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S. L. Widicus Weaver

Publications and source records attributed to S. L. Widicus Weaver.

4 recordsLinked to original sources
arXiv2026

Interstellar Complex Organic Molecules and Molecular Outflows in NGC 1333 IRAS 4B and 4B' Observed Using NOEMA

We present interferometric observations with the Northern Extended Millimeter Array (NOEMA) of NGC 1333 IRAS 4B and 4B', two young stellar objects (YSOs) within the Perseus molecular cloud. YSOs, especially Class 0 protostars, are rich in gas-phase interstellar complex organic molecules (iCOMs), but relatively little is known about the spatial distribution of these important prebiotic molecules. Various molecules were imaged within IRAS 4B and the surrounding area in the 145 GHz spectral range, revealing hundreds of molecular transitions within the warm inner envelope of IRAS 4B. This work provides derived physical parameters (rotational temperature, column density, velocity shift with respect to local standard of rest, and full-width at half-maximum spectral line width) for 11 molecules toward IRAS 4B including methanol (CH$_3$OH and isotopologues), methyl formate (HCOOCH$_3$), dimethyl ether (CH$_3$OCH$_3$), acetaldehyde (CH$_3$CHO), ethanol (C$_2$H$_5$OH), glycolaldehyde (CH$_2$OHCHO), acetone (CH$_3$COCH$_3$), and isocyanic acid (HNCO). Out of these molecules, 10 are iCOMs (excluding HNCO) that trace the inner envelope of IRAS 4B and mark it as a rich source of organic material. There is a strong spatial correlation between the continuum emission of IRAS 4B and iCOM molecular emission and among various iCOMs with each other. Physical parameter and integrated intensity maps show that IRAS 4B is a binary protostar system that drives a jet in a north-south orientation and an outflow in a northwest-southeast orientation. IRAS 4B' also drives a west-east outflow but shows no evidence of molecular emission cospatial with its continuum emission.

astro-ph.GA↗
arXiv2012

Complex Organic Molecules at High Spatial Resolution Toward Orion-KL II: Kinematics

It has recently been suggested that chemical processing can shape the spatial distributions of complex molecules in the Orion-KL region and lead to the nitrogen-oxygen "chemical differentiation" seen in previous observations of this source. Orion-KL is a very dynamic region, and it is therefore also possible that physical conditions can shape the molecular distributions in this source. Only high spatial resolution observations can provide the information needed to disentangle these effects. Here we present millimeter imaging studies of Orion-KL at various beam sizes using the Combined Array for Research in Millimeter-Wave Astronomy (CARMA). We compare molecular images with high spatial resolution images that trace the temperature, continuum column density, and kinematics of the source in order to investigate the effects of physical conditions on molecular distributions. These observations were conducted at λ= 3 mm and included transitions of ethyl cyanide [C2H5CN], methyl formate [HCOOCH3], formic acid [HCOOH], acetone [(CH3)2CO], SiO, and methanol [CH3OH]. We find differences in the molecular distributions as a function of each of these factors. These results indicate that acetone may be produced by chemical processing and is robust to large changes in physical conditions, while formic acid is readily destroyed by gas-phase processing in warm and dense regions. We also find that while the spatial distributions of ethyl cyanide and methyl formate are not distinct as is suggested by the concept of "chemical differentiation", local physical conditions shape the small-scale emission structure for these species.

astro-ph.GA↗
arXiv2011

A High Spatial Resolution Study of the λ=3 mm Continuum of Orion-KL

Recent interferometric observations have called into question the traditional view of the Orion-KL region, which displays one of the most well-defined cases of chemical differentiation in a star-forming region. Previous, lower-resolution images of Orion-KL show emission signatures for oxygen-bearing organic molecules toward the Orion Compact Ridge, and emission for nitrogen-bearing organic molecules toward the Orion Hot Core. However, more recent observations at higher spatial resolution indicate that the bulk of the molecular emission is arising from many smaller, compact clumps that are spatially distinct from the traditional Hot Core and Compact Ridge sources. It is this type of observational information that is critical for guiding astrochemical models, as the spatial distribution of molecules and their relation to energetic sources will govern the chemical mechanisms at play in star-forming regions. We have conducted millimeter imaging studies of Orion-KL with various beam sizes using CARMA in order to investigate the continuum structure. These λ;=3mm observations have synthesized beam sizes of ~0.5"-5.0". These observations reveal the complex continuum structure of this region, which stands in sharp contrast to the previous structural models assumed for Orion-KL based on lower spatial resolution images. The new results indicate that the spatial scaling previously used in determination of molecular abundances for this region are in need of complete revision. Here we present the results of the continuum observations, discuss the sizes and structures of the detected sources, and suggest an observational strategy for determining the proper spatial scaling to accurately determine molecular abundances in the Orion-KL region.

astro-ph.GA↗
arXiv2009

Tracing the Bipolar Outflow from Orion Source I

Using CARMA, we imaged the 87 GHz SiO v=0 J=2-1 line toward Orion-KL with 0.45 arcsec angular resolution. The maps indicate that radio source I drives a bipolar outflow into the surrounding molecular cloud along a NE--SW axis, in agreement with the model of Greenhill et al. (2004). The extended high velocity outflow from Orion-KL appears to be a continuation of this compact outflow. High velocity gas extends farthest along a NW--SE axis, suggesting that the outflow direction changes on time scales of a few hundred years.

astro-ph.GA↗