Hiroko Shinnaga

THE MAGNETIC FIELD MORPHOLOGY OF THE CLASS 0 PROTOSTAR L1157-mm

We present the first detection of polarization around the Class 0 low-mass protostar L1157-mm at two different wavelengths. We show polarimetric maps at large scales (10 resolution at 350xa0μm) from the SHARC-II Polarimeter and at smaller scales (1.2-4.5 at 1.3xa0mm) from the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The observations are consistent with each other and show inferred magnetic field lines aligned with the outflow. The CARMA observations suggest a full hourglass magnetic field morphology centered about the core; this is only the second well-defined hourglass detected around a low-mass protostar to date. We apply two different methods to CARMA polarimetric observations to estimate the plane-of-sky magnetic field magnitude, finding values of 1.4 and 3.4 mG.

The Initial Conditions for Gravitational Collapse of a Core: An Extremely Young Low-Mass Class 0 Protostar GF 9-2

We present a study of the natal core harboring the low-mass Class 0 protostar GF 9-2 in the filamentary dark cloud GF 9 using the Nobeyama 45 m and CSO 10.4 m telescopes and the OVRO millimeter array. GF 9-2 is unique in the sense that it shows H_2O masers, a clear signpost of protostar formation, but does not have a high-velocity large-scale outflow. These facts indicate that the GF 9-2 core is early enough after star formation that it still retains some information of initial conditions for collapse. Our 350 μm dust continuum image identified a protostellar envelope with an extent of ≃5400 AU in the center of the molecular core ≃0.08 pc in size. The envelope mass is estimated to be ≃0.6 M_⊙ from the 350 μm flux density, while the LTE mass of the core is ≃3 M_⊙ from molecular lines. We found that the core has a radial density profile of ρ(r) ∝ r^(-2) for the 0.003 ≾ r/pc ≾ 0.08 region and that the velocity width of the core gas increases inward, while the outermost region maintains a velocity dispersion of a few times the ambient sound speed. If we interpret the broadened velocity width as infall, the core collapse can be well described by an extension of the Larson-Penston solution for the period after formation of a central star. We derived the mass accretion rate of ≃3 × 10^(-5) M_⊙ yr^(-1) from infall velocity of ≃0.3 km s^(-1) at r ≃ 7000 AU. Furthermore, we found evidence that a protobinary is being formed at the core center. All of the results suggest that the GF 9-2 core has been undergoing gravitational collapse for ≾5000 yr since the protostar formation and that the unstable state initiated the collapse ≃2 × 10^5 yr (the free-fall time) ago.

Infall, outflow, and rotation in the G19.61-0.23 hot molecular core

Aims. We carried out sub-arcsecond resolution observations towards the high-mass star formation region G19.61−0.23, in both ncontinuum and molecular line emission. While the centimeter continuum images, representing ultra compact HII regions, will be ndiscussed in detail in a forthcoming paper, here we focus on the (sub)mm emission, devoting special attention to the hot molecular ncore (HMC). nMethods. A set of multi wavelength continuum and molecular line emission data between 6 cm and 890 μm were obtained with the nVery Large Array, Nobeyama Millimeter Array, Owens Valley Radio Observatory millimeter array, and Submillimeter Array (SMA). nThese data were analyzed in conjunction with previously published data. nResults. Our SMA observations resolve the HMC into three cores whose masses are on the order of 10^1−10^3 M_⊙. No submm core nexhibits detectable free-free emission in the centimeter regime, but appear to be associated with masers and thermal line emission nfrom complex organic molecules. Towards the most massive core, SMA1, the CH_3CN (18_K−17_K) lines provide hints of rotation nabout the axis of a jet/outflow traced by H_2O maser and H^(13)CO^+(1−0) line emission. Inverse P-Cygni profiles of the ^(13)CO (3−2) and nC^(18)O (3−2) lines seen towards SMA1 indicate that the central high-mass (proto)star(s) is (are) still gaining mass with an accretion nrate ≥3 × 10^(−3) M_⊙ yr^(−1). Owing to the linear scales and high accretion rate, we hypothesize that we are observing an accretion flow ntowards a star cluster in the making, rather than towards a single massive star.

Zeeman Effect on the Rotational Levels of CCS and SO in the 3Σ- Ground State

Zeeman splittings of the rotational transitions of the CCS and SO radicals in the 3Σ- ground electronic state have been calculated. Since the coupling scheme of the rotational angular momentum and the electron-spin angular momentum is intermediate between Hunds cases (a) and (b), the mixing between the F1 and F3 levels has been treated strictly. In order to confirm the calculation, Zeeman splittings of the JN = 43-32 and JN = 32-21 lines of CCS are measured by laboratory microwave spectroscopy. The effective g-factors evaluated in the present study are of particular importance in the determination of the magnetic field strength of dense cores through polarization observations.

IRC+10216'S INNERMOST ENVELOPE—THE eSMA'S VIEW

We used the Extended Submillimeter Array (eSMA) in its most extended configuration to investigate the innermost (within a radius of ~290 R_* from the star) circumstellar envelope (CSE) of IRC+10216 where acceleration of gas and dust due to strong stellar radiation is taking place. We imaged the CSE using HCN and other molecular lines with a beam size of 0.22 × 0.46, deeply into the very inner edge (~15 R_*) of the envelope where the expansion velocity is only ~3 km s^(–1). The excitation mechanisms of hot HCN and KCl lines are discussed. HCN maser components are spatially resolved for the first time on an astronomical object. We identified two discrete regions in the envelope: a region with a radius of ≾ 15 R_*, where molecular species have just formed and the gas has begun to be accelerated (Region I) and a shell region (Region II) with a radius of 23 R_* and a thickness of 15 R_*, whose expansion velocity has reached up to 13 km s–1, nearly the terminal velocity of 15 km s^(–1). The Si^(34)S line detected in Region I shows a large expansion velocity of 16 km s^(–1) due to strong wing components, indicating that the emission may arise from a shock region in the innermost envelope. In Region II, the position angle of the most copious mass-loss direction was found to be ~ 120° ± 10°, which may correspond to the equatorial direction of the star. Region II contains a torus-like feature. These two regions may have emerged due to significant differences in the size distributions of the dust particles in the two regions.

HIGH-VELOCITY MOLECULAR OUTFLOW IN CO J = 7-6 EMISSION FROM THE ORION HOT CORE

Using the Caltech Submillimeter Observatory 10.4 m telescope, we performed sensitive mapping observations of ^(12)CO J = 7-6 emission at 807 GHz toward Orion IRc2. The image has an angular resolution of 10, which is the highest angular resolution data toward the Orion Hot Core published for this transition. In addition, thanks to the on-the-fly mapping technique, the fidelity of the new image is rather high, particularly in comparison with previous images. We have succeeded in mapping the northwest-southeast high-velocity molecular outflow, whose terminal velocity is shifted by ~70-85 km s^(–1) with respect to the systemic velocity of the cloud. This yields an extremely short dynamical time scale of ~900 years. The estimated outflow mass loss rate shows an extraordinarily high value, on the order of 10^(–3) M_⊙ yr^(–1). Assuming that the outflow is driven by Orion IRc2, our result agrees with the picture so far obtained for a 20 M_⊙ (proto)star in the process of formation.

Relative Evolutionary Timescale of Hot Molecular Cores with Respect to Ultracompact H II Regions

Using the Owens Valley and Nobeyama Radio Observatory interferometers, we carried out an unbiased search for hot molecular cores and ultracompact (UC) H II 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 database. 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 nine UC H II 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 H II 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 the HC lifetime is less than ~1/3 of that of UC H II regions on the basis of the source number ratio between them.

CLUSTER FORMATION TRIGGERED BY FILAMENT COLLISIONS IN SERPENS SOUTH

The Serpens South infrared dark cloud consists of several filamentary ridges, some of which fragment into dense clumps. On the basis of CCS (

Submillimeter Observations of the Isolated Massive Dense Clump IRAS 20126+4104

J_N=4_3-3_2

MAGNETIC FIELD IN THE ISOLATED MASSIVE DENSE CLUMP IRAS 20126+4104

), HC