Huei-Ru Chen

A High-Mass Protobinary System in the Hot Core W3(H2O)

We have observed a high-mass protobinary system in the hot core W3(H2O) with the BIMA array. Our continuum maps at wavelengths of 1.4 and 2.8 mm both achieve subarcsecond angular resolutions and show a double-peaked morphology. The angular separation of the two sources is 119, corresponding to 2.43 ? 103 AU at the source distance of 2.04 kpc. The flux densities of the two sources at 1.4 and 2.8 mm have a spectral index of 3, translating to an opacity law of ?? ?. The small spectral indices suggest that grain growth has begun in the hot core. We have also observed five K components of the methyl cyanide (CH3CN) J = 12 ? 11 transitions. A radial velocity difference of 2.81 ? 0.10 km s-1 is found toward the two continuum peaks. Interpreting these two sources as binary components in orbit about each other, we find a minimum mass of 22 M? for the system. Radiative transfer models are constructed to explain both the continuum and methyl cyanide line observations of each source. Power-law distributions of both density and temperature are derived. Density distributions close to the free-fall value, r-1.5, are found for both components, suggesting continuing accretion. The derived luminosities suggest that the two sources have equivalent zero-age main-sequence (ZAMS) spectral type B0.5-B0. The nebular masses derived from the continuum observations are about 5 M? for source A and 4 M? for source C. A velocity gradient previously detected may be explained by unresolved binary rotation with a small velocity difference.

FRAGMENTATION AND OB STAR FORMATION IN HIGH-MASS MOLECULAR HUB-FILAMENT SYSTEMS

Filamentary structures are ubiquitously seen in the interstellar medium. The concentrated molecular mass in the filaments allows fragmentation to occur in a shorter timescale than the timescale of the global collapse. Such hierarchical fragmentation may further assist the dissipation of excessive angular momentum. It is crucial to resolve the morphology and the internal velocity structures of the molecular filaments observationally. We perform 05-25 angular resolution interferometric observations toward the nearly face-on OB cluster-forming region G33.92+0.11. Observations of various spectral lines, as well as the millimeter dust continuum emission, consistently trace several ~1?pc scale, clumpy molecular arms. Some of the molecular arms geometrically merge to an inner 3.0 + 2.8 ? 1.4 ? 103 M ?, 0.6?pc scale central molecular clump, and may directly channel the molecular gas to the warm (~50?K) molecular gas immediately surrounding the centrally embedded OB stars. The NH3 spectra suggest a medium turbulence line width of FWHM 2?km?s?1 in the central molecular clump, implying a 10?times larger molecular mass than the virial mass. Feedbacks from shocks and the centrally embedded OB stars and localized (proto)stellar clusters likely play a key role in the heating of molecular gas and could lead to the observed chemical stratification. Although (proto)stellar feedbacks are already present, G33.92+0.11 chemically appears to be at an early evolutionary stage given by the low abundance limit of SO2 observed in this region.

Deuterium Fractionation as an Evolutionary Probe in Massive Protostellar/Cluster Cores

Clouds of high infrared extinction are promising sites of massive star/cluster formation. A large number of cloud cores discovered in recent years allow for the investigation of a possible evolutionary sequence among cores in early phases. We have conducted a survey of deuterium fractionation toward 15 dense cores in various evolutionary stages, from high-mass starless cores to ultracompact H II regions, in the massive star-forming clouds of high extinction, G34.43+0.24, IRAS 18151–1208, and IRAS 18223–1243, with the Submillimeter Telescope. Spectra of N2H+ (3-2), N2D+ (3-2), and C18O (2-1) were observed to derive the deuterium fractionation of N2H+, D frac ≡ N(N2D+)/N(N2H+), as well as the CO depletion factor for every selected core. Our results show a decreasing trend in D frac with both gas temperature and line width. Since colder and quiescent gas is likely to be associated with less evolved cores, larger D frac appears to correlate with early phases of core evolution. Such decreasing trend resembles the behavior of D frac in the low-mass protostellar cores and is consistent with several earlier studies in high-mass protostellar cores. We also find a moderate increasing trend of D frac with the CO depletion factor, suggesting that sublimation of ice mantles alters the competition in the chemical reactions and reduces D frac. Our findings suggest a general chemical behavior of deuterated species in both low- and high-mass protostellar candidates at early stages. In addition, upper limits to the ionization degree are estimated to be within 2 × 10–7 and 5 × 10–6. The four quiescent cores have marginal field-neutral coupling and perhaps favor turbulent cooling flows.

ALMA Resolves the Spiraling Accretion Flow in the Luminous OB Cluster-forming Region G33.92+0.11

How rapidly collapsing parsec-scale massive molecular clumps feed high-mass stars, and how they fragment to form OB clusters, have been outstanding questions in the field of star-formation. In this work, we report the resolved structures and kinematics of the approximately face-on, rotating massive molecular clump, G33.92+0.11. Our high resolution Atacama Large Millimeter/submillimeter Array (ALMA) images show that the spiral arm-like gas overdensities form in the eccentric gas accretion streams. First, we resolved that the dominant part of the

INFALL AND OUTFLOW MOTIONS IN THE HIGH-MASS STAR-FORMING COMPLEX G9.62+0.19

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The Magnetized Environment of the W3(H2O) Protostars

0.6 pc scale massive molecular clump (3.0

An Evolved Disk Surrounding the Massive Main-Sequence Star MWC 297?

^{+2.8}_{-1.4}

SMA OBSERVATIONS OF THE HOT CORES OF DR21(OH)

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Wiggling Structures Along the NGC 1333 IRAS 2A Outflow

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