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Jewell, P. R.

Publications and source records attributed to Jewell, P. R..

15 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Detection of Ketenimine (CH2CNH) in SGRB2(N) Hot Cores

Ketenimine (CH2CNH) has been detected in absorption toward the starforming region Sagittarius B2(N) with the 100-m Green Bank Telescope (GBT) by means of three rotational transitions: 7(sub 16)-8(sub 08) at 41.5 GHz, 8(sub 19)-9(sub 09), at 23.2 GHz, and 9(sub 18)-10(sub 0,10) at 4.9 GHz. Ketenimine has a sparse rotational spectrum below 50 GHz. From transition line strength arguments, the spectral lines found are the ones most likely to be detected and occur in spectral regions that have little possibility of confusion with other molecular species. Partially resolved hyperfine structure is apparent in the 4.9 GHz transition which has energy levels approximately 50 K above ground state level; the absorption seen in this transition appears to be emanating from gas in close proximity to the LMH hot core that has a systemic LSR velocity of +64 kilometers per second. By comparison, the 41.5 GHz and 23.2 GHz transitions have lower energy levels of approximately 33 K and approximately 41 K, respectively; and show absorption against the two star-forming SgrB2(N) hot cores with systematic LSR velocities of +64 (the LMH) and +82 kilometers per second. These ketenimine data show that the hot core at +82 kilometers per second is cooler than the hot core at +64 kilometers per second. Ketenimine is likely formed directly from its isomer methyl cyanide (CH3CN) by tautomerization driven by shocks that pervade the star-forming region.

Lovas, F. J.↗
NASA NTRS2005

Interstellar Isomers: The Importance of Bonding Energy Differences

We present strong detections of methyl cyanide (CH3CN), vinyl cyanide (CH2CHCN), ethyl cyanide (CH3CH2CN) and cyanodiacetylene (HC4CN) molecules with the Green Bank Telescope (GBT) toward the Sgr B2(N) molecular cloud. Attempts to detect the corresponding isocyanide isomers were only successful in the case of methyl isocyanide (CH3NC) for its J(sub K) = 1(sub 0) - 0(sub 0) transition, which is the first interstellar report of this line. To determine the spatial distribution of CH3NC, we used archival Berkeley-Illinois-Maryland Association (BIMA) array data for the J(sub K) = 1(sub 0) - 0(sub 0) transitions but no emission was detected. From ab initio calculations, the bonding energy difference between the cyanide and isocyanide molecules is greater than 8500 per centimeter (greater than 12,000 K). Thus, cyanides are the more stable isomers and would likely be formed more preferentially over their isocyanide counterparts. That we detect CH3NC emission with a single antenna (Gaussian beamsize(omega(sub B))=1723 arcsec(sup 2)) but not with an interferometer (omega(sub b)=192 arcsec(sup 2)), strongly suggests that CH3NC has a widespread spatial distribution toward the Sgr B2(N) region. Other investigators have shown that CH3CN is present both in the LMH hot core of Sgr B2(N) and in the surrounding medium, while we have shown that CH3NC appears to be deficient in the LMH hot core. Thus, largescale, non-thermal processes in the surrounding medium may account for the conversion of CH3CN to CH3NC while the LMH hot core, which is dominated by thermal processes, does not produce a significant amount of CH3NC. Ice analog experiments by other investigators have shown that radiation bombardment of CH3CN can produce CH3NC, thus supporting our observations. We conclude that isomers separated by such large bonding energy differences are distributed in different interstellar environments, making the evaluation of column density ratios between such isomers irrelevant unless it can be independently shown that these species are co-spatial.

Remijan, Anthony J.↗
NASA NTRS2004

Absorption Reveals and Hydrogen Addition Explains New Interstellar Aldehydes: Propenal and Propanal

New interstellar molecules propenal (CH2CHCHO) and propanal (CH3CH2CHO) have been detected largely in absorption toward the star-forming region Sagittarius B2(N) by means of rotational transitions observed with the 100-m Green Bank Telescope (GBT) operating in the range of 18 GHz (lambda approximately 1.7 cm) to 26 GHz (lambda approximately 1.2 cm). The GBT was also used to observe the previously reported interstellar aldehyde propynal (HC2CHO) in Sagittarius B2(N) which is known for large molecules believed to form on interstellar grains. The presence of these three interstellar aldehydes toward Sagittarius B2(N) strongly suggests that simple hydrogen addition on interstellar grains accounts for successively larger molecular species: from propynal to propenal and from propenal to propanal. Energy sources within Sagittarius B2(N) likely permit the hydrogen addition reactions on grain surfaces to proceed. This work demonstrates that successive hydrogen addition is probably an important chemistry route in the formation of a number of complex interstellar molecules. We also searched for but did not detect the three-carbon sugar glyceraldehyde (CH2OHCHOHCHO).

Hollis, J. M.↗
NASA NTRS2004

Green Bank Telescope Observations of Interstellar Glycolaldehyde: Low Temperature Sugar

Interstellar glycolaldehyde (CH20HCHO) has been detected with the 100-m Green Bank Telescope (GBT) toward the star-forming region Sagittarius B2(N) by means of the 1(sub 10)-1(sub 01),2(sub 11)-2(sub 02),3(sub 12)-3(sub 0), and 4(sub 13)-4(sub 04) rotational transitions at 13.48, 15.18, 17.98, and 22.14 GHz, respectively. An analysis of these four high signal- to-noise rotational transitions yields a glycolaldehyde state temperature of ~8 K. Previously reported emission line detections of glycolaldehyde with the NRAO 12-m telescope at mm-wavelengths (71 GHz to 103 GHz) are characterized by a state temperature of -50 K. By comparison the GBT detections are surprisingly strong and seen in emission at 13.48 GHz, emission and absorption at 15.18 GHz, and absorption at 17.98 GHz and 22.14 GHz. We attribute the strong absorption observed by the GBT at the higher frequencies to the correspondingly smaller GBT beams coupling better to the continuum source(s) in Sagittarius B2(N). A possible model for the two-temperature regions of glycolaldehyde is discussed.

Hollis, J. M.↗
NASA NTRS2004

A Rigorous Attempt to Verify Interstellar Glycine

In 2003, Kuan, Charnley, and co-workers reported the detection of interstellar glycine (NH2CH2COOH) based on observations of 27 lines in 19 different spectral bands in one or more of the sources Sgr BP(N-LMH), Orion KL, and W51 e1/e2. They supported their detection report with rotational temperature diagrams for all three sources. In this paper, we present essential criteria which can be used in a straightforward analysis technique to confirm the identity of an interstellar asymmetric rotor such as glycine. We use new laboratory measurements of glycine as a basis for applying this analysis technique, both to our previously unpublished 12 m telescope data and to the previously published SEST data of Nummelin and colleagues. We conclude that key lines necessary for an interstellar glycine identification have not yet been found. We identify several common molecular candidates that should be examined further as more likely carriers of the lines reported as glycine. Finally, we illustrate that rotational temperature diagrams used without the support of correct spectroscopic assignments are not a reliable tool for the identification of interstellar molecules. Subject headings: ISM: abundances - ISM: clouds - ISM: individual (Sagittarius B2[N-

Snyder, L. E.↗
NASA NTRS2003

Kinematics of the SgrB2(N-LMH) Molecular Core

Ethyl cyanide (CH3CH2CN) emission and absorption have been imaged with the Very Large Array (VLA) toward SgrB2(N-LMH) by means of the 5(sub 15)-4(sub 14) rotational transition at 43.5 GHz (lambda approx. 7 mm). The 1.5" x 1.4" VLA beam shows two principal sources of ethyl cyanide emission: an unresolved source approx. 5" north of the LMH that is kinematically consistent with simple expansion, contraction, or small-scale turbulence, and the resolved LMH core source itself that shows kinematics indicating an edge-on rotating disk that extends 23" (approx. 0.1 pc) in the approximate east-west direction. A search for the 7(sub 07)-6(sub 06) rotational transition of the amino acid glycine (NH2CH2COOH) at 43.7 GHz toward SgrB2(N-LMH) gave negative results.

Hollis, J. M.↗
NASA NTRS2002

Interstellar Antifreeze: Ethylene Glycol

Interstellar ethylene glycol (HOCH2CH2,OH) has been detected in emission toward the Galactic center source Sagittarius B2(N-LMH) by means of several millimeter-wave rotational torsional transitions of its lowest energy conformer. The types and kinds of molecules found to date in interstellar clouds suggest a chemistry that favors aldehydes and their corresponding reduced alcohols-e.g., formaldehyde (H2CO)/methanol (CH3OH), acetaldehyde (CH3CHO)/ethanol (CH3CH2OH). Similarly, ethylene glycol is the reduced alcohol of glycolaldehyde (CH2OHCHO), which has also been detected toward Sgr B2(N-LMH). While there is no consensus as to how any such large complex molecules are formed in the interstellar clouds, atomic hydrogen (H) and carbon monoxide (CO) could form formaldehyde on grain surfaces, but such surface chemistry beyond that point is uncertain. However, laboratory experiments have shown that the gas-phase reaction of atomic hydrogen (H) and solid-phase CO at 10-20 K can produce formaldehyde and methanol and that alcohols and other complex molecules can be synthesized from cometary ice analogs when subject to ionizing radiation at 15 K. Thus, the presence of aldehyde/ reduced alcohol pairs in interstellar clouds implies that such molecules are a product of a low-temperature chemistry on grain surfaces or in grain ice mantles. This work suggests that aldehydes and their corresponding reduced alcohols provide unique observational constraints on the formation of complex interstellar molecules.

Hollis, J. M.↗
NASA NTRS2002

A Sensitive VLA Search for Small-Scale Glycine Emission Toward OMC-1

We have conducted a deep Q-band (lambda-7 mm) search with the Very Large Array (VLA) toward OMC-1 for the lowest energy conformation (conformer I) of glycine (NH2CH2COOH) in four rotational transitions: the 6(sub 15)- 5(sub 14), 6(sub 24)-5(sub 23), 7(sub 17- 6(sub 16), and 7(sub 07)-6(sub 06). Our VLA observations sample the smallest-scale structures to date in the search for glycine toward OMC-1. No glycine emission features were detected. Thus if glycine exists in OMC-1, either it is below our detection limit, or it is more spatially extended than other large molecules in this source, or it is primarily in its high energy form (conformer II). Our VLA glycine fractional abundance limits in OMC-1 are comparable to those determined from previous IRAM 30m measurements -- somewhat better or worse depending on the specific source model -- and the entire approximately 1 foot primary beam of the VLA was searched while sensitive to an areal spatial scale approximately 150 times smaller than the 24 inch beam of the IRAM single-element telescope. In the course of this work, we detected and imaged the 4(sub 14)-3(sub 13) A and E transitions of methyl formate (HCOOCH3) and also the 2(sub 02) - 1(sub 01) transition of formic acid (HCOOH). Since formic acid is a possible precursor to glycine, our glycine limits and formic acid results provide a constraint on this potential formation chemistry route for glycine in OMC-1.

Hollis, J. M.↗
NASA NTRS1995

Confirmation of interstellar methylene

Four spectral emission features of the N(sub KK) = 4(sub 04) -3(sub 13) rotational transition of methylene (CH2) have been detected at signal levels 5-7 sigma above noise toward the hot core of the Orion-KL nebula and the molecular cloud in proximity to the continuum source W51 M. Specifically, in both sources we have resolved the F = 6-5, 5-4, and 4-3 hyperfine transitions of the J = 5-4 fine-structure levels and detected the blended hyperfine structure of the J = 4-3 fine structure levels. At the J = 3-2 fine-structure levels, we have observed new transitions of NS, a known interstellar molecule, which severely contaminates the search for CH2 hyperfine transitions. These new sensitive observations finally confirm the existence of interstellar CH2 which was tentatively reported by us some years ago.

Hollis, J. M.↗
NASA NTRS1990

Comparisons of SiO maser and long-period variable positions in the R Aquarii and Omicron Ceti binary systems

It has been determined that the absolute position of the centroid of SiO maser-emitting spots toward both R Aqr and Omicron Cet are coincident with the position of the long-period variables (LPVs) in these binary systems to within the errors of measurement. The SiO positions were determined with the Hat Creek interferometer, while the LPV positions were determined with the 8-in transit circle of the US Naval Observatory. These results contradict an earlier report of a circumbinary SiO maser far removed from the LPV in the R Aqr binary system; statistical reasons for the discrepancy are suggested. High-resolution spectra of both sources are presented and possible models are discussed.

Hollis, J. M.↗
NASA NTRS1989

A search for methylene in the Orion nebula

A deep search for the J = 4-3 and 5-4 fine-structure components of the N(KK) = 4(04)-3(13) rotational transition of methylene toward the hot core of the Orion KL nebula is conducted. An approximate 4-sigma emission feature which is frequency-coincident with a hyperfine blend of the J = 4-3 component is detected, and weak features (about 2-3 sigma) frequency-coincident with the resolved F = 6-5 and 5-4 hyperfine components of the J = 5-4 component are observed. The relative intensities of these spectral features and their observational repeatability suggest that assignment to interstellar CH2 is likely correct, although the result must be confirmed.

Hollis, J. M.↗
NASA NTRS1989

Millimeter- and submillimeter-wave surveys of Orion A emission lines in the ranges 200.7-202.3, 203.7-205.3, and 330-360 GHz

A continuous spectral line survey of the Orion A position from 330.5 to 360.1 GHz was carried out. This survey covers nearly the entire 870 micron atmospheric window accessible from ground-based observations. Approximately 160 distinct spectral features composed of about 180 lines were detected, 29 of which could not be readily identified. In addition, Orion A from 200.7 to 202.3 GHz and from 203.7 to 205.3 GHz and 42 distinct new spectral lines were detected, including four that are unidentified at present. These data sets are the first thorough survey results in these spectral regions. The new interstellar lines in the survey bands are tabulated and displayed graphically. Moreover, the data are being made available to the Astronomical Data Center at the Goddard Space Flight Center for distribution by request to the astronomical community.

Jewell, P. R.↗
NASA NTRS1988

HCO emission from H II-molecular cloud interface regions

A survey of well-known molecular clouds in the four strongest HCO N(k-,k+) = 1(01)-O(60) hyperfine transitions has been carried out to determine the prevalence of HCO and to study its chemistry. HCO emission was observed in seven molecular clouds. Three of these, NGC 2264, W49, and NGC 7538, were not previously known sources of HCO. In addition, NGC 2024 and Sgr B2 were mapped and shown to have extensive HCO emission. The survey results show the HCO abundance to be enhanced in H II-molecular cloud interface regions and support a correlation between C(+) and HCO emission. The strength of the HCO emission in NGC 2024 is interpreted in terms of this enhancement and the source structure and proximity to Earth.

Schenewerk, M. S.↗
NASA NTRS1986

Monitoring observations of selected SiO maser sources at 7 mm wavelength - 1977-1979

High-spectral-resolution SiO maser observations at 7 mm wavelength were made for 13 circumstellar objects and Ori A over a 34 month interval from January 1977 to November 1979. These data precede and adjoin the SiO monitoring data taken at 3 and 7 mm wavelengths by Lane (1982) and at 3 mm wavelengths by Nyman and Olofsson (1985) and thus provide an important link in the record of the temporal behavior of SiO masers over a period of several years. The time-averaged center of the weak SiO maser emission pedestal gives the stellar radial velocity. This reinforces the idea that the SiO maser emission pedestal is representative of the true structure of a stellar SiO maser, while the more visible and stronger, narrow SiO emission spikes represent chance coherences along the velocity range of the pedestal. Similarities between the SiO maser velocity patterns of VY CMa and Ori A may suggest similarities in their evolutionary stages.

Snyder, L. E.↗