions for water masers might preferably occur at the interface between the jet and the accretion disk, rather than along the jet axis., Comment: 18 pages (postscript format); 9 figures; to be published into Astronomy & Astrophysics, Main Journal

Using the Owens Valley and Nobeyama Radio Observatory interferometers, we carried out an unbiased search for hot molecular cores and ultracompact UC HII regions toward the high-mass star forming region G19.61--0.23. In addition, we performed 1.2 mm imaging with SIMBA, and retrieved 3.5 and 2 cm images from the VLA archive data base. The newly obtained 3 mm image brings information on a cluster of high-mass (proto)stars located in the innermost and densest part of the parsec scale clump detected in the 1.2 mm continuum. We identify a total of 10 high-mass young stellar objects: one hot core (HC) and 9 UC HII regions, whose physical parameters are obtained from model fits to their continuum spectra. The ratio between the current and expected final radii of the UC \HII regions ranges from 0.3 to 0.9, which leaves the possibility that all O-B stars formed simultaneously. Under the opposite assumption -- namely that star formation occurred randomly -- we estimate that HC lifetime is less than $\sim$1/3 of that of UCHII regions on the basis of the source number ratio between them., Comment: 13 pages, 2 figs, including a color fig

We have conducted multi-epoch synthesis imaging of 2 and 3 millimeter (mm) continuum emission and near infrared K band 2.2 um imaging of a flare event in January 2003 that occurred on the young stellar object GMR-A which is suggested to be a weak-line T Tauri star in the Orion cluster. Our mm data showed that the flare activity lasted at least over 13 days, whereas the K-band magnitude did not change during this event. In addition, we have succeeded in detecting short time variations of flux on the time scales of 15 minutes. The total energy of the flare is estimated to be 10^{35-36} erg, which makes it one of the most energetic flares reported to date. Comparing the mm continuum luminosities with reported X-ray luminosities, we conclude that the mm flare was similar in nature to solar and other stellar flares. Our results will be a crucial step toward understanding magnetically induced stellar surface activities in T Tauri stars., Comment: 5 pages, 5 figures

We present results from a study of molecular gas and dust in the vicinity of the Herbig Haro object HH2. Emission from the sub-mm continuum, 12CO and HCO+ was mapped with angular resolutions ranging from 14 arcsec to 5 arcsec (or 0.01pc at the distance of HH2). The continuum shows an extended dust clump of mass 3.8Msun and temperature 22K, located downstream of the bright optical HH knots. However, a compact emission peak lies within ~0.01pc of the low-excitation H2-prominent shocks, with a luminosity consistent with local heating by the outflow. The HCO+ emission shows two velocity components: firstly, ambient-velocity gas lying in a region roughly corresponding to the dust clump, with abundance enhanced by a factor of a few close to the H2-prominent knots. Secondly a component of high-velocity emission (20 km/s linewidth), found mainly in a collimated jet linking the low-excitation HH objects. In this high-velocity jet, the line wings show an abundance ratio HCO+/CO proportional to v^2, with an HCO+ enhancement compared with ambient gas of up to 10^3 at the most extreme velocities. Such high abundances are consistent with models of shock chemistry in turbulent mixing layers at the interaction boundaries of jets. Extrapolating this effect to low velocities suggests that the more modest HCO+ enhancement in the clump gas could be caused by low velocity shocks. A UV precursor may not, therefore be necessary to explain the elevated HCO+ abundance in this gas., Comment: 8 pages. 9 figures. To be published in MNRAS

We conducted VLA observations at 0".06 resolution of the 22 GHz water masers toward the Class 0 source S106 FIR (d=600 pc; 15" west of S106-IRS4) on two epochs separated by ~3 months. Two compact clusters of the maser spots were found in the center of the submillimeter core of S106 FIR. The separation of the clusters was ~80 mas (48 AU) along P. A. = 70 degrees and the size of each cluster was ~20 mas x 10 mas. The western cluster, which had three maser components, was 7.0 km/s redshifted with respect to the ambient cloud velocity. Each component was composed of a few spatially localized maser spots and was aligned on a line connecting the clusters. We found relative proper motions of the components with ~30 mas/yr (18 AU/yr) along the line. In addition, a series of single-dish observations show that the maser components drifted with a radial acceleration of ~1 km/s/yr. These facts indicate that the masers could be excited by a 10 AU-scale jet-like accelerating flow ejected from an assumed protostar located between the two clusters. The outflow size traced by the masers was 50 AU x 5 AU after correction for an inclination angle of 10 degrees which was derived from the relative proper motions and radial velocities of the maser components. The three-dimensional outflow velocity ranged from 40 to 70 km/s assuming symmetric motions for the blue and red components. Since no distinct CO molecular outflows have been detected so far, we suggest that S106 FIR is an extremely young protostar observed just after the onset of outflowing activity., Comment: 24 pages, 6 figures, No. 5 color. Accepted, Astrophysical Journal