Sheng-Yuan Liu

Organic Molecules in Low-Mass Protostellar Hot Cores: Submillimeter Imaging of IRAS 16293?2422

Arcsecond-resolution spectral observations toward the protobinary system IRAS 16293-2422 at 344 and 354 GHz were conducted using the Submillimeter Array. Several complex organic molecules, such as CH3OH and HCOOCH3, were detected and mapped. Together with the rich organic inventory revealed, it clearly indicates the existence of two, rather than one, compact hot molecular cores (400 AU in radius) associated with each of the protobinary components identified by their dust continuum emission in the inner star-forming core.

Observations of Formic Acid in Hot Molecular Cores

We present BIMA Array observations of formic acid (HCOOH) in Galactic hot molecular cores. It has been found that among nearly 120 interstellar and circumstellar molecular species identified to date, the more complex and saturated organic species are usually observed in hot molecular cores—dense and warm molecular condensations associated with active star formation regions inside molecular clouds. Formic acid, one of the molecules in this category, shares common structural elements with both methyl formate (HCOOCH3) and acetic acid (CH3COOH). In this study, we successfully mapped HCOOH emission in three regions: Orion KL, Sgr B2, and W51. Column densities of HCOOH are above 1015 cm-2 in these sources. The derived HCOOH column density in Sgr B2(N-LMH) is comparable to the CH3COOH column density found by Mehringer et al. in 1997. Ethyl cyanide (C2H5CN) and HCOOCH3 emission spectra were also detected in several sources. The distribution of HCOOH emission is consistent with a surface chemistry origin for the species. The abundance ratios of HCOOH to C2H5CN and to HCOOCH3 vary by nearly 2 orders of magnitude from source to source.

Formic Acid in Orion KL from 1 Millimeter Observations with the Berkeley-Illinois-Maryland Association Array

We present Berkeley-Maryland-Illlinois Association array observations of formic acid (HCOOH) at 1 mm toward the Orion KL region. Near the compact ridge, HCOOH emission is spatially resolved; its partial shell morphology is different from that of other complex O-bearing molecules such as methyl formate and dimethyl ether. This unique distribution suggests that HCOOH is located in a layer that delineates the interaction region between the outflow and the ambient quiescent gas. HCOOH is also detected toward the hot core. For both cases, ejection of grain mantles is likely to be responsible for the observed HCOOH.

A Survey of Acetic Acid toward Hot Molecular Cores

We have surveyed 12 Galactic hot molecular cores for interstellar acetic acid (CH3COOH). This is the most extensive search for acetic acid to date. We have detected a new source of acetic acid toward the high-mass hot molecular core source G34.3+0.2. Using a temperature range between 70 and 185 K, we find a CH3COOH column density range of (0.77-1.64) ? 1015 cm-2 toward G34.3+0.2. This gives a relative CH3COOH/HCOOCH3 abundance ratio of ~3.3 ? 10-2, which is comparable to the abundance ratio of (3-6) ? 10-2 found toward Sgr B2(N-LMH) and W51e2 by Remijan and colleagues. All currently known acetic acid sources are within 7 kpc of the Galactic center. Furthermore, our survey suggests that hot molecular cores that have a mass range between 200 and 2000 M? and do not show a distinct differentiation between O and N chemistry may be the best places to search for acetic acid and the structurally similar biologically important molecule glycine.

Acetic Acid in the Hot Cores of Sagitarrius B2(N) and W51

We have detected interstellar acetic acid (CH3COOH) toward the hot core source W51e2. This is the first new source of interstellar CH3COOH since its discovery by Mehringer et al. toward the hot core source Sgr B2(N-LMH). In this paper, we report CH3COOH observations at two new frequencies toward Sgr B2(N-LMH) with the OVRO array and at 10 frequencies toward W51e2 with the Berkeley-Illinois-Maryland Association array. Toward Sgr B2(N-LMH) the agreement in positions, intensities, and velocities between the two lines from the previous study and the two new lines strongly indicates that all four CH3COOH lines are coming from a common source. Using all four detected transitions, we find an average column density of 6.1(6) × 1015 cm-2, a fractional abundance of (0.8-6) × 10-10 relative to H2 and (3-6) × 10-2 relative to its isomer methyl formate (HCOOCH3). Toward W51e2, we find a CH3COOH column density of 1.7(5) × 1016 cm-2 with a fractional abundance of 1.7 × 10-9 relative to H2 and (1-6) × 10-2 relative to HCOOCH3. Furthermore, we find the distribution of CH3COOH toward W51e2 is coincident with HCOOCH3, thus suggesting a similar formation mechanism.

Multiple jets from the high-mass (proto)stellar cluster AFGL 5142

We present studies of the massive protocluster AFGL 5142 in the J ¼ 2Y1 transition of the CO isotopologues, SO, CH3OH, and CH3CN lines, as well as in the continuum at 225 GHz and 8.4 GHz. The 225 GHz continuum emission reveals at least five dust continuum peaks. The strongest peaks, MM-1 and MM-2, are associated with hot cores with temperatures of 90 � 20 and 250 � 40 K, respectively. With similar core mass, the higher temperature and CH3CN abundance in the MM-2 core suggest that it might be at a more evolved stage than the MM-1 core. A total of 22 lines fromninemoleculesaredetected.Thelinestrengthvariesremarkablyintheregion.StrongSOemissionisfoundboth in molecular outflows and cloud cores. CH3OH emission, onthe contrary, is much weaker in molecular outflows, and isdetectedtowardhotcoresMM-1andMM-2,butisabsentinthelessmassiveandperhapslessevolvedcoresMM-3, MM-4, and MM-5. The CO and SO emission reveals at least three molecular outflows originating from the center of thedustcore.Theoutflowsarewellcollimated,withterminalvelocitiesupto50kms � 1 fromthecloudvelocity.Since jetlike outflows and disk-mediated accretion process are physically connected, the well-collimated outflows indicate that even in this cluster environment, accretion is responsible for the formation of individual stars in the cluster. Subject headingg s: H ii regions — ISM: clouds — ISM: individual (AFGL 5142) — ISM: kinematics and dynamics — masers — stars: formation

A Sensitive Very Large Array Search for Small-Scale Glycine Emission Toward OMC-1

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Subarcsecond Submillimeter Continuum Observations of Orion KL

Current address: NASA Goddard Space Flight Center, Earth and Space Data Computing Division, Code 930, Greenbelt, MD 20771

Subarcsecond Resolution Observations of Sagittarius B2 at 85 GHz

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